MODE-CHANGE ANALYSIS OF A 2 ELEMENT OSCILLATOR-TYPE ANTENNA-ARRAY

An array of two radiation coupled oscillator-type antennas is investig ated to confirm the behaviour of the antenna system as a function of t he strength of mutual coupling between elements. Array behaviour predi ction requires correct array mode identification; thus, a simple metho d whereby the stability of these modes can be identified is presented. An analysis is performed which assumes radiation coupling between ide ntical active antenna oscillators. Explicit equations are given for th e locked frequency and individual amplitudes of the array elements for each mode of operation. Theoretical predictions are compared with exp erimental results to confirm amplitude, frequency and phase variation features in the vicinity of the element separation where mode change o ccurs. The results compare well with those observed in practice where a mode change is observed as the element separation is increased by ha lf wavelength intervals. In addition, the available modes in a two ele ment array, the in-phase and antiphase conditions, are examined at ful l-wavelength and half-wavelength separations. The in-phase mode is see n to be stable for full-wavelength separations while the antiphase mod e is stable at half-wavelength separations.