A novel quasi-optical monopulse-tracking system for millimeter-wave application

A novel, low-loss, polarization-independent quasi-optical monopulse comparator (QOMC) has been developed as an alternative to the commonly used waveguide comparator. It has been implemented as an experimental model with an aperture of 23/spl times/23 wavelengths for a 140-GHz monopulse tracking antenna fed by a beam waveguide. The QOMC consists of two cascaded identical stages (sections) to perform azimuth and elevation angle measurements. Each comparator stage is composed of only two plane-parallel reflectors and a low-loss quasi-optical 3-dB beam splitter symmetrically positioned in between them. Extensive model calculations of a single QOMC stage with square aperture dimensions between 10 and 25 wavelengths, and experimental investigations of the realized two-stage QOMC in a beam-waveguide field were performed. Owing to its sufficient high dynamic range at bandwidths of up to about 300 MHz, and particularly, its low absorptive loss of less than 3.5% per stage at 140 GHz, this QOMC is suited ideally for millimeter-wave applications.