A reconfigurable five-element Yagi-Uda monopole array is presented that utilizes pressure-driven liquid-metal elements. There is one centrally located driven element and six parasitic elements in the array, all of which utilize liquid metal so that their physical lengths can be varied. This allows the array to tune to different operational frequencies, vary the number of director elements, and change parasitic elements from reflectors to directors, and vice versa. The measured results show beam steering along a single axis and 1.33 dB of gain tuning at 2.4 and 3.87 GHz.

Liquid metal is used to tune the operational frequency of a monopole antenna by adjusting its length. The centre frequency can be continuously tuned over two octaves, 2.0-9.5 GHz, while maintaining a gain of ∼5.2 dBi.Introduction: Previously demonstrated frequency-reconfigurable monopole antennas used reactive loading and switching, which provided preset discrete tuning states and tuning bandwidths typically less than an octave [1-3]. One design was tunable over two octaves, but showed degradation in its radiation pattern at higher frequencies [4]. This Letter presents a quarter-wave monopole antenna that can reconfigure its operational frequency over two octaves while maintaining a radiation pattern close to that of an ideal monopole, by using a liquid-metal radiating element whose length physically changes; this allows continuous, rather than discrete tunability compared with the cited work above. Recently, liquid metals have been implemented in a variety of microwave components such as switches [5], tuners [6], resonators [7], filters [8,9] and antennas [10][11][12][13].

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