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112 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 1, NO. 1, SEPTEMBER 2011

Progress in Antenna Coupled KineticInductance Detectors

Andrey Baryshev, Jochem J. A. Baselmans, Angelo Freni, Senior Member, IEEE,Giampiero Gerini, Senior Member, IEEE, Henk Hoevers, Annalisa Iacono, Student Member, IEEE,

and Andrea Neto, Senior Member, IEEE

(Invited Paper)

Abstract—This paper describes the combined Dutch effortstoward the development of large wideband focal plane arrayreceivers based on kinetic inductance detectors (KIDs). Takinginto account strict electromagnetic and detector sensitivity re-quirements for future ground and space based observatories, thiswork has led to the identification of well-suited coupling strategiesbased on the use of lens antenna and the demonstration of theirfeasibility. Moreover, some specific antenna design difficultiesthat characterize KIDs-based designs have been investigated, andinnovative feeds for the focal plane array which could allow thereceivers to be sensitive over a decade of Bandwidth have beenproposed.

Index Terms—Arrays, kinetic inductance detectors (KIDs),losses, reflector antenna feeds, THz antennas.

I. INTRODUCTION

T HE current revolution in far-infrared and millimeter waveastronomy is a direct result of the emergence of supercon-

ducting detector arrays over the last 30 years. In the future, de-tector technology development will continue to determine whatis scientifically possible, [1]. The key goal is to develop instru-ments with large arrays of detectors that are capable of achievingthe so-called photon noise limit. This implies that the detectorsensitivity, or noise equivalent power, is equal to, or lower than,the background noise of the observatory in which the detector isplaced. Recently introduced kinetic inductance detectors (KIDs)[2], [3], [5] are among the most sensitive cryogenic sensorsavailable for detection of electromagnetic radiation and prob-ably the most promising sensors to be employed in large focalplane array configurations. This is mainly due to the fact thatthousands of detectors can be coupled to a single on-chip mi-crowave transmission line enabling the read-out of thousands

Manuscript received March 02, 2011; revised April 04, 2011; accepted May27, 2011. Date of current version August 31, 2011.

A. Barishev, J. A. Baselmans, H. Hoevers are with the Netherlands Institutefor Space Research, SRON, Utrecht, The Netherlands.

A. Freni is with the Telecom Department, University of Florence, 50100 CD,Firenze, Italy (e-mail: [email protected]).

G. Gerini and A. Iacono are with TNO Defence, Security and Safety,Den Haag 2597 AK, The Netherlands (e-mail: [email protected] [email protected]).

A. Neto is with the Telecom Department, Delft University of Technology,Mekelweg 4, 2628 CD, Delft, The Netherlands (e-mail: [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TTHZ.2011.2159532

of detectors with just a single coaxial cable pair connecting theon-chip transmission line to room temperature read-out elec-tronics. This number should be compared to the multiplexingrate of transition edge sensors (TES), which reaches about 50detectors per read out line, where additional cryogenic elec-tronics and a separate multiplexing chip are needed [6]. Op-portunities for background limited THz radiation detections ap-pear in the frame of SPICA, a Japanese future satellite mis-sion which will include an European far infrared detection in-strument called SAFARI [7]. Moreover, opportunities are alsoin ground based astronomical observatories, which will benefitfrom imaging arrays capable of filling the entire field of view ofcurrent and future telescopes [1].

The Netherlands Institute for Space Research (SRON),Utrecht, The Netherlands Organization for Applied ScientificResearch (TNO), Delft University of Technology (TU Delft),Eindhoven University of Technology (TU Eindhoven), andthe University of Florence have been collaborating toward thedesign of an efficient way to couple electromagnetic radiationinto the KIDs detectors. While the system implementation hasbeen entirely a task of SRON, the joined efforts were aimed atthe sub-topic of enhancing the throughput of the THz radiatedenergy into the KIDs. In this paper, the technical status of thiscollaboration is summarized. After recalling the main operatingprinciples of the KIDs, this paper describes the main electro-magnetic requirements that characterize the instruments to beused for future THz imaging and low resolution spectroscopyof deep space. A well suited strategy to couple electromagneticradiation into the KIDs, based on the use of lens antennas, ishighlighted. The feasibility of this strategy is demonstrated witha 675-GHz demonstrator. In light of the results, some specificantenna design difficulties characteristic of KID designs areshown in Section IV. Furthermore the sensitivities outlined inthe first experiments are presented and discussed. Finally, aninnovative feed structure for the focal plane array, which couldallow thousands of receivers sensitive over a decade bandwidthis described and demonstrated at lower frequencies.

II. KINETIC INDUCTANCE DETECTORS

KIDs were originally proposed by researchers at Caltech [2],and significant work has taken place on the device physics andpotential performance for astronomy [3], [4]. They are currentlyproposed as a viable option to reach the photon noise limitedsensitivities required by some of the most stringent applications.

2156-342X/$26.00 © 2011 IEEE

BARYSHEV et al.: PROGRESS IN ANTENNA COUPLED KINETIC INDUCTANCE DETECTORS 113

Fig. 1. KID operation principle. (a) Photons break Cooper pairs in a supercon-ductor creating quasiparticles. (b) Optical micrograph of a CPW �� resonator.(c) By making the superconductor part of a resonance circuit it is possible toread out changes in the complex surface impedance of the superconductor dueto radiation absorption as a change in microwave transmission. The response ofthe circuit depicted in (b) and (c) is given in (d), where the blue line representsthe equilibrium situation and the red line the one after photon absorption.

These sensitivities, expressed in noise equivalent power, can beas low as for ground based imagingand for space based grating spec-troscopy with a resolution (implying that velocityof stars can be detected with accuracy of one thousandth of thespeed of light).

In this section the basic principles necessary for the optimiza-tion of a THz front end that properly transfers to the KIDs themaximum power incoming from the sky are summarized. TheKID concept is explained in Fig. 1. Photons from the sky signalbreak Cooper pairs in a superconducting material at a tempera-ture , where is the superconducting transition tem-perature of the material, thereby creating quasi-particle exci-tations (a). This process takes place if the photon energy ex-ceeds the binding energy of the Cooper pairs ( , where

), that is when the frequency, , of the incomingradiation is above the gap frequency. This gap frequency canbe estimated from the transition temperature of the supercon-ducting material, [3]). For instance in the case of Aluminium

the gap frequency is roughly 80 GHz (meV). The result is a change in the complex surface impedanceof the superconductor. By making the superconductor part of ahigh Q resonance circuit as depicted in (c), this change can bemeasured very accurately.

A possible implementation of the circuit depicted in (c) isshown in (b): it shows an optical micrograph of a capacitivelycoupled distributed coplanar waveguide (CPW) resonator madeof a thin aluminium film. The design of the coupler sets theresonator Q factor. The shorted end of the resonator createsthe boundary condition that the circuit reaches a lowest fre-quency resonance at a length , with the effectivewavelength of a readout signal sent through the CPW throughline from contact 1 to 2, as indicated in Fig. 1(b). This wave-length is , with the

wave-number in silicon and the free space wave-number. Ac-cordingly, mm at GHz for a CPW on a Sisubstrate. Since 6 GHz is well below the gap frequency of Al, theresonator is essentially lossless at its operating temperature ofTc/10 (100 mK for aluminium), which allows very high Q fac-tors up to one million. Eventually, the THz photon absorptionand consequent mechanism of destruction of the Cooper pairsmodifies the distributed inductance and losses of the transmis-sion line resonator. This effect in turn shifts the resonant fre-quency of the resonators and reduces the depth of the resonancedip. These effects can be observed in a measurement of theparameters. This is shown in (d): the blue line in (d) depicts thetransmitted magnitude as a function of frequency of the reso-nance circuit in equilibrium around its resonance frequency ,the red line shows the situation after photon absorption: the res-onance dip shifts of toward lower frequencies and the reso-nance dip reduces in depth.

The THz radiation is detected by the KID by means of achange of resonant frequency and resonance dip depth of a high

GHz resonator with a bandwidth of about10 KHz around a specific frequency. Up to several thousands ofresonators, each with a different nominal frequency, can be de-ployed over a practical bandwidth of 4–8 GHz. This is achievedby making the resonators all of slightly different lengths. There-fore, a large 2-D array of detectors, all sensitive to the same THzfrequency, will encode the spatial information of the detectedpower in the GHz frequency domain.

Note that in Fig. 1 we have shown the readout line and the res-onator, but the latter is not an efficient detector of THz radiationby itself as it does not include a radiation coupling structure. Inprinciple there are two possible routes to allow radiation absorp-tion in a superconducting resonant circuit: 1) direct absorptionof radiation by making the resonator in such a shape that it formsan impedance matched absorber, a route pioneered by Cardiffuniversity [5] and 2) antenna coupling to the KID resonator, asproposed in [8] and of which an implementation is shown inFig. 3. The latter allows for a more flexible design as the KIDresonator and antenna are separate entities that can be indepen-dently optimized. For instance a single broadband antenna couldallow for multicolor pixels by coupling several resonators to thesame antenna fed line with built-in power dividers and filters.Only antenna coupled KID will be discussed in this paper.

III. USE OF SUBSTRATE LENSES

Focal plane arrays composed of many detectors can be used toenhance the acquisition speed with respect to single pixel detec-tion. Imaging arrays are composed by many identical elements(for instance 5 in Fig. 2) located on the focal plane of a reflector(of diameter and focal distance ). The lateral displacement

of the feed element with respect to the central focus corre-sponds to a new pointing direction shifted by(valid only for large F/D ratios). Thus, imaging arrays allow toreconstruct an image, of a sector of deep space for example,without the necessity of moving the main reflector to point atdifferent directions.

Up to ten thousand elements are proposed for the future SA-FARI instrument but also for ground based astronomic imaging


Fig. 2. Schematic view of a reflector system and focal plane suited to host feedsfor multiple beam imaging.

arrays. A large number of elements imply that the ef-fective ratios of the desired telescopes have to be quite large

to avoid degradation of the off focus beams. Forground based applications (frequencies below 1 THz) ’smuch larger than 3 are impractical because they lead to verylarge focal plane arrays. In fact, as a rule of thumb, focal planecells of diameter typically support efficient excitationsof optical systems characterized by . That is because,independently from the actual value of , directive antennafeeds need to be used in order to maximize the coupling to thetelescope’s optics. In the specific case of KIDs detectors theminimum dimensions of a cell of the focal plane array are dic-tated by the necessity to include in the elementary cell the entireresonating structure, Fig. 1(b).

Apart from the large number of pixels, the second stringentrequirement, especially valid for soace born instruments, de-rives from the suggested use of a broad spectral band. This re-quirement comes with great difficulties that will be discussed inSection VII. To partially solve some of these difficulties a dedi-cated novel antenna concept, the Leaky Lens antenna, [11], hasbeen developed and demonstrated at mm wave frequencies. Theexpectation of this team is that the Leaky Lens concept will bedemonstrated to be feasible at THz frequencies in the near fu-ture. Based on this expectation, the lens antenna coupled type ofarchitecture for the focal plane has been selected. Another majoradvantasge of lens-antenna detection is that it enables post de-tection filtering of the THz power, which in principle opens thedoor to multicolor pixels or even on-chip spectrometers. On theother hand, could be converted into broad band receptors of ra-diation, but at the cost of degraded performance or added systemcomplexity.

In the rest of this paper, depending on the science objectives,we will consider a dual polarized antenna or a single polarizedantenna.

IV. FIRST SUB-MILLIMETER WAVE IMPLEMENTATION

The aim of the very first design implemented was to demon-strate clean beam couplings to KID detectors and a measure-ment set up adequate to the task. Accordingly, the first antennadesign was linearly polarized and conceived to operate on anarrow frequency band.

In correspondence of the outer end of the resonator, an an-tenna can be included that will couple the incoming THz radia-tion into the resonator (see for example Fig. 3). The THz antenna

Fig. 3. Through line in the bottom of the picture, the resonating quarter wave-length (at GHz frequencies) line realized in Coplanar waveguide, and the twinarc slot antenna.

is electrically small at the resonator frequency (GHz), so it canbecome integral part of the resonator with only a small pertur-bation in its behavior. However, in THz regime, the resonator iselectrically long and lossy, so it acts, and can be modeled, as aninfinite lossy transmission line that absorbs (and hence detects)the incoming THz radiation.

Following the well-established design strategy in [12], it wasdecided to print planar radiating slots in the focal plane of ex-tended hemispherical lens antennas. The elliptical shape of thelens gives high focusing properties provided that its eccentricityis properly related to its dielectric constant . Thelens, made of silicon and of radius 1.7 mm, is cut in the lowerfocus and then mounted on top of the silicon wafer hosting theslot antennas and the KID resonator. Typically, only the upperportion of the lens is used efficiently (left portion of Fig. 4).In fact, rays reaching the dielectric-air interface at a low angleare not focused in useful directions and undergo multiple reflec-tions (see the right portion of Fig. 4). This fact evidently callsfor a directive feed which would also guarantee that an arrayof lenses can be manufactured in a unique integrated solution,with the depth of the lens only a few hundreds of micrometers.Such feeds can be achieved with the twin slot feeds proposed in[13]. Two CPW feeding lines are used to feed the slots. The twolines are then connected in parallel to the common feeding line,chosen to present characteristic impedance equal to 50 Ohm,that essentially constitutes the microwave resonator. Accord-ingly, each of the two slots is designed to present an impedanceof about 100 Ohm and to be connected to a matched line of char-acteristic impedance of 100 Ohm. The dB matching band-width is in the order of 15%. The curved shape of the double slot


Fig. 4. Dielectric lens, cut in the lower focus, mounted on top of the siliconwafer hosting the twin slot antenna and the KID resonator.

antenna is fairly peculiar. This shape was adopted in order to fur-ther enhance lens efficiency by means of the inclusion of leakywave supporting dielectric layers, as described in [14]. Even-tually the leaky wave supporting layers were not used becausethe directivity enhancement would have implied a reduction ofimpedance BW. The arched shape was in fact expected to benot influential on the performance. This turned out to be false,as will be discussed in Section V.

The system is designed for measurements on a relativelynarrow band centered around 675 GHz which is a compromisechosen in such a way that the frequency is high enough todemonstrate feasibility in the THz regime but low enough foroptical lithography manufacturing.

A. Measurement Set Up

Most of the initial work from SRON went into the prepara-tion of the measurement set up. For optical test, antenna-coupledKIDs are aligned and glued to a silicon lens, and then mountedin a sample holder [Fig. 5(a)], inside a 300mK base tempera-ture cryostat with an optical access [Fig. 5(b)]. A narrow bandsource, 675 GHz, was chosen so that the most of the radia-tion associated to the room temperature could be eliminated. Abeam pattern can be measured by scanning an external radiationsource outside the cryostat window and measuring the deviceresponse as a function of position. Given the high optical load,Tantalum devices, with limited sensitivity but high capable towithstand the loading from 300 K were fabricated for the mea-surement of the device patterns. Devices used to calculate thesensitivities are made from Aluminum, they require lower basetemperature of 100 mK, a lower optical load but are much moresensitive [4]. These measuremenst have been realized using acryogenic thermal calibration source (between 4 and 40 K).

B. Even Mode and Air Bridges

The first responsivity patterns detected by Tantalum KIDswere of very poor quality, i.e., too broad with respect to theexpected focusing from the lens. This fact was attributed to thespurious radiation associated to the co-existence, on the CPWlines, of both the propagating (odd in magnetic currents) andradiating (even in magnetic currents) modes. This latter mode isundesired because it is associated to the radiation described in[15] and [16]. This undesired mode can be avoided by shortingthe CPW external ground planes by using multiple air bridgesspaced along the waveguide at samplings higher than a quarter

Fig. 5. (a) Sample holder, with visible connectors and lens; (b) inside view ofthe cryostat.

of the effective (THz) wavelength on the KID. Air bridges arecommon practice in the microwave (GHz) range, but non trivialfor these devices which are realized using microfabrricationtechniques. The air bridges were realized (see Fig. 6) usinga shaped photo-resist profile with the photo-resist removedafter deposition and processing of a bridge layer. Note that thepresence of the air bridges is also required in principle for thepower combining structure in the antenna, where the radiationof the 2 slots is coupled to 1 transmission line.

C. First Results

The introduction of air bridges led to an improvement of theresponsivity patterns quality. The co-polarized and cross polar-ized fields are shown in Fig. 7(a) and (b), respectively. In thisfigure the and dimensions indicate the scan of the 675 GHzsource in front of the cryostat window. These patterns show thearising of an unexpectedly high cross polarized field level, in theorder of 10 dB below the main co-polar component. Despite thecurvatures of the two slots, this effect was not expected. The ob-servation of the unexpected cross polarized fields was actuallyvery beneficial as it allowed this team to investigate a problem


Fig. 6. Details of the air bridges realized in order to suppress the even electricfield mode in the CPW lines.

Fig. 7. (a) Co-polar planar measured distribution. (b) Cross polar planarmeasured distribution.

that would have gone otherwise unnoticed: the problem of in-coherent reception.

V. COHERENT AND INCOHERENT PATTERNS

The reflector system is designed to make a coherent focusedfield in the focal plane where the lenses are hosted. Even if thedifferent plane waves to be detected are associated to thermalsources in space and thus are associated to incoherent signals,the desired pattern from the twin slots antenna (Fig. 3) is real-ized when the two signals received by the two different slots are

coherently summed. If the system is lossless, the coherent sum-mation of the two signals from the curved slots will not intro-duce important cross polarized field components. In fact, evenif each slot is susceptible to cross-polarized fields, the superpo-sition of the two is designed to have these effects cancel out, aswas demonstrated in [17], where dB of max cross polarizedfields were observed for all observation angles. However, at THzfrequencies significant losses occur in the two different CPWlines that connect the two slots to the summing point. Theselosses are actually linked to the KID characterizing absorptionmechanism described in Section II.

This mechanism highlights the arising of a responsivity pat-tern composed of a coherent and an incoherent component. Toexplain this phenomenon the two antennas can be considered,separated by distance m as in Fig. 3, each one charac-terized by pattern . Here and are the standard azimuthand elevation angles defined with respect to a z axis normal tothe ground plane and a reference system pin jointed at the centerof the two antennas. The electric currents, and , induced ineach feeding line just in correspondence of the slot-CPW junc-tion can be represented as .

The term includes all the factors that build up the antennaefficiency in transforming the incoming electric field in receivedcurrents: match of the incident field distribution to the antennacurrent distribution, the antenna impedance, the polarizationmatch. We can assume that all these effect coalesce to have acurrent distribution and which are as high as possible,with 100% coupling efficiency (even if this is not realisticfor resonant antennas). Each antenna is considered matchedto its feeding transmission line, of characteristic impedance

. The power which is absorbed in the first portion of lengthm of each of these lines is associated to the pattern

of each slot.Each of the two lines absorbs a power,

, where is the imaginary part of theeffective propagation constant that characterizes the absorptionmechanisms in the THz regime. This portion of power canbe referred to as the power absorbed incoherently, where thecoherence is referred to the two slots.

After a length the two feeding lines are coher-ently summed up in the feeding junction that introducesthe resonator. Assuming that the common path trans-mission has characteristic impedance , thepower absorbed after the junction can be expressed as

. This isthe power absorbed coherently by the two slots. Clearly bothmechanisms contribute to the responsivity of the KIDs, withthe exact proportion and consequently the effective receiveradiation pattern, depending on the actual value of the attenu-ation constant, , [19]. The actual value of depends on thetemperature, the material, the thickness and the geometry of thesuperconducting structures composing the feeding lines. In ourcase the average width of the inner conductor was mand the width of each of the two gap slots composing in theCPW was m. Moreover the thickness of the tantalumfilm was nm which comparable to the penetrationdepth at the experiment frequency.


Fig. 8. Normalized E-plane radiation patterns in the lens, parametrized withrespect to the attenuation constant in the CPW transmission lines.

In the initial phase of this design it was imagined that thelosses in the first portion of the feeding lines would have beennegligible and only the coherent power would have been of im-portance. However, the losses add up to almost 10 dB’s in eachof two CPW lines of length . Thus, even the simplified mod-eling just described allows us to develop the expected radiationpatterns from the twin slot including both coherent and inco-herent contributions as a function of the attenuation constants.The E-plane pattern, normalized to the maximum value is re-ported in Fig. 8. The patterns are those obtained when the twinslot antenna is radiating in an infinite dielectric medium whichsimulates the dielectric lens. The parametric investigation in-cludes different attenuation constants for the THz CPW propa-gation constant , with the highest losses corresponding to theactual structure realized in the first experiment, Section IV. Themost striking effect highlighted by including coherent and in-coherent contributions is that the radiation pattern of the twinslot antenna is much less directive than the one including onlythe coherent contribution, the case with . Since the powerradiated toward low angles is essentially lost, see Fig. 4, it is pos-sible to conclude that the expected efficiency of the double slotantenna is easily two dB’s lower than was originally expected.

Given the importance of the coherent and incoherent recep-tion mechanisms a much more detailed characterization hasbeen performed. In [20] the perturbation of the input impedanceof the GHz resonator, accounting for the alteration of the trans-mission line characteristic impedance and propagation constantdue to the absorption of THz power has been evaluated. Thismodeling effectively accounts for the actual distribution of theTHz power in the lines and does not resort to the simplifyingassumptions that antennas and transition junctions are matched.Moreover, the model also includes the focusing of the patternrealized through the lens resorting to the usual physical opticsapproximation [13].

The preliminary results indicate that the cross polarizationlevels reported in Fig. 7 are entirely due to incoherent radiationeffects, in fact the cross-polarized field components received by

Fig. 9. Comparison between simulated and measured patterns in the E-plane.

each slot should cancel out if the lines were performing an idealcoherent summation of the current contributions at the junction.Finally, Fig. 9 shows a comparison between the radiation pat-terns simulated and measured in the E plane. Apart from minoroscillations of the measured pattern due to inaccuracies of theoptical set up, the improved model, label as total pattern, isclearly more capable to account for the pattern broadening andhigher side lobe levels than the pattern predicted accountingonly for the coherent absorption, where the losses accounted forare pertinent to Np/m. Note that also in this graph thepatterns are normalized to their maximum.

Overall it must be said that the measured results from thefirst GHz implementation, and the following data inter-pretation, led to the conclusion that future implementation oflens antenna coupled KID resonators would greatly benefit fromprinting the antennas and array feeding networks entirely on su-perconducting materials operated below their critical frequen-cies (where they are virtually lossless and only coherent radia-tion would play a role). This is not always possible especiallywhen the frequency of operation reach frequencies as high as 3THz. In this case it appears that accurate modeling of coherentand incoherent receptions are truly essential for the use of an-tenna coupled KID structures. Note that similar considerationsprobably apply also to the directly coupled arrays, [5].

VI. SENSITIVITY

The noise performance of direct detectors of radiation is usu-ally quantified via the Noise Equivalent Power. This param-eter is introduced in the Appendix for the readers that are un-familiar to it. In [2] and [3] the dark NEP was measured toquantify the dependence of the output from the THz powerabsorbed by the resonator, . could be the phase or am-plitude power spectrum of the of the CPW line throughline the resonator is coupled to. In [3] a typical experimentalcharacterization set up is described. Optical signals were simu-lated by mounting the device on a heater, allowing the controlof thermally excited quasi-particles within the KID resonator, asshown in Fig. 10. In this work 100-nm-thick sputter depositedAluminum on high resistivity silicon was used to realize high


Fig. 10. Schematic set up for the measurements of the noise equivalent powerof the KIDs, dark measurements and optical measurements.

Q microwave resonators . These devices led todark . The NEP was obtained by mea-suring and calculating the terms in the expression (1) of [3].Eventually, as explained in the Appendix, the key observable pa-rameters are the noise, , associated to the output and the re-sponsivity . In dark NEP measurements quasi-par-ticles are created by increasing the temperature of the devicesbetween 100 mK and 300 mK. The number of quasi particles,

, is related to the temperature through the Mattis Bardeenexpression [21]. The quasi-particle number is convertedinto an effective absorbed power using equation:

, where is the Cooper-pair binding en-ergy, the quasi particle creation efficiency, andthe quasi-particle life time. Therefore, can be cal-culated by actual measurements of and calculations of ,while changing the temperature .

A. Optical NEP

In antenna coupled KIDs the attention is directed to the sen-sitivity of the device to incoming THz photons. The key expres-sion for the sensitivity requires the measurement of , andthe evaluation of , where is the powerprovided by a black body source, see Fig. 10. The temperatureof the black body is varied between 4 K and 40 K to evaluate

.It is interesting to compare the values that one obtains for

the optical NEP and for the dark NEP. An important differencebetween the dark and optical NEP is that in the first the tem-perature increase of the device is uniformly distributed, whilein the latter the impact on photons is localized into certain por-tions of the circuit: in antenna coupled KID most of the power isconcentrated in the end point of the resonator (i.e., close to theantenna). Actually, the evaluation of the power distribution onthe resonators is not trivial and it is the subject of an on goingparallel work [20].

In first approximation this team has, up to now, assumed thatthe power contributing to the quasi particles generation is de-fined by a unique parameter, the optical coupling efficiency,

, which accounts for how much power generated by theblack body contributes to the generation of quasi particles. Con-tributions to the reduced optical efficiency are the effective

Fig. 11. Measured NEPs, dark and and optical measurements pertinent to theamplitude (Q factors) and the phase (resonating frequencies) of the resonatorsas a function of the frequencies. Data is for 100-nm Aluminum resonator withAluminum bridges.

quasi-particle generation efficiency , the polarization effi-ciency and the antenna efficiency : .

• is approximated to be 50% assuming that only halfof the THz absorption induced quasi-particles generated atthe antenna-resonator entry point will diffuse in the direc-tion of the resonator. The other half will diffuse toward theground plane and will not be detected. As mentioned theeffect of a more detailed analysis distribution of power isnot accounted for yet, but is under study [20].

• is expected to be 50% because the antenna is designedto be sensitive only to one polarization.

• is expected to be in the order of 40%. In fact in [13]was demonstrated that an ideal elliptical dielectric lens an-tenna without matching layers would present overall an-tenna efficiencies in the order of 50%. Here a further dropof efficiency to 40% is due to the losses in the ground plane,and the perturbation of the radiation patterns due to co-herent and incoherent radiation which further deterioratesthe lens reflection losses.

Overall % is a reasonable approximation andshould provide the main relationship between the dark NEP andthe optical NEP. This relation is in good agreement with theone measured in the experiment described in Section IV. Thetwo graphs pertinent to the baseband frequency dependenceof the dark and optical NEP are reported in Fig. 11. Note thatthe predicted efficiencies are in line with measurements and inline with efficiencies reported in literature [8], once the singlepolarization is accounted for.

B. Most Recent Results

The optical NEP shown in Fig. 11 suffers from poor polar-ization efficiency and quasi-particle generation efficiency. Thequasi-particle generation efficiency has already been improvedto 100% by fabricating the entire resonator and antenna struc-ture on a superconducting material with a gap frequency abovethe THz observation frequency. The radiation in this case isabsorbed in a short section where the material of the central


Fig. 12. Recently measured NEPs, using NbTiN ground plane (� � �� GHz), and Aluminium central line (�� GHz).

line of the resonator has a gap frequency below the observa-tion frequency. This was implemented using a NbTiN groundplane ( THz), and Aluminium centralline ( GHz). Also in recent experiments lenses withmatching layers where used. Using this improved design latestmeasurements of the quasi optical NEP’s are shown in Fig. 12,which shows measured improvements of the optical efficiencyto about 40%, with respect to a dual polarized beam impingingon the lens surface (again the results correspond to a situation inwhich the temperature of the load is varied from 4 k to 40 K).

Note that the dark NEP quoted in this section are relativelyhigh due to stray light impinging in the devices that are not fullyscreened. Completely screened NEP have been measured to be

[4]. Finally the polarization efficiency canbe brought to 100% by utilizing a dual polarized antenna. Withthese improvements we believe that the optical efficiency canbe improved to %, corresponding to an ideal optical NEP of

, given that highly effective stray light rejectionis implemented.

VII. BROAD BAND FOCAL PLANE FEEDS

As anticipated, besides the increased number of pixels in thefocal planes, the second requirement for the future detector arrayis wide bandwidth of operation. For SAFARI, the receivers arerequired to detect signals on an broad band from 1.2 THz to 8.5THz. However, efficient and truly wideband, large focal planearrays have never been realized in any frequency regime due tothe lack of adequate antenna feeding elements. As an example,in optics all existing focal plane arrays are narrow band: thephotographic cameras that address the entire visible spectrumcover a relative bandwidth (BW) in the order of 40% withvarying from 400 to 700 nm.

One should consider the following.• Absorber-like filled arrays, see [5], that are typically used

in optics can be used efficiently over an octave BW (factor1:2), beyond which an important reduction of efficiencyoccurs, due to the presence of the ground plane.

• Focal plane integrated antenna elements that are suited tobe arrayed in large numbers, that can operate efficiently

even over an octave bandwidth are not known to these au-thors.

For these reasons, current design efforts are focusing onachieving instruments composed of a few different focal planeseach one of them addressing an octave BW, or less. In thispaper, even though the THz front ends demonstrated are op-erating over relatively narrow bands % , care has beentaken that the solutions developed can be extended to operateover truly wide bandwidth.

A. Problems With Wide Band Reflectors

A reflector design capable of hosting many beams withoutdramatic alteration of the off focus beams performance (largeF/D) would need to be fed by narrow beam antennas with stablephase centers as a function of the frequency [9]. However, all di-rective wideband antennas, that have been used until now, havephase centers that move as a function of the frequency. As perti-nent example, Fig. 13 depicts a horn type feed that is located inthe vicinity of the focus of a parabolic reflector. Wide band hornfeeds obtain a significant directivity only when their length issignificant in terms of the wavelength (10–20 for an apertureof about 5 ). However, the phase center of the far field radiatedby an horn moves along the horn axis as a function of frequency.At high frequency it is located toward the lower feeding point ofthe horn, while at low frequency it is closer to the aperture. As aconsequence, drastic losses associated to the phase center errorwould occur if a wideband horn is used to feed a reflector over awide frequency band. These losses can be simply approximatedfollowing the design curves given in [10]

VIII. LEAKY LENS ANTENNA

To overcome these problems a novel antenna, the LeakyLens antenna, compatible with integration in dielectric lensesand KID structures, was developed at TNO, [11]. This antennasolves the problem of the phase center movement as a functionof the frequency by exploiting a traveling wave radiation mech-anism. The basic concept is that a slot antenna, of width andvery long in terms of the wavelength, printed on a membranethat is kept at a short distance , from a dielectric lens (seeFig. 14), when it is fed at the center, supports an outgoing wavethat slowly leaks power into the lens. The lens is an extendedhemisphere, characterized by a certain extension length, E, andradius of the sphere, R., exciting only the upper portion of thelens. Thnaks to the fact that the slot’s plane is kept at a smalldistance from the lens, the traveling waves on the slots are sofast that they only excite the upper part of the lens. Such agoal was also achieved by the famous double slot feed in [13],however in that case the effect was only achieved over a 10%relative BW. This mechanism is essentially frequency indepen-dent, not only in the input impedance but also in terms of beamwidth and phase center location. That is why the basic radiationmechanism is essentially well represented by the simplified raypicture in Fig. 14 at all frequencies. The apparent phase centeris essentially identified by the union of the approximate dashedrays in the figure, relevant for a choice of R. Notethat the picture is appropriate for both E and H planes of thelens. The first antennas, designed and manufactured in printedcircuit board technology, and characterized at microwave


Fig. 13. Schematic view of a reflector system and focal plane suited to host feeds for multiple beam imaging.

frequencies, showed excellent performance in the range from5 to 70 GHz, [23]. The lenses were realized with TMM10material from Rogers . Some of these antennas weremanufactured including 3 matching dielectric layers, whileothers were realized without matching layers as it is assumedthat these latters could have been not simple to manufactureat the sub-millimeter wave frequencies. The measurementspresented in [23] show that the planarly fed UWB Leaky Lensantenna has, over a BW 1:5, directive and circularly symmetricradiation patterns withvery low cross-polarization (with respectto other wideband antennas). The measurements were limitedto 75 GHz. However, simulations [24] show that the leaky lensantenna can be used with outstanding pattern quality on bandsexceeding 1:20.

A. Phase Center

To demonstrate the phase center stability of Leaky Lenses,the link between two of such antennas have been realized. Thelink, both for lenses with and without matching layers, showedexcellent pulse fidelity. A parameter typically used to quantifythe pulse fidelity is the fidelity factor: the correlation integral be-tween a transmitted and a received signal in time. Specifically,even without matching layers, fidelity factors higher than 0.91(with 1 being the value that would be otained using a completelynon dispersive ideal transmission line) were measured on theband 5–70 GHz. From the pulse preservation, the stability ofthe phase center for observation points at broadside was derived.To this regard, Fig. 15 shows the measured variation of the ef-fective distance between two Leaky Lenses located one in frontof the other as can be deducted from the Fourier transform ofthe measured parameters. It is evident that in the frequencyrange from 20 to 70 GHz the apparent phase center at broad sidemoves only 0.5 mm, which is roughly a tenth of the wavelengthat the highest frequency.

It must be observed that the phase center stability at broad-side is only a sufficient condition for the antenna to be used

Fig. 14. Geometry of the leaky lens structure. The slot is etched on a membranekept at a small distance from the dielectric lens.

efficiently as a reflector feed; in fact the phase center stabilityshould be guaranteed at all directions spanned by the dBbeam. The phase center stability of the fields radiated in direc-tions different from broad side were theoretically and numeri-cally demonstrated in [11] and in [24] respectively. The specificlocation of the phase center is essentially dependent on the ex-tension lens chosen for the hyper hemispherical lens, but it isnot, in any case, a function of the frequency. As consequence of


Fig. 15. Effective distance between two antennas as a function of the frequencyand corresponding phase center variation as a function of the frequency. Caseof the leaky lens without matching layers.

Fig. 16. Lens-based multibeam imaging, capable of operating over decades ofbandwidth thanks to the phase center stability of the leaky lenses.

this unique quality of the Leaky Lens antenna, and because ofits high directivity, it can be used as feed for reflector systemscapable of operating over decade bandwidths and characterizedby large . This antenna is thus suited also for focal planearrays where thousands of beams are required for imaging ap-plications (Fig. 16).

B. Efficiency Aspects

The efficiency that relates the gain of the Leaky Lens to itsdirectivity, , was measured to be about higher than 85%on a bandwidth 1:5 (15 GHz to 75 GHz) in the presence ofthe matching layers. Most of these losses are due to the dielec-tric losses that grow significantly from 30 GHz on (the materialwas TMM10 from Rogers). These dielectric losses are expectedto be insignificant for silicon lenses used in the THz regimeas shown in [25]. The efficiency without matching layers washigher than 68%. Note that this high efficiency even in absenceof matching layers stems from the capacity of the leaky feedto focus power in the center of the lens only. Since dielectriclosses will probably not be a concern for silicon lenses at THzfrequencies, the efficiency without matching layers in Thz lenssystem could be higher than 75%. The entire feed array systemincluding lens could be manufactured in a unique integrated so-lution, as the depth of the lenses is only from tens to hundredsof micrometers.

In other THz telescope contexts, the efficiency of a feed is alsoa term used to relate the captured power to the physical apertureof an antenna feed (distribution efficiency). This is especiallyimportant in narrow band imaging systems, where the tendencyis to fill the focal planes as densely as possible to capture everypossible photon impinging from deep space. However, in de-signing a broad band imaging array (decade bandwidth) it is alsoimportant to use efficiently the main reflector across the entirebandwidth. This effect can be obtained if the detector beamspresent only minor variations as a function of the frequency, aneffect that can be achieved with Leaky Lenses characterized by

. This configuration leads to the under sampling of thefocal plane as the price to pay for a truly broad band imagingsystem. This price seems moderate and affordable when con-sidering that only one focal plane, possibly with many more el-ements, and only one cooler needs to be hosted, instead of threeor more, each characterized by smaller bandwidth.

C. Leaky Lenses With KIDS

The coherent and incoherent detection mechanism discussedin Section V are essentially due to the extension of physicaldimension of the twin slot array (including the feeding lines).In the case of a leaky lens antenna, the physical dimensions arealso significant in terms of the wavelength and the incoherentdetection could significantly alter its pattern and efficiency. As aconsequence these antennas should be used in conjunction withKID detectors only at frequencies below the critical frequenciesof the used superconductors. Otherwise the advantages derivingfrom use of the leaky lens antennas in terms of pattern qualityand phase center stability would be essentially lost.

D. Polarization Aspects

So far all the discussion has been mainly focused on singlypolarized antennas. However, for some of the proposed futureapplications a dual-polarized detector array would be benefi-cial, given that this would double the signal in comparison to re-ceiving only one polarization. In order to achieve this goal overa broad range of frequencies, a version of the Leaky Lens an-tenna concept operating very efficiently over two polarizationshas been proposed, [26]. The antenna has been analyzed withfull wave commercial simulations and leads to two orthogonalchannels ( dB) with 90% efficiency over a relativeBW of . Note that this efficiency is the the ratio betweengain and directivity (it does not include distribution efficiency,i.e., loss due to undersampling of the focal plane.).

IX. CONCLUSION

This paper has described a strategy for the efficient and sensi-tive imaging of THz sources resorting to a truly broad band focalplane array composed of thousands of antenna coupled KIDs.The results of the preliminary 675-GHz demonstrators indicatethe maturity of the measurement set up, the reliability of themanufacturing processes, and the reproducibility of expectedresults. The measurements of the feed prototypes at 70 GHzdemonstrate the validity of the innovative antenna concept pro-duced. Future work will proceed by building on these measure-ments using new devices and antennas to obtain optimal opticalperformance, i.e., optical efficiency and frequency response of


the detectors to satisfy the most stringent requirements. For ex-ample, very sensitive devices and a very low optical load setupwill need to be developed to demonstrate the optical sensitivityrequired for SAFARI.

APPENDIX

NOISE EQUIVALENT POWER (NEP)

The characterization of sensitivity via the NEP is not familiarto many scientists with an Electrical Engineering background,hence this Appendix. Let us call P and F the input and outputsignals, respectively, of a detector under analysis. It is assumedthat the output of a detector can be expanded by Mc Laurinseries as follows:

(1)

Here is the output in absence of input, i.e., the noise in-troduced by the receiver: in the following it will be indicated as

. The Noise Equivalent Power for detector, by definition, isthe signal power in input that would provide in output a signal ofamplitude equal to , in absence of any noise. In this situation

(2)

Solving for the NEP one can obtain. So the evaluation of the NEP in

first approximation only requires the evaluation of , theoutput noise, and , which is typically indicatedas the responsivity of with respect to .

In the present KID context, the output quantity is eitherthe phase or the amplitude power spectrum of the of theMicrowave Transmission line, and P is the power absorbed bythe KID as a function of the temperature variations (dark NEP),or the power provided by a Black Body (Optical NEP).

ACKNOWLEDGMENT

The authors would like to thank Dr. N. Llombart and Dr. S.Yates for useful and fruitful discussions.

REFERENCES

[1] Infrared, Submillimeter, and Millimeter Detector Working Group,”Detector Needs for Long Wavelength Astrophysics,” 2002 [On-line]. Available: http://www.sofia.usra.edu/det_workshop/report/IS-MDWG_final.pdf

[2] P. K. Day, H. G. LeDuc, B. A. Mazin, A. Vayonakis, and J. Zmuidz-inas, “A broadband superconducting detector suitable for use in largearrays,” Nature, vol. 425, Oct. 23, 2003.

[3] J. Baselmans, S. J. C. Yates, R. Barends, Y. J. Y. Lankwarden, J. R.Gao, H. Hoevers, and T. M. Klapwijk, “Noise and sensitivity of alu-minum kinetic inductance detectors for sub-mm astronomy,” J. LowTemp. Phys., vol. 151, pp. 524–529, 2008.

[4] P. J. deVisser, J. J. A. Baselmans, P. Diener, S. J. C. Yates, A. Endo,and T. M. Klapwijk, “Number fluctuations of sparse quasiparticles ina superconductor,” Phys. Rev. Lett., vol. 106, p. 167004, 2011.

[5] S. Doyle, P. Mauskopf, J. Naylon, A. Porch, and C. Duncombe,“Lumped element kinetic inductance detectors,” J. Low Temp. Phys.,vol. 151, pp. 530–536, 2008.

[6] J. A. Chervenak,a), K. D. Irwin, E. N. Grossman, J. M. Martinis, C. D.Reintsema, and M. E. Huber, “Superconducting multiplexer for arraysof transition edge sensors,” Appl. Phys. Lett., Device Phys., vol. 74, no.26, June 1999.

[7] Core Science Requirements for the European SPICA Instru-ment [Online]. Available: http://sci.esa.int/science-e/www/ob-ject/index.cfm?fobjectid=42283

[8] P. K. Day, H. G. LeDuc, A. Goldin, T. Vayonakis, B. A. Mazin, S.Kumar, J. Gao, and J. Zmuidzinas, “Antenna coupled microwave ki-netic inductance detectors,” Kinetic Nucl. Instrum. Meth. Phys. Res. A,vol. 559, pp. 561–563, 2009.

[9] Y. Rahmat-Samii, “Chapter 15 reflector antennas,” in “Antenna Hand-book” from Y. T. Lo and S. W. Lee. New York: Van Nostrand Rein-hold, 1988.

[10] T. Milligan, Chapter 8, Modern Antenna Design. Hoboken, NJ:Wiley, 2005.

[11] A. Neto, “Planarly fed leaky lens antenna. Part 1: Theory and design,”IEEE Trans. Antennas Propagat., vol. 58, no. 7, pp. 2238–2247, Jul.2010.

[12] D. B. Rutledge and M. S. Muha, “Imaging antenna arrays,” IEEE Trans.Antennas Propagat., vol. AP-30, no. 4, pp. 535–540, Jul. 1982.

[13] D. F. Filippovic, S. S. Gearhart, and G. M. Rebeiz, “Double sloton extended hemispherical and elliptical silicon dielectric lenses,”Microwave Theory Tech., vol. 41, no. 10, 1993.

[14] A. Neto, D. Bekers, G. Gerini, J. Baselmans, S. Yates, and H. Ho-evers, “EBG enhanced dielectric lens antennas for imaging at sub-mmwaves,” presented at the Antennas and Propagation Symp., San Diego,CA, Jul. 2008.

[15] A. Neto and S. Maci, “Green’s function of an infinite slot printed be-tween two homogeneous dielectrics. Part I: Magnetic currents,” IEEETrans. Antennas Propagat., vol. 51, no. 7, pp. 1572–1581, Jul. 2003.

[16] S. Maci and A. Neto, “Green’s function of an infinite slot line printedbetween two homogeneous dielectrics. Part II: Uniform asymptoticfields,” IEEE Trans. Antennas Propagat., vol. 52, no. 3, pp. 666–676,Mar. 2004.

[17] N. Llombart, A. Neto, G. Gerini, M. Bonnedal, and P. de Maagt, “Im-pact of mutual coupling in leaky wave enhanced imaging arrays,” IEEETrans. Antennas Propagat., vol. 56, no. 4, pp. 1201–1206, Apr. 2008.

[18] A. Iacono, T. J. Coenen, D. J. Bekers, A. Neto, and G. Gerini,“Trade-offs in multi-element receiving antennas with superconductingfeed lines,” presented at the Eur. Conf. Antennas and Propagation,Barcelona, Spain, Apr. 12–16, 2010.

[19] C. L. Holloway and E. F. Kuester, “A quasi-closed form expressionfor the conductor loss of CPW lines, with an investigation of edgeshape effects,” IEEE Trans. Microw. Theory Tech., vol. 43, no. 12, pp.2695–2701, Dec. 1995.

[20] A. Iacono, A. Freni, A. Neto, and G. Gerini, “Pattern broadeningphenomenon in antenna arrays fed by superconducting corporate feedlines,” IEEE Trans. Antennas Propagat., to be published.

[21] D. C. Mattis and J. Bardeen, “Theory of the anomalous skin effect innormal and superconducting metals,” Phys. Rev., vol. 111, no. 2, Jul.15, 1958.

[22] S. Bruni, A. Neto, and F. Marliani, “The UWB leaky lens antenna,”IEEE Trans. Antennas Propagat., vol. 57, no. 10, pp. 2642–2653, Oct.2007.

[23] A. Neto, S. Monni, and F. Nennie, “Planarly fed leaky lens antenna.Part 2: Demonstrators and measurements,” IEEE Trans. AntennasPropagat., vol. 58, no. 7, pp. 2248–2258, Jul. 2010.

[24] N. Llombart and A. Neto, “Non dispersive extended hemispherical lensantennas for wide band THz sources,” IEEE Trans. Antennas Propagat., to be published.

[25] P. Haring Bolivar, M. Brucherseifer, J. G. Rivas, R. Gonzalo, I. Ederra,A. L. Reynolds, M. Holker, and P. de Maagt, “Measurement of thedielectric constant and loss tangent of high dielectric-constant materialsat terahertz frequencies,” IEEE Trans. Microw. Theory Tech., vol. 51,no. 4, pp. 1062–1066, Apr. 2003.

[26] O. QuevedoTeruel and A. Neto, “CPW fed dual polarized leaky lensantenna,” presented at the EUCAP, Rome, Italy, Apr. 2011.

Andrey Baryshev received the M.S. degree (summacum laude) in physical quantum electronics in 1993from the Moscow Physical Technical institute,Russia, and the Ph.D. degree from the TechnicalUniversity of Delft, Delft, The Netherlands, in 2005on the subject of Superconducting Integrated Re-ceiver combining SIS mixer and Flux Flow oscillatoron one chip.

He is a senior instrument scientist and has benewith the SRON Low Energy Astrophysics Divisionand Kapteyn Astronomical Institute, University of

Groningen, The Netherlands, since 1998. In 1993, he was an instrument sci-entist with the Institute of Radio Engineering and Electronics, Moscow, in the


field of sensitive superconducting heterodyne detectors. In 2000, he joined aneffort to develop an SIS receiver (600–720 GHz) for Atacama Large MillimiterArray, where he designed the SIS mixer, quasi-optical system, and contributedto a system design. Currently, his main research interests are in the area ofapplication heterodyne and direct detectors for large focal plane arrays in THzfrequencies and quasi-optical systems design and experimental verification.

Dr. Baryshev received the NWO-VENI grant for the research on heterodynefocal plane arrays technology in 2008, and in 2009 he received the EU com-mission Starting Researcher Grant for research on focal plane arrays of directdetectors.

Jochem J. A. Baselmans graduated in 1998 on a re-search project from the University of Groningen, TheNetherlands, and received the Ph.D. degree (summacum laude) from the University of Groningen in 2002with a dissertation entitled “Controllable JosephsonJunctions”.

He is instrument scientist and has been withSRONs Sensor Research and Technology divisionsince 2002. He started with SRON, Utrecht, TheNetherlands, in 2002 as postdoctoral InstrumentScientist at the SRON Netherlands Institute for

Space Research. Until 2004, he worked on hot electron Bolometer mixers,very sensitive heterodyne radiation detectors for frequencies between 1–5 THz.He now leads the Dutch effort on the development of imaging arrays basedupon KIDs. SRON MKIDs have shown superior sensitivity and single pixelcoupling efficiency using antenna based radiation coupling. Currently, he ismainly working towards very large arrays (30.000+ pixels) for ground-basedobservatories. He has published about 20 papers and is a coauthor of more than20 other papers.

Dr. Baselmans received a NWO-VENI grant to start research on KIDs inSRON in 2004.

Angelo Freni (S’90–M’91–SM’03) received theLaurea (Doctors) degree in electronics engineeringfrom the University of Florence, Italy, in 1987.

Since 1990, he has been with the Department ofElectronic Engineering, University of Florence, firstas Assistant Professor and, in 2002, as Associate Pro-fessor of electromagnetism. During 1994, he was in-volved in research at the Engineering Department,University of Cambridge, UK. From 1995 to 1999, hewas an Adjunct Professor at the University of Pisa,Italy, and in 2010, he was visiting professor at the

Technical University of Delft, The Netherlands. Between 2009 and 2010, healso spent one year as a researcher at the Netherlands Organization for AppliedScientific Research (TNO), The Hague, The Netherlands. His research interestsinclude meteorological radar systems, radiowave propagation, numerical andasymptotic methods in electromagnetic scattering and antenna problems, and re-mote sensing. In particular, part of his research concerned the extension and theapplication of the finite element method to the electromagnetic scattering fromperiodic structures and to the electromagnetic interaction with moving media.

Giampiero Gerini (M’92–SM’08) received theM.Sc. (summa cum laude) and Ph.D. degrees in elec-tronic engineering from the University of Ancona,Italy, in 1988 and 1992, respectively.

From 1992 to 1994, he was Assistant Professor ofelectromagnetic fields at the University of Ancona.From 1994 to 1997, he was Research Fellow at theEuropean Space Research and Technology Centre(ESA-ESTEC), Noordwijk, The Netherlands, wherehe joined the Radio Frequency System Division.Since 1997, he has been with the Netherlands Organ-

ization for Applied Scientific Research (TNO), The Hague, The Netherlands.At TNO Defence Security and Safety, he is currently Chief Senior Scientist ofthe Antenna Unit in the Transceiver Department. In 2007, he was appointedas part-time Professor at the Faculty of Electrical Engineering, EindhovenUniversity of Technology, The Netherlands, with a chair on Novel Structuresand Concepts for Advanced Antennas. His main research interests are phasedarrays antennas, electromagnetic bandgap structures, frequency selective sur-faces and integrated antennas at microwave, and millimeter and sub-millimeter

wave frequencies. His main application fields of interest are radar, imaging,and telecommunication systems.

Dr. Gerini was co-recipient of the 2008 H. A. Wheeler Applications PrizePaper Award of the IEEE Antennas and Propagation Society. He was also co-re-cipient of the Best Innovative Paper Prize of the 30th ESA Antenna Workshopin 2008 and of the best antenna theory paper prize of the European Conferenceon Antennas and Propagation (EuCAP) in 2010.

Henk Hoevers received the Ph.D. degree in experi-mental solid state physics from the University of Ni-jmegen, The Netherlands.

As a postdoctorate, he worked in the field ofinstrumentation for high-resolution electron mi-croscopy for material research in the Particle OpticsGroup of the Delft University of Technology, TheNetherlands. In 1995, he joined the SRON Nether-lands Institute for Space Research, Utrecht, TheNetherlands, and worked on cryogenic radiationdetectors. Since 2003, he has been the Head of the

division Sensor Research and Technology. The main activities in his groupcomprise R&D on arrays of KIDs, arrays of Transition Edge Sensors for IR andX-ray astronomy as well as their readout, and Hot Electron Bolometer Mixers.He is an author and co-author of about 120 papers on cryogenics detectors,solid state physics, and instrumentation.

Annalisa Iacono (S’09) received the M.Sc. degree(summa cum laude) in electronic engineering fromthe University of Naples “Federico II”, Naples, Italy,in 2006. She is currently pursuing the Ph.D. degreein the Telecommunication Technology and Electro-magnetics Group (TTE/EM), Eindhoven Universityof Technology, Eindhoven, The Netherlands.

Since March 2008, she has been with the AntennaGroup at TNO Defence, Security and Safety, TheHague, The Netherlands. Her research interestsinclude the analysis and design of antennas, with

emphasis on sub-millimeter waves applications.Ms. Iacono was co-recipient of the best paper for antenna theory prize at the

European Conference on Antenna and Propagation (EUCAP) in 2010.

Andrea Neto (M’00–SM’10) received the Laureadegree (summa cum laude) in electronic engineeringfrom the University of Florence, Italy, in 1994and the Ph.D. degree in electromagnetics fromthe University of Siena, Italy, in 2000. Part of hisPh.D. was developed at the European Space AgencyResearch and Technology Center, Noordwijk, TheNetherlands, where he worked for the antennasection for over two years.

In 2000 and 2001, he was a Postdoctoral Re-searcher at the California Institute of Technology,

Pasadena, working for the Sub-Millimeter Wave Advanced Technology Group.From 2002 to January 2010, he was a Senior Antenna Scientist at TNODefence, Security and Safety, The Hague, The Netherlands. In February2010, he was appointed Full Professor of applied electromagnetism at theEEMCS Department, Technical University of Delft, The Netherlands. Hisresearch interests are in the analysis and design of antennas, with emphasis onarrays, dielectric lens antennas, wideband antennas, EBG structures, and THzantennas.

Dr. Neto was co-recipient of the H.A. Wheeler award for the best applica-tions paper of the year 2008 in the IEEE TRANSACTIONS ON ANTENNAS AND

PROPAGATION. He was co-recipient of the best innovative paper prize at the 30thESA Antenna Workshop in 2008. He was co-recipient of the best antenna theorypaper prize at the European Conference on Antennas and Propagation (EuCAP)in 2010. He presently serves as an associate editor of the IEEE TRANSACTIONS

ON ANTENNAS AND PROPAGATION and the IEEE ANTENNAS AND WIRELESS

PROPAGATION LETTERS (AWPL). He is a member of the Technical Board of theEuropean School of Antennas and organizer of the course on Antenna ImagingTechniques. He is a member of the steering committe of the network of excel-lence NEWFOCUS, dedicated to focusing techniques in millimeter and sub-mil-limeter wave regimes.

delft university of technology - 112 ieee transactions...

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