A loop antenna coupled to a four-wire line and its possible use as an element in a circularly polarized end-fire array

A loop antenna coupled electromagnetically to a four-wire transmission line is studied theoretically and experimentally in terms of two mutually perpendicular two-wire lines that carry currents that are 90° out of phase. The size of the loop at which resonance occurs is determined. The zero-order and first-order solutions of the current distribution are evaluated, and it is found that at resonance the induced currents in the loop due to each two-wire line oscillate in a dipole mode of the loop. The currents induced by the four-wire line circulate as a travelling wave. The radiation field pattern is also evaluated. The square loop is studied first; it is later shown that the circular loop closely resembles the square loop. An array that consists of many loop antennae coupled electromagnetically to a four-wire transmission line may be expected to have a very high gain with circularly polarized radiation.