Constant impedance combiners consist of the following units: two 3 dB couplers, two identically tuned band-pass filters and a dummy load.

These combiners isolate the transmitters and translators from one another, and any amplitude or phase-quadroture imbalance shows up as power in the reject load. One of the two inputs has narrow-band characteristics corresponding to the filter’s band-pass curve; the other has broadband characteristics conducting all frequencies outwith the filter’s pass-band to a common output. The impedance of both inputs is frequency independent and corresponds to the characteristic impedance of filters and couplers.

Constant impedance combiners are factory tuned to the desired operating channels. The broadband input accepts any frequency within the specified frequency range.