An approximate formula is proposed for the equivalent susceptance of a circular iris in a parallel plate waveguide when the TEM mode cylindrical wave is incident from the center of the iris. Schwinger's variational method for a linear iris is generalized to the cylindrical case, and an approximate closed form formula is obtained which recovers the result of the linear iris when the radius of the circular iris is sufficiently larger than the wavelength. For verification of the formula, an exact integral equation is formulated and solved numerically by Galerkin's method. A comparison between them shows good agreement.

Simple approximate formulas are obtained for the mutual impedance and admittance by using a product of radiation patterns of antennas. The formulas come from a stationary expression of the reaction integral between two antennas where far-field approximations are employed. The theory deals with antennas in free space as well as under the presence of a wedge. Two applications are given for microstrip antennas with experimental verifications.

In this paper we propose a new far-field RCS prediction method using cylindrical or planar near-field RCS data. First we derive the relation between RCS and the scattering coefficient using physical optics technique. The far-field RCS prediction algorithm is obtained by approximating the relation using the condition of Fresnel region and the paraxial constraint of scanning angle in the case of cylindrical or planar scanning. Finally we predict the far-field RCS using measured or calculated near-field RCS data of the conducting rectangular prism or plate. The validity of the proposed algorithm is demonstrated.

This paper shows quantitative evaluation of coupling between a monopole antenna outside a shield case and a strip line inside that for a portable telephone. The amount of the coupling is calculated using FDTD method together width EMF method. This combination of methods can raise the calculation efficiency. Dependence of the coupling on the length of gaps, the height of the strip line and the length of the antenna is clarified. The correspondence between calculated and measured results shows the validity of the calculation.