Design considerations for an X-band spaced antenna weather radar

Having been employed routinely for Ionospheric sounding and boundary layer profiling, the Spaced-Antenna (SA) technique to estimate tangential (cross-beam) winds from a single location has recently attracted attention in the weather radar community. The SA method offers finer spatial resolution as compared to Velocity-Azimuth-Display (VAD) and wider spatial coverage as compared to dual-doppler methods.

As the correlation time of the backscattered signal is inversely proportional to the radar frequency and intensity of turbulence, the design parameters for a practical SA antenna at microwave frequencies are challenging. This paper presents considerations for a spaced-antenna phased array weather radar implemented at X-band. The approach is based on a dual polarized phased-array antenna currently in development at the University of Massachusetts, with phase scanning in azimuth and mechanical actuation in elevation. The antenna consists of 64 center-fed microstrip patch columns, each with a 3.5◦ degree beamwidth in elevation and 120◦ beamwidth in azimuth. Behind each column, a transmit-receive module provides independent amplitude and phase control. The GaAs power amplifiers on the T/R modules produce upto 1W of peak radiated power.

Although the phased array is capable of dual-polarization operation, only one polarization is used for the spaced-antenna implementation. On transmission, the entire array is employed while on reception alternate sub-arrays are used on alternate pulses. The result is an interleaved time-series of the echoes from separate portions of the array. These portions may overlap, as the receive aperture is dictated strictly by the amplitude tapering on receive, which is programmable. The receive apertures and the spacing of the receive aperture phase centers can be set nearly arbitrarily. Computer simulations based on these parameters are presented to show the anticipated performance of such an antenna. Plans to test the concept are described.