13-08-2014, 02:34 PM
Printed Antenna for Satellite Communications
[attachment=66613]
Abstract
— An antenna which has been conceived as a portable
system for satellite communications based on the
recommendations ITU-R S.580-6 [1] and ITU-R S.465-5 [2] for
small antennas, i.e., with a diameter lower than 50 wavelengths,
is introduced. It is a planar and a compact structure with a size
of 40x40x2 cm. The antenna is formed by an array of 256 printed
elements covering a large bandwidth (14.7%) at X-Band with a
VSWR of 1.4:1. The specification includes transmission (Tx) and
reception (Rx) bands simultaneously. The printed antenna has a
radiation pattern with a 3dB beamwidth of 5º, over a 31dBi gain,
and a dual and an interchangeable circular polarization.
INTRODUCTION
This printed antenna for satellite communications has been
designed to be a planar, compact, modular, low losses and
dual circular polarized antenna, for Tx and Rx bands
simultaneously (Fig. 1).
Planar antennas are very suitable for personal
communications systems due to its capacity to be portable,
low profile and low weight. Usually, slots [3] and printed
elements [4] are most used as radiating elements.
In this case a square planar array of 16x16 double stacked
microstrip patches, fed by two coaxial probes in order to
generate the circular polarization, is used. A hybrid circuit
creates the 90º phase shift to excite two orthogonal modes in
the microstrip patch [5]. The array has been divided in 16
square subarrays of 4x4 elements making possible separate the
fabrication of the subarrays from the global distribution
network, simplifying the corporative network and getting a
modular structure which is suitable in a serial fabrication
process. The power distribution network is connected to each
subarray with SMP-type coaxial connectors and there are two
global inputs/outputs with SMA-type connectors.
. Hybrid circuit
To achieve two orthogonal modes in the circular polarized
patch it is necessary to excite probes with a quadrature signal.
Moreover, using a 3dB hybrid circuit it is possible to work
with a RHCP and a LHCP simultaneously with an isolation
that will depend on the frequency band and on the matching
impedances in the antenna terminals.
A three branches periodic 3dB branch-line coupler (BLC)
has been chosen in order to cover the working bandwidth [6].
This BLC is located in the stripline layer and its dimensions
are shown in Fig. 10(a). It takes up an area of 116mm2
which
is big compared with the radiating element and the subarray
subsystem size. Therefore, it is needed to miniaturize this
BLC using the equivalence between a λ/4 transmission line
and a line with an open-ended shunt stub [7], as can be seen in
Fig. 9. There are other miniaturization alternatives such as
using fractal shapes [8] or interdigitally-coupled lines [9],
but this solution has been chosen due to its simplicity and
good results.
.CONCLUSIONS
The complete design of a portable printed antenna for
satellite communications at X-Band has been introduced. This
antenna has been conceived as a planar, compact, modular,
low losses and dual circular polarized antenna for Tx and Rx
bands simultaneously. Its size is of 40x40x2 cm and covers a
14.7% of bandwidth with a VSWR of 1.4:1. The antenna has a
radiation pattern with 5º of 3dB beamwidth in its main lobe
and 31dBi of maximum gain.
The array has been divided in 16 square subarrays of 4x4
elements which are double stacked microstrip patches. Each
subarray has a two-layered feeding network, in stripline and in
microstrip line, one for each polarization (RHCP and LHCP)
to avoid couplings inside network. A miniaturized branch-line
coupler has been designed in order to reduce couplings and to
simplify the subarray feeding network. The sequential rotation
elements technique has been imposed between two by two
patches to improve the polarization purity of the antenna. The
complete subarray can be fabricated as a unique multilayer
board.
[attachment=66613]
Abstract
— An antenna which has been conceived as a portable
system for satellite communications based on the
recommendations ITU-R S.580-6 [1] and ITU-R S.465-5 [2] for
small antennas, i.e., with a diameter lower than 50 wavelengths,
is introduced. It is a planar and a compact structure with a size
of 40x40x2 cm. The antenna is formed by an array of 256 printed
elements covering a large bandwidth (14.7%) at X-Band with a
VSWR of 1.4:1. The specification includes transmission (Tx) and
reception (Rx) bands simultaneously. The printed antenna has a
radiation pattern with a 3dB beamwidth of 5º, over a 31dBi gain,
and a dual and an interchangeable circular polarization.
INTRODUCTION
This printed antenna for satellite communications has been
designed to be a planar, compact, modular, low losses and
dual circular polarized antenna, for Tx and Rx bands
simultaneously (Fig. 1).
Planar antennas are very suitable for personal
communications systems due to its capacity to be portable,
low profile and low weight. Usually, slots [3] and printed
elements [4] are most used as radiating elements.
In this case a square planar array of 16x16 double stacked
microstrip patches, fed by two coaxial probes in order to
generate the circular polarization, is used. A hybrid circuit
creates the 90º phase shift to excite two orthogonal modes in
the microstrip patch [5]. The array has been divided in 16
square subarrays of 4x4 elements making possible separate the
fabrication of the subarrays from the global distribution
network, simplifying the corporative network and getting a
modular structure which is suitable in a serial fabrication
process. The power distribution network is connected to each
subarray with SMP-type coaxial connectors and there are two
global inputs/outputs with SMA-type connectors.
. Hybrid circuit
To achieve two orthogonal modes in the circular polarized
patch it is necessary to excite probes with a quadrature signal.
Moreover, using a 3dB hybrid circuit it is possible to work
with a RHCP and a LHCP simultaneously with an isolation
that will depend on the frequency band and on the matching
impedances in the antenna terminals.
A three branches periodic 3dB branch-line coupler (BLC)
has been chosen in order to cover the working bandwidth [6].
This BLC is located in the stripline layer and its dimensions
are shown in Fig. 10(a). It takes up an area of 116mm2
which
is big compared with the radiating element and the subarray
subsystem size. Therefore, it is needed to miniaturize this
BLC using the equivalence between a λ/4 transmission line
and a line with an open-ended shunt stub [7], as can be seen in
Fig. 9. There are other miniaturization alternatives such as
using fractal shapes [8] or interdigitally-coupled lines [9],
but this solution has been chosen due to its simplicity and
good results.
.CONCLUSIONS
The complete design of a portable printed antenna for
satellite communications at X-Band has been introduced. This
antenna has been conceived as a planar, compact, modular,
low losses and dual circular polarized antenna for Tx and Rx
bands simultaneously. Its size is of 40x40x2 cm and covers a
14.7% of bandwidth with a VSWR of 1.4:1. The antenna has a
radiation pattern with 5º of 3dB beamwidth in its main lobe
and 31dBi of maximum gain.
The array has been divided in 16 square subarrays of 4x4
elements which are double stacked microstrip patches. Each
subarray has a two-layered feeding network, in stripline and in
microstrip line, one for each polarization (RHCP and LHCP)
to avoid couplings inside network. A miniaturized branch-line
coupler has been designed in order to reduce couplings and to
simplify the subarray feeding network. The sequential rotation
elements technique has been imposed between two by two
patches to improve the polarization purity of the antenna. The
complete subarray can be fabricated as a unique multilayer
board.