Design Circularly Polarized of Equilateral Triangular Hole Antenna for SAR (Synthetic Aperture Radar)

摘要

The interest in the SAR (Synthetic Aperture Radar) systems is expected to increase the research about the antenna which can be applied for developing SAR systems. Hence, its many information can be obtained from earth if the antenna whose has characteristic circular polarization applied on SAR systems. The research aims is the development of a technology enabling the transmission and reception of many information, such as images, imagery, topography, climate, etc by use of the geostationary satellite. The antenna should be designed as thin, compact, and simple as possible for it to be mounted on the geostationary satellite. This antenna is expected conduct orbital experiments on the geostationary satellite at S-band frequency (2.5 GHz - 2.7 GHz). This paper describe the design of circularly polarized of equilateral triangular hole antenna (h_7) comparing with the previous antenna (without hole, h_0) using a conventional substrate (relative permittivity 2.17 and loss tangent 0.0009). The antenna is fed by proximity feed with microstrip-lines whose width W is 3.0 mm for Tx/Rx to obtain a thin configuration. A novel dual feed type with a hole is proposed for the generation of a compact LHCP using a compact equilateral triangular-patch, where one of the microstrip-line feeds is longer than the other introducing a 90° phase delay. In the same manner, a right-handed circular polarization (RHCP) could be realized by swapping the microstrip-lines with respect to the y-axis. The proposed feeding technique is designed to obtain an ideal and stable current distribution on the triangular-patch surface hence improving the previously developed antennas. The results of hole antenna (h_7), especially gain and axial ratio are 6.82 dBic and 0.66 dB, respectively. Moreover, the S-parameter of hole antenna at the target frequency is about by -18 dB, and the input impedance characteristic of Tx/Rx, the real and reactance parts of simulation are by 50 Ω and by closed 0 Ω, respectively. The bandwidth and beamwidth of hole antenna are also match with the specification and target for SAR using the geostationary satellite at S-band frequency.