Engineering, 2009, 1, 1-54
Published Online June 2009 in SciRes (http://www.SciRP.o rg/journal/eng/).
Copyright © 2009 SciRes. Engineering, 2009, 1, 1-54
Microstrip Antennas Loaded with Shorting Post
Pradeep Kumar, G. Singh
Department of El ectroni cs a n d C ommu nication Engineeri n g,
Jaypee University of Information Technology, Solan, India
Received April 28, 2009; revised May 7, 2009; accepted May 14, 2009
Abstract
In this paper, a technical review with recent advances of the microstrip antennas loaded with shorting posts is
presented. The overall size of the antenna is significantly reduced by a single shorting posts and the effect of
the various parameters of shorting posts on short-circuit microstrip antenna is also discussed.
Keywords: Microstrip Antennas, Loading, Shorting Post, Efficiency, Gain, Bandwidth
1. Introduction
An explosive growth of the wireless radio communica-
tion systems is currently observed in the microwave
band. In the short range communications or contactless
identification systems, antennas are key components,
which must be small, low profile, and with minimal
processing costs [1-4]. The microstrip patch antennas
are of great interest for aforementioned mentioned ap-
plications due to their compact structure. The flexibility
afforded by microstrip antenna technology has led to a
wide variety of design and techniques. The main limita-
tions of the microstrip antennas are low efficiency and
narrow impedance bandwidth. The bandwidth of the
microstrip antenna can be increased using various tech-
niques such as by loading a patch, by using a thicker
substrate, by reducing the dielectric constant, by using
gap-coup led multi-r esonato r etc [3-5]. However, using a
thicker substrate causes generation of spurious radiation
and there are some practical problems in decreasing the
dielectric constant. The spurious radiation degrades the
antenna parameters. Among various antenna bandwidth
enhancement configurations, the two gap-coupled circu-
lar microstrip patch antenna is most elegant one. So,
gap-coupling is the suitable method for enhancing the
impedance bandwidth of the antennas [6,7]. In the con-
figuration of gap-coupled microstrip antennas method,
two patches are placed close to each other. The gap-
coupled microstrip antennas generate two resonant fre-
quencies and the bandwidth of the microstrip antennas
can be increased [6].
There exist a wide range of basic microstrip antenna
shapes such as rectangular, circular and triangular patch
shapes which are commonly used patches. For these
patches, operating at their fundamental mode resonant
frequency, are of the dimension of the patch is about
half wavelength in dielectric. At lower frequencies the
size of the microstrip antennas becomes large. In mod-
ern communication systems the compact microstrip
patch antennas are desirable. There are various tech-
niques to reduce the size of the microstrip antennas. A
common technique to reduce the overall size of a micro-
strip patch antenna is to terminate one of the radiating
edges with a short circuit. The short circuit can be in the
form of a metal clamp or a series of shorting posts [1 ]. It
was shown that by changing the number of shorting
posts and the relative position of these posts, the reso-
nance frequency of the short-circuited microstrip patch
can be adjusted [2]. In fact, by reducing the number of
shorting posts the resonance frequency of the modified
patch can be reduced. Thus for a set resonance frequen-
cies, a significantly smaller element can be achieved
using this technique compared to conventional micro-
strip patches. Further decrease in size can be obtained by
loading the basic shapes by shorting post or slots [1,8,9].
In [10,11], circular microstrip patch antenna with dual
frequency operation is designed by shorting the patch
and the results are compared with the conventional cir-
cular microstrip antenna (without a shor ting post) which

42 P. KUM A R ET AL.
Copyright © 2009 SciRes. Engineering, 2009, 1, 1-54
shows that the size of the circular microstrip antenna can
be reduced for the same frequency application. It is also
observed that the resonant frequency of the circular
microstrip antenna with shorting post can be varied by
varying its location. In [1 2,13], the technique of shor ting
post is used for dual frequency operation.
2. Need of Loading with Shorting Post
The trend for technology in recent times is towards
miniaturization and the demand for more compact and
robust designs has been growing. The revolution in
semiconductor manufacturing and device design meth-
odologies has helped to achieve very high data rates
transmission and compact size. In wireless devices, the
antenna still remains a matter of concern as regards to its
size. In some applications, operation at two or more
discrete bands and an arbitrary separation of bands is
desired. Further, all bands may be required to have the
same polarization, radiation pattern and input impedance
characteristics. Therefore, short circuit microstrip anten-
nas are widely used because the short circuit antenna can
realize the same resonant frequency, at about half the
size of the standard microstrip antenna [2]. The shorted
microstrip antenna is constructed by short-circuiting the
zero-potential plane of an ordinary microstrip antenna
excited with a dominant mode. Physically, this short
circuit may be complete, by wrapping a copper strip
around the edge of the antenna, or it may be simulated
by shorting posts. From manufacturing point of view,
construction of shorting posts is much easier than wrap-
ping a copper strip around the edge of the antenna.
By loading of the microstrip antenna with shorting
post, the size of the microstrip antennas can be reduced
as well as multi-frequency operation, change of polari-
zation etc can be achieved [11,14]. Depending on the
application, the shorting pin may be located at the edge
or at the center of the patch. However, the effect of the
shorting posts depends on different parameters like the
number of the posts, the radius of each post and the
thickness of the microstrip antenna which determines the
length of the posts.
Basically, the shorting post is modeled as an induc-
tance parallel to the resonant LC circuit describing a
reference resonant mode of the unloaded (without short-
ing post) patch. In an equivalent circuit, new resonance
mode (with shorting post) can be viewed as resulting
from the inductance (due to shorting post) in series with
static capacitance of the patch configuration. Larger the
inductive part smaller will be the resulting resonance
frequency, that is, the larger will be the degree of minia-
turization achieved for a fixed operating frequency [1].
This technique is used to reduce the resonance fre-
quency has been proposed first time by Waterhouse [15]
and has been demonstrated on a variety of different
patch shapes [16]. Microstrip antennas were miniatur-
ized by using shorting post in [1,17]. As shown in [15],
the maximum reduction in physical size can be achieved
if a single shorting post is used. Here the radius of circu-
lar patch was reduced by a factor of three, making the
antenna size suited for compact communication systems.
In [10], circular microstrip antenna with dual frequency
operation is designed by shorting the patch. The results
are compared with the conventional circular microstrip
antenna (without a shorting pin). In [11], a rectangular
microstrip antenna with dual frequency operation is
designed by shorting the patch. It is observed that the
size of the antenna can be reduced by shorting the patch
at its edge.
3. Shorting Post Loaded Microstrip Patch
Antennas for Various Applications
For lower frequencies, the size of the microstrip antenna
is large. So, reduction in the size of the antenna is de-
sired. The size of the antenna can be reduced by using
microstrip antennas the size of the antenna can be re-
duced. The microstrip antennas loaded with shorting
post for various applications are discussed as follows:
3.1. Circular Microstrip Antennas
Loaded with Shorting Post
In [8], the rectangular and the circular microstrip anten-
nas are loaded with shorting pin/post. The rectangular
and circular microstrip antennas loaded with shorting
post are shown in Figure 1(a) and Figure 1(b) respec-
tively. The antennas are fed by probe feeding. The sizes
of the antennas are reduced and the antennas are de-
signed for mobile communication handsets.
In [1], an analytical theory for the eigenfrequencies
and eigenmodes of shorting post loaded microstrip an-
tennas is presented. It is shown that the zero mode of the
unloaded MSA plays a central role for reducing the
lowest operating frequency of the loaded microstrip
antenna. For a circular patch loaded with single post, it
was shown that a larger shorting post radii lead to
stronger suppression of the inductive part of the short-
ing-post impedance and, therefore, resonates at higher
resonant frequencies. The lowest values for the resonant

P. KUMAR ET AL. 43
Copyright © 2009 SciRes. Engineering, 2009, 1, 1-54
frequency are obtained when positioning the shorting
post at the edge of the patch. In general, the resonant
frequencies obtainable from a loaded circular patch are
larger than those of a rectangular patch of equal cross
section. It is also seen that the sensitivity of the reso-
nance frequency against variations of the shorting-post
position of the circular patch is stronger than in the rec-
tangular patch.
3.2. Rectangular Microstrip Antennas
Loaded with Shorting Post
In [11], the rectangular microstrip antenna is lo aded with
shorting post at the center line of the patch as shown in
Figure 2. This type of loading produces two lowest
resonant frequencies with the same polarization. The
size reduction of the antenna at the lowest frequency is
roughly 2. 6.
(a)
(b)
Figure 1. (a) Rectangular microstrip antennas loaded with
shorting post, (b) circular microstrip antennas loaded with
shorting post.
A dual frequency compact antenna capable of receiv-
ing both linearly and circularly polarized radiation has
been reported in [18]. It generates linear polarization at
the lower frequency and circular polarization at the up-
per frequency. It consists of a square patch with two
symmetrical shorting pins. A reduction factor of 5 in
area has been achieved at the lower frequency end.
3.3. Triangular Microstrip Antennas
Loaded with Shorting Post
In [19] equilateral and 30o-60o-90o triangular micro-
strip antennas are shorted along the zero field to reduce
the size of the antennas. The equilateral and 30o-60o-
90o triangular microstrip antennas loaded with shorting
post is shown in Figure3. These equilateral an d 30o-60o-
90o triangular microstrip antennas yield shorted 60 and
30o sectoral microstrip antennas, respectively and result
in area reduction by factors of 2.5 and 5 respectively.
3.4. Pin Shorted Microstrip Antenna for
Mobile Communication
In [20], pin shorted rectangular antenna is designed for
mobile communication applications as shown in Figure4.
The desired resonant frequency is obtained by shorting
the patch. The designing is performed by simulation
using Method-of-moments based software (IE3D). The
shorting pin diameter as well as location of pin is varied
and the antenna is made for mobile communicatio n.
In [21], the size of the gap-coupled microstrip anten-
nas is miniaturized using shorting post. The fed patch is
loaded and the gap-coupled microstrip antennas produce
triple frequency operation. The mutual coupling and
input impedance of the gap-coupled circular microstrip
antennas loaded with shorting post can be controlled by
changing the diameter of shorting post [22-24]. In [25],
Figure 2. Rectangular microstrip antenna loaded with
shorting post at the center line.

44 P. KUM A R ET AL.
Copyright © 2009 SciRes. Engineering, 2009, 1, 1-54
using shorting pin and multi-layer dielectric concept, a
broadband and small antenna is designed. The designed
antenna can be used in communication systems. In
[12,13], the microstrip ante nnas are loaded with shorting
post and the antennas are designed for dual frequency
operation.
4. Conclusions
The size of the microstrip antennas can be reduced by
using the concept of loading a microstrip antenna with
shorting posts. For multi-frequency applications shorting
posts loaded microstrip antenna can be used. A review
of shorting post loaded microstrip antenna as well as
need of the shorting post loaded microstrip antenna is
presented. The different types of shorting post loaded
microstrip antennas can be used for different applica-
tions.
(a)
(b)
Figure 3. Triangular microstrip antennas loaded with
shorting post, (a) Equilateral, (b) 30o-60o-90o.
Figure 4. Pin shorted microstrip antenna for mobile com-
munications.
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