A Comparative Study of Conventional and Modern Phase Coded Radar Transmitters

Abstract: The main objective of this paper is to present the most important techniques applied to pulse radar transmitters such as a delay-line-type modulator (DLM) for conventional radars and a binary phase modulation for modern ones. A pulse forming network (PFN), comprising of a delay line with LC-sections, charging chock, blocking diode and silicon-controlled rectifier (SCR), is investigated. The pre-trigger signal with 2-kHz pulse repetition frequency is responsible for beginning of the transmission period. The duration of transmitted pulse, generated by DLM, depends mainly on the number of LC-sections and their element values. The formed pulse feeds the radio- frequency (RF) oscillator (magnetron) as a high bias voltage to give the RF carrier. A 7-bit code generator is designed to control the phase of carrier signal using the ring modulator circuit aiming to minimizing the jamming signals effect and achieving security for the communication systems. Furthermore, the phase coding modulation facilitates the design and implementation of pulse compression circuit, digital correlator in our work, for modern radar receivers. This improves the resolving power in range and angle, signal to noise ratio (SNR) of the detected targets and the associated probability of detection.

Keywords: Ring Modulator; Pulse Compression; Signal to Noise Ratio, SNR; Pulse Forming Network; Binary Phase- coded Signal.