Multiport network model for evaluating radiation loss and spurious coupling between discontinuities in microstrip circuits

A convenient method for evaluating radiation from microstrip discontinuities is presented. The multiport network model is used to find voltage distribution around discontinuity edges, and an equivalent magnetic current model is used to compute the external fields produced. For a 10- Omega -to-50- Omega step change ( epsilon /sub r/=2.2, h=0.79 mm) in width, the radiation loss at 10 GHz is 0.7 dB. For a 90 degrees bend in 50- Omega line on a 10-mil-thick substrate with epsilon /sub r/=2.2, the radiation loss at 40 GHz is 0.17 dB. Electromagnetic coupling between two discontinuities is evaluated by finding the currents induced by the field of one of the discontinuities at the location of the second discontinuity. It is noted that the multiport network model can be used for calculating radiation and coupling associated with complicated discontinuity configurations such as chamfered bends, compensated T-junctions, and cross-junctions.<>