Envelope Modification of the Hyperbolic Frequency Modulated Signal with LC-Filters in order to have a Better Range Resolution in Radar Systems

The theme of this paper is to realize a continuous time domain window similar to the Hamming window. Windowing is used in signal processing to smooth the spectral content and for reducing the spectral leakage as well. Long time duration windows with narrow spectral content can provide much better smoothing compared with short duration windows with broad spectral content. The other advantage of the windowing in the time domain is the reduction of sidelobe levels in the output of the matched filter (MF). In radar systems which use the MF, this reduction in the relative sidelobe level improves the resolution of the system. Radar systems use the hyperbolic frequency modulated (HFM) signals to have the better range and velocity resolutions since these waveforms are Doppler invariant. To further improve the range resolution, the envelope of the HFM signal has been modified using a continuous time domain Hamming window and its Doppler invariant property has been observed. In order to realize the practical circuit that implements the analogous continuous time domain Hamming window for the HFM signal, Butterworth notch filter, and Butterworth highpass filters (HPF) has been considered and it is observed that HPF is approximating the characteristics of the Hamming window.