Compact-size Electronically Steerable Parasitic Array Radiator antenna

In this paper, a compact electronically steerable parasitic array radiator (ESPAR) antenna that covers the frequency band from 2.4 GHz to 2.5 GHz is proposed. The top-disk-loaded monopole and folded monopole structure are employed to reduce the height of proposed ESPAR antenna. The height of top-disk-loaded monopole and folded monopole have been reduced to be lower than 1/8 wavelength, much smaller than 1/4 wavelength, i.e. the height of traditional ESPAR antenna. Furthermore, the distance between the driven element and parasitic elements, i.e. the radius of the ESPAR module, is also reduced. The proposed ESPAR module achieves a gain of 4.01 dBi and a front-back ratio of 13.9 dB despite its compactness. The beam forming is achieved by tuning the reactive load of the varactors series whose parasitic elements surround the central driven element.