Multifunction Phased Array Radar - design strategy to fulfill weather and aviation requirements

We propose a design concept that can satisfy the requirements for weather observations with polarimetric radar at about 1 min volume update time and also fulfill the aviation needs to monitor location of airplanes at volume update times of 4.8 s. Potentially available resources considered are power, time, and bandwidth, and our solution is frugal on bandwidth. Other resources such as beamwidth, spacing of samples in azimuth, and range resolution are fixed and therefore our solution interleaves separate volume scans for aviation use with a partial weather scans to build up volumes of observations. The basic design uses four simultaneous beams pointing in azimuths separated by 90 deg. The beams are synchronized and pairs that point opposite each other use the same frequency. Within the pulse, beam multiplexing is proposed to quickly point the beam in azimuths into several directions (two to three suffice). Thus truly simultaneous reception from different directions is achieved. Blind zones for aircraft observations and weather observations are kept within prescribed limits by having different sub pulse lengths in the scans. This basic design is equally applicable to cylindrical phase array radar and radar with four flat panels. Relaxing the stringent standards for quantitative estimates of polarimetric variables is possible by using two schemes. In the surveillance scan and simultaneous mode of H and V transmission, pulse to pulse coding is applied. It relaxes impositions on cross coupling to about 25 dB while preserving the unambiguous range to over 460 km. Similar coding can be applied to other transmission sequences such as staggered pulse repetition time (PRT), or the PRTs as in the Doppler scans of the WSR-88D network. But this coding is not compatible with systematic phase codes for mitigation of the range and velocity ambiguities that are operational on the WSR-88D network. The code is suitable for combining with random phase codes of any length. For application to systematic codes time multiplexed (back to back) pulses are proposed, that is H pulse is immediately (within tens of nano seconds) followed by a V pulse. Similar time multiplexing can be exclusively applied in all scans for polarimetric weather observations. Its advantage is that the full transmitted power is applied to the H and V channels resulting in some hardware simplification. In that case the blind zone for weather observations doubles but can be easily kept below 2 km. The conceptual design is on the verge of being as simple as possible and in all its simplicity it still requires average transmitted power of about 4 to 8 kW.