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A low RCS (radar cross section) slot array antenna based on a liquid metal metasurface is proposed. The metasurface consists of 6 × 6 nested ring‐shaped element. The inner ring with a checkerboard distribution can realise 180° ± 37° phase difference, which can effectively reduce the scattering performances for the slot array. The outer and inner ring together can excite more energy from the slot array, thus resulting in increased radiation gains. Therefore, by changing the layout of liquid metal on the metasurface, scattering and radiation enhancement modes can be switched. The measured results show that in the scattering mode, the RCS can be reduced from 8.1 to 17 GHz. While in the radiation enhancement mode, the proposed array with the metasurface can achieve a −10‐dB impedance bandwidth of 9.4–11.2 GHz (17.4%) with a maximum gain of 8.12 dBi. Compared with the slot array without the metasurface, the realised gain is enhanced by 1.2 dBi from 6.9 dBi. The measured results correspond well with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper presents a continuous frequency tuning Fabry–Perot Cavity (FPC) antenna of which the operating frequency can be varied from 4.87 to 5.84 GHz (18.1%). The cavity of the proposed antenna is excited by a double-layer antenna structure, which is made up of a main square patch and a parasitic one. The superstrate is a frequency-selective surface, consisting of 6 × 6 square-patch-type unit cells. The frequency tuning property is realized by employing 48 phase-changing elements placed around the main patch, which forms a reconfigurable high impedance surface (HIS). By controlling the biasing voltages of the varactors inserted in the HIS element, its capacitances and reflection phases can be varied continuously, which leads to a variation of the operating frequency. An antenna prototype has been fabricated and measured for validation. The measured results are in good agreement with the simulated ones. In the frequency tuning range, the measured realized gains have a smaller variation from 10.2 to 14.1 dBi compared with other reported frequency tuning FPC antennas. [ABSTRACT FROM AUTHOR]

A novel design concept to excite and produce the broadside circularly polarized (CP) radiation is presented in a shorted-patch antenna (SPA). First, the far-zone radiated fields of the SPA under radiation of TM0,1/2 and TM1,1/2 modes are theoretically studied. It demonstrates that the broadside |Eθ| component of its TM0,1/2 mode is generated in yoz plane. In contrast, the orthogonal |Eϕ| component of its TM1,1/2 mode is produced in this plane. Then, the resonant frequency of the TM0,1/2 mode is gradually pushed up to around that of TM1,1/2 mode, aiming to generate the normal CP radiation between these dual modes. After that, a linear slot is etched out on the core radiator so as to counteract the equivalent inductance caused by the loaded pins and feeding probe. Finally, the proposed antenna is fabricated and tested. The measured results reveal that it's operating bandwidth (|S11|<–10 dB and AR<3 dB) is kept at about 1.2% or at a range of 2.720–2.752 GHz. Most importantly, the CP radiation (AR<3 dB) of the antenna at the broadside direction is indeed resonated at around 2.738 GHz, while keeping the reduced length, single-layer, and single-fed properties. [ABSTRACT FROM AUTHOR]

In this work, a new reconfigurable discrete 1D beam-steering Fabry–Perot cavity antenna with enhanced radiation performance is presented. It consists of a probe-fed patch antenna printed on the ground plane and a reconfigurable metasurface acting as the upper partially reflective surface to realize beam steering. By utilizing 6 × 6 proposed reconfigurable unit cells on the superstrate, the beam-steering angle can be effectively enhanced from ±7° to ±17° with fewer active elements and a much simpler biasing network. The proposed antenna was fabricated to validate the feasibility. Good agreement between the simulated and measured results is achieved. Moreover, the measured realized gains are over 11 dBi with a gain variation from the boresight direction to the tilted direction <0.2 dBi. [ABSTRACT FROM AUTHOR]

In this paper, an offset reflector antenna with dual-beam and dual-polarization characteristics is developed to provide the angular diversity function for troposcatter communication system. The antenna system consists of a parabolic reflector and a dual-beam feed. For the dual-beam feed, two identical Ku-band feed elements are arranged side by side to generate two beams toward the reflector. The two beams are substantially nonoverlapping. The feed element is composed of a dielectric rod, a square waveguide, and an ortho-mode transducer. The dielectric rod is effective in reducing the beamwidth of the feed and providing more tapered illumination on the reflector in order to increase the antenna gain. Moreover, the developed antenna is able to produce two independent beams with the vertical and horizontal polarizations. The antenna was fabricated and tested with good agreement between the simulation and measurement results. The measured voltage standing wave ratios of the four feed ports are less than 1.5:1, and the beam separation angle is not more than 0.7° or about one time half-power beamwidth, and the antenna gain is higher than 45 dBi over the operating band from 14.5 to 15.35 GHz. [ABSTRACT FROM AUTHOR]

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]

A substrate-integrated waveguide (SIW) cavity-backed annular ring slot antenna with multiband multimode characteristics is proposed in this communication. The antenna consists of an SIW cavity and an annular slot on top surface as the radiator. Two patch-like radiation patterns and one monopolar radiation pattern at three different frequencies are excited by the single fed antenna. Moreover, each operating frequency can be individually adjusted. A prototype is fabricated and measured to validate the theoretical analysis. Good agreement between the simulated and measured results of the input reflection coefficients and radiation patterns is achieved. Compared with other designs, the proposed antenna has features of simple structure, multiband multimode and frequency-tunable characteristics. [ABSTRACT FROM PUBLISHER]

The design of a novel partially reflective surface (PRS) antenna with the capability of beam steering is presented in this paper. The beam steering is realized by employing a reconfigurable PRS structure to achieve a changeable reflection phase as well as using a phased array as the source to excite the PRS antenna. A prototype antenna including the biasing network is fabricated and measured. It achieves a consistent beam steering from – 15° to 15° with respect to the broadside direction across an overlapped frequency range from 5.5 to 5.7 GHz with measured realized gains over 12 dBi. Good agreement between the simulated and measured results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design principle. Compared with other beam steering PRS antennas, the proposed one enables a larger beam steering angle with comparable gains, requires a simpler biasing network, and is more compact. [ABSTRACT FROM PUBLISHER]

A compact monopolar microstrip patch antenna (MPA) with enhanced‐bandwidth is proposed. In order to achieve the miniaturized patch, the zeroth‐order mode of the MPA instead of its higher‐order modes is employed at first by loading the shorting pin around the center of the patch. After that, a L‐shaped microstrip line with a shorting pin is introduced at the periphery of the patch radiator to excite an additional non‐radiative mode for bandwidth enhancement. In final, the proposed MPA is fabricated and measured. The results illustrate that the antenna generates an enhanced‐bandwidth of about 4.1% ranging from 2.39 to 2.49 GHz, which is significantly larger than that of the traditional MPA around 1%. Meanwhile, the dimensions of the radiating patch are obviously decreased down due to the employment of zeroth‐order mode, which are kept as small as about 0.17 λ0 × 0.22 λ0 × 0.026 λ0 (λ0 is the free‐space wavelength). [ABSTRACT FROM AUTHOR]