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This thesis presents and describes designs of small antennas that operate in UHF and VHF frequency bands. The proposed antennas are designed for integration into small volumes, therefore low profile, compact size and good radiation properties are the key parameters in this work. A further investigation on miniaturization techniques, as well as the ground plane effects on the general performance, is also made. The main objective is the design of novel compact sized geometries, lightweight and cost efficient, operating in the lower UHF and VHF frequency bands. The groundplane size and the antenna position with respect to it, are two parameters which are investigated and contribute to optimum design performance. Compact solutions are realised in this work based on folded, meander-line and inverted-F geometries providing broadband operation and omnidirectional radiation properties. The investigation of broadband properties of a dual band folded monopole led to a controllable frequency-ratio with wide range, operating in the WLAN frequency spectrum. The proposed solution offers high efficiency and gain and stable omnidirectionality across the operating frequency band. The study also deals with planar inverted-F antennas (PIFA) operating in the LTE frequency bands. The two highly efficient broadband antennas provide compactness, gain
stability and are fabricated using low-cost materials. By configuring an optimised position of the PIFA on the groundplane, the impedance bandwidth, the gain and the total efficiency can be significantly improved. A more compact solution of a dual band PIFA structure is provided with omnidirectional radiation characteristics and large frequency ratio for machine-to-machine applications. A novel tuneable meander line structure operating over the frequency range of 412 − 475 MHz is designed for integration into smart meter devices. The resonant frequency of this antenna can be tuned using a sliding via connector. A matching stub is introduced into the proposed geometry to improve the impedance matching and to shift the resonant frequency to lower values. This innovative solution overcomes material loading problems when installed on a concrete wall, as well as the S11 characteristic are not impaired with the small sized ground plane. Finally, a dual band meander line folded monopole antenna in the lower UHF and VHF frequency bands is proposed for smart metering and Wireless M-Bus applications. The miniaturization of the proposed solution is based on a double-sided meandering structure which also offers good isolation between the two sections and an easily controlled large frequency-ratio. The introduction of a shunt lumped inductor improves the impedance matching at both frequencies. The antenna despite its compact size offers high total efficiency and gain across the operating frequency bands.
Loutridis, A. (2015). Study of UHF and VHF compact antennas. Doctoral thesis. Technological University Dublin. doi:10.21427/D7NW2T