H. M. Elkamchouchi and G. Abouelseoud [114] presented a fractal patch to enhance
the impedance bandwidth of microstrip antenna��,Q�WKLV�UHVHDUFK��WKH�DXWKRU¶V�VKRZHG�
how the bandwidth of a conventional tria ngular patch antenna can be greatly
enhanced while maintaining the compactness of antenna using a Sierpinski Gasket
fractal patch. It has been also shown that using a double layer substrate (a lower layer
with a low dielectric constant and an upper layer with a higher dielectric constant) can
shift the wide band towards lower frequencies.
T. Luintel and P. F. Wahid [115] presen ted a modified stacked Sierpinski patch
antenna obtained by merging the top grid layer with the fractal antenna. This resulted
in an additional resonance but has a very poor return loss. According to authors,
truncating the corner of Sierpinski structure helped to improve the return loss. A gap
structure was analyzed next to obtain an increase in bandwidth. The gap was
introduced along the non-radiating edge of the antenna. Authors in their studies found
that the effect of gap is more noticeable at higher frequencies. This also produced
patterns that were more omni-directional. The proposed designs provide more
parameters allowing one to control the resonance and pattern.
N. A. Murad et. al. [116] explored the design of a set of microstrip fractal antennas.
The chosen configuration is the Sierpinski Gasket. The antennas were first simulated
and optimized. Upon achieving good perf ormance at the desired frequency of
operation of 1.575GHz, each iterative fractal design was then fabricated using a
microwave board. The antennas were then soldered with 50 ohm SMB connector at
the input. Measurements were performed for one and two-port parameters. The
measured antennas were found to perform well at their corresponding frequencies of
operation.
J. Anguera et. al. [117] discussed a triple-frequency antenna combining a dual-band
and a monoband antenna with broadside radiation patterns. The dual-band antenna is
also based on the Sierpinski fractal. It was formed by stacking over a monoband
antenna. Authors designed this antenna using a MoM commercial code and using the
experimental studies, they obtained three bands with a broad bandwidth, high
efficiency, and similar radiation patterns. This antenna was claimed to resonate at 0.8,
1.6 and 2.77GHz with gain of 5.3, 6.3 and 7.1dBi respectively.
N. S. Song et. al. [118] described that fractal antennas have the characteristic of
radiating in multiple frequencies through the property of self-similarity that fractal
shapes posses. Authors mentioned in this study that microstrip patch antennas with
28
Sierpinski fractal geometry can be designed to work exactly at the bands of interest,
through judicious choice of the fractal designs and iteration. Therefore, a broadband
dual frequency microstrip patch antenna with modified Sierpinski fractal geometry
was designed by using Microwave Office 2002 simulation software. The broadband
and multiple frequency characteristics of fractal antennas were also demonstrated.
The performance of microstrip patch an tenna with the original and modified
Sierpinski fractal geometries was also discussed.
S. Lin et. al. [119] investigated a multiband fractal triangle antenna developed from
the Sierpinski Gasket antenna. The antenna consisted of nesting triangles with
different heights and degrees of the apex angle. The antenna showed multiband
characteristics. Three parameters (height of the triangle, apex angular degree of the
triangle and the nesting number) were found to influence the central frequency of the
pass bands. Authors adjusted these parameters to design antennas with three pass
bands 900MHz, 1.8GHz and 2.4GHz. Authors claimed that the multiband fractal
triangle antenna is a novel antenna with controllable frequency bands and promising
application.
R. Ghatak et. al. [120] explored a new technique for designing Sierpinski Gasket
fractal microstrip antenna. In the absence of any available closed-form formulae, this
scheme uses an evolutionary method, based on real coded genetic algorithm (RCGA)
in conjunction with electromagnetic simulations. This method determines the side-
length and the fractal iteration number of the antenna, for operation at 4.56, 7.51 and
11.78GHz. The design simulation of th e antenna uses two different RCGA
implementation strategies.
R. K. Kanth [121] discussed the analysis of a dual band fractal antenna operating
simultaneously at L and S band. A L/S band Sierpinski fractal stacked multilayer
SDWFK�DQWHQQD�ZDV�GHVLJQHG��DQG�DQDO\]HG�IRU�DFKLHYLQJ�±�G%L�JDLQ�DW�����GHJUHH�
using Ansoft designer tool. The analyzed performance of the antenna indicated two
distinct frequency bands, meeting the VSWR requirement and its gain radiation
pattern. Author mentioned that the designed topology of the dual band fractal antenna
can be employed for satellite navigation. The attempt has also been made to achieve
the required specifications of the antenna in terms of bandwidth and gain radiation
pattern for a new resonant frequency 1.176GHz and 2.487GHz allotted to Indian
navigational satellite systems.
29
Z. Hu [122] proposeda modified Sierpinski fractal broadband antenna for multiband
application. Author employed the perturbed fractal patch and the modified ground
plane to obtain the wider bandwidth at the resonance frequencies. The implemented
antenna, with nearly omni-directional radiation pattern was designed with dimensions
of 50.8mm×69mm×1.6mm. The results obtained by authors showed that the antenna
resonated at the expected low frequencies and the return loss with bandwidths below
-10dB are 0.75-1.03GHz and 1.42-2.15GHz. It covers all the GSM, WCDMA,
CDMA2000 and TD-SCDMA bands.
M. Waqas [123] discussed afractal monopole antenna based on the Sierpinski Gasket.
The monopole antenna based on the Sierpinski Gasket was constructed through three
iterations. It displayed a multiband behaviour with three bands that was log
periodically spaced by a factor of 2, the same scale factor that defines the geometrical
self-similarity of the Sierpinski fractal. The simulated as well as measured input
return loss and radiation patterns all display multiband behaviour. Author changed the
geometrical scale factor of the Sierpinski fractal to investigate whether the bands are
shifted according to the new scale factor or not. The simulated results, mentioned by
author, showed that the band positions could be controlled by changing the scale
factor but on account of poor input matching. This poor input matching of Sierpinski
fractal monopole antenna with modified scale factor is rectified using microstrip feed
technique.
Y. K. Choukiker and S K Behera [124] presented a printed monopole antenna with
microstrip-fed Sierpinski fractal geometry for dual wide band application. The
operating bands were adjusted with the design of modified Sierpinski triangle
(radiating patch), ground plane and scale factor used to create a fractal shape. The
simulated -10dB (VSWR 2:1) reflection bandwidth obtained by authors for first
resonant frequency is 60% (1.47GHz to 2.7GHz). It covers GPS, DCS-1800,
PCS-1800, UMTS, IMT-2000, WiBRO (Wireless Broadband Internet Services) and
WLAN bands. For second resonant frequency the band width is 8% (4.991GHz -
5.4GHz) and covers 5.2GHz WLAN (802.11a). The radiation characteristics and gain
of the modified Sierpinski fractal antenna were also presented and discussed by
authors.
30
3.2 Koch fractal antenna
C. Borja et. al. [125] described a Koch snowflake antenna with three iterations. The
fractal patch was etched on a 0.8mm substrate having a dielectric constant of 3.38.
Authors mentioned that the antenna resonated at 1.11and 3.52GHz.
A. Sabouni et. al. [126] presented a Koch island microstrip patch antenna in order to
reduce antenna size. According to author, the patch antenna had a lower resonant
frequency compared to the square patch, and this property contributed to the antenna
VL]H�UHGXFWLRQ��)URP�WKH�DXWKRU¶V�PHQWLRQHG�results, the resonant frequency of the
patch decreases for the first iteration patch. Authors also mentioned that as the
iteration number increases, the resonant frequency of the patch also decreases.
However, the resonant frequency does not decrease significantly after the first
iteration.
T. P. Wong et. al. [127]reported a wideband vertical patch antenna (VPA), which is
devised from fractal antenna technology. By using a dual-Koch loop structure, authors
designed and tested a wideband VPA with 42% bandwidth and 8dBi gain at the center
frequency. Symmetrical broadside patterns were obtained at the pass band. The
resonant frequencies of the antenna measured by authors were 4.4 and 6.92GHz.
D. D. Krishna et. al. [128] investigated a dual wide-band CPW-fed modified Koch
fractal printed slot antenna, suitable for WLAN and WiMAX operations. In this study,
the operating frequency of a triangular slot antenna was lowered by the Koch iteration
technique resulting in a compact antenna. This study on the impedance and radiation
characteristics of the designed antenna indicated that a modified Koch fractal slot
DQWHQQD�KDV�DQ�LPSHGDQFH�EDQGZLGWK�IURP����������*+]�DQG�����±����*+]�
covering 2.4/5.2/5.8GHz WLAN bands and the 2.5/3.5/5.5GHz WiMAX bands.
Authors mentioned that the antenna exhibits omni-directional radiation coverage with
a gain better than 2.0dBi in the entire operating band.
M. N. Jahromi [129] described a planar monopole antenna using the Penta-Gasket-
Koch (PGK). Author claimed that this design achieves a good input impedance match
and linear phase throughout�WKH�SDVV�EDQG�����±��*+]� and 5dB criterion for
impedance bandwidth).The measured gain is approximately 4dBi, as mentioned by
author. This antenna is suitable for applications in ICMS, DECT, UMTS, Bluetooth,
and WLAN systems.
31
of the K-Sierpinski Carpet fractal an tennas are studied based on Ansoft HFSS
simulations. It was found by authors that the size reductions of the K-Sierpinski
Carpet fractal antennas are determined by K value and it is hardly related to the size
of antennas.
3.4 Sierpinski antenna array
V. F. Kravchenko [135] described thetheory of fractal antenna arrays. According to
authors, fractal antenna engineering based on atomic-fractal functions represented a
relatively new field of research that combines attributes of fractal geometry and
theory of functions with antenna theory. Research in this area yielded a rich class of
new designs for antenna elements as well as arrays. It has been demonstrated that
there are several desirable properties of atomic-fractal arrays, including frequency-
independent multiband behaviour, schemes for realizing low-sidelobe design,
systematic approaches to thinning, and the ability to develop rapid beam-forming
algorithms by exploiting the recursive nature of fractals and properties of atomic
functions.
R. Hu et. al. [136] presented a novel fractal folded-slot antenna using Sierpinski
curves which are generated by L systems. In the reported research, a simple folded-
slot antenna, Sierpinski fractal folded-slot antenna were designed and simulated. The
simple folded-slot antenna obtained a return loss of -37.5dB at the resonant frequency
of 10GHz. The first iteration Sierpinski fractal folded-slot antenna provided a return
loss of -30.5dB at the resonant frequency of 9.4GHz. The return loss of the second
iteration Sierpinski fractal folded-slot antenna is -35.5dB at the resonant frequency of
6.7GHz. Authors also reported a downward shift in the resonant frequency of these
antennas when the fractal iteration increases.
3.5 Hexagonal fractal antenna
P. W. Tang and P. F. Wahi [137] developed design of a new fractal multiband antenna
based on the hexagon. Three iterations of the hexagonal fractal multiband antenna
arranged in the dipole configuration were examined. Experimental results were
compared with those obtained using the method of moments and the fractal antenna
was found to possess predictable multiband characteristics. Authors claimed that the
hexagon shaped antenna resonates at 0.263, 1.403 and 4.263GHz.
D. Liu and B. Gaucher [138] elaborated an antenna which is a combination of an
inverted-F antenna, a coupled element and a branch element. As a tri-band antenna,
33
the inverted-F antenna is for the low band, while the branch element is for the middle
band and the coupled element for the high band. In some applications, the middle and
high bands can be combined as one band to form a dual band antenna. The antenna is
best suited for the 2.4GHz Bluetooth/WLAN and the 5GHz (5.15-5.85GHz) WLAN
applications or the 800/900MHz and the 900/1800MHz cellular applications.
3.6 Minkowski fractal antenna
L. X. Zheng et. al. [139] analyzed the Minkowski fractal patch antenna to reduce the
antenna size. The simulation results show that fractal iteration, and the iteration factor
has different effect on the reduction of patch antenna. Their experimental work
showed that the 1st iteration Minkowski fractal patch antenna reduced the antenna size
by 47%; while, maintaining the same resonant frequency as that of the normal square
patch antenna.
N. Abdullah et. al. [140] proposed a Minkowski fractal antenna which is fabricated
with FR4 material with side length of 38.78mm. The resonant frequencies mentioned
by authors are 1.49 and 1.81GHz. Authors claimed that this type of antenna which is
based on Minkowski pattern is the one of multiuse antenna and can be utilized for
future broadband wireless communications.
P. N. Rao and N V S N Sarma [141] emphasized on a Minkowski fractal strip
boundary linearly polarized microstrip antenna with different indentation depth
factors. They demonstrated that the resonance frequency can be systematically
controlled by changing the boundary indentation depth factor. Authors mentioned that
the resonance frequency is varied by more than 25% when the boundary is replaced
by the fractal curve. The reduction in frequency of 25% is equivalent to about 50%
size reduction of the patch compared to the corresponding square patch. According to
authors, this antenna can be used for RFID, GPS applications and mobile satellite
communications.
M. Comisso [142] did the theoretical an d numerical analysis of the resonant
behaviour of Minkowski fractal dipole antenna. The resonant behaviour and the size
reduction capabilities of the Minkowski fractal dipole an tenna were investigated.
Authors analyzed their antenna at each resonant frequency by considering the
radiation efficiency and fractional bandwidth. In addition, a method for deriving the
approximate position of resonant frequencies of Minkowski dipole at each iteration is
34
to perform well in terms of bandwidth, beamwidth and low cross polarization, despite
its small size. The antenna is reported to resonate at 5.53, 6.51, 8.5 and 9GHz.
W. L. Chen et. al. [164] proposed amicrostrip-line fed printed wide-slot antenna with
a fractal shaped slot for bandwidth enhancement and this antenna is also
experimentally studied. By etching the wide slot as fractal shapes, it is experimentally
found that the operating bandwidth can be significantly enhanced, and the relation
between the bandwidth and the iteration order and iteration factor of the fractal shapes
is experimentally studied. Experimental results performed by authors indicated that
the impedance bandwidth, defined by -10dB reflection coefficient, of the designed
fractal slot antenna can reach an operating bandwidth of 2.4GHz at operating
frequencies around 4GHz, which is about 3.5 times that of a conventional microstrip-
line fed printed wide-slot antenna. It also achieved a 2dB gain-bandwidth of at least
1.59GHz.
Y. B. Thakare and R. Kumar [165] presented a novel design of star-shaped fractal
patch antenna for miniaturization and backscattering radar cross-section reduction.
Authors mentioned that this antenna is useful for wireless application in 0.85-4GHz
frequency band. They also mentioned that increase in number of fractal iterations
included in the conventional patch to design fractal antenna geometry reduces
backscattering RCS at multiband compared to the conventional patch antenna. This
reduction in backscattering RCS by the antenna is observed at multiband. Authors
also mentioned that the antenna can be tuned for low backscattering by variation in
the substrate dielectric constant and thickness. For maximum RCS reduction by the
antenna, optimization of substrate thickness becomes necessary. The study also deals
with effect of frequency and aspect angle variation on backscattering RCS reduction.
Authors mentioned that the study helps antenna designer to tune the antenna for
minimum RCS, as RCS reduction is usually important for various defense and civilian
applications.
A. Azari [166] explored new fractal geometry to a wire monopole antenna. Modelling
and simulation is performed using SuperNEC electromagnetic simulator. Results of
simulation show that proposed antenna is applied in 11-52GHz frequency range.
Radiation patterns are also studied.
J. Pourahmadazar et. al. [167] discussed a new form of a hybrid design of a
microstrip-fed parasitic coupled ring fractal monopole antenna with semi-ellipse
ground plane for modern mobile devices having a wireless local area network module
41
along with a Worldwide Interoperabili ty for Microwave Access function. In
comparison to the previous monopole structures, the miniaturized antenna dimension
is only about 25mm x 25mm x 1mm, which is 15 times smaller than the previous
proposed design. By only increasing the fractal iterations, very good impedance
characteristics are obtained. It is shown that by incr easing fractal iteration and
optimizing antenna parameters with proper values, a very good impedance matching
and improvement in bandwidth can be obtained. The measured results illustrate that
the proposed antenna offers a very good bandwidth and omni-directional pattern up to
10GHz.
G. Srivatsun and S. Subha Rani [168] reported a compact, low profile, low cost
self-affine antenna developed to operate in 402-405MHz and found to provide a wide
bandwidth. The return loss of the self-affine antenna is maintained more than -35dB
except iteration (K1). Therefore, the proposed antenna shall be incorporated in textile
material or through handheld devices for monitoring the physiological parameters.
The antenna shall also be used in military applications for communication between
two persons. Since the antenna exhibits wideband characteristics it can be used in
variety of application.
A. Kumar and T. K. Sreeja [169] descri bed the design of a planar broadband
Sierpinski fractal antenna for multiband communication systems. A modified three-
iteration Sierpinski patch and a slotted ground plane are used to enhance the
bandwidth. The implemented antenna including the ground plane has a total
dimension of 24mm x 14mm x 0.8mm. The simulated return loss, radiation patterns
and gain of the proposed antenna has been presented. The proposed antenna has
operational bands from 2.55-2.8GHz, 4.9-5.3GHz, 6.4-9.8GHz, 9.8-12GHz which
cover the satellite DMB/CIX bands. The radiation pattern is isotropic like. Therefore,
the designed antenna was feasible for used as a multiband communication antenna.
S. R. Anoop et. al. [170] discussed a higher order fractal patch antenna for multiband
operation. Fractal structure was introduced in this research in order to obtain the
multiple frequency operation and to preserve the patch antenna properties like small
size and low profile. Authors considered the square shaped fractal antenna and three
iterations of the basic structure are simulated. Authors mentioned that the number of
resonant frequencies increases with the iteration order of the fractal antenna structure.
The minimum number of resonant frequencies needed for every iteration, is one more
42
than the iteration order. The multiband behaviour of the proposed fractal antenna was
proved by the results of simulations performed by authors.
R. Kumar et. al.� [171] discussed the design of an inscribed square circular fractal
antenna with notch, having adjustable frequency characteristics. The position and
width of the notch band can be adjusted in the entire operating band. A prototype of
the antenna was designed on FR4 substrate, with dielectric constant 4.3 and thickness
h=1.53mm with a U-shape slot in coplanar waveguide feed of length L=11mm and
slot width W=0.4mm. A band-notched characteristic with position and width
adjustable over the entire UWB bandwidth from 3.1 to 10.6GHz was achieved by
incorporating a U-shaped slot on the feed line. Authors mentioned that their designed
antenna show measured return loss greater than -10dB for the frequency band from
3.1 to 15GHz, with a rejection band between 3.635GHz to 3.935GHz. The inscribed
square circular fractal antenna with notch can thus, be used for ultra wide band
system, microwave imaging and precision position system.
A. Azari [172] reporteda multiband and broadband microstrip antenna based on new
fractal geometry. The designed antenna in this study was an octagonal fractal
microstrip patch antenna. The simulation and optimization were performed using CST
microwave studio simulator. The results showed that the proposed microstrip antenna
FDQ�EH�XVHG�IRU���*+]±��*+]�IUHTXHQF\�UDQJH��L�H���LW�LV�D�VXSHU�ZLGHEDQG�
microstrip antenna with 40GHz bandwidth. The designed structure had a dimension of
6cm x 6cm.
Y. K. Choukiker et. al. [173] presented a new form of modified microstrip-line feed
fractal patch antenna for wideband application. The fractal shape is based on
triangular geometry, modified with circle and iteration of self-similar design. The
-10dB return loss (VSWR 2:1) impe dance bandwidth was 80% ranging from
2.4-5.6GHz. The EM characteristics of the antenna were presented by the current
distribution. The single layer microstrip-line fed modified fractal shape antenna was
designed for wideband operation. The iterative model was presented using circle
generation in sectorial shape antenna. The simulated result showed that the antenna is
suitable for 2.4/3.5/5.2/5.5GHz wideband application. The current distribution was
simulated to investigate the EM characteristics of the antenna. According to authors,
the designed antenna has good radiation characteristics and gain at entire bandwidth
(2.4-5.7GHz).
43
S. Suganthi et. al. [178] investigated the performances of a newly shaped fractal
structures using Ansoft HFSS 3D electromagnetic simulation tool. The design was
carried out using FR4 as the substrate and copper as antenna material. The patch
fractal antenna resonates at two frequencies. Authors mentioned that the thin
microstrip type fractal sh aped antenna resonate at four frequencies (5.54GHz,
7.02GHz, 8.68GHz and 9.81GHz) with cons iderable amounts of bandwidths.
According to authors, there was no backward radiation because of the use of separate
ground plane at the bottom of substrate.
Anuradha et. al. [179] presented a design procedure for making custom-made fractal
antennas using artificial neural networks (ANN) and the Particle-Swarm Optimization
technique. The role of the artificial neural network was to form a mapping between
the design parameters of the fractal antenna and its operational frequencies. The role
of Particle-Swarm Optimization was to find the shape of antenna for the required user
defined frequencies, using the previously trained artificial neural network. Sierpinski
Gasket and Koch monopole antennas were taken as the candidate antennas, and the
effectiveness of the developed appr oach was confirmed by simulation and
experimental results. Antenna shapes at various user defined frequencies were
designed and tested.
T. N. Chang et al. [180] discussed an aperture-coupled ring antenna. The antenna was
fed by a microstrip line through a unique aperture configuration. The aperture
contained a square slot ring with four short branch slots protruding toward the center
of ring. According to authors, the axial-ratio and return-loss bandwidths of 8.7%
FHQWHUHG�DW�����*+]�FDQ�EH�DFKLHYHG��:LWKLQ�����*+]±����*+]��WKH�JDLQV�DUH�DOO�
greater than 7dBi.
Y. Dong et. al. [181] analyzed the design of compact patch antennas loaded with
complementary split-ring resonators (CSSR) and reactive impedance surface (RIS).
The CSRR was incorporated on the patch as a shunt LC�resonator providing a low
resonance frequency and the RIS is realized using the two-dimensional metallic
patches printed on a metal-grounded substrate. According to authors, both the meta-
resonator (CSRR) and the meta-surface (RIS) were able to miniaturize the antenna
size. By changing the configuration of the CSRRs, multiband operation with varied
polarization states can be obtained. An equivalent circuit was developed for the
CSRR-loaded patch antennas to illustrate their working principles. Six antennas with
different features were designed and compared, including a circularly-polarized
45
antenna, which validate their versatility for practical applications. These antennas
were fabricated and tested.
D. Kim [182] proposed a high-gain wideband resonant-type mobile communication
base station antenna using a Fabry-Perot cavity (FPC) tec hnique. To overcome
inherent narrow radiation bandwidth of FPC-type antennas while keeping relatively
high gain, new super-strate structure composed of square patches and loops was
introduced, which satisfied an FPC resonance condition at a target frequency region.
To do that, the super-strate geometry was optimized with the help of a real-value
coding hybrid genetic algorithm (RHGA). According to authors, the designed antenna
was able to operate in a wide bandwidth with a relatively high realized gain.
Y. Watanabe and H. Igarashi [183] introduced a fast FDTD method for the analysis of
antennas loaded by nonlinear electric circuits. The modified nodal analysis (MNA)
method was coupled with the FDTD me thod. The time-periodic explicit error
correction (TP-EEC) method was applied to the MNA method for accelerated
computation of the transient processes. The method was applied to analysis of
simplified models of an RFID tag composed of a nonlinear electric circuit and line
antenna. Authors showed that this method can effectively shorten the computational
time by accelerating the transient processes.
L. Bras et. al. [184] developed a pentagonal patch-excited sectorized antenna (SA)
VXLWDEOH�IRU����±���*+]�ORFDOL]DWLRQ�V\VWHPV��The integration of six patch-excited
structures converges into a sectorized antenna called Hive5 that provided gain
improvement compared to a patch antenna, maximum variation of 3dB beam width
over the radiation pattern and circular polarization (CP). This antenna was presented
and analyzed taking into account the tap length and the flare angle. According to
authors, the designed antenna in combination with a RF-switch provides a cost
effective solution for localization based on Wireless Sensor Networks (WSN) and can
be used for implementing angle of arrival (AoA) techniques combined with RF
fingerprinting techniques.
H. T. Liu et. al. [185] proposed a compacted low-cost and low-power smart antenna.
To reduce the cost and power consumption, authors employed the structure of an
Electronically Steerable Parasitic Array Radiator (ESPAR) antenna. The proposed
DQWHQQD�ZDV�FDOOHG�³IROGHG�PRQRSROH�(63$5�DQWHQQD´��$Q�HTXLYDOHQW�FLUFXLW�PRGHO�
was also proposed for analyzing the antenna. To validate the concept, a prototype was
developed and the antenna operated from 2.3GHz to 2.55GHz. The measured results
46
confirmed that the folded monopole ESPAR antenna can achieve electronically beam
scanning in horizontal plane. The prototype antenna achieved a gain of 4.0dBi and a
front-back ratio of 20dB.
Nasimuddin et. al.�[186] described a compact cross-shaped slotted microstrip patch
antenna for circularly polarized (CP) radiation. A symmetric, cross shaped slot was
embedded along one of the diagonal axes of the square patch for CP radiation and
antenna size reduction. The structure was asymmetric (unbalanced) along the diagonal
axes. The overall size of the antenna with CP radiation can be reduced by increasing
the perimeter of the symmetric cross-shaped slot within the first patch quadrant of the
square patch. The performance of the CP radiation was also studied by varying the
size and angle variation of the cross-shaped slot. A measured 3-dB axial-ratio (AR)
bandwidth of around 6.0MHz was achieved with the CP cross-shaped slotted
microstrip antenna, with an 18.0MHz 10-dB return-loss bandwidth.
G. A. E. Vandenbosch [187] discussed a simple network model with closed form
formulas involving just a parallel capacitor for single and double layers. In practice,
the proposed model combines a detailed feed description (normally requiring a very
dense mesh), with a negligible computational cost. The effect of the capacitor
explains part of the typical frequency shift between measurements and simulations of
1 to 2% that is typically seen for this type of structures.
F. J. Jibraeland M. H. Hammed [188] investigated a new second iteration Plusses
fractal patch microstrip antenna for multiband wireless communications systems.
Authors mentioned that the designed antenna structure showed high degree of self-
similarity and space-filling property. Aut hors also mentioned that the designed
antenna has four resonance bands at frequencies of 2.471GHz, 7.032GHz, 8.651GHz
and 11.86GHz, and at these frequencies the antenna has S11
< -10dB (VSWR < 2).
According to authors, this antenna can operate as a multiband antenna in the wireless
applications.
L. Varshney et. al. [189] designed a broadband patch antenna with CPW-fed. First,
the CPW-fed conventional slot antenna was designed and then the rectangular shape
was modified to achieve higher bandwidth. In this antenna, the side-plane conductor
is ground and centre strip act as a feed. The patch works as a radiator. The analysis
was done using IE3D software based on the method of moments. The results for
return loss, gain and efficiency showed that the proposed patch antenna with CPW-
47
fed can be used for UWB communication. According to authors, the antenna has
small size with the maximum gain of 6dB i. Authors also mentioned that the
bandwidth of antenna is approximately 9GHz ranging from 6.2GHz to 15GHz.
J. G. Joshi et. al. [190] described a planar meta-material antenna using offset fed
diamond shaped split rings (DSSR). It is observed that in normal cut configuration the
DSSR behaves as patch antenna; whereas if the antenna structure is excited at offset
cut then it exhibits meta-material characteristics. Authors also mentioned that the
effect of microstrip discontinuities at the right angled bending near to the splits
introduces excess inductance and capacitance which makes the structure to behave as
normal patch antenna. As compared to planar configuration, in meta-material, high
bandwidth is achieved for the same dimensions of structure.
B. L. Ooi and I. Ang [191] proposed a flower-shaped microstrip patch antenna
proximity coupled by a semicircle probe -fed. In this res earch, an impedance
bandwidth of about 63% was achieved; with the largest achievable impedance
bandwidth was obtained through the probe proximity-coupled technique. A
comparison of the proposed antenna with a similar-size rectangular patch and a
diamond-shaped antenna was also conducted. Among these antennas, according to
authors, their designed antenna outperforms the two other antennas in terms of
impedance bandwidth.
3.14 Crown square shaped antenna
J. Y. Park et. al. [192] proposed a comp act subdivided square microstrip patch
antenna, consisting of the interconnection of four corner pads with four strip lines and
a central pad. According to authors, this antenna is characterized by the very small
size of only 0.23h x 0.23h at 5.76GHz, which represents a size reduction of 60%
when compared to a conventional squa re microstrip patch antenna. Authors
mentioned that the antenna presents the following performances: 40MHz bandwidth,
4.27dBi gain, and front-back-ratio better than 18.7dB, and cross polarization less than
22.3dB.
F. Arazm et. al. [193] presented a fractal model for antenna miniaturization that
allows an increase in the total electric length without occupying more space. The
fractal shape allows the square loop antenna to be effectively reduced in size without
significantly impairing performance. Authors also mentioned that the 3/2 curve fractal
increases the electrical length of original loop by 4 times in two iterations; however,
48
Minkowski fractal increases the electrical length of original loop by 2.75 times in two
iterations. Therefore, according to authors, 3/2 curve is superior compared to
Minkowski fractal.
P. Dehkhoda et. al [194] introduced a new self-similar fractal antenna called Crown
square fractal antenna. It is based on nearly square shape with a circular polarization.
This antenna displays lower first mode frequency than a normal nearly square
microstrip patch antenna which results in reduced antenna size. Authors mentioned
that this antenna showed four adjacent resonances that produces a pair of circularly
polarized bands in a large VSWR bandwidth at high frequency modes.
W. Yong and L. Shaobin [195] proposed a modified Crown square fractal antenna
that is used not only to get multiband, but also to get changed frequency separation as
desired. In practice, fractal antenna is used to cover the frequency of global
positioning system (GPS, 1.57GHz), digital multimedia broadcasting
(DMB, 2.6-2.655GHz). In this research, the microstrip feed technique was employed
to enhance the poor matching properties and the measured return loss was presented
and compared with the simulated results. According to authors, Crown square fractal
antenna is a suitable configuration for use in applications where multiband operation
with a small and changed frequency separation is required.
J. Yang et. al. [196] described that Low-profile directional ultra-wideband (UWB)
antennas are strongly demanded in many UWB applications. However, few such
UWB antennas have been reported. To meet the demands, an original novel low-
profile directional UWB antenna- the self-grounded Bow-Tie was developed by
authors. The author claimed that the UWB antenna has a compact and simple
geometry, and ultra-wideband performance, such as presented here over a frequency
UDQJH�RI��±���*+]�ZLWK�DERXW����G%�UHIOHFWLRQ�coefficient, stable radiation patterns,
and good time-domain impulse response. Measurements of a prototype of the antenna
have verified the design and the simulation. It can be foreseen that this new antenna
will find many applications in the different areas in UWB technology.
49