View of PLIS antennas (a), RF unit (b) and aircraft configuration (c)
PLIS is a L-band radar which can measure the surface backscatters at HH, HV, VH, and VV polarisations. The PLIS is composed of two main 2x2 patch array antennas inclined at an angle of 30° from the horizontal to either side of the aircraft to obtain push broom imagery over a cross track swath of +/-45°. Both antennas are able to transmit and receive at V and H polarisations. Additional secondary antennas can be deployed for interferometry (there was only one small flight in this configuration during SMAPEx-3). The antenna’s two way 6-dB beam width is of 51°, and the antenna gain is 9dB ± 2dB. In the cross-track direction, the antenna gain is within 2.5dB of the maximum gain between 15° and 45°. PLIS has an output frequency of 1.245-1.275GHz with a peak transmit power of 20W. The instrument can radiate with a pulse repetition frequency of up to 20kHz and pulse width of 100ns to 10μs. The minimum detectable Normalized Radar Cross Section is -45dB for the main antenna. Each antenna has a size of 28.7cm × 28.7cm × 4.4cm and weighs 3.5kg. Calibration of PLIS was performed using six triangular trihedral Passive Radar Calibrators (PRCs)
and three Polarimetric Active Radar Calibrators (PARCs).