Standing Waves and Notches in a Parallel-Plate Type of EMP Simulator and Their Reduction.

The high standing-wave ratio SWR in a model simulator in the mid-frequency range defined by kh 2 pi hdelta approx. 2 pi where h is the height of the parallel-plate region is investigated experimentally. It is shown that the isolated deep minimum or notch is due to the mutual cancellation of the imaginary parts of the TM01 and TEM modes. The effects on the SWR and the deep minimum of changes in the magnitude and location of the termination resistance are investigated. Also studied are the introduction of a bifurcating plate, resistive modal filters, and series aprons. It is shown that with the proper adjustment of the last named, the notch can be eliminated and the SWR reduced to near two at discrete frequencies that span the entire mid-frequency range. Since the low-frequency ranges already have low SWRs, the simulator has been made effective over the entire frequency band in the sense that the SWR is low.