Controlling coupling in an electrically steerable parasitic array

ESPAR antennas can direct radiation and steer nulls by using variable passive elements like varactors, avoiding the cost and complexity of devices like phase shifters. Past attempts to design multi-band ESPARs have often superimposed multiple antenna arrays, each scaled for a different frequency band. This often results in large, cluttered, complicated designs. To accommodate multi-band operation the radiators can be loaded with reactive elements. To preserve the array properties across bands, a means to control the coupling between driven and parasitic elements is needed. The control mechanisms must be inexpensive and simple to implement. They should not fundamentally alter the array design procedure, but rather compliment it. This study investigates the effects of different approaches to controlling coupling through reactive loading, develops a design procedure and implements it to synthesize an ESPAR that operates at 2.4 GHz and 3.5 GHz. These experiments help further develop a principled method of designing frequency-reconfigurable ESPARs. Since stationary base station antennas can afford to be larger and more complex, these low-profile and inexpensive antennas can find use in femtocells for mobile ad-hoc networks and other portable devices