A Technique for Determination of Filter Insertion Loss as a Function of Arbitrary Generator and Load Impedances

Insertion loss is derived in terms of generator impedance, load impedance, and filter open-circuit and short-circuit impedances. This expression contains a difference term which places great weight on the accuracy with which filter impedances are measured. It is shown that the use of this difference term can be avoided by introducing the filter insertion loss in a circuit with known generator and load impedances. The resulting exact expression contains terms which are easily measurable with sufficient accuracy to provide reliable insertionloss values for the filter for any combination of generator and load impedances. Also shown is a simplified approximate expression for insertion loss which is applicable in a filter attenuation band. A discussion of experimental verification of the expressions is followed by curves showing application of the approximate insertion-loss expression to a particular filter.