Frequency notching effects on GPR imagery while operating in crowded spectrum scenarios

Over the past decade, the radio frequency (RF) spectrum in which radar, telecommunication, navigational, and other systems operate has become increasingly crowded. The Army Research Laboratory has developed a Stepped-Frequency Radar (SFR) which can avoid areas of the RF spectrum in which systems are already operating. This allows for mitigation of RF interference (RFI) on the radar, as well as reduction in the interference from the radar that might affect other systems. This paper addresses the impact of frequency notching on GPR imagery, and methods of mitigating negative effects. The SFR operates over 300-2000 MHz, with a minimum frequency step size of 1 MHz. The radar transmits and receives in pulsed intervals, allowing for receiver blanking of close-in targets. The SFR is vehicle mounted and utilizes two dualpolarized transmit (Tx) horn antennas on either side of the receiver (Rx) antenna aperture, which consists of 16 Vivaldi notch antennas (which can be rotated to either H or V polarization). The radar is capable of completing a sweep over its entire operating band in <250 μsec. Furthermore, the radar is capable of coherently averaging directly on the field programmable gate array (FPGA) in which it digitizes the Rx channels, albeit at the cost of increased data collection time.