The Smith tube: Selection of radar chirp waveform bandwidth and power amplifier load impedance using multiple-bandwidth load-pull measurements

The operation of a radar system requires a trade-off between detection capabilities, power efficiency, and adjacent channel power minimization. Specifically, wide signal bandwidth is important for range detection. This paper presents how load-pull data taken for multiple linear frequency-modulated chirp waveforms with different bandwidths can be used to select the chirp waveform with the largest bandwidth possible, while meeting adjacent-channel power ratio and power-added efficiency requirements. This approach utilizes plots of adjacent-channel power ratio and power-added efficiency surfaces within a Smith tube, a three-dimensional, cylindrical extrapolation of the traditional Smith chart. A measurement example is given to illustrate the design approach. This approach will be useful in the design of range radars, and also is likely to find use in enabling real-time reconfiguration of future radars for varying spectral environments and efficiency requirements.