Passivity, reciprocity and causality are three physicality rules that can apply to electrical networks. Due to the nature of random and/or deterministic errors that are a part of all measurements, instruments measuring S-parameters may return S-parameters that do not obey passivity, reciprocity or causality This can lead to problems when using S-parameters in simulations.
The SPARQ includes options to enforce passivity, reciprocity and causality in the output S-parameters. Here is a brief description of each rule.
Passivity Enforcement: Ensures that the S-parameter matrix obeys passivity, which must hold for devices that do not generate power (i.e. passive devices)
Reciprocity Enforcement: Ensures that the S-parameter matrix is reciprocal, meaning that Sij = Sji. Most (but not all) passive devices are reciprocal.
Causality Enforcement:Ensures that the impulse response derived from an S-parameter does not include an inversion of cause and effect; i.e. the response should not occur before the impulse.
See the individual FAQs on each of these rule for more information.