Modes on a four-conductor line

Transmission lines which consist of four conducting strips on a suspended substrate are sometimes used in microwave mixers. The ideal line yields impedance levels and isolation properties which make it suitable for this application. An analysis of the suspended microstrip version of this line in terms of its four natural modes, shows to what extent it departs from the performance of an ideal line. The calculated results are in agreement with measurements carried out on a low-frequency scaled model of the line and with other published results.