Phased array radars (PAR) are being proposed as an alternative to replacing the Next Generation Weather Radar (NEXRAD) network, which has been in service for more than 30 years, reaching the end of its life cycle. The PAR can improve the temporal resolution of weather coverage compared to reflector antennas (currently implemented on NEXRAD). Temporal resolution is crucial for severe weather detection and surveillance, especially rapid-evolving phenomena such as tornadoes and hail storms. An all-digital PAR design is presently being explored based on their performance and flexibility improvement. Nevertheless, even all-digital PARs are not free from limitations. This work proposes two signal processing solutions to mitigate two significant limitations observed in those radar systems, i.e., blind range resulted from pulse compression technique and cross-polar contamination inherent in the patch antenna implementation, which is currently the only viable solution to an all-digital PAR system. The mitigation techniques to these two limitations are called Progressive Pulse Compression and Cross-Polar Canceler, respectively.

The Progressive Pulse Compression (PPC) technique is proposed to mitigate the blind range problem observed in radars using a frequency modulated waveform and pulse compression. The blind range is caused by the strong leak-through coupled into the receive chain during the transmission cycle. The PPC technique is based on partial decoding. It uses a portion of the uncontaminated received signal in conjunction with pulse compression to estimate the target characteristics from the incomplete signal. The technique does not require using a fill pulse or any hardware modifications. The PPC technique can be divided into three steps. First is to apply a smooth taper to discard all the contaminated samples in the received signal that corresponds to the transmission cycle. The second step is to perform pulse compression using the so called matched filter. Finally, the third step is to calculate and apply a calibration factor to compensate for the progressively changing return signal (affected by the tapering) to recover the proper reflectivity values. This technique is implemented on the PX-1000 radar. In the near future, PPC will be implemented on the Horus phased array radar system. The PX-1000 and Horus radar systems have been designed by the Advanced Radar Research Center (ARRC) at the University of Oklahoma (OU).

Nevertheless, PPC has some limitations caused by the different frequency content between the modified (tapered) return signal and the matched filter used for compression. This difference causes a shift in the mainlobe peak and an asymmetrical increase in the sidelobe levels producing a “shoulder” effect. This work proposes improving PPC by compressing the modified return signal with amplitude-modulated versions (range dependent) of the original matched filter. The improved PPC is termed PPC+ and is planned as a software update from PPC. The PPC+ has been tested using data from the PX-1000 and will be presented in this dissertation.

The Cross-Polar Canceler (XPC) technique is proposed to mitigate the cross-polar contamination observed on phased array radars. The cross-polar contamination is especially problematic when steering the beam away from the broadside. It is defined as a leakage from the intended polarization observed in the perpendicular one. In the XPC technique, the elements on the array are divided into two groups: main elements and canceler elements. The main elements transmit without any modification. However, the canceler elements transmit a modulated version of the inverse (i.e., the mathematical negative) of the original waveform in the perpendicular polarization. After integration, the field radiated by the canceler elements cancels the cross-polar contamination produced by the main ones. The XPC technique involves calculating the correct number of canceler elements, their location in the array, and the complex scaling factor that better mitigates the cross-polar contamination. This technique has been designed for polarimetric radars transmitting in simultaneous transmission and simultaneous reception of H/V polarization (STSR). The XPC technique will be implemented on the Horus radar system, currently under development.

For polarimetric radars, the difference in the element patterns on each polarization produces an angular mismatch between the peaks on the H and V array patterns. This angular mismatch affects the maximum performance achievable with the XPC. Calibration is included as part of XPC to mitigate this effect. Iterative calibration is necessary in the XPC technique. Additionally, calibration is performed before and after XPC is implemented on an operational PAR system. This enhanced version of XPC (including calibration) is termed improved XPC. Like the XPC, the improved XPC is intended to be implemented on the Horus radar system.