Compact Floating-Deck Modulator for HAX Transmitter

The present X-band Long-Range Imaging Radar at the MIT/Lincoln Laboratory Haystack Hill Observatory is being augmented by a K_U-band radar, having its own, dedicated, 40-foot diameter Cassegrain-optics antenna, and having twice the range-resolution capability of the X-band system. The HAX (Haystack Auxiliary) transmitter is built around the Varian VTU-5692 coupled-cavity Travelling-Wave tube, specially-developed for this application, and producing 60kW peak power (highest achieved to date), over 2 GHz instantaneous bandwidth, twice that of the Xband tubes. (This tube is the first to use the ultra-wideband, reentrant double-staggered-ladder interaction circuit, reported upon at the 1992 Microwave Power Tube Symposium, at Monterey CA). This paper describes the floating-deck modulator designed to pulse the modulating anodes of a pair of these tubes. The space available (in an equipment enclosure mounted behind the antenna reflector) is extremely limited. Compact physical design, therefore, was as important as the high-voltage, high PRF, and amplitude control electrical requirements.