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A wideband optically-transparent water patch antenna with a compact size is proposed. Both the water patch and the water ground plane are made of distilled water to realize the highly optical transparency. Particularly, by simply incorporating an annular water ring under the water patch, the center frequency can be reduced from 2.3 GHz to 1.95 GHz, while the corresponding size of the water patch can be reduced by 28%. Both the simulation and the measurement are carried out for verification. The measured results turn out that a wide impedance bandwidth of 41.8% with SWR < 2, the maximum gain of 1.56 dBi, radiation efficiency up to 78% and stable monopolar radiation pattern with linear polarization can be achieved. Additional, the effects of the annular water ring on the antenna performance are analyzed and discussed.INDEX TERMS Water patch antenna, transparent antenna, compact size, monopolar radiation pattern, annular water ring.

Acoustic bullets are defined to be waves which maintain their peak amplitude and/or general shape as they propagate in free space. A general theoretical approach is presented to investigate the space-time properties of a new class of acoustic bullets which are defined here as acoustic transient Bessel beams. The approach encompasses both baseband and modulated carrier signal wave fields. Closed form space-time expressions are developed using Fourier and Hilbert transform methods for several special cases of transient Bessel beams. The space-time source distributions for generating such wave fields from planar apertures are developed from the free space wave fields via the use of the Rayleigh surface integral solution for time-dependent fields. Finally, numerical results are presented to illustrate the general space-time characteristics of the acoustic transient Bessel beams.

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