Electrically Small and Low Cost Smart Antenna for Wireless Communication

A compact low-cost low-power smart antenna has been proposed in this paper. To reduce the cost and power consumption, it employs the structure of an Electronically Steerable Parasitic Array Radiator (ESPAR) antenna. To reduce the size of the antenna, a top-disk loaded monopole and six folded monopoles are employed as the driven element and parasitic elements, respectively. The proposed antenna is called “folded monopole ESPAR antenna”. The heights of the top-disk loaded monopole and folded monopoles are reduced to be less than . Furthermore, the radius of the folded monopole ESPAR antenna is reduced by using capacitive loading technique. An equivalent circuit model is proposed for analyzing the antenna. To validate the concept, a prototype is developed and the antenna operates from 2.3 GHz to 2.55 GHz. The measured results confirm that the folded monopole ESPAR antenna can achieve electronically beam scanning in horizontal plane over a 360 range. The prototype antenna achieves a gain of 4.0 dBi and a front-back ratio of 20 dB. The parasitic elements are loaded by varactors and beam forming is achieved by controlling the DC voltages applied to the varactors.

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