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.

中文翻译：

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液体天线：过去，现在和未来

液体天线作为天线家族的一个新成员，由于其独特的功能而引起了学术界和工业界的越来越多的关注。本文对这种技术进行了全面的综述，涵盖了金属和非金属液体天线。非金属液体天线进一步分为水基和非水基液体天线。我们首先回顾和比较不同的液体天线，并强调过去的主要发展。然后介绍了有关最新设计和当前技术挑战的详细讨论，最后提出了未来的发展方向。作为一项特殊功能，我们对液体天线的材料进行了深入的回顾和讨论，而在过去的文献中并未对此进行全面介绍，所选材料的重要特性在三个比较表中给出，它们可以用作天线材料的选择参考。结果表明，Galinstan可能是金属液体天线的最佳选择，而离子液体材料则是电介质液体天线的首选。确定并讨论了制造用于实际应用的液体天线所面临的挑战。可以相信，在无线电系统中实现的液体天线可能指日可待。确定并讨论了制造用于实际应用的液体天线所面临的挑战。可以相信，在无线电系统中实现的液体天线可能指日可待。确定并讨论了制造用于实际应用的液体天线所面临的挑战。可以相信，在无线电系统中实现的液体天线可能指日可待。