Coherent Matched Filter Detection of Quadratically Phase-Distorted Carrier-Band Pulses, with Application to Transionospheric Signaling

Abstract

The distortion of pulse amplitude modulated carriers by quadratically phase dispersive media is discussed, and it is shown that the emerging waveform consists of quadrature carriers, one of which is modulated by the original signal plus certain derivatives of that signal, and the other by different signal derivatives. The coherent demodulation and detection of the former by a filter matched to the undistorted signal is considered for the cases of sin t/t and Gaussian pulses, and it is shown that the output SNR decreases rapidly as the signal pulse bandwidth is increased above a certain threshold. The results are applied to the case of transionospheric microwave pulse transmission; as a typical example, video pulse bandwidths of at least 200 Mc can be handled at 4 kMc, with the bandwidth increasing as the three-halves power of the carrier frequency.