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HEWLETT-PACKARD
JOURNAL
T E C H N I C A L I N F O R M A T I O N F R O M T H E - h p - L A B O R A T O R I E S
12 No. 10
IBLISHED BY THE HEWLETT-PACKARD COMPANY, 1501 PAGE MILL ROAD, PALO ALTO, CALIFORNIA JUNE, 1961
A Microwave Power Meter with
a Hundredfold Reduction of Thermal Drift
A>asic limitation in bolometer type power stable at this low level than previous meters
meters has been the drift that thermal were at higher levels.
changes cause in the power meter zero reading. The new power meter measures down to 10
microwatts full scale on its lowest range and
Such drift not only sets a practical limit to
up to 10 milliwatts full scale on its highest
the lowest power levels that the meter can range. Its frequency coverage is determined by
measure but has often constituted a consider accessory bolometer mounts which have been
able inconvenience at designed both in waveguide and in coaxial ver
higher levels as well. sions. For waveguide use, a series of mounts
A new microwave has been designed for guide sizes between 2.6
power meter has been developed which has and 40 gc (kmc). For coaxial systems, a single
mount operates over the full range from 10 me
only about a hundredth of the thermal drift
to 10 gc.
susceptibility of uncompensated power meters. The new power meter further includes an
This has permitted the new meter to have a important feature for power-measuring equip
10 times increase in sensitivity and to be more ment. This is an output for operating an ex-