Impact of Transmitter Elevation Pattern on Multi-frequency DVB-T Passive Radar Detection of Airborne Targets

In this paper, some aspects of passive radar air surveillance are addressed. It is well known that multiple antennas and frequency channels increase detection capability and that transmitter antenna pattern plays an important role in target detection. In order to evaluate the capability in a practical scenario, a measurement campaign was conducted, in which two airborne targets flew in pre-determined trajectories, covering different flight headings, altitudes and distances from a DVBT DTV broadcasting station. The three most important factors with regard to SNR on both targets were identified as receiver and transmitter antenna pattern and receiver positioning. For the transmitter pattern, the pattern causes nulls at some angles. As these null positions are frequency dependent, a good choice of transmitter bands will minimize risk of lost target detection. This fact could clearly be observed in the measurement data. Another aspect studied was the antenna placement. The measurement campaign consisted of two days. The first day, the surveillance antennas were placed on the top of a hill, with LOS to transmitter and the next day hidden behind a small ridge on the hill, relative to the transmitter. There was a significant improvement in SNR just by placing the antennas protected from LOS.