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