Numerical simulations on beam and/or null forming performance of ESPAR antennas

The radiation pattern of the ESPAR antenna is controlled by variable reactances loaded to its passive elements. In this paper, the effects of the number of elements and the variable range of the reactance value on the beam and null forming capability are studied by simulation using the method of moments. It is found that a beam with a directivity of more than 8 dBi and a null of less than -40 dBi can be scanned independently in all directions when the number of elements is more than 5 and the reactance value range is ±50 Ω. The reactance range of ±50 Ω is needed for simultaneous forming of a single beam of more than 5 dBi and a single null of less than -30 dBi, while ±100 Ω is needed for simultaneous forming of a single beam of more than 5 dBi and multiple nulls of less than -15 dBi. The direction of the beam and null can be close as the number of elements is increased. The input impedance of the feed element is also studied and the standard return loss of a seven-element antenna is found to be 15.8 dBi.