Surface Waves in Microstrip Circuits

The launching of surface waves by discontinuities in microstrip circuits can cause extra coupling between adjacent devices. This paper gives measurements of the efficiency of an open circuit in microstrip to both launch and receive surface waves. The measurement technique is described in which the radiated waves from the open circuit are distinguished from the surface waves. These results are then applied to the linear resonator and the open-circuited tuning stub in microstrip circuits. In particular, how their position on the microstrip substrate can effect their performance. Finally, the paper discusses how the surface waves can be reduced to increase isolation.