Chapter 2

Literature Survey of

Reconfigurable Antenna

2.1 Background

The reconfigurable antennas have the advantage of being able to produce good ra-

diation patterns with better bandwidth, compared to patch antennas. In addition

antennas with desired reconfigurability can be produced by using a combination

of strip conductors and slots arranged along the sides of a microstrip feed and

probe feed. The basic element of the spiral slot is presented at first, and the is-

sues evolved from the probe feeding are presented. Based on the concepts already

discussed about the microstrip and probe fed rectangular slot, the probe fed spi-

ral slot and the loaded spiral slots are introduced. In the second section, the

work done by other researchers on multi band and reconfigurable slot antennas

is noted. Finally some information about varactor diodes and pin diodes which

implement the switches for the reconfigurable antenna is provided.

In designing a small antenna there is always a compromise between size, band-

width, and efficiency. Reconfigurable antenna architecture makes very efficient

use of limited area by taking advantage of combined multiple functions in one

single antenna. This result in significant reduction in the area occupied by the

multiple antenna elements with enhanced functionality and performances. The

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exhaustive literature survey starting from 1983-2013 in brief is presented in this

chapter.

2.2 Literature survey

An antenna is a structure or device used to collect or radiate electromagnetic

(EM) waves. In some sense the first antenna dates from 1887, when Hein-

rich Hertz designed a brilliant set of wireless experiments to test James Clerk

Maxwell’s hypothesis. Hertz used a flat dipole for a transmitting antenna and a

single turn loop for a receiving antenna. For the next fifty years antenna tech-

nology was based on radiating elements configured out of wires and generally

supported by wooden poles. These “wire” antennas were the mainstay of the

radio pioneers, including: Guglielo Marconi, Edwin Howard Armstrong, Lee de-

forests [Lewis, 1991] [40]-[44]. Each of these “engineers” has been called the

Father of the Radio [Lewis, 1991]. Dr. deforest was conducted an experiment on

long-distance wireless broadcasts one hundred years ago from the Illinois Institute

of Technology. The first generation antennas were narrow band and were often

arrayed to increase directivity. Development of the arrayculminated in the work

of Hidetsu Yagi and Shintaro Uda in 1926.

Daniel H. Schaubert et al [45], University of Massachusetts, was a frequency

reconfigurable antenna pioneer who experimented with frequency agile, polar-

ization diverse microstrip antennas and frequency scanned arrays to achieve

frequency-agility without changing the physical dimensions of the antenna el-

ements. A typical thin microstrip antenna will only operate over a frequency

range of two or three percent. These types of antennas that have the capability

of radiating energy over a wide range of frequencies with the frequency changes

being made very rapidly. Since the instantaneous bandwidth of the microstrip

antenna is small, i.e., approximately 2-3 percent, the capability of switching fre-

quencies over a wide range would provide a considerable immunity to interfering

signals.

In 2001, [46]-[47] the first reconfigurable antenna project in China was sup-

29

ported by the high-technology research program.This project, electromagnetic

theory and key techniques of reconfigurable antenna, has been carried out by

researchers in Computational Electromagnetic Laboratory (CEMLAB) at Uni-

versity of Electronic Science and Technology of China (UESTC).

Z. D. Liu et al [48], reported on a new dual-frequency planar inverted-F an-

tenna (PIFA) is developed for GSM 900 and DCS 1800. A U-shaped slot and a

rectangle shaped slot are cut in the antenna radiation patch, which obtains dual

operating frequencies. It has been demonstrated by simulation and measured

that the presented antenna can cover the operating frequencies of GSM 900 and

DCS 1800.

Huff G. H. et.al [49], reported in 1998 on a novel pattern and frequency recon-

figurable microstrip antenna that uses switched connections. The basic antenna

operates with linear polarization around 3.7 GHz. He discussed about two types

of antenna. One set of connections provides a re-directed radiation pattern while

maintaining a common operating impedance bandwidth with the baseline config-

uration. The second set of connections results in operation at a higher frequency

band at 6 GHz with broadside patterns.

Kolsrud A. T. et.al [50], discussed about CPW-fed coplanar strip (CPS) dipole

antenna for dual frequencies.. The CPS dipole antenna was found to have two

distinct operating frequencies of 2.065 GHz and 3.955 GHz, respectively. In

this antenna varactor junction capacitance is varied when the bias voltage was

changed from 0 to -30 V, the tuning range for the lower frequency was measured

to be 14.5% or 300 MHz upwards (from 2.065 GHz to 2.365 GHz), and the higher

operating frequency was tuned 11.5% or 450 MHz downwards (from 3.955 GHz

to 3.505 GHz).

Jung-Chih Chiao et.al [51], demonstrated a new architecture for microelec-

tromechanical system (MEMS) reconfigurable Vee-antennas. This Vee-antenna

designed for 17.5 GHz and predicts an optimal angle of 82.50 will give a maxi-

mum directivity of 5.6. The antenna directivity using 3 dB beamwidths is 37.9.

30

Y.Qian et.al [52], in 1999 reported on reconfigurable aperture where different

types of antennas and arrays with multiband coverage and multiple functions

share a common planar physical aperture. The measured bandwidths (VSWR ¡

2) of the reconfigured and reference antennas are 18% and 16% respectively. The

gains of these two antennas were also measured and were found to be at the same

level of 12 dB at 8.5 GHz.

Shun-Shi Zhong and Jun-Hai Cui [53], reported compact dual frequency mi-

crostrip antenna. This compact and broadband, patches with single slot on its

non radiating edges have been cut to yield a 2:1 VSWR bandwidth in the range

of 10-20%. This antenna operating for two resonant frequencies at 1.04 GHz and

2.49 GHz. Bandwidths determined from the -10 dB rectum loss are 5.77% for 1.04

GHz band and 8.03% for 2.49 GHz band. The ratio of these two frequencies is 2.4.

Hattan F Abutarboush et.al [54], studied and presented a reconfigurable wide-

band and multiband C-Slot patch antenna with dual-patch elements. This an-

tenna operates in two dual-band modes and a wideband mode from 5 to 7.5

GHz, corresponding impedance bandwidth of 4.2% and 2.4% is obtained. In the

ON-ON state, both patch elements are radiating. A wide bandwidth of 33.52%,

covering the frequency range from 4.99 to 7 GHz is obtained.

M. Ali and G. Hayes [55], demonstrated an integrated planar inverted-F an-

tenna (PIFA). This antenna presents input impedance data around 2.45 GHz.

By varying the size of F-slot the antenna resonant resistance is also varies as 31

l2 Ω and 43.7 Ω.

Vinoy K J and Varada V K [56], in 2001 reported on the devices and systems

that use RF microelectromechanical systems (RF MEMS) switching elements

which typically use one switch topology. This technique gives the deferent reso-

nant frequencies for deferent iterations. For first iteration it gives 360, 980, and

1440 MHz, and for next iteration: 270, 720, 1000 and 1370 MHz. This shows a

reduction in the resonant frequency (in this case by 25%) with an increase in the

31

fractal iteration.

Dimitrios Peroulis et.al [57], presented a novel electronically tunable slot an-

tenna. This design is based on a resonant slot structure loaded with a series of

PIN diode switches. These sources of radiation also affected the E-plane pattern

measurements and they caused a difference of 3-4 dB between the minimum and

maximum measured value. The design relies on changing the effective length of

a resonant slot structure by controlling combinations of electronic RF switches

and achieves an effective bandwidth of 1.7: l. The fabricated antenna is capable

of resonating at four different frequencies ranging from 550 to 900 MHz.

Yang F. and Y. Rahmat Samii [58], reported a novel design of a microstrip

patch antenna with switchable slots (PASS) is proposed to achieve circular polar-

ization diversity. By turning the diodes on or off, this antenna can radiate with

either right hand circular polarization (RHCP) or left hand circular polarization

(LHCP) using the same feeding probe. By using this, best axial ratio at boresight

is achieved at 4.64 GHz with 3% CP bandwidth An acceptable axial ratio (AR¡3

dB) is obtained in a broad angular range from -70 to 70 degrees from boresight

direction.

F. Yang and Yahya Rahmat-Samii [59], described reconfigurable antennas are

becoming popular in antenna engineering because of their capability in frequency

agility, bandwidth enhancement, and polarization diversity. The best axial ratio

at boresight is achieved at 4.64 GHz with 3% CP bandwidth for both RHCP and

LHCP patterns compared to normal designs, when the switch is ON, a 2.9 dB

axial ratio is achieved at 4.0 GHz. When the switch is OFF, a 1.6 dB axial ratio

is obtained at 4.37 GHz.

C. Y. Huang et.al [60], have discussed a technique for obtaining a single-

layer single-feed dual-band microstrip antenna loaded with narrow slots and chip

capacitors. The range of the frequency ratio (FR) is extended to 1.25 by using

chip capacitor loading across the narrow slots to produce further capacitive loads.

32

Matthias K. Fries [61], presented reconfigurable slot antenna architecture al-

lowing polarization switching. This designed antenna shape consists of a slot-ring

with perturbations which are switched on and off using pin-diodes. It shows the

axial ratio bandwidth (ARB) of 4.2% and the minimum axial ratio is 0.9 dB.

Also the antenna gives ARB’s of 4.3% and 3.4% for the LHCP and the RHCP,

respectively.

J. T. Bernhard et.al [62], presented reconfigurable portable antenna systems

for high-speed wireless communication (2-100 Mb/sec). Wireless data communi-

cation whether it is for land or satellite based-faces two challenges: (1) high error

rates caused by interference and unpredictable environments, and (2) limited sig-

nal processing capability and battery life at the portable unit. ‘Intelligent’ or

’smart’ antenna systems can help meet these challenges. Current ’smart’ systems

reside mainly at base stations and rely largely on signal processing to achieve their

goals. Second, the bandwidth of the antenna (currently at around 1%) needs to

be increased to at least 3.5% for it to be broadly useful in 802.11 networks.

N. T. Herscovici and C. Christodoulou [63], analyzed and demonstrated new

technologies in communications electronics, such as software-defined radio (SDR)

and RF switches implemented using micro-electromechanical systems (MEMS).

The antenna is designed which ability to realize electrically small antennas is

for both efficient and broadband. As a result covering several frequency bands

concurrently with a single antenna having enough efficiency and bandwidth is a

major challenge. One possible solution to this problem is to use reconfigurable

antennas that tune to different frequency bands. Such an antenna would not

cover all bands simultaneously, but provides narrower instantaneous bandwidths

that are dynamically selectable at higher efficiency than conventional antennas.

J. Costantine et.al [64], presented a new reconfigurable multiband microstrip

antenna. The patch has the shape of six armed star printed on a hexagonal sub-

strate. When the different switches are activated multi frequencies are generated

around 3 GHz and 4.5 GHz. The antenna also presented wide band operation,

from 3.5 GHz to 3.8 GHz and from 4.3 GHz to 4.7 GHz.

33

James T. Aberle et al [65], proposed and demonstrated reconfigurable anten-

nas for wireless communication. In his work, pin diodes and shorting patches are

used for achieving the high Qs factor of 150 and obtain a 12 MHz to 15 MHz

antenna bandwidth, which could cover each of GSM bands in three to four steps

with radiation efficiencies of 20% to 30%.

Lon N. Pringle et.al [66], have described a reconfigurable aperture (RECAP)

antenna in which a planar array of electrically small, metallic patches are inter-

connected by switches. The antenna can be reconfigured to meet different per-

formance goals by changing the switches that are open and closed. This switch

configuration gives deferent frequency ranges of 0.85 GHz - 1.25 GHz, a band-

width of 38 % and for frequency range is 1.10 GHz-1.45 GHz bandwidth of 27%.

Shynu S. V. et.al [67], reported a compact electronically reconfigurable dual

frequency microstrip antenna for L-band applications. The frequency ratio of the

antenna varies in the wide range of 1.2 to 1.4 with a good bandwidth of 2.82%

and 2.42% for the two resonant modes. This antenna has achieved size reduction

of 72.21% and 46.81%for the two resonating frequencies.

B.A.Cetiner et.al [68], demonstrated multi functional reconfigurable MEMS

integrated antenna for multi-input multi-output systems. This antenna provides

ten different reconfigurable modes of operation corresponding to the combina-

tion of two operating frequencies of 4.1 GHz and 6.5 GHz and five reconfigurable

polarizations of the radiated field of linear X, linear Y , dual linear, right hand

circular, and left hand circular. Frequency reconfigurability is also achieved by

simply changing the size of the antenna and it operates with dual frequency

bands. The upper frequency is 6.4 GHz and lower frequency is 4.1 GHz obtained

by using MEMS.

Joshua S. Petko and Douglas H. Werner [69], introduced a design method-

ology for miniature multiband as well as reconfigurable (i.e., tunable) antennas

that exploits the self-similar branching structure of three-dimensional (3-D) frac-

tal trees. The resulting antenna can be reconfigurable from 770 to 1570 MHz with

34

a bandwidth of 800 MHz with a VSWR under 3:1.The another fractal shape is

reconfigurable from 970 to 1570 MHz for a bandwidth of 560 MHz with a VSWR

below 2:1 is obtained.

B.A. Cetiner et.al [70], presented a reconfigurable spiral antenna for use in

adaptive MIMO systems. By using RF-MEMS actuators in the antenna average

half power beam width (HPBW) is approximately 105 is obtained. The antenna

radiates almost entirely circularly polarized wave with axial ratio value of 0.9

dB. The gain of the antenna is 5.3 dB. The circular polarization bandwidth over

which the axial ratio is less than 3 dB is approximately 11%. Gain of the antenna

with average value of 4.9 dB shows small variation over this bandwidth.

D. Peroulis et.al [71], have designed and presented a compact, efficient and

electronically tunable antenna. A single-fed resonant slot loaded with a series of

PIN diode switches constitutes the fundamental structure of the antenna. Four

PIN switches are used in order to tune the antenna over a range of 540 - 950

MHz and calculated return loss where a matching level of better than has been

achieved is 20 dB for all the operating frequencies. The measured gain is -1.1

dBi, which corresponds to an antenna efficiency of 47%.

Shynu S.V et.al [72], presented a novel reconfigurable, single feed, dual fre-

quency, dual polarized operation of a hexagonal slot-loaded square microstrip

antenna. A pin diode incorporated in the slot. When the diode is switched OFF,

the antenna resonates at 1.48 GHz and 1.99 GHz with a frequency ratio of 1.34

and antenna provides a size reduction of 61% and 26% for the two resonating fre-

quencies. This design also gives considerable bandwidth up to 3.3% and 4.27%,

for the two frequencies with a low operating frequency ratio. Once the diode is

turned ON, the first resonant frequency shifts to 105 MHz and second resonant

frequency to 60 MHz, thus giving excitation at 1.585 GHz and 2.05 GHz respec-

tively.

Shynu S.V. et.al [73], reported in 2005, a novel design of a varactor controlled

electronically reconfigurable dual frequency microstrip antenna. Varactor diodes

35

integrated with the slot arms are used to tune the operating frequencies consid-

erably, by applying reverse bias voltage. Tuning ranges of 21% and 12.9% are

realized for the two resonant frequencies respectively, when the bias voltage is

varied from 0 to -30 V. This design has an added advantage of size reduction

up to 80% and 70.18% for the two resonant frequencies compared to standard

rectangular patch. A maximum bandwidth of 6.2176% and 10.4255% for the

two frequencies with an operating frequency ratio varying in the range 1.0645 to

1.2180 is observed.

M. A. Saed [74], investigated a novel reconfigurable two-layer microstrip an-

tenna fed using a coplanar waveguide through a slot/loop combination. The

slot/loop combination allows for easy reconfigurability of the frequency band of

operation by incorporating switches in the feed network. By this impedance

bandwidths of about 23% were obtained for two selectable frequency bands using

two switches. The two frequency bands 8.73 GHz - 10.95 GHz and 7.68-9.73 GHz

are obtained.

Sunan Liu et.al [75], have demonstrated a microstrip antenna with integrated

RF mircoelectromechanical system (MEMS) switches to operate at dual frequen-

cies with circular polarization. The switches are incorporated into the diagonally-

fed square patch for controlling the operating frequency and a rectangular stub

attached to the edge of the patch acts as the perturbation to produce the cir-

cular polarization at 6.69 GHz and 7.06 GHz giving rise to frequency ratio of 1.05.

Zhang Y et.al [76], presented a novel fractal microstrip patch antenna, which

has the feature of linearly polarized reconfigurable radiation patterns. By con-

trolling RF MEMS switches on/off, two sets of connection states can be obtained

at 10 GHz and the return losses are less than -20 dB and radiation patterns can

be reconfigured in the upper half-space is also observed.

Kyungho Chung et.al [77], presented a novel reconfigurable microstrip patch

antenna with frequency and polarization diversities. A U-slot is incorporated into

a square patch and a PIN diode is utilized to switch the slot on and off, which

36

obtained the frequency diversity characteristic. By using PIN diodes on U-slot

the obtained 3 dB CP bandwidths are about 35 MHz and 40 MHz.

Carla Mederia and Carlos Fernandes [78], presented an evaluation of frequency

reconfigurable patch antennas for multi-standard personal communication sys-

tems, using PIN diodes as switches This antenna resonates at f1 = 1.89 GHz and

f2 = 2.37 GHz, with an impedance bandwidth of 0.48% and 2.45% respectively.

The experimental results shift 0.89% towards lower values for the first operating

frequency and 2.39% for the second one, when compared to the simulated oper-

ating frequencies, f1 = 1.93 GHz and f2 = 2.43 GHz; is observed.

In 2006 S. V. Shynu et.al [79], reported a design of compact, single feed, dual

frequency dual polarized and electronically reconfigurable microstrip antenna. A

square patch loaded with a hexagonal slot having extended slot arms constitutes

the fundamental structure of the antenna. The tuning of the two resonant fre-

quencies is realized by varying the effective electrical length of the slot arms by

embedding varactor diodes across the slots. A high tuning range of 34.43% (1.037

GHz - 1.394 GHz) and 9.27% (1.359 GHz - 1.485 GHz) is achieved for the two

operating frequencies respectively, when the bias voltage is varied from 0 to - 30

V. The antenna has size reduction up to 80.11% and 65.69% for the two operating

frequencies are achieved.

S. Nikolaou et.al [80], demonstrated an antenna use of pin diodes to recon-

figure the impedance match and modify the radiation pattern of an annular slot

antenna (ASA). Matching stubs are used to match the antenna to three different

frequencies, 5.2, 5.8 and 6.4 GHz. PIN diodes are used to connect or disconnect

the stubs creating a reconfigurable matching network.

N. Behdad and K. Sarabandi [81], introduced a new technique for designing

dual-band reconfigurable slot antennas. This technique is based on loading a slot

antenna with a lumped capacitor (or varactor) at a certain location along the

slot. Based on this technique, an electronically tunable dual-band antenna with

a frequency ratio in the range of 1.2 - 1.65 is designed and tested using a single

37

varactor with a capacitance range of 0.5 - 2.2 pF. Frequency of the first resonance

is increased from 1.8 GHz to 1.95 GHz and the second band increases from 2.15

GHz to 3.22 GHz. The antenna has similar radiation patterns with low cross-

polarization levels at both bands and across the entire tunable frequency range.

Lower efficiency of 70% and 85% for the first and second bands are calculated.

Cesar Lugo and John Papapolymerou [82], demonstrated a six-state reconfig-

urable band-pass filter intended to add frequency tunability to antenna systems.

The present topology produces filter responses with center frequencies of f0 =

9, 10, and 11 GHz and achieves independent bandwidth control with an average

tunable passband ratio of 1.73:1 between the wideband configurations ranging

from 13.4% and 14.7% and the narrowband configurations ranging from 7.7%

and 8.5%. PIN diodes are implemented as switching elements and the distinct

states are discretely accomplished by the connection and isolation of strategically

placed transmission line sections. The insertion loss of the filter ranges between

1.74 and 1.92 dB. The measured gain is greater than 48 dBm for tones separated

by 1 MHz around the center frequencies.

Nader Behdad and Kamal Sarabandi [83], presented a new technique for

designing dual-band reconfigurable slot antennas. Dual-frequency operation is

achieved by loading a slot antenna with two lumped variable capacitors (varac-

tors) placed in proper locations along the slot. The antenna efficiency values are

calculated from the measured gain and calculated directivity values at broadside.

When V1 = 0 V and V2 = 1 V for and the directivity of the antenna at the first

band 1.3 GHz and second band is 2.67 GHz are, 1.76 and 1.96 dBi respectively

which corresponds to an efficiency of 58% and 59% for the first and second bands,

respectively. As the bias voltages increase, so do these efficiency values. When

V1 = V2 = 30 V, the directivity of the antenna at the first and second bands are

1.82 and 2.16 dBi, respectively. This corresponds to efficiency values of 87% and

92% at the first and second bands respectively.

Dimitrios E. Anagnostou and Guizhen Zheng [84], reported reconfigurability

in an antenna system is a desired characteristic that has been the focus of much re-

38

search in recent years. In his work, ohmic contact cantilever RF-MEMS switches

are integrated with self-similar planar antennas to provide a reconfigurable an-

tenna system that radiates similar patterns over a wide range of frequencies. In

this antenna when the probes are placed away from the pads, a resonance at 16.5

GHz (with a 14.2 GHz - 17.5 GHz bandwidth) is measured. The weak resonance

at 21 GHz can also be noticed. Next, when the dc probes come down and touch

the biasing pads, but no voltage is applied on them, the antenna resonates at 15

GHz, with a bandwidth from 12.75 GHz up to 17.5 GHz and covers the desired

band at 14 GHz.

Greg H. Huff and Jennifer T. Bernhard [85], described about the integration of

commercially available packaged radio frequency microelectromechanical system

(RF MEMS) switches with radiation pattern reconfigurable microstrip antennas.

The overall shared 2:1 VSWR (impedance) bandwidth is 80.0 MHz The (VSWR)

shows that the center frequency of the shared broadside and endfire impedance

bandwidths is shifted down by 400 MHz from fc = 6.88 GHz.

Malcolm Ng Mou Kehn et.al [86], presented a compact reconfigurable multi-

band microstrip antenna. The multiplicity of bands is achieved by the use of

concentric external metallic semirings around a central internal semicircular mi-

crostrip patch antenna. A 56% effective bandwidth and demonstrated that the

operating frequencies can be increased up to 75%.

Hakim Aissat et.al [87], reported the design of a compact microstrip patch

antenna with polarization reconfigurable features (right-handed circular polariza-

tion (CP)/left-handed CP). The basic antenna is a circular coplanar-waveguide

CPW-fed microstrip antenna excited by a diagonal slot and the CPW open end.

The reconfigurable antenna is used as a transmitter antenna and fed by a power

generator, of which output power level ranges from 16 to 26 dBm. The gain is

6.02 dB increased with low power level 16 dBm as well as axial ratio is 2.06.

Zhen Zhou and Kathleen.Melde [88], demonstrated the frequency agility that

can be achieved when a broadband antenna is integrated with a reconfigurable

39

RF tuner as a impedance matching circuit. The reconfigurable tuner uses a

microstrip loaded line structure with four stubs that are each terminated by a

varactor diode. In this case, the frequency sub bands are 0.88 GHz to 0.98 GHz

and 1.24 GHz to 1.34 GHz. Two of the diodes were allowed to have capacitances

that are slightly higher than 5 pF. The antenna results for 0.9 GHz and 1.3 GHz

nearly 10% of the incident power is reflected due to mismatch.

Mohammod Ali et.al [89], presented a reconfigurable stacked microstrip patch

antenna. The antenna operates at an upper frequency fu with a broadside pat-

tern, 7.5 dBi right-hand circularly polarized gain and achieved 15.8% bandwidth.

At a lower frequency fl, the antenna operates as a planar inverted-F antenna

(7.3% bandwidth and 3.9 dBi peak gain) with the main beam directed close to

the horizon.

Mathieu Riel and Jean-Jacques Laurin [90], presented a C-band electronically

beam scanning reflectarray antenna. The reconfigurable reflectarray element con-

sists of a microstrip patch, printed on a flexible membrane substrate, aperture-

coupled to a transmission line loaded with two varactor diodes. The designed

element allows continuous tuning of the reflected signal’s phase over a 360 range

with a maximum loss of 2.4 dB at 5.4 GHz.

Nickolas Kingsle et.al [91], reported devices and systems that use RF mi-

croelectromecha nical systems (RF-MEMS) switching elements typically use one

switch topology. In this paper, three sets of RF MEMS switches with differ-

ent actuation voltages are used to sequentially activate and deactivate parts of

a multiband Sierpinski fractal antenna. This reconfigurable antenna operates at

several different frequencies between 2.4 and 18 GHz and it gives 0% error for

these operating frequencies.

Seung-Bok Byun et.al [92], presented a reconfigurable ground slotted patch

antenna using a PIN diode connection in slots to achieve dual-frequency opera-

tion. Slots on the ground plane increase the electrical length and thereby reduce

antenna size by 53%. With the diodes in the off-state, near 1.85 GHz for K-PCS,

40

the measured bandwidth of -10 dB return loss is approximately 60 MHz. Mea-

sured gains of 2 and -3 dBi were achieved.

B. Z. Wang et.al [93], designed and reported on reconfigurable patch antenna

with a wide operational bandwidth for wireless communication and radar systems.

The reconfigurable patch possesses an E-shaped structure and its operation fre-

quency can be changed by integrated switches. The operational frequency of the

antenna can cover an octave frequency range by utilizing only two switch states.

In state 1, the antenna operates from 9.2 GHz to 15.0 GHz and in state 2, from

7.5 GHz to 10.7 GHz. Relative bandwidths of 48% and 35% are obtained in the

two states respectively.

In 2007, Yildirim B et.al [94], designed and tested reconfigurable penta-band

(GSM900, GPS 1575, GSM1800, PCS 1900, UMTS2100) planar inverted-F an-

tenna (PIFA) having microelectromechanical switches (MEMS). A number of RF

MEMS actuators within the geometrical structure of the antenna are constructed

as part of the design. In this design, PIFA operates for both lower and higher

bands. In low-band, the antenna is matched -6 dB from 748 MHz - 912 MHz.

This represents a fractional bandwidth of 19.9%. Another identical antenna with

MEMS having slightly different capacitance values achieved 765 MHz - 950 MHz

(fractionally, 22%) without any matching, showing that a wide bandwidth reso-

nance is obtained. The higher bands with matching -6 dB bandwidths are 1840-

2151 MHz, 1849 MHz - 2156 MHz and 1901 MHz - 2185 MHz for the UTRA

bands III, II and I respectively (fractionally, approximately 15%) are obtained.

W.B.Wei et.al [95], proposed and presented a novel reconfigurable microstrip

antenna with switchable polarization technique. Using PIN diodes independently

biased on the patch, it can produce linear polarization, left- or right-hand circular

polarization according to bias voltages. Two antennas are having same geometry;

their return losses are extremely uniform. Both resonant frequencies of them are

1.5175 GHz. The measured gains are 5.12 dB and 5.26 dB respectively.

Angus C. K et.al [96], proposed a new design for compact reconfigurable an-

41

tennas are introduced for mobile communication devices. The uniqueness of the

antenna designs are that they allow various groups of their operating frequency

bands to be selected electronically. From this, it clears that both modes to-

gether can cover GSM850, GSM900, DCS, PCS, and UMTS bands with 50% or

greater efficiency. When the active switches are implemented in the design the

first mode excites one lower frequency around 900 MHz and the high-frequency

band at around 1.8 GHz. The second mode excites two resonating frequencies

that are around 900 MHz and 2 GHz.

Giuseppe Ruvio et.al [97], reported a novel technique to reconfigure the fre-

quency range of a planar monopole antenna. The proposed antenna is capable

of covering the frequencies in the range from 2.9 to 15 GHz, depending on the

degree of spiral tightness. The behavior of the gain and the total efficiency is for

the four configurations investigated and at three frequencies: 3, 5 and 7 GHz.

The maximum gain was found to be between 7.5 and 8.5 dBi in the broadside

direction for between 10.0 and 11.0 mm. The patterns are broad beamwidth.

The antenna yields a high-efficiency across the full operating bandwidth.

Alireza Pourghorban et.al [98], presented a novel reconfigurable slot antenna

with three switchable frequencies. The uniqueness of this design is that it al-

lows various groups of its frequency resonances to be selected electronically using

three switches. The antenna resonance frequencies are maximized at the third

resonance, where it is 140 MHz (2.4% shift). Finally, the measured resonances of

the antenna that can support the mentioned frequency bands are 2.46, 3.59 and

5.69 GHz. The measured maximum gain values of the antenna in boresight at

2.46, 3.59 and 5.69 GHz are 2.33, 3.14 and 2.89 dBi respectively.

D. Piazza et.al [99], presented an evaluation of frequency reconfigurable patch

antennas for multi-standard personal communication systems using PIN diodes

as switches. Two different configurations are studied with dual-band behavior: a

patch antenna with two switchable slots and a rectangular patch with a switch-

able parasitic element. On average, the novel antenna solution achieved a 10%

improvement in capacity (with a peak of 28%) for a SNR of 10 dB and 8% (with

42

a peak of 16%) for a SNR of 20 dB with respect to a system with a fixed antenna

configuration.

Shing-Lung Steven Yang et.al [100], presented a frequency reconfigurable mi-

crostrip patch antenna. It is found that by incorporation of a U-slot in the patch

can provide a flat input resistance and a linear input reactance across a wider

bandwidth than the conventional patch antenna. By placing a variable capacitor

and an inductor at the antenna input, the impedance matching frequency of the

antenna is varied. The fabricated prototype antenna attains a tunable frequency

range from 2.6 to 3.35 GHz. It is observed that the antenna attains a tunable

range from 2.6 to 3.35 GHz (return loss is less than -10 dB) in the full-scale range

of the trimmer.

Joshua D. Boerman and Jennifer T. Bernhard [101], reported the poten-

tial benefits of using pattern reconfigurable antennas in multiple-input multiple-

output (MIMO) communication systems. In his calculations for the three antenna

configurations, demonstrates that large capacity improvements are possible. At

the points average received SNR = 10, 20 and 30 dB, the percent improvements

of the capacities of the RDDR mode with respect to the DDDD mode are 70%,

40% and 26% respectively, which reports average gains of 10% at SNR = 10 dB

and 8% at SNR = 20 dB, and peak gains of about 28% at SNR = 10 dB and 15%

at SN R= 20 dB using a variable-length dipole reconfigurable array.

Andrew R.Weily et.al [102], proposed a high-gain partially reflective surface

(PRS) antenna with a reconfigurable operating frequency. The operating fre-

quency is electronically tuned by incorporating an array of phase agile reflection

cells on a thin substrate above the ground plane of the resonator antenna, where

the reflection phase of each cell is controlled by the bias voltage applied to a pair

of varactor diodes. The antenna’s operating frequency is defined by the peak

directivity. As increasing the bias voltage from 6.49 to 18.5 V, the operating

frequency increases from 5.2 to 5.95 GHz. The tuning range of the reconfigurable

PRS antenna is 13.5%. When tuned to 5.2 GHz the antenna covers the 5.15-5.25

GHz WLAN band and when tuned to 5.775 GHz the antenna covers the 5.725-

43

5.825 GHz WLAN band Measured gain of the reconfigurable antenna varied from

10 to 16.4 dBi over the tuning range of 5.2 to 5.95 GHz as the bias voltage was

tuned from 6.49 to 18.5 V.

Zhengyi Li et.al [103], studied and reported the properties of reconfigurable

antenna arrays which increase the flexibility of adaptive multiple-input-multiple-

output (MIMO) systems by their reconfigurable configurations and radiation or

polarization. In this work, a compact reconfigurable antenna array operating in

the UMTS band is proposed. The antenna array consists of two hybrid-monopole

and dipole elements.

D. E. Anagnostou and A. Gheethan [104], presented the design of a reconfig-

urable single folded slot antenna. The design of a single folded slot is reconfigured

and resonance frequency is used for WLAN applications. The measured resonant

frequency for the OFF state is 5.14 GHz and the simulated is 5.25 GHz (a 2.1%

shift). The measured resonant frequency for the ON state is 5.75 GHz, which

is very close to the simulated 5.775 GHz resonant frequency (0.43% shift). The

measured maximum gain is approximately 5.2 dBi at 5.25 GHz and 5.6 dBi at

5.775 GHz are observed.

Shing-Hau Chen et.al [105], designed and presented a single-feed reconfig-

urable square-ring patch antenna with pattern diversity. The antenna radiation

patterns of the reconfigurable patch antenna at 2020 MHz are measured which

correspond to the cases of switching ON and OFF the diodes, whose maximum

antenna peak gain including the ohmic loss of the pin diodes is about 2.5 dBi. It

is also observed that the main beam has good broadside radiation patterns with

a peak gain of 6.8 dBi are obtained. Also, the antenna efficiencies are estimated

to be about 60% and 75% when the antenna is operated at the monopolar plate-

patch and theTM11 modes.

Elyas Palanteil et.al [106], presented a patch with folded dipole antenna ele-

ments was found to be an effective reconfigurable antenna. This antenna allows

for three bands operation such as 5 GHz, 10 GHz and 15 GHz as required for

44

WiMax applications. The antenna must be supported by an RF control unit as

an integrated part of the transceiver circuitry to maintain the appropriate direc-

tion and frequency of operation.

Daniele Piazza et.al [107], reported a MIMO system equipped with MEMS

reconfigurable circular patch antennas that allows selecting the antenna config-

uration at the receiver without the need for estimating the wireless channel for

each configuration of the reconfigurable multi element antenna. By using the

MEMS, a gain of 1.8 dB is achieved for a BER of 0.1%.

Julien Sarrazin et.al [108], presented a new single-feed reconfigurable antenna

for pattern diversity. The proposed structure is based on a metallic cubic cavity

which radiates through rectangular slots. The antenna impedance matching is

achieved around 5.2 GHz in the three cases. The -10 dB frequency bandwidths

are from 5.4% for the antenna configuration 2 upto 8.8% for the configuration 1.

By considering the three configurations, a -10 dB shared bandwidth of 285 MHz

is available between 5.025 and 5.31 GHz is observed.

Nazia Hasan et.al [109], designed a dual band reconfigurable antenna with

embeded of RF-MEMS to achieve dual band operation. The switching between

the different frequency bands is achieved by using RF-MEMS switches. The an-

tenna gives frequency of 2.2 GHz and 3.6 GHz.

Bedri A. Cetiner et.al [110], developed a double and single-arm cantilever type

DC-contact RF MEMS actuators has been monolithically integrated with an an-

tenna architecture to develop a frequency reconfigurable antenna. By activat-

ing/deactivating the RF MEMS actuators, which are located within the antenna

geometry and microstrip feed line, the operating frequency band is changed. The

two reconfigurable modes of operation fh = 5.2 GHz and f1 = 2.4 GHz are ob-

served. The VSWR ( =-10 dB reflection coefficient), the corresponding frequency

bandwidths are 100 MHz and 650 MHz for 2.4 GHz and 5.2 GHz respectively cov-

ering the ISM allocated frequency range.

45

Julien Perruisseau Carrier et.al [111], presented a antenna exhibiting a very

wide bandwidth with reconfigurable rejection within the band. The proposed

topology is versatile in terms of the number of available antenna states and lo-

cation of the rejection frequencies and also allows the operation of the antenna

in an ”all-pass” state. The reliable measurement between 2.0 GHz and about

4.25 GHz consists in the slightly lower measured overall efficiency, which however

remains between 50% and 70%. The measured transmitted IP3 levels at 1.8 GHz

and 4.0 GHz are 35.6 dBm and 40 dBm respectively.

Sean Victor Hum and Hui Yuan Xiong [112], reported the design of a fre-

quency agile microstrip patch antenna that is readily interfaced with differential

RF transceivers. By integrating three pairs of varactor diodes with the patch

antenna and tuning them in unison frequency tuning ratios approaching 2 are

possible with the design. Considering tuning capacitances in the 0.1 - 2.0 pF

range a tuning range between 1.859 GHz and 3.672 GHz corresponding to a fre-

quency ratio of 2 can be easily achieved while maintaining a reflection coefficient

magnitude below -10 dB. The upper frequency limit of the tuning is 3.15 GHz

corresponding to an overall tuning factor of 1.75.

Pei-Yuan Qin et.al [113], in 2010 presented a compact U-slot microstrip patch

antenna with reconfigurable polarization is proposed for wireless local area net-

work (WLAN) applications. PIN diodes are appropriately positioned to change

the length of the U-slot arms, which alters the antenna’s polarization state. It is

observed that axial ratio for the CP mode of antenna for the LP and CP modes

are 6.1% and 13.5% respectively, with almost the same center frequency of 5.9

GHz, which can cover the entire 5.725 GHz - 5.85 GHz WLAN band. The mea-

sured 3 dB axial ratio bandwidth at boresight extends from 5.7 GHz - 5.86 GHz.

The antenna uses two PIN diodes to switch between the two circular polarization

and achieved the 3 dB axial ratio bandwidth is greater than 2.8%.

H. Li et.al [114], reported on simple and compact slot antenna with a very

wide tuning range. To achieve the tunability, only two lumped elements, namely,

a PIN diode and a varactor diode are used in the structure. A compact slot

46

antenna that can be continuously tuned over a very wide frequency band. With

only two lumped elements (a PIN diode and a varactor diode), a wide tuning

range from 0.42 GHz to 1.48 GHz (with the frequency ratio of 3.52:1) has been

achieved and the measured gain is above -0.4 dB.

L.Jong-Hyuk et.al [115], presented a reconfigurable planar inverted-F antenna

using a switchable PIN-diode and a fine-tuning varactor for mobile communica-

tion applications. Selection of operating modes is achieved by switching the

PIN-diode between radiators and tuning the varactor on an antenna’s shorting

line. The varactor used to achieve frequency fine-tuning does not need a DC

bias circuit and can expand the bandwidth without increasing the physical size.

When the PIN-diode is off, the radiation efficiencies have near 90%. On the other

hand, when the PIN-diode is on, the radiation efficiency abruptly decreases to

63% for the m-WiMAX (3.35-3.69 GHz) band due to the resistance effect of the

PIN-diode but remains 93% for the USPCS (1.85-1.99 GHz) band due to no ra-

diation through the PIN-diode for this band. The measured radiation antenna

peak gains are 2.84 and 2.81 dBi at the USPCS and WCDMA bands respectively.

Jeen-Sheen Row and Ting-Yi Lin [116], described a design for frequency-

reconfigurable antennas with conical-beam radiation. The design is based on the

TM02 mode of a coplanar annular-ring microstrip antenna and several shorting

strips are symmetrically placed along the circumference of the radiating patch to

vary its resonant frequency. To achieve multi frequency operations pin diodes are

used instated of shorting strips, antenna resonates at frequencies between 4.85

GHz to 5.79 GHz.The impedance bandwidth of antenna is between 1.6 to 3.1%(in

GHZ) and mea gain of the antenna is 1.0 to 2.6 dBi is observed.

Xavier Artiga et.al [117], reported in 2010, a Vivaldi antenna having the capa-

bility of dynamically rejecting interferers mainly aiming at multi standard com-

munication with dynamic frequencies allocation. This Vivaldi antenna suitable

for vehicle to vehicle communications operating at 2.5 - 8 GHz with a stopband

whose central frequency can be continuously tuned in the 1.8 - 5.8 GHz range.

The antenna presents good matching from 2.5 to 8 GHz while rejecting a band

47

whose central frequency can be tuned from 1.8 to 6 GHz, thereby covering the

principle standards such as WiFi, WiMAX, Bluetooth, WLAN (802.11a) etc.

Measured absolute gain values are 5 dBi at 2.5 GHz, 7.9 dBi at GHz and 11 dBi

at 8 GHz are obtained.

Shahrzad Jalali Mazlouman et.al [118], demonstrated in 2011, a reconfigurable

structures based on smart materials offer a potential solution to realize adaptive

antennas for emerging communication devices. In his paper, a reconfigurable ax-

ial mode helix antenna is studied. A shape memory alloy spring actuator is used

to adjust the height of a helix antenna. Measurement results for some heights

of the helix antenna (60, 70, 80 mm) as well as the simulation results for the 80

mm for comparison. It can be seen that good impedance matching is attained

around 4 - 4.5 GHz for all sweep points conical helix with a maximum radius of

18 mm and a radius ratio of 0.55, with 6 turns and its height varied between 50

to 90 mm confirm reasonable matching for a wideband around 3 GHz. Similar

to the cylindrical helix, the patterns of the conical helix at 3 GHz (not shown)

demonstrate that by varying the height of the helix from 40 to 95 mm, the gain

ranges from 10 to 11.5 dB and the HPBW from 65 to 50 with the total length of

the helix wire fixed, the pitch spacing and pitch angle are varied as the height is

varied.

Yufeng Yu et.al [119], proposed an electrically small frequency-reconfigurable

antenna with a very wide tuning band. Three varactor diodes are used to achieve

the tunable capacitance. With a modified feeding structure, the measured tuning

range of the fabricated antenna reaches from 457.5 to 894.5 MHz is observed.

When the capacitance of the varactor diodes changes from 0.12 to 4.0 pF, the

tunable frequency with reflection coefficients lower than -10 dB is from 517 to

856 MHz, with a tuning range of about 339 MHz. When the capacitance of the

varactor varies from 4 to 0.12 pF, the operating frequency of the antenna ranges

from 387.5 to 947 MHz. This tuning range (around 560 MHz) is very wide for

electrically small antennas.

Y. Tawk et.al [120], presented a new antenna system designed for cognitive

48

radio applications. The antenna structure consists of a UWB antenna and a fre-

quency reconfigurable antenna system. The UWB antenna scans the channel to

discover “white space” frequency bands while tuning the reconfigurable section

to communicate within these bands. The frequency agility is achieved via a ro-

tational motion of the antenna patch. Antenna designed for cognitive radio that

is able to tune throughout the whole band covered by the antenna is 2 GHz -

10 GHz.The measured gain of the antenna is 6.2, 6.67, 7.4, 7.77 and 8.4 dB for

deferent shapes of antenna.

Peter Ludlow and Vincent Fusco [121], reported on a reconfigurable small-

aperture evanescent wave guide antenna. Tuning and waveguide matching to free

space are simultaneously achieved by placing a printed iris with a shunt varactor

diode connected across the aperture of a below-cutoff waveguide. The maximum

dimension of the antenna is 0.36 at 2.49 GHz and it operates over an operating

frequency range of 2.05 GHz - 2.49 GHz with maximum realized gain of 5 dBi.

The measured results of the antenna as the reverse voltage on the varactor diode

are tuned from 0 V to 30 V. Here the antenna is operating at 2.05 GHz and 2.49

GHz over an operating frequency range of 19.4%.

Hattan F. Abutarboush et.al [122], proposed and presented a reconfigurable

wideband and multiband C-Slot patch antenna with dual-patch elements. It oc-

cupies a compact volume of 50 50 1.57 (3925 mm3) including the ground plane.

The antenna is operating in two dual-band modes and a wideband mode from 5

GHz to 7 GHz. Two parallel C-Slots on the patch elements are employed to per-

turb the surface current paths for excitation of the dual-band and the wideband

modes. By using two PIN diodes the operating frequencies are 5 GHz to 7 GHz

are obtained and impedance bandwidth of 33.52% measured gain of the antenna

is 3.72-4.92 dBi is also achieved.

Yue Li et.al [123], designed and discussed a folded loop-inverted F reconfig-

urable antenna for mobile phone applications. It is shown that loop antenna

mode and an inverted F antenna (IFA) mode are controlled by only one PIN

diodes with simple bias circuit. When the PIN diode is forward biased it works

49

as a series resistance. In the frequency band of 0.5 GHz - 2.5 GHz, the insertion

loss introduced by p-i-n diode is 0.1-0.2 dB at its typical bias current of 10-100

mA. When the PIN diode is reverse biased it is equivalent to series capacitance

approximately 0.45 pF the isolation is better than -15 dB. The Hepta-band is

covered with loop mode line the achieved bands are 790-870 MHz and 1490 MHz

- 2225 MHz covering GSM850, GPS, DCS, PCS and UMTS bands. For the IFA

mode the achieved bands are 845 - 980 MHz and 2240 - 2565 MHz covering

GSM900 and WLAN bands.

Xue Xia Yang et.al [124], presented a reconfigurable microstrip patch antenna

with polarization states being switched among linear polarization (LP), left-hand

(LH) and right-hand (RH) circular polarizations (CP). In his work he measured

10 dB bandwidths of for LHCP and RHCP are about 60 MHz. Good axial ratio

is about 0.5 around 2.438 GHz is obtained. The measured patterns of the recon-

figurable patch for LHCP at 2.439 GHz, RHCP at 2.433 GHz and LP of E-plane

at 2.42 GHz are achieved. For the LP the cross polarization in the broadside

direction is about 30 dB and the measured gain is 5.83 dBi.

J. Desjardin et.al [125], described the full implementation of a slot fed frequency-

reconfigurable rectangular dielectric resonator antenna (DRA). It uses two con-

ducting walls on opposite vertical faces of the DRA which are switched via con-

ducting tabs to be in contact or not with the ground plane. This antenna is de-

signed to operate between 3-8 GHz. The PIN diode loaded and varactor-loaded

DRAs achieved a tuning range of 91% and 55% respectively.

Chang Won Jung and Franco de Flaviis [126], investigated a double rectan-

gular patch antenna with 4-bridges is for use in IEEE 802.11b/g (2.4 GHz) and

802.11a (5.5 GHz) WLANs. A rectangular patch for the 5.5 GHz frequency band

is printed on the PCB substrate and is connected by 4-bridges to another rectan-

gular patch for the 2.4 GHz band to obtain dual band operation in one antenna

element. The 4-bridges can modify the desired frequency band from its original

frequency by changing their width. The gain of the 2.4 GHz patch is 5 dBi and

of the 5.5 GHz patch is 3.7 dBi at θ = 0..

50

S. V. Shynu Nair and Max J. Ammann [127], proposed and presented a recon-

figurable microstrip antenna for low cost adaptive beam-switching applications.

A small patch slotring structure is used as the radiating element where an asym-

metrical arrangement of PIN diodes is employed to switch the pattern in four

directions. The antenna provides pattern switching of 65 and 45 in its fundamen-

tal mode for the elevation and azimuth planes respectively. The 6 dB impedance

bandwidth commonly available to all modes is 2.6% centered at 2.055 GHz. The

designed antenna is resonating at frequency of 2.1, 2.05, 2.08 and 2.03 GHz, the

measured peak gain is 4.58, 2.71, 1.11 and 3 dBia respectively.

Won-Sang Yoon et.al [128], described a square patch antenna with a switch-

able circular polarization (CP) sense. The proposed antenna has four L-shaped

slots on the ground plane and the CP radiation is generated by current perturba-

tion due to the slotted ground plane. The bandwidths of the proposed antenna

are measured for the impedance bandwidth of the -10 dB RL and CP bandwidth

within a 3 dB AR. The impedance bandwidths of the 10 dB RL for both RHCP

and LHCP are 110 MHz (2.41 - 2.52 GHz) and the CP bandwidths in a 3 dB

AR in the direction are 30 MHz (2.47 - 2.50 GHz) for both LHCP and RHCP.

The minimum ARs in the direction are obtained at 2.49 GHz and the values are

1.90 dB for RHCP and 1.94 dB for LHCP. The peak gains at 2.49 GHz are 2.97

dBi for RHCP and 2.90 dBi for LHCP. For both directions antenna has great loss

tangent and antenna may yield low radiation efficiencies and gains.

Daniel Snchez-Escuderos et.al [129], presented a reconfigurable slot-array an-

tenna with RF-MEMS. By this technique obtained an isolation of 12 dB at max-

imum between two states of the switch. Due to switch effect radiation efficiency

was computed for both states, and it obtained an radiation efficiency of 36% for

the ON state and 93% for the OFF state is observed.

Y. K. Park and Y. Sung [130], presented a reconfigurable antenna for a quad-

band (GSM900/GSM1800/GSM1900/UMTS) mobile handset application. In this

structure a bias network related to PIN diode and it is simple compared with other

51

passive quad-band. When the antenna is operating in the PIFA mode the 7 dB

bandwidth covers the GSM 900 (880 - 60 MHz) band. When operating in the loop

mode the 7 dB bandwidth covers the GSM1800 (1710 - 1880 MHz), GSM1900

(1850 - 1990 MHz) and UMTS (1920 -2170 MHz) band.

Huda A. Majid et.al [131], demonstrated a frequency reconfigurable microstrip

slot antenna. The antenna is capable of frequency switching at six different fre-

quency bands between 2.2 and 4.75 GHz. Five RF PIN diode switches are posi-

tioned in the slot to achieve frequency reconfigurability. The measured resonant

frequency bands are shifted from 4.60 GHz to 2.30 GHz and corresponding band-

width is shifted from 250 MHz to 210 MHz respectively. The resonant frequencies

are shifted with the average of 532 MHz. The average measured gain is 1.9 dBi

and antenna size reduction 33% is achieved.

Gang Chen et.al [132], presented a novel frequency-reconfigurable folded slot

antenna that could operate in two modes. Both modes have two resonant fre-

quencies. The measured resonant frequencies for Mode 1 are 3.29 GHz and 5.2

GHz. For the Mode 2 the measured frequencies are 2.36 and 5.7 GHz. For this

antenna the measured peak gain for Mode 1 is 5.22 dBi at 3.29 GHz and 5.4 dBi

at 5.21 GHz. The measured peak gain of Mode 2 is 4.45 dBi at 2.36 GHz and 4.9

dBi at 5.7 GHz is obtained.

Yong Cai et.al [133], demonstrated reconfigurable Yagi-Uda antenna with 46%

frequency tunability for the UHF band. With a simple and efficient biasing cir-

cuitry a design with multiple directors loaded with varactors was realized which

allows a high gain to be maintained. By changing the dimensions of this antenna

which is generates multiple frequency bands between 478 MHz to 74 MHz is ob-

served and radiation efficiency is above 85% over the entire tuning bandwidth is

achieved.

Changying Wu et.al [134], designed and implemented a reconfigurable patch

antenna using reed switches. The antenna comprises a pair of hexagonal patches

and a reed switch that connects the two patches at their adjacent vertices. En-

52

ergizing a coil that either closes or latches the reed switch will shift the resonant

frequency of the antenna. Because the coil and associated electronics are located

beneath the ground plane they do not materially affect the radiation performance

of the antenna. The reed switches have the potential to be used in full-band and

full-polarization antennas and design concepts are explained.

Parisa Lotfi et.al [135], presented a compact reconfigurable asymmetric copla-

nar strip (ACS)-fed monopole antenna. This reconfigurable performance with

capability to operate in the ultra wideband (UWB) frequency from 3.2 GHz to

11 GHz with two stop bands of 3.3 - 4.2 and 5 - 6 GHz and triple WLAN fre-

quency bands of 2.4 - 2.9, 3.6 - 4.4 and 5-6 GHz. The UWB antenna uses a

simple rectangle patch with folded shape slit and stub as rejecting elements and

the mobile antenna uses an arc-shaped stub and inverted L-shaped stub as res-

onating elements. The performance agility and reconfigurable ability is achieved

via a circular rotational motion of the patch.

A. Zohur et.al [136], presented a frequency reconfigurable electrically small

antenna with a high reconfigurable frequency between two frequency bands (718

and 4960 MHz).The reconfigurability is obtained using a single RF MEMS switch.

The antenna achieves a reasonably wide measured bandwidth of 2.6% at 718 MHz

for electrically small lateral dimensions.

Francesca Venneri et.al [137], described an aperture-coupled reflectarray ele-

ment giving a full phase tuning range with a single varactor diode. The full phase

agility is achieved by a proper optimization of the phase tuning line thus provid-

ing an alternate inductive/capacitive effect able to avoid the use of two varactor

diodes usually adopted in similar existing configurations. Furthermore, an own

synthesis procedure is applied to obtain the proper biasing voltages giving the

prescribed H-plane field. A reconfigurable reflectarray element is tuned by a sin-

gle varactor diode and has been considered for the realization of a reconfigurable

reflectarray prototype.

M. J. Ammann and R. Farrell [138], described a dual-band miniaturized

53

printed monopole for integration in modern wireless systems. The printed monopole

is augmented with two arms, resonant at slightly different frequencies providing

a broadened response for the upper band. The achieved bandwidth for the high

band is 36%. These antennas are proposed for the emerging dual-mode multi-

band WLAN transceivers which operate over a wide range of bands as dictated

by national authorities.

Hamid Boudaghi et.al [139], presented a novel compact frequency-reconfigurable

monopo-le antenna with five switchable states including an ultra wideband (UWB)

state, three narrowband states and a dual-band state. The frequency-reconfigurable

capability of the antenna is achieved by using a switchable slotted structure on

the ground plane. The antenna which supports most applicable frequency bands

above 2 GHz is used in multiradio wireless systems.

Chi-Yuk Chiu et.al [140], studied a new frequency-reconfigurable antenna

structure which we denote as a pixel slot antenna for communication. The an-

tenna makes use of a canonical switched slot element that is concatenated together

to form various radiating structures. The resonant path of the pixel slot antenna

can be a conventional slot or a slot plus a loop so higher degrees of freedom in

generating various resonant frequencies are achieved. The maximum-to-minimum

achievable resonance values of a demonstrated 4-switch single-pixel slot antenna

are 3.30 GHz to 1.56 GHz in which the feed mechanism remains unchanged.

Abubakar Tariq and Hooshang Ghafouri-Shiraz [141], introduced a novel copla-

nar waveguide (CPW) bandpass filter using short-circuit slotlines and varactor

diodes. This bandpass filter is integrated with a CPW wideband antenna it

produces frequency agility with a wideband mode and a continuous narrowband

mode. The design of another CPW filter based on a square ring resonator with

switches is present and applied to a wideband antenna making it reconfigurable.

Jia Fu Tsai and Jeen Sheen Row [142], described a reconfigurable design for a

dual-feed square-ring microstrip patch antenna. The dual feeds are used to excite

two orthogonal modes of the antenna and each feed network is composed of a cou-

54

pling patch, an impedance transformer and a variable capacitor. In addition the

two feeds are connected to a single input port through a T-junction power divider.

The proposed design can perform polarization diversity at different frequencies

by tuning the capacitance values of the two capacitors. A prototype integrating

with a pair of varactor diodes and related dc bias circuits is constructed. Both

of them demonstrate that the prototype can provide one linear polarization and

two circular polarizations at one operating frequency moreover the operating fre-

quency can also be tuned to adjacent frequencies.

Lim J.H et.al [143], presented a frequency reconfigurable planar inverted-F

antenna (PIFA) using real PIN-diodes for mobile worldwide interoperability for

microwave access (m-WiMax) applications. This antenna not only alters the fre-

quency band of the m-WiMax using PIN-diode switching but it also has a small

profile using capacitive load within an FR4 dielectric constant substrate. The

PIFA consists of the following: a main radiator, an additional radiator, a band-

switchable capacitive load, two PIN-diodes and control circuits. Depending upon

whether the diodes are on or off the antenna operates for deferent frequencies

for worldwide m-WiMAX bands. They are also investigating the effect of load

capacitance, a parametric analysis is performed by sweeping the length and width

of the capacitive load is also presented.

Hattan F. Abutarboush and R. Nilavalan [144], proposed and presented a re-

configurable antenna based on E-shaped structure with bandwidth controlled..The

bandwidth of the antenna is increased and controlled from 3.4% to 23% by vary-

ing the capacitance of the varactor diodes. The bandwidth is cover the frequency

range from 1.85 GHz - 2.33 GHz is observed.

Zhouyuan Li et.al [145], reported a new class of multifunctional reconfigurable

antenna array (MRAA). The main goal of enhancing the spectral efficiency of ex-

isting and future wireless networks. The MRAA presented in this paper is formed

by the linear combination of four identical multifunctional reconfigurable antenna

(MRA) elements. MRAA prototypes operating in the frequency range of 5.4 GHz

- 5.6 GHz have been measured. The realized gain values of the MRAA prototypes

55

were found to be 13.5 and 0.2 dB. These gain values are 2-3 dB higher than those

of the standard array compared to patch.

M. S. Nishamol et.al [146], presented a novel compact dual frequency mi-

crostrip antenna with frequency and polarization tunability. The tuning is real-

ized by varying the effective electrical length of slot with an embedded capacitor

at the center of X-slot. The impedance matching by increasing the value of C

from 2.2 pF to 100 pF and increase in C offers tuning to 1.594 GHz from 1.748

GHz is observed. The antenna offers a frequency ratio of 1.66 and 1.09 for first

and second resonances with linearly polarized radiation. The measured antenna

peak gain of 3.39 dBi in the direction of maximum radiation. A high tuning range

of 34.48% and 14.3% is achieved resonant frequencies.

Ahmed Khidre et.al [147], proposed and presented a polarization reconfig-

urable E-shaped patch antenna with wideband performance for wireless com-

municaton.The antenna is capable of switching its polarization from right hand

circular polarization (RHCP) to left hand circular polarization (LHCP) and vice

versa. Its structure is simple and consists of a single layer single feed E-shaped

patch and two RF switches placed at appropriate locations in the slots. The de-

sign targets the WLAN IEEE 802.11 b/g frequency band (2.4 - 2.5 GHz) is used

in various wireless communication systems. The antenna exhibits a 7% effective

bandwidth from 2.4 GHz to 2.57 GHz with an 8.7 dBi is achieved.

2.3 Motivation for Present Work

From the above exhaustive review of the literature it is clear that an enormous

amount of work has been done on few types of reconfigurable antenna geome-

tries with different feeding techniques. Each type of geometry is having its own

merits and demerits in terms of antenna performance. In all the above cases

size reduction and bandwidth are moderate. In order to improve the parameters

further different techniques have been used. Also the work on reconfigurability

property with size reduction has been rarely found in the literature survey. Most

56

of the research work has been considered for higher frequencies and a less work

has been performed on lower frequencies. In view of the above, study has been

made by incorporating new designs of reconfigurable antenna geometry for lower

frequencies which are suitable for wireless applications.

Further from the literature survey it is observed that band width and impedance

of band width has not yet been studied with respect to reconfigurable antenna

designs at lower frequency. So, we implemented proposed geometry with antenna

structure and different feed techniques in order to improve the return loss, band-

width and impedance band width of the antenna.

In view of this a systematic study of reconfigurable microstrip antennas is

carried out in following steps.

• Design and development of reconfigurable microstrip antenna with rectan-

gular spiral slots for Bluetooth, GSM and wireless applications.

• In the next step design and implementation of slotted reconfigurable mi-

crostrip antenna for wireless application has been studied.

• Another configuration is varactor diode loaded double square reconfigurable

microstrip patch antenna for wireless applications has been studied.

• To improve the performance of the microstrip antenna, design of compact

reconfigurable multi frequency microstrip antennas for wireless applications

has been made.

• To improve the size reduction of antenna E-slot reconfigurable microstrip

antenna has been made and studied.

• One more antenna configuration is Design of U and E-shape slots Recon-

figurable Microstrip Antenna (UES -RMSA) for wireless applications has

been studied.

• To improve the compactness of the microstrip antenna, Design of T-slot

reconfigurable microstrip antenna (TS-RMSA) has been made.

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The above extensive study has been made by designing and simulating the var-

ious reconfigurable antenna geometries with different feed technique using IE3D

software and then fabricated to carry out the measurements using vector network

analyzer.

The next chapter deals with the methodology and experimental setup in detail.

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