Overview of Tunable Notch Filters for Radar Systems

Tunable notch filters (TNFs) can be used in radar receivers to reject interference in crowded, dynamic spectral environments. Given many spectrum reallocations of radar bands, causing increasingly congested spectrum near radar operating frequencies, interfering signals can cause radar receiver low-noise amplifier (LNA) saturation, resulting in errors in radar signal processing. An overview of TNF technology and its benefits and challenges for application to radar systems are presented. TNFs are needed to efficiently block the high interference power levels presented to radar receivers. Additionally, impedance mismatches within the receiver chain can cause multiple signal reflections, resulting in ghost targets. Impedance matching, if included in the TNFs, could solve the problem of unwanted perceived targets due to multiple reflections. State-of-the-art TNFs exhibit passband loss ranging from 0.5 dB to 3.0 dB, notch depth ranging from 12 dB to 53 dB, 3 dB bandwidth (BW) ranging from 3% to 7%, and notch tunability ranging from 1.07:1 to 1.45:1. The commercial off the shelf (COTS) market is limited to only single-notch TNFs. Given the status of available TNF technology, multiple areas of potential innovation for TNFs related to radar system improvement are discussed.