A010340105

IOSR Journal of Electronics and Communication Engineering (IOSR-JECE)
e-ISSN: 2278-2834,p- ISSN: 2278-8735.Volume 10, Issue 3, Ver. IV (May - Jun.2015), PP 01-05
www.iosrjournals.org
DOI: 10.9790/2834-10340105 www.iosrjournals.org 1 | Page
A Review on Microstrip Patch Antennas for WLAN and Wimax
Applications
Amrutha.M.V, Manoj.K.C
PG Scholar, Dept. of ECE Vimal Jyothi Engineering College
Assistant Professor, Dept. of ECE Vimal Jyothi Engineering College
Abstract: Wireless local area network (WLAN) and Worldwide Interoperability for Microwave
Access(WiMAX) has been widely applied in mobile devices such as intelligent phones and handheld computers.
For miniaturizing the wireless communication system the antenna which is being used must also be small
enough to be placed inside the system. So microstrip antennas are becoming very popular in the field of
mobile,radar,WiMAX,WiFi,LTE system, satellite,UWB etc .This paper presents a comparative study of
microstrip patch antenna for WLAN and WiMAX application with changes in length and width of the patch,
variety of substrates, feed techniques and slots. Here we also discuss the basics of microstrip antenna, antenna
parameters,design models, various feeding techniques, with their advantages and disadvantages. A microstrip
antenna is characterized by its length, width, gain, input impedance, and radiation pattern .The slot structure on
the printed antenna that satisfies the requirements of the mobile WLAN and WiMAX applications such as the
impedance bandwidth ,radiation pattern and gain is also presented. This paper in overall provides recent
development, technologies and designs in the field of printed antennas for WLAN and WiMAX applications.
Index Terms: WLAN and WiMAX, microstrip patch, substrate, feeding techniques, bandwidth
I. Introduction
As the communication devices are becoming smaller due to greater integration of electronics, the
antenna becomes a significantly larger part of the overall package volume. This results in a demand for similar
reductions in antenna size. When designed at lower microwave frequency spectrum,the size of a conventional
microstrip antenna is somewhat large. Sometimes the size of the antenna even exceeds the dimension of the
repeater or receiver system and thus is unsuitable for mounting conformably on the existing repeater/receiver
system. For many antenna applications, such as handheld transceivers and handheld computers, small size is
extremely important. For fixed wireless applications also, the small sized antennas plays an important role. The
new trends in antenna design mainly focuses on the compactness of antenna,its robustness and integration with
the existing RF circuit components. Antennas are basic components of any electric system and they are the
connecting links between the transmitter and free space or free space and the receiver. Thus antennas play very
important role in finding the characteristics of the system in which antennas are employed. Antennas are
employed in different systems in different forms. That is, in some systems the high gain of the antenna is
considered,or the directional properties,or the omnidirectional radiation pattern ,or the high beam width is
considered.That is the selection of the antenna depends on its application.
II. Microstrip Antennas
A. Structure
A microstrip antenna in its simplest form consists of a radiating patch,which may be square or circular
or rectangular in shape, on one side of a dielectric substrate and a ground plane on the other side. The radiating
elements and the feed lines are usually photoetched on the dielectric substrate. The microstrip antenna radiates
relatively broad beam broadside to the plane of substrate. Thus the microstrip antenna has a very low profile and
can be fabricated using printed circuit technology. The radiating patch may be square, rectangular, thin strip
(dipole), elliptical, triangular, circular,or any other configuration.
B. Feeding Techniques
A feedline is used to excite the antenna by direct or indirect contact. There are different techniques of
feeding and four most popular techniques are coaxial probe feed, microstrip line, aperture coupling and
proximity coupling. In microstrip feed technique, a conducting strip is connected directly to the edge of the
microstrip patch. The conducting strip is smaller in width as compared to the patch .This type of feed
arrangement has the advantage that the feed can be etched on the same substrate,so that it provides simple a
planar structure.Microstrip line feed is one of the easier methods to fabricate because, it is a just conducting strip
connecting to the patch and therefore can be considered as an extension of patch. The coaxial feed or probe feed
is a very common technique used for feeding microstrip patch antennas. Coaxial feeding is feeding method in

A Review on Microstrip Patch Antennas for Wlan and Wimax Applications
which the inner conductor of the coaxial is attached to the radiating patch of the antenna while the outer
conductor is connected to the ground plane. Aperture coupling consist of two different substrates separated by a
ground plane. On the bottom side of lower substrate there is a microstrip feed line whose energy is coupled to
the patch through a slot on the ground plane separating these two substrates. This arrangement allows
independent optimization of the feed mechanism and the radiating element. Normally top substrate is thick,and
which is having a low dielectric constant while for the bottom substrate it is the high dielectric substrate.
Proximity coupled type of feed technique is also called as the electromagnetic coupling scheme. The main
advantage of this feed technique is that it eliminates spurious feed radiation and also it provides very high
bandwidth (as high as 13%), due to overall increase in the thickness of the microstrip patch antenna.
C. Advantages of microstrip antenna
The antenna is broadly classified in two categories – unidirectional antenna and directional antenna.
Most of the conventional antennas like yagi uda, helical, horn, parabolic etc are directional. They are quite good
in terms of their bandwidth and gain. In spite of all these advantages they have some disadvantages.The
disadvantages includes their large volume, very bulky structure, complex 3d structure etc. Microwave
applications require small sized antennas so all these antennas are not well suited for microwave applications.
Microstrip antenna is the one which is well suited for wireless and microwave applications. Compared with
conventional antennas, microstrip patch antennas have more advantages and better performance. They are
lighter in weight, low cost, low volume,low profile, smaller in dimension and ease of fabrication, simplified 2d
structure and conformity. Moreover, the microstrip patch antennas can provide dual and circular polarizations,
dual-frequency operation, broad band-width, feedline flexibility, beam scanning omnidirectional patterning and
also high gain.
Microstrip antennas are extremely compatible for embedded antennas in handheld wireless devices
such as pagers,cellular phones, etc. These low profile antennas are also useful in satellite,aircraft, and missile
applications, where size, weight, cost, performance, ease of installation are considered. However, one of the
major drawbacks of this microstrip patch antenna is the low bandwidth. Narrow bandwidth and gain are main
disadvantages of this patch antenna. To overcome these disadvantages various techniques are used like varying
the substrate thickness, changing the dielectric value of substrate, using the various patch configurations, using
stacked configuration etc.
D. Disadvantages
Although patch antenna has numerous advantages, it has also some drawbacks such as narrow
bandwidth, low gain, excitation of surface waves and a potential decrease in radiation pattern. Various
techniques like using Frequency Selective Surface, Employing stacked configuration, using thicker profile for
folded shorted patch antennas, slotted antennas like U-slot patch antennas together with shorted patch, double
U-slot patch antenna, L-slot patch antenna, annular slot antenna, double C shaped patch antenna, E-shaped patch
antenna, and feeding techniques like circular coaxial probe feed,L probe feed, proximity coupled feed are used
to enhance bandwidth of patch antennas. The substrate height and dielectric constant of the substrate are very
important factors that influence the changes of bandwidth as well as the surface waves. The substrates of
dielectric constants are usually in the range of 2.2 to 12.The antennas with thick substrates whose dielectric
constants are in the lower end of the range,provide better efficiency, larger bandwidth, loosely bound fields for
radiation in the space and also it provides high gain.
III. Methods For Improving Bandwidth
The bandwidth of a dual patch antenna can be improved by etching dummy EBG pattern on the
feedline. In spite of many advantages, these antennas suffer from some disadvantages which include their low
efficiency, low power, poor polarization purity, spurious feed radiation and very narrow bandwidth . A possible
way for increasing the bandwidth is to either increase the height of the dielectric or decrease the dielectric
constant. However, the first approach would make it unsuitable for low profile structures while the latter
approach will make the matching circuit to the patch difficult due to excessively wide feeding lines. Bandwidth
of small size microstrip antennas has been improved by the use of U slot and L probe . By using compound
techniques a new type of stacked microstrip patch antenna that increases the frequency bandwidth has also been
studied. the bandwidth of an aperture coupled microstrip patch antenna has been improved by using an
appropriate impedance-matching network using filter design techniques. The use of two triangular structures for
microstrip patch antennas to improve the bandwidth has been studied. Unbalanced structures have also been
used to design patch antennas to improve bandwidth. Performance parameters especially bandwidth, of patch
antennas which are usually considered as narrowband antennas can be improved using metamaterial.
Metamaterials are also the basis of further miniaturization of microwave antennas. The main interest behind

using metamaterial substrate is :Increase bandwidth and gain of a patch antenna and Miniaturization of
microstrip patch antenna.
IV. Comparison Table

When rectangular slot is cut in the ground plane and the microstrip line is made perpendicular to it,then
there occurs an increase in the bandwidth of the antenna.High bandwidth is obtained on the thin substrate,and
this occurs because of the presence of the resonant modes created.RT duroid 5880 substrate with dielectric
constant of 2.2 is used here.The duo triangular shaped patch antenna also provides high bandwidth.It makes use
of the FR4 substrate with dielectric constant of 4.4 and thickness of 1.6mm.The circular microstrip antenna with
DGS provides high bandwidth,in which the the shape defected in the ground structure will disturb the current
distribution,and thus the excitation is effected and also the propagation of EM waves through the substrate
layer.In the U slot patch antenna ,RT duroid 5880 with dielectric constant of 2.2 is used.In this ,the height of the
substrate is varied and changes occurring in the bandwidth is observed.In the circular microstrip array antenna ,3
different substrate height and 3 different dielectric constants are considered.The change in the bandwidth is
observed.High bandwidth is obtained for the thicker substrate.
Wireless communications have progressed very rapidly in recent years, and many mobile units are
becoming smaller and smaller. To meet the miniaturization requirement, compact antennas are required in this
field. Planar printed antennas have the attractive features of low profile, small size ,low volume and
conformability to mounting hosts. The dielectric constant of the substrate is closely related to the size of the
antenna and also the bandwidth. Low dielectric constant of the substrate produces larger bandwidth, while the
high dielectric constant of the substrate results in smaller size of antenna. A trade-off relationship exists between
antenna size and bandwidth.
substrate Dielectric constant Loss tangent
Bakelite 4.78 0.03045
FR4 Glass Epoxy 4.36 0.013
RO4003 3.4 0.002
Taconic TLC 3.2 0.002
RT Duroid 2.2 0.0004
V. Conclusion
The choice of an antenna for a particular frequency depends on following factors like radiation
efficiency, antenna gain, radiation pattern,knowledge of antenna impendence for efficient matching of the
feeder,frequency characteristics, bandwidth, and the structural considerations too. A theoretical survey on

microstrip patch antenna is presented in this paper. After the study of various research papers, it is concluded
that the bandwidth can be improved by various methods like changing the substrate thickness , by changing the
dielectric constant of the substrate,by allowing slots in the patch,by using EBG structures and DGS etc.
Microstrip patch antennas are well suited for wireless LAN application systems due to their low profile,
conformability, low cost and low sensitivity to manufacturing tolerances. From the reference papers which are
considered here,we could understand one thing that,the substrate thickness has influence on the bandwidth of the
antenna.The aim of this project is to design efficient and reliable microstrip patch antennas showing high gain
and wider bandwidth and which shows signs of directivity leading to adequate area coverage and sufficient
bandwidth usage.
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