Design and analysis of a frequency and pattern reconfigurable microstrip patc

International Journal of Electronics and Communication Engineering & Technology (IJECET),
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 4, July-August (2013), © IAEME
262
DESIGN AND ANALYSIS OF A FREQUENCY AND PATTERN
RECONFIGURABLE MICROSTRIP PATCH ANTENNA USING VARIOUS
ELECTRONIC SWITCHING COMPONENTS
Ros Marie C Cleetus1
, T.Sudha2
Department of Electronics and Communication Engineering, N.S.S. College of Engineering,
Palakkad, Kerala, India
ABSTRACT
Regardless of the emerging wireless applications, most of the systems demand for increased
functionality, improved performance and compact size. The multitude of different standards in cell
phones and other personal mobile devices requires compact multi-band antennas and smart antennas
with reconfigurable features. The use of the same antenna for a number of different purposes, with
multiple functional capabilities has become inevitable. This paper attempts to design a frequency as
well as pattern reconfigurable microstrip patch antenna using various electronic switching
components such as PIN diodes, Radio Frequency-micro electromechanical system (RF-MEMS)
switches, and Varactors. Three switching cases are being taken into account. The first case results in
an operation at 5.2 GHz and the remaining two cases offer operations at 5.2GHz and also at 1.9
GHz/ 2.76 GHz/ 2.4 GHz, according to various switching components. In the 5.2GHz band a ‘figure
8’ E-plane pattern and an equal gain H-plane pattern are obtained in all the cases, whereas in the 1.9
GHz/ 2.76 GHz/ 2.4 GHz band, an equal gain E-plane pattern and 180º switchable H-plane patterns
resulted according to the switching status. This antenna is an attractive candidate for various wireless
applications.
Keywords: Electrical reconfiguration, gain pattern, microstrip patch antenna, reconfigurable
antenna, return loss.
1. INTRODUCTION
Wireless communications, being the fastest growing segment of the communication industry
is in need of high performance reconfigurable antennas that are able to generate patterns towards
different directions and are able to operate with different resonant frequencies and polarizations. The
characteristics of antenna, such as resonant frequency, radiation pattern, polarization, etc. can be
reconfigured and be used in a more effective manner. Reconfiguration of the antenna can be done by
INTERNATIONAL JOURNAL OF ELECTRONICS AND
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 4, July-August, 2013, pp. 262-271
© IAEME: www.iaeme.com/ijecet.asp
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263
different techniques. The first one, that uses radio frequency-micro electromechanical systems (RF-
MEMS) [1], PIN diodes [2] or varactors [3] as switching devices are called Electrically
Reconfigurable Antennas. Optical switches are used to achieve reconfiguration in the second
technique, and such antennas are called optically reconfigurable Antennas [4]. In the third technique,
antenna radiating parts are physically altered to achieve reconfiguration and these are called
Physically Reconfigurable Antennas [5]. And also, the antennas can be reconfigured by introducing
some changes in the substrate characteristics by using materials such as ferrites, liquid crystals, etc
[6].
Out of these four techniques, here adopted the electrical reconfiguration method that uses PIN
diodes, RF-MEMS switches, and varactors for the switching purpose. While RF-MEMS represent an
innovative switching mechanism, their response is slower than PIN diodes and varactors which have a
response on the order of nanoseconds. All these switches and especially varactors add to the
scalability of reconfigurable antennas [7]. The ease of integration of such switches into the antenna
structure is matched by their nonlinearity effects (capacitive and resistive) and their need for high
voltage (RF-MEMS, varactors).
In this paper, a microstrip line-fed rectangular patch with a partial ground plane base equipped
with two electronic switching components is proposed to get both frequency and pattern
reconfigurability. The switches are mounted over the slots in the ground plane. Three switching cases
are considered. The Ansoft High Frequency Structure Simulator (HFSS) software is used as the tool
for simulation. Section II presents antenna configuration, Section III shows the results and discussion.
Finally, conclusion is given in Section IV.
2. ANTENNA CONFIGURATION
The antenna is designed so as to operate at 5.2 GHz, as per the designing criteria specified in
[8]. The geometrical structure of the antenna, including dimensions, is shown in Fig. 1. The antenna
is based on a Rogers RT/Duroid 5880™ substrate with a dimension of 50 mm X 32 mm with the
dielectric constant, εr of 2.2 and a thickness of 1 mm. The patch which is rectangular is of 22.8 mm
X 18.92 mm dimension, and is fed using a 2.8 mm wide microstrip line. The ground plane is
constructed in such a way that, a rectangle of dimension 39 mm X 22 mm is subtracted from the full
ground plane at (5.5,10,-1). Later, two symmetrical 1.4 mm wide rectangular slots are created onto
the ground plane. Both the slots are at 8.6 mm from the antenna's symmetry axis. Two 1.4 mm X 2.5
mm switches are mounted across the slots, as indicated in Fig. 1.
Fig. 1 Antenna configuration

264
3. RESULTS AND DISCUSSION
The antenna is designed and simulated using Ansoft HFSS [9], an EM simulator based on the
Finite Element Method (FEM).
3.1 Situation 1: Switches are PIN diodes
Two 1.4 mm X 2.5 mm PIN diodes are mounted across the slots as PD1 and PD2 in place of
Switch 1 and Switch 2, as indicated in Fig. 1. The PIN diodes used here are Skyworks SMP 1340
[10]. In the simulation, uses 1.5 for the ON state and 0.35 pF for the OFF state of the PIN diodes.
The three switching conditions considered are given in TABLE 1. The HFSS-computed operating
frequency (fr), return loss (S11), peak gain (G0), operable band of frequencies, bandwidth and peak
directivity are also listed in TABLE 1.
TABLE 1: Performance parameters for each switching condition with PIN Diodes
Case 1 2 3
PD1/PD2 OFF/OFF ON/OFF OFF/ON
f r (GHz) 5.2 1.9 5.2 1.9 5.2
Return Loss (dBi) -15.16 -24 -16.17 -24.44 -16
G0 (dBi) 5.82 1.37 5.97 1.4 5.89
Operable
Band (GHz)
4.4 to 5.9 1.8 to 2.11 4.38 to 5.92 1.8 to 2.11 4.38 to 5.92
Bandwidth
(%)
28.84 16.32 29.62 16.32 29.62
Peak Directivity (dBi) 5.63 1.7 5.79 1.73 5.74
A Gain higher than 1.3 dBi is recorded at 1.9 GHz, whereas a gain higher than 5.8 dBi is
obtained in all cases at 5.2 GHz. The peak directivity is higher than 5.6 dBi and 1.7 dBi at 5.2 GHz
and 1.9 GHz respectively. The return loss is less than -15 dBi at 5.2 GHz and less than -24 dBi at 1.9
GHz. The percent bandwidth is 28.84 for the first case. And these are 29.62 and 16.32 at 5.2 GHz and
1.9 GHz respectively for cases, 2 and 3. Figs. 2 to 4 depict the simulated return loss plots for the 3
switching cases.
Fig. 2 Simulated return loss of the antenna for case 1

265
5.2 GHz
(a)
1.9 GHz 5.2 GHz 1.9 GHz 5.2 GHz
(b) (c)
Fig. 5 Normalized gain pattern of the antenna in the X–Z (red line) and Y–Z (black line) planes for
(a) case 1, (b) case 2 and (c) case 3

266
The simulated gain patterns in the X–Z (H) plane and Y–Z (E) plane are shown in Fig. 5, for
each case. At 5.2 GHz, all three cases result in almost similar radiation patterns in the H-plane and a
‘figure 8’ pattern in the E plane. The H-plane pattern is 180º switchable in the two cases 2 and 3 and
the E-plane patterns are of equal gain. At 1.9GHz band, the antenna exhibits patterns suitable for
wireless mobile application.
This structure finds its applications in PCS (1.85-1.99 GHz), MSS (2-2.02 GHz) refers to
Advanced Wireless Service-4, 5.2/5.8 GHz (5.15–5.35 GHz/5.725–5.825 GHz) WLAN standards and
5.5 GHz (5.25–5.85 GHz) WiMAX bands.
3.2 Situation 2: Switches are RF-MEMS
Two 1.4 mm X 2.5 mm MEMS Switches are mounted across the slots as MEMS1 and
MEMS2 in place of Switch 1 and Switch 2, as indicated in Fig. 1. Radant MEMS SPST-RMSW100
[11] electrostatic switches can be used for achieving reconfigurability. In this case, On Resistance is
<1.0 and Off Resistance is >1 G . The three switching conditions considered are given in TABLE
2. The HFSS-computed operating frequency (fr), return loss (S11), peak gain (G0), operable band of
frequencies, bandwidth and peak directivity are also listed in TABLE 2.
TABLE 2: Performance parameters for each switching condition with RF-MEMS
Case 1 2 3
MEMS1/MEMS2 OFF/OFF ON/OFF OFF/ON
f r (GHz) 5.2 2.76 5.2 2.76 5.2
Return Loss (dBi) -14.92 -13.6 -15.55 -13.69 -15.56
G0 (dBi) 5.6 3.8 5.73 3.87 5.47
Operable
Band (GHz)
4.42 to 6 2.6 to 2.9 4.35 to 6.03 2.6 to 2.9 4.35 to 6.03
Bandwidth
(%)
30.38 10.71 32.31 10.71 32.31
A Gain higher than 3 dBi is recorded at 2.76 GHz, whereas a gain higher than 5.4 dBi is
obtained in all cases at 5.2 GHz. The peak directivity is higher than 5.3 dBi and 3 dBi at 5.2 GHz
and 2.76 GHz respectively. The return loss is less than -14 dBi at 5.2 GHz and less than -13 dBi at
2.76 GHz. The percent bandwidth is 30.38 for the first case. And these are 32.31 and 10.71 at 5.2
GHz and 2.76 GHz respectively for cases, 2 and 3. Figs. 6 to 8 depict the simulated return loss plots
for the 3 switching cases.

267
5.2 GHz
(a)
2.76 GHz 5.2 GHz 2.76 GHz 5.2 GHz
(b) (c)

268
‘figure 8’ pattern in the E plane. At 2.76 GHz band, E plane patterns are of equal gain and H plane
patterns are 180° switchable.
The structure can cover 5.2/5.8 GHz (5.15–5.35 GHz/5.725–5.825 GHz) WLAN standards
and 5.5 GHz (5.25–5.85 GHz) WiMAX bands.
3.3 Situation 3: Switches are Varactors
Two 1.4 mm X 2.5 mm varactor diodes are mounted across the slots as Varactor 1 and
Varactor 2 in place of Switch 1 and Switch 2, as indicated in Fig. 1. The diodes that can be used are
Skyworks SMV1405-074 silicon abrupt-junction common-cathode pairs [12] that are connected in
parallel to achieve a capacitance range of 1.2–5.4 pF from 0–30 V with an equivalent series
resistance of almost 0.55 .
The three cases, with the biasing conditions (reverse and forward bias) of varactors considered
to achieve the desired frequency and pattern reconfigurability are given in TABLE 3. It is considered
that the varactors operate with the capacitance value of 1.2pF. The HFSS-computed operating
frequency (fr), return loss (S11), peak gain (G0), operable band of frequencies, bandwidth (%) and
peak directivity (dB) are also listed in TABLE 3.
TABLE 3: Performance parameters for each biasing condition with Varactors
Case 1 2 3
f r (GHz) 5.2 2.4 5.2 2.4 5.2
Return Loss (dBi) -16.18 -21.99 -15.27 -21.58 -15.62
G0 (dBi) 5.98 2.01 5.63 2.01 5.6
Operable
Band (GHz)
4.35 to 5.92 2.22 to 2.83 4.37 to 6 2.22 to 2.83 4.37 to 6
Bandwidth
(%)
30.19 25.42 31.35 25.42 31.35
Good gain, directivity and return loss characteristics are exhibited by the antenna. A Gain
higher than 2 dBi is recorded at 2.4 GHz, whereas a gain higher than 5 dBi is obtained in all cases at
5.2 GHz. The return loss is less than -15 dBi at 5.2 GHz and less than -21 dBi at 2.4 GHz. The
percent bandwidths are 30.19% for the first case, 25.42% and 31.35% at 2.4GHz and 5.2GHz for the
second and third case. Figs. 10 to 12 depict the simulated return loss plots for the 3 switching cases.

269
5.2 GHz
(a)
2.4 GHz 5.2 GHz 2.4 GHz 5.2 GHz
(b) (c)

270
‘figure 8’ pattern in the E plane. At 2.4 GHz band, the antenna exhibits patterns very much suitable
for wireless mobile application. The H-plane pattern in both cases show similar characteristics as at
5.2 GHz but with a null in one of the ±90 direction. The H-plane pattern is 180º switchable in the two
cases 2 and 3. The E-plane pattern exhibited omnidirectional patterns in both cases which makes it
suitable for WLAN application.
This structure can cover 5.2/5.8 GHz (5.15–5.35 GHz/5.725–5.825 GHz) and 2.4 GHz (2.4-
2.48 GHz) WLAN bands. Also, it can cover 5.5 GHz (5.25-5.85 GHz) and 2.5 GHz (2.5-2.69 GHz)
WiMAX bands.
3.4 Comparison of situations
Comparing the cases of the three situations, all the three ended up with 5.2 GHz band in the
first case and at 1.9 GHz/ 2.76 GHz/ 2.4 GHz band in the other 2 cases. It can be seen that both peak
gain and peak directivity are better for the situation 2, that is when the switches are RF-MEMS. And,
better bandwidth is obtained for the situation 3, with the switches are varactors. All the situations
resulted in almost similar gain patterns with ‘figure of 8’ E plane patterns and equal gain H plane
patterns in 5.2 GHz band and equal gain E plane patterns and 180º switchable H plane patterns in 1.9
GHz/ 2.76 GHz/ 2.4 GHz band. And, the normalized gain patterns could be better seen in situation 3.
4. CONCLUSION
This antenna structure uses two switches, that can be PIN diodes, RF-MEMS switches, or
Varactors mounted over two slots in the ground plane so as to obtain both frequency and pattern
reconfigurability. In the first switching scenario, the antenna is operable over the 5.2 GHz band,
whereas a dual-band operation at 1.9 GHz/ 2.76 GHz/ 2.4 GHz, and 5.2 GHz according to the
switching status of various components in the other two scenarios. An equal gain pattern in the H-
plane and a ‘figure 8’ pattern in the E-plane are obtained in all cases in the 5.2 GHz band. And when
it becomes operable at 1.9 GHz/ 2.76 GHz/ 2.4 GHz, the antenna has equal gain E-plane patterns and
180º-switchable H-plane patterns. The comparison of the three situations shows better gain and
directivity are obtained at situation 2. Better bandwidth and good normalized gain patterns could be
obtained with situation 3. This antenna structure generally finds its applications in PCS, MSS refers to
Advanced Wireless Service-4, 2.4/5.2/5.8 GHz WLAN standards and 2.5/5.5 GHz WiMAX bands.
5. REFERENCES
[1] C. W. Jung, M. Lee, G. P. Li, and F. De Flavis, Reconfigurable scan-beam single-arm spiral
antenna integrated with RF-MEMS switches, IEEE Trans. Antennas Propag., vol. 54, no. 2,
pp. 455–463, Feb. 2006.
[2] S. Shelley, J. Constantine, C. G. Christodoulou, D. E. Anagnostou, and J. C. Lyke, FPGA-
controlled switch-reconfigured antenna, IEEE Antennas Wireless Propag. Lett., vol. 9, pp.
355–358, 2010.
[3] E. Antonino-Daviu, M. Cabedo-Fabres, M. Ferrando-Bataller, and A. Vila-Jimenez, Active
UWB antenna with tunable band-notched behavior, IEEE Electron. Lett., vol. 43, no. 18, pp.
959–960, Aug. 2007.
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[5] S. Jalali Mazlouman, M. Soleimani, A. Mahanfar, C. Menon, and R. G. Vaughan, Pattern
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