A Coaxial Load for Ultra-High-Frequency Calorimeter Wattmeters

A design is described for a broad-band coaxial water load suitable for use in ultra-high-frequency calorimeter wattmeters. The load utilizes a water-filled coaxial line as an attenuating section. The low input impedance of this line is matched to the standard transmission-cable impedance in a broadband matching section using a tapered dielectric composed of titanium dioxide. Several requirements influenced the design: the needs for broadband impedance characteristics, sturdy construction, small physical size, and for the ability to measure low powers quickly, being of prime importance. As a practical illustration, a brief description is given of a unit designed to operate in the 1000- to 3000-megacycle frequency ranges and the 5- to 150-watt power range.