Antenna Beam Steering Without Phase Shifters – an ‘Old’ Technique Revisited

Antenna arrays are of perennial interest and relevance to RF wireless system designers, indeed the rise of 5G is showing their importance is only growing. Most implementations of linear arrays use phase shifters to feed the array and hence form the main-lobe beam. In the 1960s, a technique using RF switches and Fourier analysis was discovered to be a viable alternative to phase shifters - called the Time Modulated Array (TMA). Little modern research has been conducted in this area, despite its likely cost-effective implementation and technical relevance. This paper presents a brief overview of the TMA, followed by our work into prediction and control of the RF harmonic levels in TMAs. The effect of RF ramping on the switching waveform is analysed first, followed by a novel way of reducing the carrier fundamental (due to the Fourier DC term) produced by TMAs. Finally, a novel RF transistor cascode fast switch is introduced, using 3 gain states, to pragmatically implement the reduction of the carrier fundamental. The transistor cascode in the TMA utilizes binary logic control interfaces, rather than analogue control interfaces, for hardware efficiency. Early simulation results are included.