Analysis of a normal-mode helical antenna including non-uniform wire surface current effects

Computer modelling of a parasitically excited normal-mode helical antenna ( NMHA) is reported and compared with measurements. This structure is particu larly suitable for realisation with high-temperature superconductors (HTS). However, attempts to model it using standard method of moments (MOM) techn iques are very prone to instability; they also do not give the detailed sur face current distribution needed for the evaluation of the benefits of supe rconductor usage. A MOM program for curved wire structures was written, usi ng polynomial basis functions to describe the average current on a subsecti on, combined with trigonometric series basis functions to represent the cir cumferential variation of the surface current density. The results were in excellent agreement with measurements.