A coaxial film bolometer for the measurement of power in the u.h.f. band

The requirements to be satisfied by a transfer element for the comparison of u.h.f. with d.c. power are stated under the headings of transfer properties and matching and residual losses, and the need for a new type of coaxial bolometer is discussed in the light of them. A coaxial film bolometer which satisfies these requirements for all frequencies between 200 Mc/s and 4 Gc/s is described, and the factors affecting its accuracy are discussed. The range of power that can be handled directly by the instrument is 2-200 mW, the v.s.w.r. relative to 50 ohms is of the order of 0.98 and the uncertainty in measurement is within 1% for powers between 20 and 200 mW. The design is not confined to a particular size. A smaller bolometer element, which handles powers down to 0.1 mW with an upper frequency limit of about 20 Gc/s, and a larger bolometer element, which handles powers up to 2 watts with an upper frequency limit of 3 Gc/s, are feasible.