Abstract
The liquid antenna, as a new member of the antenna family, has drawn significant and increasing attention from both academia and industry due to its unique features. In this paper, a comprehensive review on this technology is presented which covers both metallic and non-metallic liquid antennas. Non-metallic liquid antennas are further divided into water-based and non-water-based liquid antennas. We first review and compare different liquid antennas and highlight the major developments in the past. Detailed discussions on state-of-the-art designs and current technical challenges are then presented, and finally the ways forward for the future are suggested. As a special feature, an in-depth review and discussion on materials for liquid antennas are provided which was not well covered in the literature in the past, important properties of selected materials are given in three comparison tables which can serve as antenna material selection references. It is shown that Galinstan is probably the best choice for metallic liquid antennas while ionic liquid materials are the preferred choice for dielectric liquid antennas. The challenges of making the liquid antenna for real-world applications are identified and discussed. It is believed that a liquid antenna implemented in radio systems is probably just around the corner.
Highlights
A N ANTENNA is a critical component in radio communications and radar systems as it can transmit and/or receive electromagnetic signals efficiently and act as the interface between circuits and radio waves
The highest one we found is a PEDOT:PSS:RTIL mixture with a conductivity of 13600 S/m, it is possible to use such a non-metallic liquid to make conductive liquid antennas which is an area of considerable interest but yet to be properly investigated and explored
Two liquid metal antenna examples are provided in Fig. 3: (a) shows a liquid metal antenna with reconfigurable and steerable beams which can be effectively steered over the horizontal plane from 0 to 360 degrees, whilst the antenna achieved radiation efficiency over 80% at 1.8 GHz in all reconfigurable cases [13]; (b) is a monopole antenna based on simple configurations using microfluidic channel and liquid metal (Hg in this case) pumping technology [18] which resulted in an extremely wide frequency tuning range from 1.29 to 5.17 GHz (1:4 ratio) and high efficiency over the frequency band
Summary
A N ANTENNA is a critical component in radio communications and radar systems as it can transmit and/or receive electromagnetic signals efficiently and act as the interface between circuits and radio waves. It is interesting to note that water was first employed to make an antenna in 1999 [6] – because the researchers found it hard to make their complex DRA prototype using solid materials in the lab. The main objective of this paper is to conduct a comprehensive review on various liquid antennas (not limited to reconfigurable antennas) and related materials, highlight the major developments in the past, discuss current state-of-the-art antenna designs and technologies, and identify the best possible ways forward for the future. A detailed discussion on technical challenges is presented It is concluded with our views on the future research directions and potential applications
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