Design and Analysis of Wideband Water Patch Antennas


Student thesis: Doctoral Thesis

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Award date24 Dec 2019


This thesis presents a series of wideband water patch antenna designs for emerging applications in future wireless communications. As water is a low-cost, readily available, optically transparent and eco-friendly material, using it to construct antennas is an attractive and useful approach. Most water antenna designs reported in the literature, use water as the dielectric in resonator antennas or monopole antenna designs, while a few studies use water to design patch antennas. The patch antenna is one of the most versatile antennas that has extensive applications in practical wireless communications. In 2015, the first patch antenna using distilled water was proposed, based on the concept of dense dielectric patch antennas (DDPA). Thus, following the first water patch design, some novel water patch antenna designs are shown in this thesis.

First, three novel water patch antenna designs with a metallic ground plane are presented. The first design is a 2 × 2 aperture-coupled water patch antenna array. Aperture-coupled feeding method is used in this design, and it has the advantage of forming an array configuration. The performance demonstrates that a wide impedance bandwidth of 19.6%, a realized gain of up to 13.2 dBi and stable unidirectional radiation pattern can be achieved. The second design is a wideband circular water patch antenna with monopolar radiation pattern. A disk-loaded metallic probe is employed in the center position to excite the antenna. Results show that a wide impedance bandwidth of 39.5%, a realized gain of up to 6.9 dBi, a high efficiency of over 80% and stable omnidirectional conical beam radiation pattern can be achieved. The third design is a 3-D printed water patch antenna with broadside radiation pattern. The 3-D printing technique can realize a water patch with a small thickness, which makes the geometry much lower in profile. The experimental results show that it has a bandwidth of 13%, a realized gain of up to 5.55 dBi, a measured radiation efficiency of up to 68% and broadside radiation pattern. All the prototypes demonstrate that the distilled water patch antenna with a metallic ground plane shows almost the same operation mechanism and radiation performance characteristic as conventional metallic patch antennas.

Second, three wideband water patch antennas with both the patch and ground plane replaced by a distilled water layer are presented. In the first two designs, wideband and low-cost optically-transparent water patch antennas with monopolar radiation pattern and broadside radiation pattern respectively, have been proposed. Both the patch and the ground plane composed of a layer of distilled water are enclosed by a transparent container made of plexiglass, leading to high optical transparency. A disk-loaded metallic probe and an L-shaped metallic probe are respectively utilized to excite the antennas and obtain wide impedance bandwidth. The simulated and experimental results show that both configurations of optically-transparent water patch antennas can obtain a wide impedance bandwidth of over 30%, along with stable radiation pattern and comparable radiation efficiencies and realized gains over the corresponding operating bandwidth. A circularly-polarized water patch is also proposed using a 3-D printed container. By employing a square water patch with two diagonal truncated corners, an axial-ratio (AR) bandwidth of 8.0% can be obtained. The experimental results show that an impedance bandwidth of 29.0%, a realized gain of 3.05 dBic and broadside radiation pattern with left-hand circular polarization as the co-polarization can be achieved over the corresponding AR bandwidth.

Third, two types of compact water patch antennas with monopolar radiation pattern are studied. In the first design, a wideband compact water patch antenna is proposed by simply incorporating an annular water ring under the water patch. In this configuration, the center operating frequencies can be reduced from 2.3 GHz to 1.95 GHz, while the corresponding area of the water patch is decreased by 28%. In the second design, by using a high-permittivity liquid as the middle substrate, the center operating frequency can be reduced to some extent. A popular choice for the middle liquid substrate is ethyl ethanoate, which is an optically transparent liquid with a relatively large permittivity of 7.8 at microwave frequencies at room temperature. The results demonstrate that the center frequency can be shifted down from 2.85 GHz to 2.1 GHz by employing the ethyl acetate. Furthermore, radiation performance characteristics of the proposed water patch antenna using liquid substrates with different dielectric constants and dielectric loss tangents are also investigated and discussed.