Waveform and Receiver Filter Selection for Wideband Radar Applications

Doctoral thesis, 2015

This thesis concerns the design of transmitter-receiver chains for wideband radar systems. The transmitter side employs one, or several, highly flexible signal generators, which are able to generate signals with a large bandwidth. At the receiver side, when we are are able to select receiver filters, we have the freedom to optimize also the receiver filters. Herein, the transmit waveforms and receiver filters are designed to fulfil user-defined criteria. In general, a high probability of target detection, while maintaining a low false alarm rate, is desired. For a scenario in which interference is present, this means to achieve a high Signal-to-Interference-and-Noise Ratio. When advanced transmitter-receiver technology is implemented, the possibility to adapt the system through a feedback loop arises. Information about the the radar operating environment is provided by signal processing techniques. We propose a Kalman filter to follow a time-evolving cluttermap, based on the complex received signal samples. The estimates of the complex clutter reflections are utilized to determine parameters of the clutter distribution. The system should, in addition, experience a robust target detection property. This is important when targets are not confined on a user-specified grid of time-delays and time-scalings. We derive an algorithm where the mainlobe width of the correlation function is adapted according to a desired resolution. The thesis also deals with hardware restrictions. A study on how to synthesize time domain signals from achieved power spectra is performed. We synthesize signals with given spectral properties that experience a low peakto- average-power ratio. A signal with constant envelope is also achievable by allowing the power spectrum to deviate somewhat from its desired shape.