With the current trend towards fielding phased array radars that utilize low peak-power transmitters, methods of recovering potentially lost performance are being examined in greater detail. As such, weather radars that incorporate pulse compression technologies are being analyzed to provide equivalent or better performance to those currently in use.
Pulse compression involves transmitting a coded, wideband signal and compressing the return signal through filtering, which results in increased signal power and enhanced range resolution. Phase codes involve partitioning the transmitted pulse into equal segments, or subpulses, and then switching the phase of the signal at specified intervals. In particular, binary phase codes switch the phase between two values.
The amount of compression possible is equivalent to the time-bandwidth product (BT) of the code, which is the product of the signal bandwidth and total duration. Bandwidth is calculated in a phase-coded signal by taking the inverse of the subpulse length. The return signal power increase is proportional to the code length while the range resolution is inversely proportional to the transmitted signal bandwidth. The weakness of such systems is in the creation of range sidelobes that can cause strong returns at other ranges to contaminate weaker signals at the desired range, resulting in erroneous estimations of reflectivity, mean velocity, and spectral width.
This research focuses on utilizing phase coding in the TSWRS to evaluate the performance of various pulse compression schemes. The TWSRS is a 3-dimensional radar simulator consisting of an ensemble of thousands of scatterers placed within the field of view of the virtual radar. It is capable of operating in a dish mode akin to a WSR-88D weather radar as well as in a phased array mode. Scatterer characteristics are initialized from a known data set whose positions and properties are then updated according to the wind field. The meteorological fields used in the radar simulator correspond to output data from the Advanced Regional Prediction System (ARPS) numerical simulation model developed at the Center for the Analysis and Prediction of Storms (CAPS) at OU. The spatial and temporal resolution of the ARPS output used in this study is 25 m and 1 s, respectively. The return signal amplitude and phase of each scatterer are then processed via Monte Carlo integration to calculate time series of the desired meteorological parameters.
In this presentation we will illustrate the performance of various phase coding and filtering combinations with emphasis on minimizing Integrated Sidelobe Levels (ISL) as well as assessing Doppler tolerance and accuracy. The variables under consideration include code length, code type, total pulse duration, and filtering method. The test case for all simulations will consist of a small time segment of a tornadic supercell thunderstorm as modeled by the ARPS model. The data presented will be gathered by using dish mode of the TSWRS operating in the S-band at 3.2 GHz. Future iterations of this research include the use of the TWRS in a phased array mode to simulate performance of a Multifunction Phased Array Radar (MPAR) incorporating pulse compression.
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