Radio Science, Volume 25, Number 5, Pages 1095-1100, September-October 1990 Effect of signal path distortions on the decoding performance in a pulse compressionradar system Y. G. K. Patro, K. R. Suresh Nair, and P. Balamuralidhar Soceityfor Applied Microwave Electronics Engineering and Research, Indian Institute of Technology Campus Powai, Bombay, India (Received May 31, 1989; revised November 6, 1989; accepted November 9, 1989.) Computer simulation studies have been conducted on the range side lobe performance of a pulse compression radar system which uses a complementarybiphase-coded signal transmission.Such a coding scheme is widely used in mesosphere-stratosphere-troposphere (MST) radars expecting to achieve ideally zero range side lobes to ensure unambiguous detection of signals.However, system parameters, like overall system bandwidth, delay distortion, limiting, amplitude and phase droop within the pulse, can lead to spillover of a target return into adjacent range bins by raising the range side lobe level. The results of the study indicate that a goal of 20-dB range side lobe level can be achieved with matched filter bandwidth and reasonablelevels of amplitude and phase distortions in the signal path. 1. INTRODUCTION The .complementary biphase-coded signal is known to result in zero range side lobes for a stationary point target in an ideal situation [Loriot, 1983]. But the system parameters, like receive bandwidth, delay distortion, limiting level, ampli- tude and phase droop within the pulse, can degrade the range side lobe performance in a practical radar system. Though this problem was recognized [Sato and Woodman, 1982] and the use of quasi-comple- mentary code sets was recommended instead of the above complementary code pairs [Sulzer and Woodman, 1984], short code sets are preferable when the expectedDoppler shift in the frequency of target return is high. The presentpaper analyzesthe effect of individual signal path distortions on the range side lobes of the final decoded pulse in order to arrive at the right subsystem design specifica- tions to meet a desired performance goal. Indian mesosphere stratosphere troposphere (MST) radar, which uses a complementary biphase- coded signal, is modeled to analyze the effects of various factors like transmit bandwidth, signal-to- noise ratio, delay distortion, limiting level, ampli- tude droop, and the intrapulse phase distortion, on the range resolution characteristics of the radar when coded pulse transmission is used. The real- time waveforms at different stages are plotted. Ambiguity diagrams give the output of the decoder Copyright 1990 by the American GeophysicalUnion. Paper number 89RS03545. 0048-6604/90/89RS-03545508.00 an arbitrary position of target with respect to the sample.For convenience the simulation is performed for an 8-bit complementary code sequence, though a 16- or 32-bit code is planned to be used in the radar. REFERENCE OSCILLATOR --[MODUL CODE GENERATOR ISAMPLE =-iCLOCK IGENERATOR •,TOR H BPF ' ! %•X ANTE •,/RX ANTENNA •" )-• • NOISE I 1 OUT PUTS Fig. 1. Simulated model of the signal-processing scheme of MST radar. 1095