MAXIMUM AND MINIMUM RETURN LOSSES FROM A PASSIVE 2-PORT NETWORK TERMINATED WITH A MISMATCHED LOAD

An analytical expression is derived for determining load-reflection co efficient phase-angle values that will lead to maximum and minimum ret urn losses from a terminated two-port network. The expression is deriv ed in terms of two-port network S-parameters and a load whose reflecti on-coefficient magnitude is a constant but can be any value greater th an zero and less than or equal to unity. The equation is useful for ca ses where it is desirable to know how to position a load (1) to obtain maximum return loss for network-matching purposes or (2) to obtain mi nimum return loss for some types of reflector antenna applications. Tw o examples are given: One shows that for some types of reflector anten nas with a mesh-type surface that is backed by another reflecting surf ace, a resonance phenomenon can occur and cause unexpectedly large dis sipative losses (>30 dB) to occur. The other example shows that when a particular type of reflector antenna with a dielectric layer becomes wet from rain or condensation, large (>10 dB) signal losses can occur. For both examples, equations presented in this article were used to c alculate the exact load-reflection coefficient phase values that led t o worst-case return loss values. In practical situations, once the phe nomenon is understood and predictable, steps can be taken to avoid the se resonance regions.