A 35-GHz Beam Waveguide System for the Millimeter-Wave Radar

II The millimeter-wave radar is a broadband, dual-polarized Cassegrain system operating in the Ka band (35 GHz) and W band (95 GHz). To upgrade system sensitivity and bandwidth, we replaced the 35-GHz microwave system with a reflecting beam waveguide (BWG), which is a quasi-optical system. This article describes the design and performance of the BWG retrofit. The goal is to increase sensitivity of the millimeter-wave radar by 10 dB. Two new high-power amplifiers, each ofwhich produces double the power of the existing source, are paralleled with a quasi-optical combiner for a 6-dB increase in total power (to 100 kW). In addition, the BWG system reduces the microwave transmit-andreceive line losses by 4 dB. The new BWG system is the first quasi-optical, high-power, dual-polarized, angle-tracking radar; its advantages include lower losses, broader bandwidths, and power levels well beyond the capabilities of conventional waveguide systems. In particular, the quasi-optical components are superior to their waveguide co~terparts. As a rule of thumb, if the main aperture in a Cassegrain system is greater than 400 wavelengths, then a BWG system becomes a viable option.