Spurious radiation from microstrip

All discontinuities in microstrip radiate either by intention or spuriously. Such elements as corners, T-junctions, open or closed circuits, as may occur in matching or phase-shifting networks, are encountered in antenna feed systems, and their spurious radiation sets a limit to the accuracy with which design radiation patterns can be achieved. Disturbances due to a number of discontinuities encountered in typical antenna feed and network structures are calculated by the method of an earlier paper (1960). Error estimates resulting from secondary effects are calculated and found to be generally negligible. A detailed study of the open circuit reveals both the utility and limitations of treating it as a discrete radiator. The results give qualified approval to the continued use of Lewin's method for microstrip radiation calculations until such time as a more advance theory should become available.