Electronically Steerable Passive Array Radiator (ESPAR) antennas are proposed for low-cost analog adaptive beamforming. The configuration and design of these antennas and some simulation results, especially on their beam/null steering capability, are presented. From the results of a numerical analysis, it was found that 5-element ESPAR antennas can offer a beam gain of 9dBi ± 1dB and a null deeper than -50dBi in an arbitrary direction. In this case, the beam gain and null were obtained separately. It was also found that 7-element ESPAR antennas can achieve continuous steering in almost all directions, with a simultaneous 8dBi beam gain and -30dBi null, excluding the region where the direction of the beam and the direction of the null are within about 45-degrees however 5-element ESPAR antennas are unable to achieve steering in a number of directions, even with a simultaneous 5dBi beam gain and -15dBi null.