Design of Signal Processors for Automatic Microwave Impedance Measuring Schemes Using Fixed Multiple Probes

As derived in a previous paper (IEEE-MTT, Dec. 1980, 1422-28), if three fixed, equi-distance, non-resonating probes are placed on a lossless waveguide terminated by an unknown impedance ZL as shown in Fig. 1, then the real and the imaginary components of the unknown reflection coefficient k¿ seen under the central probe can be expressed by the following equations: ku = e12 + e32 - 2e22 / 4(1 - cos ¿) (1) ku = e32 - e12 / 4 sin ¿ (2) where e12, e22, e32 are square-law outputs of the three probes normalized with respect to the incident power. ¿ is the round-trip phase distance between the adjacent probes.