Sensitivity enhancement system for pulse compression weather radar

Pulse compression is a technique that allows a radar system to transmit a long coded waveform and compress the received echo to obtain an equivalent narrow pulse response. This technique has been used in military radars since 1950s and recently has been employed in weather radar systems. The main use of pulse compression technique is to enable use of low peak power transmitters to retain sensitivity.

In a weather radar system, there are three main factors that determine system sensitivity; namely transmit power, transmit pulse duration and system's noise. Intuitively, a system with high power transmitter will provide better sensitivity. However, high power radar transmitter and amplifier are very expensive and in some case may not be available. Alternatively using pulse compression one can use long transmit waveforms to increase the measurement sensitivity. For example, with the same peak transmit power,a system using 40μs pulses is nearly 15dB more sensitive than the one utilizing 1μs simple pulses. On the other hand, to attain good range resolution and low peak sidelobe level (PSL) waveforms with pulse compression techniques require wider bandwidth, compared to their narrow pulse counterparts. Since the system noise is proportional to the receiver bandwidth, the system sensitivity decreases accordingly.

In this paper, a sensitivity enhancement system (SES) for weather radar is developed to mitigate this problem. SES utilizes a dual-waveform scheme. The two waveforms are related and can be transmitted sequentially. An adaptive filter is designed based on the self-consistency of signals from the two waveforms to estimate the output. The advantage of SES is that the system sensitivity is improved significantly and the PSL is very low. Theoretical simulations are used to show that, SES can achieve about 10dB improvement in sensitivity compared to the conventional mismatched filter system. The sensitivity enhancement system has been implemented in the CSU WiBEX X-band solid state radar systems and the experimental results are presented.