Determination of Current Pattern on a Linear Antenna

Determination of Current Pattern on a Linear Antenna

Student(s):

Linda Holyoke´╗┐

Abstract

In this project the spatial distribution of electric currents along linear antennas are studied. The antennas are idealized: the two coaxial cylindrical wire components are assumed to be perfectly conducting, and the electric field in the gap between the wires is given a Dirac delta-function position dependence. The antennas are taken to be transmitting and are driven with sinusoidal time dependence.

Applying Maxwell’s equations to such an antenna leads to a linear nonhomogeneous integral equation for the current along the antenna. The kernel of the equation involves elliptic functions and has a logarithmic singularity. Considerable effort was made, therefore, to ensure that the kernel was accurately calculated for all parameter values especially arbitrarily close to the singularity. The method of moments employing a delta-function basis was used to solve the integral equation numerically.

The current and the input impedance of the antenna were calculated for several antenna lengths and wire radii. These quantities were examined for their dependence on M, the number of subintervals used on each half antenna. For M=100 or less results of others were confirmed, but new results with M ranging up to 300 were obtained. The several percent change in the calculated currents for locations near the antenna center as M changes from 200 to 300 suggests the disturbing possibility that the solution of M going to infinity may differ considerably from existing results.