Attenuation Transfer Standards for International and National Intercomparisons

Abstract

Some examples are given of mechanically and electrically stable attenuation transfer standards, developed or assembled for the international intercomparisons GT-RF 75-A 3 and 78-1 proposed by the radio frequency working group of the CCE. A 4-port directional coupler with matched loads terminating the ports of the side arm and a switchable short interrupting the power flow in the side arm between two coupling sections was constructed for 0.01 dB in waveguide R 140 at 15 GHz. At frequencies of 8 GHz < v < 18 GHz in coaxial systems, switchable transfer standards consisting of commercially-available components incorporating a waveguide directional coupler and two isolators are the most stable and have the best repeatability. For comparing 100 dB at 30 MHz, two transfer standards applying the WBCO principles (using an R 100 rectangular waveguide) were developed, one of them for insertion into and removal from the line, the other fitted with a coaxial switch of optimal repeatability for remaining in line during the measurement.The total uncertainty of these standards is < 0.01 dB at 100 dB.

International Intercomparison of Attenuation in Waveguide R 140 (WG 18, WR 62) at the Frequency 15 GHz

“…which results in A = 0.01 dB for C = 29.4 dB [4]. The 0.1 dB travelling standard consists of a section of R 140 waveguide with a hole bored through the broad wall and tubes soldered on each side to serve as a guide for a rexolite pin which is inserted through the whole waveguide.…”

“…The coupling between the main guide and the side arm of a waveguide directional coupler (with coupling coefficient C) is used to produce the desired attenuation values which are set by actuating a precise waveguide switch. The attenuation value to be measured is approximately given by ( 4) 2) waveguide isolator, (3) waveguide switch, (4) waveguide directional coupler, ( 5 ) terminating matched load, (6) output port. RF power flow: ABDH (for attenuation pad off), ABCFGEDH (for attenuation pad on) where S3, is the applicable scattering coefficient of the directional coupler's scattering matrix giving the ratio of the side-arm's output amplitude to the main guide's input amplitude.…”

“…Detailed descriptions and circuit diagrams are given in Refs. [2] and [4]. Photographs of all travelling standards are shown in Fig.…”

“…3. Circuit scheme of switching travelling standards with directional-coupler attenuation pad (Example: Transfer standard PTB-2.22-311) (1) input port, (2) waveguide isolator, (3) waveguide switch,(4) waveguide directional coupler, ( 5 ) terminating matched load, (6) output port. RF power flow: ABDH (for attenuation pad off), ABCFGEDH (for attenuation pad on)…”