Tai Tsun Wu

Driving Point and Input Admittance of Linear Antennas

An infinity in the input admittance of linear antennas owing to the use of an idealized delta‐function generator is investigated. It is shown that the infinity may be interpreted in terms of an infinite capacitance between the two halves of the antenna. The conclusion is reached that conventionally used iterative procedures are not invalidated by difficulties with respect to the driving point.

Theory of the Microstrip

A procedure is presented for finding by successive approximation the current distribution, and thus the electromagnetic field, of the lowest mode of the microstrip transmission line. The approximation is valid provided that the strip is not too wide and the dielectric sheet not too thick. Each iteration consists of essentially solving two electrostatic problems.

Standing Waves and Notches in an EMP Simulator and Their Reduction

The high standing-wave ratio in a model simulator in the midfrequency range defined by kh = 27¿h/¿ ~ 2¿ (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 terminating 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 midfrequency range. Since the low-frequency and high-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.