05-01-2013, 04:36 PM
Design and Performance Analysis of Microstrip Array Antenna
[attachment=46582]
INTRODUCTION
Microwave equipments require low pro¯le and light-weight to assure reliability, an antenna with
these characteristics is essentially required and a microstrip antenna satis¯es such requirement.
The key features of a microstrip antenna are relative ease of construction, light weight, low cost
and either conformability to the mounting surface or, at least, an extremely thin protrusion from
the surface. Microstrip arrays are limited in that they tend to radiate e±ciently only over a narrow
band of frequencies and they can not operate at the high power levels of waveguide, coaxial line,
or even stripline [1]. In various communications and radar systems microstrip antenna is greatly
desired. Microstrip antennas are very versatile and are used, among other things, to synthesize
a required pattern that cannot be achieved with a single element. In addition, they are used to
scan the beam of an antenna system, increase the directivity, and perform various other functions
which would be di±cult with any one single element. The elements can be fed by a single line or by
multiple lines in a feed network arrangement. The ¯rst is referred to as a series-feed network while
the second is referred to as a corporate-feed network [2]. This paper presents the characteristic of
microstrip array antennas, series-feed, corporate feed and their combination. There performance
comparisons are also given for better understanding. Substrate selection and element spacing for
grating lobe minimization are also given. For microstrip antennas, the dielectric constants are
usually in the range of 2:2 · "r · 12. Dielectric constants in the lower end of the range can
give us better e±ciency, large bandwidth, loosely bound electric ¯eld for radiation into space, but
at the expense of large element size. In microwave circuit that requires tightly bound ¯elds to
minimize undesired radiation and coupling, and lead to smaller element size. In some application
we need small size antennas, substrate with high dielectric constant is a better choice in this
application. High dielectric constants have greater losses so they are less e±cient and have relatively
small bandwidth [2]. In our design, we consider all these things. Simulated antennas can be
easily fabricated on FR-4 ("r = 4:4), RT/duroid 5880 ("r = 2:2) or high dielectric constant of
("r = 10:2, R03010) substrate. Recessed microstrip line feeding techniques is used as this gives a
good impedance matching at inputs of the radiating elements.
MICROSTRIP SERIES-FEED ARRAY ANTENNA
If we reduce the width of the patch, the radiation conductance is insu±cient to match the input. We
can use the microstrip patch as a transmission line and connect a line opposite the feed to lead to
other patches. If we space the patches by half wavelengths, the impedances of the patches will add
in phase at the input, because it rotates once around the Smith chart in ¸=2. The Characteristic
impedance of the connecting lines has no e®ect at center frequency. The junction of transmission-
line feeder and the patch introduces extra phase shift [3].
MICROSTRIP CORPORATED-FEED ARRAY ANTANNA
The corporate-feed network is used to provide power splits of 2n (i.e., n = 2; 4; 8; 16; 32, etc.). This
is accomplished by using either tapered lines or using quarter wavelength impedance transformers.
Corporate-fed arrays are general and versatile. With this method the designer has more control of
the feed of each element (amplitude and phase) and it is ideal for scanning phased arrays, multibeam
arrays, or shaped-beam arrays [2]. The radiated ¯eld formula that is given in Equation (4) is same
COMBINATION OF SERIES AND CORPORATE FEED MICROSTRIP ANTENNAS
The combination of series feed and corporate feed can be used for array antenna. A 16-elemant array
antenna can be constructed using this method. It's a two dimensional, rectangular planar array
whose aperture illumination can be separated into two orthogonal planes such as the horizontal and
vertical planes, the radiation pattern may then be written as the product the radiation patterns in
these two planes. The array factor of this antenna with element spacing in the x and y direction
are dx and dy respectively as given in [4, 8] as
for this array and array factor as given in [4, 8] as
[attachment=46582]
INTRODUCTION
Microwave equipments require low pro¯le and light-weight to assure reliability, an antenna with
these characteristics is essentially required and a microstrip antenna satis¯es such requirement.
The key features of a microstrip antenna are relative ease of construction, light weight, low cost
and either conformability to the mounting surface or, at least, an extremely thin protrusion from
the surface. Microstrip arrays are limited in that they tend to radiate e±ciently only over a narrow
band of frequencies and they can not operate at the high power levels of waveguide, coaxial line,
or even stripline [1]. In various communications and radar systems microstrip antenna is greatly
desired. Microstrip antennas are very versatile and are used, among other things, to synthesize
a required pattern that cannot be achieved with a single element. In addition, they are used to
scan the beam of an antenna system, increase the directivity, and perform various other functions
which would be di±cult with any one single element. The elements can be fed by a single line or by
multiple lines in a feed network arrangement. The ¯rst is referred to as a series-feed network while
the second is referred to as a corporate-feed network [2]. This paper presents the characteristic of
microstrip array antennas, series-feed, corporate feed and their combination. There performance
comparisons are also given for better understanding. Substrate selection and element spacing for
grating lobe minimization are also given. For microstrip antennas, the dielectric constants are
usually in the range of 2:2 · "r · 12. Dielectric constants in the lower end of the range can
give us better e±ciency, large bandwidth, loosely bound electric ¯eld for radiation into space, but
at the expense of large element size. In microwave circuit that requires tightly bound ¯elds to
minimize undesired radiation and coupling, and lead to smaller element size. In some application
we need small size antennas, substrate with high dielectric constant is a better choice in this
application. High dielectric constants have greater losses so they are less e±cient and have relatively
small bandwidth [2]. In our design, we consider all these things. Simulated antennas can be
easily fabricated on FR-4 ("r = 4:4), RT/duroid 5880 ("r = 2:2) or high dielectric constant of
("r = 10:2, R03010) substrate. Recessed microstrip line feeding techniques is used as this gives a
good impedance matching at inputs of the radiating elements.
MICROSTRIP SERIES-FEED ARRAY ANTENNA
If we reduce the width of the patch, the radiation conductance is insu±cient to match the input. We
can use the microstrip patch as a transmission line and connect a line opposite the feed to lead to
other patches. If we space the patches by half wavelengths, the impedances of the patches will add
in phase at the input, because it rotates once around the Smith chart in ¸=2. The Characteristic
impedance of the connecting lines has no e®ect at center frequency. The junction of transmission-
line feeder and the patch introduces extra phase shift [3].
MICROSTRIP CORPORATED-FEED ARRAY ANTANNA
The corporate-feed network is used to provide power splits of 2n (i.e., n = 2; 4; 8; 16; 32, etc.). This
is accomplished by using either tapered lines or using quarter wavelength impedance transformers.
Corporate-fed arrays are general and versatile. With this method the designer has more control of
the feed of each element (amplitude and phase) and it is ideal for scanning phased arrays, multibeam
arrays, or shaped-beam arrays [2]. The radiated ¯eld formula that is given in Equation (4) is same
COMBINATION OF SERIES AND CORPORATE FEED MICROSTRIP ANTENNAS
The combination of series feed and corporate feed can be used for array antenna. A 16-elemant array
antenna can be constructed using this method. It's a two dimensional, rectangular planar array
whose aperture illumination can be separated into two orthogonal planes such as the horizontal and
vertical planes, the radiation pattern may then be written as the product the radiation patterns in
these two planes. The array factor of this antenna with element spacing in the x and y direction
are dx and dy respectively as given in [4, 8] as
for this array and array factor as given in [4, 8] as