Evaluation of active admittance of radiating apertures for the purpose of performance analysis in a dynamic environment

Almost all the electronic instruments, and systems do experience unwanted interference from external sources. A particular configuration on the body of or within the instrument may act as a single element or an array of similar elements in which case it can be treated as an antenna problem in the receiving/transmitting mode. The authors evaluate the active/input admittance of any particular element in an array through the evaluation of self/mutual admittance of/between elements which gives an idea of the contribution of that particular element towards causing or receiving interference. The evaluation of self/mutual admittance is carried out, in the transmission mode, for the case of two identical rectangular waveguide radiating apertures backed by an infinite ground plane using method of moments (MOM) and plane wave spectrum approach. Assuming that only one of the apertures is excited and that too by a y-directed electric field of TE₁₀ mode, the boundary conditions are found out by matching the transverse component of the magnetic field at both apertures and the magnetic field is calculated from the consideration of the exciting electric field present there. Using the principle of superposition, the boundary conditions on both the apertures in terms of the incident, internal and external x-directed magnetic fields are evaluated. Following MOM, the reflection coefficient and transmission coefficient or coupling are evaluated. Once these parameters are known, the Y-matrix can be obtained. Then the admittance is obtained from the corresponding excitations of the array and the self/mutual admittance by using the element by element approach