Accurate microwave high power measurements using a cascaded coupler method

The use of directional couple rs 10 e xte nd the ra nge o f low-le ve l power mete rs is a we ll eS la bli shed technique. Calibration of bolome te r-couple r unil s up 1020 dB is routin e a l N BS a nd olh e r labora lories and allows powe r measure me n I 10 the I W le ve l. For hi g her couplin g ra lios , howeve r, Ihe proble ms in calibration us ing conve ntiona l lechniqu es becomes mo re diffi c ult. Thi s pape r describes a cascade method whi ch a llows ca libra lion of low powe r me ter-couple r co mbin a l ions for meas ure me nl up 10 th e mega wa lt ra nge. Th e technique is based upo n s ys le m lin ea ril Y a nd th e unce rt a inty limil s are s how n 10 be 1 pe rcenl to 1.5 pe rcenl us ing NBS low powe r sla nda rd s . By using the N BS ca libra li on se rvices and co mm e rc ia ll y ava il a bl e equipme nt , th e above power le ve ls ca n be me asured with un ce rtainty limil s less Ih a n 2.7 pe rce n!. The me thod ca n a lso be adapted to measure me nl of la rge couplin g ra lios (2080 dB). Res ult s are given for power (200 wa il S in WR90 waveguide) a nd co upling ra lio (40 dB coax ia l coupl e r) meas ure me nts.