A Low-loss Waveguide Filter for Harmonic Rejection in a Polarimetric Automotive Radar

A 75-83GHz waveguide band-pass filter is designed and fabricated for harmonic rejection of a multiplier chain used in a polarimetric automotive radar. The radar uses a multiplier/amplifier chain to achieve the desired signal at E-band from a source at X-band. It is shown that this filter can provide more than 50 dB signal suppression at 72 GHz (7th harmonic) and 35 dB suppression at 85.5 GHz (9th harmonic) with less than 1 dB ripples in the pass-band and less than 500 ps group delay. The filter is made of a perforated septum placed in the E-plane of a rectangular waveguide. Fabrication error was successfully minimized by using a brass sheet and a high precision laser cutter. This high-performance filter is shown to improve the performance of the FMCW MMW radar by significantly lowering the noise floor and eliminating other interference effects.