Rectangular microstrip array antennas for wide triple band operation

International Journal of Electronics and CommunicationTechnology (IJECET),
International Journal of Electronics and Communication Engineering &
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 1, Number 1, Sep - Oct (2010), © IAEME
Engineering & Technology (IJECET)
ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online)
IJECET
Volume 1, Number 1, Sep - Oct (2010), pp. 53-61 ©IAEME
© IAEME, http://www.iaeme.com/ijecet.html

RECTANGULAR MICROSTRIP ARRAY ANTENNAS FOR
WIDE TRIPLE BAND OPERATION
Gangadhar P Maddani
Department of PG Studies and Research in Applied Electronics
Gulbarga University, Gulbarga
E-Mail id: gangadharmaddani@rediffmail.com

Sameena N Mahagavin
E-Mail id: sameena.nm@rediffmail.com

Shivasharanappa N Mulgi
E-Mail id: s.mulgi@rediffmail.com

ABSTRACT
This paper presents a novel design of two elements rectangular microstrip array
antenna with parasitic wire around (TERMAA) for triple band operation and omni
directional radiation pattern. Further, quadruple bands are obtained by simply minimizing
the area of ground plane of TERMAA. Later, by truncating the corners of minimized
ground plane, the upper two bands are merged together resulting wider triple band
operation. The magnitude of each operating band is found to be 19.1, 15.43 and 79.23%
respectively with a maximum gain of 3.9 dB. This enhancement does not affect the nature
of radiation characteristics. The proposed antennas may find applications for microwave
systems operating at WLAN (2.4 – 5.2 GHz), HIPERLAN/2 (5.725 – 5.825 GHz) and X
to Ku (8 – 18.5 GHz) band of frequencies. Details of antenna design are described and
experimental results are discussed.
Keywords: microstrip antenna, array antenna, minimized ground plane, triple-band,
omni directional.

53

International Journal of Electronics and Communication Engineering & Technology (IJECET),

1. INTRODUCTION
Recent developments in wireless communication system often require antenna
with planar geometry, light weight, ease in fabrication and capable of operating at more
than one band of frequencies. The microstrip patch antenna can meet these requirements.
Further, dual or triple band frequency operations have gained wide attention in many
microwave communication system. When system requires operating at two or more
distinct band of frequencies, dual or triple frequency patch antennas may avoid the use of
separate antennas for each operating band [1].
Most of the dual frequency microstrip antenna design uses reactively loaded
elements, while other design uses a multistructer or multipatches [2-5] and hence,
becomes complex in their manufacturing procedure. To overcome this, in present study
an experimental effort is made to get triple band operation by using simple two elements
rectangular microstrip array antenna wound with a parasitic strip around the patches i.e.
TERMAA. Further, by minimizing the ground plane of this antenna, the quadruple and
enhancement of impedance bandwidth is achieved.
2. DESCRIPTION OF ANTENNA GEOMETRY
The proposed antennas are designed using low cost glass epoxy substrate material
of thickness h = 0.16 cm, permittivity εr = 4.2 and area = A×B. The antennas may be
designed using low dielectric constant substrate material but the use of high dielectric
constant of substrate materials reduces radiation losses because most of the EM field is
concentrated in the dielectric between the conductive strip and the ground plane [6]. The
artwork of the proposed antennas is sketched using computer software Auto-CAD 2006
to achieve better accuracy. The antennas are fabricated using photolithography process.
Figure 1 shows the top view geometry of TERMAA comprising of parasitic strip
around the radiating patches. The length L and width W of the patch is designed for
resonant frequency of 5 GHz, using the equations available for design of rectangular
patch [7]. The width of parasitic strip is Wp and is kept away from the side edges of the
patch by a distance R. The gap between the edges of strip and quarter wave transformer is
again R. The distance D between the two radiating elements from their centre should be
λo/2 for minimum side lobes [8], where λo is the free space wavelength in cm. But in

54


Figure 1, D is taken as λo/2.33 in order to keep the feed line as compact as possible for
minimum feed line loss. Further, when D is less than λo/2.33; it becomes difficult to
accommodate the feed arrangement between the array elements. Hence D = λo/2.33 is
treated as optimum in this case. The parallel feed arrangement has wideband performance
over series feed and hence selected in this case to excite the array elements of Figure 1.
The feed arrangement shown in Figure 1 is a contact feed and has advantage that it can be
etched simultaneously along with antenna elements. The parallel feed arrangement of
Figure 1 consists of a 50 microstrip feedline of length L50 and width W50 is connected
to 100 microstrip feedline of length L100 and width W100 to form a two way power
divider. A 100 quarter wave matching transformer of length Lt and width Wt is
connected between 100 microstrip feedline and mid point of the radiating elements in
order to ensure perfect impedance matching. The bottom plane of TERMAA is tight
ground plane copper shielding. The ground plane shielding of TERMAA is minimized as
shown in Figure 2 retaining its top geometry. This antenna is named as modified ground
plane two elements rectangular microstrip array antenna (MGTERMAA). The size of
copper area on the ground plane is taken as A1×B. Later, the corners of the ground plane
of MGTERMAA are truncated as shown in Figure 3 retaining its top geometry. This
antenna is named as corner truncated ground plane two element rectangular microstrip
array antenna (CTGTRMAA). The corners are truncated by length Lc and width Wc. The
various antenna parameters of Figure 1 to Figure 3 are given in Table 1.

Figure 1 Geometry of TERMAA

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Figure 2 Ground plane geometry of MGTERMAA

Figure 3 Ground plane geometry of CTGTRMAA
3. EXPERIMENTAL RESULTS
The impedance bandwidth over return loss less than −10 dB of the proposed
antennas is measured on Vector Network Analyzer (Rohde & Schwarz, Germany make
ZVK model 1127.8651). The variation of return loss versus frequency of TERMAA is as
shown in Figure 4. From this figure, it can be seen that the antenna resonates for three
band frequencies BW1, BW2, and BW3. The impedance bandwidth of each operating
band is determined by using the equation,
 (f − f ) 
Impedance bandwidth =  2 1  ×100 %
 fc 
where, f1 and f2 are the lower and upper cut-off frequencies of the band
respectively, when its return loss becomes −10 dB and fc is the center frequency between
f1 and f2.

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Figure 4 Variation of return loss verses frequency of TERMAA
The magnitudes of impedance bandwidth BW1, BW2 and BW3 are found to be
5.5, 14.04 and 16.08% respectively. These triple bands are due to the independent
resonance of radiating elements and parasitic strip [9-10]. The variation of return loss
versus frequency of MGTERMAA is as shown in Figure 5. From this graph, it can be
seen that the antenna resonates for four bands of frequencies BW4, BW5, BW6 and BW7
with corresponding magnitudes of impedance bandwidth is found to be 17.22, 14.22,
10.38 and 67.76% respectively. The additional bands between BW4 to BW7 are due to the
effect of modified ground plane in MGTERMAA.

Figure 5 Variation of return loss verses frequency of MGTERMAA

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Figure 6 shows the variation of return loss versus frequency of CTGTRMAA.
From this figure, it can be seen that the antenna resonates again for triple bands BW8,
BW9 and BW10 with corresponding magnitude of impedance bandwidth is found to be
19.1, 15.43 and 79.23% respectively. It is clear that the two bands BW6 and BW7 of
MGTERMAA as shown in Figure 5 which are close to each other combines together
resulting into a single band BW10 as shown in Figure 6. Thus CTGTRMAA enhances the
operating bandwidth of triple band operation.

Figure 6 Variation of return loss verses frequency of CTGTRMAA
The co-planar radiation pattern of antenna under test (AUT) is measured by
connecting a standard pyramidal horn antenna in far field region. The AUT is connected
in receiving mode and is kept in phase with respect to transmitting pyramidal horn
antenna. The power received by AUT is measured from 00 to 3600 with steps of 100. The
typical radiation patterns of TERMAA, MGTERMAA and CTGTRMAA measured at
12.55, 9.81 and 9.81 GHz respectively is as shown in Figure 7. From the figure, it can
observe that the patterns are omni directional in nature. Hence the enhancement of
impedance bandwidth of triple band operation through CTGTRMAA does not affect the
nature of radiation characteristics.

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Figure 7 Radiation pattern of TERMAA, MGTERMAA and CTGTRMAA
For the calculation of gain of proposed antennas, the power transmitted ‘Pt’ by
pyramidal horn antenna and power received ‘Pr’ by AUT are measured independently.
With the help of these experimental data, the gain G (dB) of AUT is calculated using the
absolute gain method [11],
 Pr   λ0 
( G ) dB=10 log   − ( Gt ) dB − 20 log   dB
 Pt   4πR 
Where, Gt is the gain of the pyramidal horn antenna and R is the distance between
the transmitting antenna and the AUT. The gains of TERMAA, MGTERMAA and
CTGTRMAA are found to be 0.71, 3.60, and 3.90 dB respectively. Hence CTGTRMAA
gives highest gain among the proposed antennas.
4. CONCLUSION
From the detailed experimental study, it is concluded that, triple band operation
with omni directional radiation pattern of antenna is achieved by designing TERMAA.
Further, by minimizing the area of ground plane, quadruple bands are observed. Later, by
truncating the corners of the minimized ground plane, the enhancement of impedance
bandwidth at each operating bands in the triple band operation is possible without
changing the nature of omni directional radiation characteristics. This technique also
enhances the gain from 0.71 t0 3.90 dB. The proposed antennas are simple in their

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design, fabrication and they use low cost substrate material. The proposed antennas may
find applications for microwave systems operating at WLAN (2.4 – 5.2 GHz),
HIPERLAN/2 (5.725 – 5.825 GHz) and X to Ku (8 – 18.5 GHz) band of frequencies.
ACKNOWLEDGEMENTS
The authors would like to thank Dept. of Sc. & Tech. (DST), Govt. of India, New
Delhi, for sanctioning Network Analyzer to this Department under FIST project.
TABLE 1
Design Parameters of Proposed Antennas
Antenna Dimensions Antenna Dimensions
Parameters (cm) Parameters (cm)
A 5.00 L100 0.38
B 3.50 W100 0.07
L 1.41 R 0.10
W 1.86 D 2.33
Lt 0.38 A1 1.16
Wt 0.015 Lc 0.30
L50 1.54 Wc 0.20
W50 0.32 λ0 60.00
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7. I. J. Bhal and P. Bhartia (1980), “Microstrip Antennas”, Artech House, New
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Rectangular microstrip array antennas for wide triple band operation

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