Design of wideband small spiral antenna for SAR

A design of a wideband small spiral antenna for SAR is proposed. First, to miniaturize the spiral size, characteristics of input impedance and axial ratio for equiangular and Archimedean spiral antennas are analyzed regarding the effects of substrate and spiral turn. It is found that the miniaturized 6-turn Archimedean spiral antenna on a FR-4 substrate which is 4.4 cm in diameter has the good characteristics over a frequency range of 3 GHz to 20 GHz. Second, by experimentally observing time domain radar characteristics, it is confirmed that a cavity 6.1 cm deep sufficiently filled with an EM absorber is effective to obtain clear radar signals. It is also found that leaving a space between Tx and Rx antennas is important to improve the power ratio of a reflected wave to a direct wave.