Effects of hysterisis level and switching time on the performance of a cellular base station multibeam antenna

Experimental test results are used to examine the tradeoff between hysterisis level, switching time, and gain improvement for a multibeam antenna array. The multibeam antenna uses selection combining to switch the signals from the two strongest directional beams to the base station´s main and diversity receivers. To assess the impact of beamwidth on overall system performance, the following two multibeam antennas were tested: a 12 beam 30° beamwidth array and a 24 beam 15° beamwidth array. Both antennas were field tested in typical cellular base station sites located in heavy urban and light urban environments. The effects of hysterisis level and switching time are characterized based on gain reductions relative to a reference case with no hysterisis and one-half second switching decision time. Switching probabilities are presented as a function of hysterisis level. Gain reductions are determined as functions of hysterisis level, switching time, environment type, and number of directional beams. Rule of thumb approximations are developed for the gain effects associated with changing hysterisis levels and switching times. The resulting design curves and rules allow engineers to quantify multibeam antenna performance, while making appropriate parameter selections