Impedance Tuning with Notched Waveforms for Spectrum Sharing in Cognitive Radar

In a congested radio spectrum, radar systems must be capable of sharing spectrum in real time. Two possible radar transmission approaches involve either avoiding interferers or placing a notch in the sub-bands of interference. Impedance tuning allows the radar transmitter power amplifier to maximize its output power while adjusting its linearity to meet notch and/or out-of-band spectral requirements. In real-time spectrum sharing, the system controller decides whether to provide a waveform that notches around the interference or to avoid the interference altogether. Considerations in this decision include the maximum detection range obtainable from a tuned amplifier versus the finest achievable range resolution, based on transmitted bandwidth. This paper describes a comparison of real-time impedance tuning for notched, random FM waveforms versus a contiguous-band chirp used for avoidance. Comparisons are made between the range (calculated from output power) and the range resolution (calculated from bandwidth) obtained by the optimized circuits in these two cases.