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A novel broadband horizontally polarized (HP) omnidirectional antenna is proposed for meteor-burst communication system in VHF. The proposed antenna is composed of three bowtie dipoles, which are concentrically placed to form a loop antenna. The bowtie dipole is shorted at the terminal by folded elements in order to reduce antenna size. The bowtie dipoles are fed by a three-way power divider. A slotted line balun is employed to achieve broadband impedance matching and realize balanced-to-unbalanced transformation. The designed HP omnidirectional antenna exhibits a fractional bandwidth of 24.7% with VSWR < 2 ranging from 39 to 50 MHz. Uniform omnidirectional radiation patterns in the azimuth plane with HP have been obtained. The loop antenna provides a relatively low gain of no more than 1.5 dBi. Therefore, a two-element HP antenna array is developed to enhance its gain. In order to reduce longitudinal dimension of the array, the two loop antenna elements are placed in reverse and employ differential feeding method to realize in-phase current. Both the simulation and measured results are used to verify the design approach. [ABSTRACT FROM PUBLISHER]

A new quad-layer partially reflective surface (PRS) is presented in this letter for dual-polarized Fabry–Perot (FP) cavity antennas with an improved gain bandwidth. Four layers of metallic square rings are printed on each side of two dielectric substrates separated by an air gap of about λ/27 (λ is the wavelength in the open air) at 5.5 GHz. The total profile of the FP cavity is about λ /2. By properly choosing the dimensions of square rings and the distance between the two substrates, the phase of the reflection coefficient of the PRS increases with the operating frequency, demonstrating a broadband property. In order to validate the performance of the proposed PRS, a dual-polarized FP antenna is designed, which has peak realized gains of 14.7 and 15.5 dBi with 1 dB bandwidths of more than 10% for two polarizations. Furthermore, the input reflection coefficients are lower than −15 dB in the 5.05–5.8 GHz band, and the isolation of the dual-polarized modes is more than 30 dB. [ABSTRACT FROM AUTHOR]

A novel partially reflective surface (PRS) antenna is proposed, which can electronically alter its polarization between linear polarization, left-hand circular polarization (CP), and right-hand CP. The antenna consists of a shorted annular patch antenna as the source, a PRS structure to enhance the gain, and a reconfigurable Wilkinson power divider as the feed network. Four p-i-n diodes are inserted into each branch of the power divider to change its electrical length. By switching the p-i-n diodes ON and OFF, a phase difference of 0°, 90°, or −90° can be realized at the two output ports of the feed network, hence enabling the antenna to radiate either a linearly polarized signal or left/right-handed circularly polarized signal. A prototype antenna with the biasing network is designed, fabricated, and measured. Good agreement between the simulated and measured results is achieved. Measurement results show that the proposed antenna has an overlapped 10-dB impedance bandwidth and 3-dB axial-ratio bandwidth of 4.7–5.36 GHz (13.1%). The average realized gains are $\sim 9$ dBi/dBic, which remain reasonably stable for different polarizations. The proposed antenna outperforms most of the reported polarization reconfigurable antennas for its wide bandwidth and relatively high gain. [ABSTRACT FROM PUBLISHER]