Mode change analysis of a two element oscillator-type antenna array

Abstract

An array of two radiation coupled oscillator-type antennas is investigated to confirm the behaviour of the antenna system as a function of the strength of mutual coupling between elements. Array behaviour prediction requires correct array mode identification; thus, a simple method whereby the stability of these modes can be identified is presented. An analysis is performed which assumes radiation coupling between identical active antenna oscillators. Explicit equations are given for the locked frequency and individual amplitudes of the array elements for each mode of operation. Theoretical predictions are compared with experimental results to confirm amplitude, frequency and phase variation features in the vicinity of the element separation where mode change occurs. The results compare well with those observed in practice where a mode change is observed as the element separation is increased by half wavelength intervals. In addition, the available modes in a two element array, the in-phase and antiphase conditions, are examined at full-wavelength and half-wavelength separations. The in-phase mode is seen to be stable for full-wavelength separations while the antiphase mode is stable at half-wavelength separations.