This document summarizes research on designing rectangular slot loaded monopole microstrip antennas to achieve triple-band operation, virtual size reduction, and enhanced bandwidth. The antennas were simulated and tested experimentally. Adding a vertical rectangular slot to the patch produced three resonant bands from 1-16 GHz with 62% virtual size reduction. Rotating the slot 30 degrees retained the triple-band operation while increasing bandwidth. Rotating it 60 degrees converted the three bands to six bands. All designs exhibited omnidirectional radiation patterns. Experimental results matched simulations. The antennas could potentially be used in microwave communication systems.

1. INTERNATIONAL JOURNAL OF ELECTRONICS AND
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 4, Issue 1, January- February (2013), pp. 176-182
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RECTANGULAR SLOT LOADED MONOPOLE MICROSTRIP
ANTENNAS FOR TRIPLE-BAND OPERATION AND VIRTUAL SIZE
REDUCTION
M. Veereshappa1, and S. N. Mulgi2
1
Department 0f Electronics, L.V.D.College, Raichur -584 103,
Karnataka, India
2
Department of PG Studies and Research in Applied Electronics,
Gulbarga University, Gulbarga – 585 106, Karnataka, India.
mveeresh27@rediffmail.com, s.mulgi@rediffmail.com
ABSTRACT
This paper presents the design and development of rectangular slot loaded monopole
microstrip antennas for triple-band operation and virtual size reduction. The antenna operates
for three band of frequencies in the frequency range of 1 to 16 GHz and gives maximum
virtual size reduction of 62 %. If vertical rectangular slot on the patch is rotated by an angle
of 300 the antenna retains three bands of frequencies and gives the maximum band width at
each operating band keeping same virtual size reduction .The three bands may be converted
to six bands by further rotating 300 slot on the patch to 600. In all the cases antenna gives
ominidirectional radiation characteristics. Experimental results are in close agreement with
the simulated results. The proposed antenna may find application for microwave
communication systems.
Key words: monopole, virtual size, ominidirectional.
1. INTRODUCTION
Microstrip antennas are useful in microwave communication systems because of their
diversified applications such as compact in size, simple in design, planar configurations,
compatibility with integrated circuits, low cost, low profile, light weight, and easy to
fabricate[1-2]. Number of investigations have been reported in the literature for the
realization of dual, triple and multi-band operation [3-6] and enhancement of impedance
bandwidth [7-8]. Designs of single feed equilateral triangular microstrip antennas are
obtained with an virtual size reduction is up to 22 % by embedding cross slots on radiating
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2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
patch [9]. Most of the antennas presented in the literature are complex in their design and
large in antenna size. In this paper a simple technique has been demonstrated to construct the
monopole antenna for triple band operation, virtual size reduction and enhancement of
impedance bandwidth at each operating band by varying the angle of vertical slot on the
patch without affecting the nature of radiation characteristics.
2. DESIGN OF ANTENNA GEOMETRY
The art work of the proposed antennas is sketched by using computer software Auto-
CAD to achieve better accuracy and are fabricated on low cost FR4-epoxy substrate material
of thickness of h = 0.16 cm and permittivity εr = 4.4.
Figure 1 shows the top view geometry of rectangular slot monopole microstrip antenna
(RSMA). The selected area of the substrate is A = L × W cm. On the top surface of the
substrate a ground plane of height which is equal to the length of microstripline feed Lf is
used on either sides of the microstripline with a gap of 0.1 cm. On the bottom of the substrate
a continuous ground copper layer of height Lf is used below the microstripline. The RSMA is
designed for 3 GHz of frequency using the equations available for the design of conventional
rectangular microstrip antenna in the literature [2]. The length and width of the rectangular
patch are Lp and Wp respectively. The feed arrangement consists of quarter wave transformer
of length Lt and width Wt which is connected as a matching network between the patch and
the microstripline feed of length Lf and width Wf. A semi miniature-A (SMA) connector is
used at the tip of the microstripline feed for feeding the microwave power. In Fig.1 the
rectangular slot is placed along the center axis of the patch at a distance of 1.42 cm from the
vertical sides of the patch. The length and width of rectangular slot is Ls and Ws respectively,
and are to be in terms of operating wave length.
Figure 1 Top view geometry of RSMA
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3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
Figure 2 shows the geometry of inclined thirty degree rectangular slot monopole microstrip
antenna (ITRSMA). In this figure a rectangular slot is rotated by an angle of 300 on the patch
when compared to Fig.1 The feed arrangement of Fig. 2 remains same as that of Fig.1.
Figure 2 Top view geometry of ITRSMA
Figure 3 Top view geometry of IRSSMA
Fig.3 shows the geometry of inclined sixty degree rectangular slot monopole microstrip
antenna (IRSSMA). In this figure rectangular slot is rotated on the patch by an angle of 600
with respect to Fig.1. The feed arrangement of this antenna is also remain same as that of
Fig.1. The design parameters of the proposed antennas is as shown in Table 1
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4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
TABLE 1 Design Parameters of Proposed Antennas
Antenna Dimension Antenna Dimension
Parameters (cm) Parameters (cm)
Lp 2.34 L 8.0
Wp 3.04 W 5.0
Lf 2.48 Ls 1.666
Wf 0.30 Ws 0.2
Lt 1.24 h 0.16
Wt 0.05
3. EXPERIMENTAL RESULTS
The antenna bandwidth over return loss less than -10 dB is simulated using HFSS
simulating software and then tested experimentally on Vector Network Analyzer (Rohde &
Schwarz, Germany make ZVK model 1127.8651). The variation of return loss verses
frequency of RSMA is as shown in Fig. 4. From this graph the experimental bandwidth (BW)
is calculated by using the equations,
f −f 
BW =  2 1  ×100 % (1)
 fc 
were f1 and f2 are the lower and upper cut of frequencies of the band respectively when its
return loss reaches – 10 dB and fc is the center frequency between f1 and f2. From this figure,
it is found that, the antenna operates between 1 to 16 GHz and gives three resonant modes at
f1 to f3, i.e. at 1.14, 4.70, and 14.01 GHz. The magnitude of experimental -10 dB bandwidth
measured for BW1 to BW3 by using the equation (1) is found to be 130 MHz (9.6 %), 80
MHz (1.68 %), and 8.81 GHz (76.24 %) respectively.
Figure 4 Variations of return loss versus frequency of RSMA
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5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
The resonant mode at 1.14 GHz is due to the fundamental resonant frequency of the patch and
others modes are due to the novel geometry of RSMA. The triple band response obtained is due
to different surface currents on the patch. The fundamental resonant frequency mode shifts from 3
GHz designed frequency to 1.14 GHz due to the coupling effect of microstripline feed and top
ground plane of RSMA. This shift of frequency gives a virtual size reduction of 62 %.
Figure 5 Variations of return loss versus frequency of ITRSMA
Figure 5 shows the variation of return loss verses frequency of ITRSMA. It is seen that, the
antenna operates for three bands of frequencies. The magnitude of these operating bands
measured at BW4 to BW6 is found to be 340 MHz (27 %), 190 MHz (4.02 %), and 8.88 GHz
(76.81 %) respectively. Hence by comparing Fig.4 and 5 it is clear that the each operating band of
Fig.5 is enhanced by changing vertical slot on the patch by 300 when compared to Fig.1.
The variation of return loss verses frequency of IRSSMA is as shown in Fig. 6. From this figure it
is clear that, the antenna operates for six bands BW7 and BW12. The magnitude of each operating
band is found to be 220 MHz (18.33 %), 90 MHz (1.9 %), 2.76 GHz (32.74 %), 2.26 GHz (19.96
%), 790 MHz (6.04 %) and 2.42 GHz (16.36%) respectively. This shows that, the rotation of slot
on the patch is effective in increasing the number of operating bands. The simulated results of
RSMA, ITRSMA and IRSSMA are also shown in Fig. 4 to 6. The experimental and simulated
results are in good agreement with each other.
Figure 6 Variations of return loss versus frequency of IRSSMA
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6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
The co-polar and cross-polar radiation pattern of RSMA, ITRSMA and IRSSMA is
measured in their operating bands. The typical radiation patterns for the proposed antennas
are shown in Fig 7 to 9 respectively. The obtained patterns are ominidirectional in nature.
The gain of RSMA, ITRSMA and IRSSMA is measured by absolute gain method. The
maximum gain found to be 8.18, 9.93 and 8.38 dB respectively.
Figure7 Typical radiation pattern of RSMA Figure 8 Typical radiation pattern of TRSMA
.
Figure 9 Typical radiation pattern of IRSSMA
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7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN
0976 – 6464(Print), ISSN 0976 – 6472(Online) Volume 4, Issue 1, January- February (2013), © IAEME
4. CONCLUSION
From the detailed experimental study, it is concluded that the RSMA operates for
three band of frequencies in the frequency range of 1 to 16 GHz and gives maximum virtual
size reduction of 62 %. If rectangular slot is rotated with an angle of 300 the enhancement of
each operating band in triple band operation is possible .The three band of frequencies may
be converted into six bands by further rotating rectangular slot on the patch by an angle of
600. In all cases the antenna gives virtual size reduction of 62 % with ominidirectional
radiation characteristics. Experimental results are in close agreement with the simulated
results. The proposed antenna may find application for microwave communication systems.
ACKNOWLEDGEMENT
The authors would like to thank Dept. of Sc. & Tech. (DST), Govt. of India. New
Delhi, for sanctioning Vector Network Analyzer to this Department under FIST project. The
authors also would like to thank the authorities of Aeronautical Development Establishment
(ADE), DRDO Bangalore for providing their laboratory facility to make antenna
measurements on Vector Network Analyzer.
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