Single-Motor Controlled Mechanically Frequency Reconfigurable Unidirectional Antenna Array With Stable Radiation Patterns

Abstract

This article presents a mechanically frequency-reconfigurable monopole antenna and array that offers a wide tuning range, gain enhancement, and stable beamwidth. The monopole is positioned above a large reflector plate to achieve unidirectional radiation and increased gain. By adjusting the height between the monopole and reflector plate at λ/4 according to resonant frequencies, the frequency band and gain stability can be achieved. A single-motor controlled mechanical system enables the reconfiguration of resonant frequencies and gain enhancement. Measured results demonstrate that the frequency can be adjusted from 1.17 to 3.08 GHz (basic mode) with a relative bandwidth of 89% for a single monopole over the reflector. In the tuning frequency band, the gain and radiation efficiency are 7.51±0.88 dBi and 91.9±6%, respectively. To further enhance and stabilize the gain, a method is proposed and implemented in the array application. An advanced single-motor controlled mechanical system is designed to simultaneously adjust the resonant frequencies, height between the monopole and reflector plate, and inter-distance between the elements. Measured results show that the frequency can be adjusted from 1.15 to 3.0 GHz with a relative bandwidth of 86%. The achieved gain is 11.81±0.38 dBi, and the radiation efficiency is 89.9±8.2% at the basic mode. Additionally, the 3 dB beamwidth in the reconfigured band is 61.5o±6.5o and 39.5o±5.5o for E-planes and H-planes, respectively, indicating stable radiation patterns.