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A concurrently dual-polarized, simultaneous transmit and receive (STAR) antenna system with high transmit (TX)-receive (RX) isolation is presented. The STAR antenna consists of four dual-polarized patches, two for TX and two for RX. The radiators are fed using a network consisting of four 90° hybrids and four 180° hybrids. The input ports of the feed network constitute the inputs/outputs of the STAR antenna system. The system supports concurrent transmission and reception of waves with both right- and left-hand circular polarization. Due to the phase cancellation and geometrical symmetry of the antenna, the TX/RX coupling between ports with the same polarization is canceled using the feed network. In addition, four right-angle slots are inserted in the ground plane and a cross-shaped, high-impedance surface is inserted between the radiating patches to further suppress the coupling between the differently polarized TX and RX ports. Simulation and measurement results of a fabricated prototype show good agreement and demonstrate TX/RX isolation levels greater than 38 dB for all polarization combinations over a 6.5% bandwidth (6.0–6.4 GHz). Moreover, the fabricated prototype provides broadside axial ratios below 2.5 dB and realized gains above 7.8 dBic for all TX and RX modes, demonstrating good, concurrent-dual-polarization performance. [ABSTRACT FROM AUTHOR]

We present a design strategy for platform-based antennas operating on electrically small platforms such as unmanned ground vehicles (UGVs). Specifically, we report the design of a platform-based antenna operating at the lower end of the very-high-frequency (VHF) band for a small UGV with physical dimensions of 99 cm × 67 cm × 39 cm. The antenna is mounted on the bottom of the platform resulting in an extremely low-profile design and generating vertically polarized, monopole-like radiation patterns. Using characteristic-mode theory (CMT), performance metrics of the antenna including its maximum potential bandwidth and radiation patterns are investigated. The performance of the antenna when operating in a realistic operational environment is analyzed using full-wave electromagnetic simulations. A full-scale prototype of the antenna mounted on the bottom of the vehicle was fabricated and experimentally characterized. Finally, the design of this low-profile antenna is extended to a two-element antenna array mounted on the same platform and a prototype of this two-element array was fabricated. Basic experiments were conducted to study impedance matching and mutual coupling effects in this electrically small antenna array. The performance of this array as part of a two-element direction-finding system was investigated through computer simulations. [ABSTRACT FROM AUTHOR]

We present a systematic method for designing dual-polarized, platform-mounted, high-frequency (HF) antennas for near vertical incidence skywave (NVIS) applications. To overcome the bandwidth (BW) and efficiency limitations of electrically small antennas, the characteristic mode (CM) theory is used to exploit the metallic platform as the main radiator. Low-profile coupling elements are mounted on different locations of the platform to excite two orthogonal, horizontally polarized CMs. This way, dual-polarized operation is achieved with a high isolation and sufficiently wide BW. In the design process, several key practical issues are taken into account and their impacts on the performance of the antenna are examined carefully. These include the type and design of the coupling elements, the presence and type of the earth, and the non-idealities and power handling capability in the impedance matching network components. The simulation results of both a full-scale and a 1:50 scaled model of the proposed structure are presented. The scaled-model prototype was fabricated and characterized in the presence of a ground plane emulating the properties of real earth at the scaled frequency of operation. The measurement results show a good agreement with the simulations, demonstrating the efficacy of the proposed approach in designing dual-polarized, platform-based HF antennas. [ABSTRACT FROM AUTHOR]

A two-element tunable biomimetic antenna array (BMAA) that uses a single varactor to achieve tunability over a relatively wideband is presented. The proposed device consists of two closely spaced quarter-wavelength monopole antennas operating at 600 MHz. The antennas are spaced at a distance of 2.5 cm and are coupled together using a tunable external coupling network (ECN). The ECN is designed to allow for tuning the response of the BMAA over the frequency range of 580–700 MHz. Over this frequency range, the proposed BMAA can enhance the phase difference between the output signals compared with a conventional array while extracting the maximum available power from the incoming wave. A prototype of the proposed tunable BMAA is designed, fabricated, and experimentally characterized. Measurement results are shown to be in good agreement with the theoretical analysis. The proposed tunable BMAA can be used to alleviate the bandwidth limitations of the previously reported two-element BMAAs. [ABSTRACT FROM PUBLISHER]

In this paper, an $X$ -band electronically steerable parasitic array radiator (ESPAR) of circularly polarized dielectric resonator antennas (CP-DRAs) is proposed. The array consists of one driven CP-DRA coupled to four parasitic CP-DRAs. The parasitic elements are placed adopting a sequential rotation approach and are terminated by tunable varactors to steer the beam into the desired direction. The proposed CP-ESPAR technique eliminates the need of expensive phase shifters, which significantly reduces cost and fabrication complexity. For performance evaluation, a prototype of the proposed antenna is designed, fabricated, and measured. It is observed that the proposed antenna has a monotonic CP beam scanning from −22° to 22° operating at 10.5 GHz. In addition, the peak value of the realized gain is 6.6 dBic with 0.9 dB variation within the entire scanning range. [ABSTRACT FROM PUBLISHER]

We present a three-element biomimetic antenna array (BMAA) with an electrically small triangular lattice. The proposed array consists of three identical quarter-wavelength-long monopoles each positioned at a corner of an equilateral triangle whose side length is 0.05 \lambda 0 , where \lambda 0 is the free-space wavelength. Using a triangular lattice allows for maximizing the phase sensitivity of the array over a 360° angular range. Moreover, it will allow for resolving ambiguities when such BMAAs are used in small-aperture direction finding systems. The three strongly coupled antennas are connected to an external coupling network with three inputs and three outputs. This network augments the mutual coupling between the strongly coupled antennas and is designed to maximize the output phase difference between each two antenna elements without sacrificing the output power level of the array compared with a conventional array occupying the same aperture. A modal analysis technique is also presented and used to design a prototype of the proposed array operating at 600 MHz. This prototype was fabricated and experimentally characterized. Measurement results are shown to be in very good agreement with theory. [ABSTRACT FROM PUBLISHER]

A large array of dielectric resonator antenna (DRA) is designed in $X$ -band based on electrically steerable parasitic array radiator (ESPAR) concept. This large array consists of 240 perforated DRAs, which are uniformly excited by a parallel-series feeding network. By employing the perforation technique, the need for aligning and bonding individual DRA is eliminated. The subarrays are placed in an interleaved arrangement to suppress the grating lobes. To best explore the differences and advantages of our approach, the proposed ESPAR is compared with the beam steerable reflectarray antenna and traditional phased array antenna. The present large ESPAR can incredibly reduce the number of phase shifter by 80% in comparison with the conventional phased array, which makes it inexpensive. A prototype is fabricated, which achieves a maximum boresight realized a gain of 22.4 dBi. The agreement between measured and simulated results is very good. [ABSTRACT FROM AUTHOR]

A dielectric resonator antenna (DRA) with ${{{\varepsilon }}_{\text{r}}} = 35.9$ and excited by a printed microstrip line is considered. Such an element achieves 4% matching bandwidth with unidirectional radiation patterns. However, when a rectangular slot is fabricated on the ground plane under the DRA, a 60% bandwidth is achieved with bidirectional radiation patterns. The mutual coupling between two elements is found to be of low level for the entire bandwidth. To improve the front-to-back ratio of the antenna, a reflector made of conducting strips parallel to the antenna polarization is placed behind the slot window. Linear (H- and E-planes) and planar arrays are fabricated and tested achieving good agreement between simulated and measured results providing high confidence on the simulation. [ABSTRACT FROM PUBLISHER]

A simple and high gain aperture coupled rectangular dielectric resonator antenna (RDRA) array with parasitic elements is investigated. The dielectric constants and dimensions of all elements are identical. A significant increase in gain is obtained by using close inter-element spacing, with no degradation in pattern characteristics. Two possible radiation patterns can be obtained; High-gain broadside patterns or vane beam patterns are possible. [ABSTRACT FROM PUBLISHER]

A three elements compact low-cost phased array of rectangular dielectric resonator antenna (RDRA) is presented. The scanning phase is based on using mutual coupling and capacitor loading. The center DRA is made of high dielectric constant, \varepsilonr=35.9 and fed by a microstrip line. The two parasitic dielectric resonators (DRs) are electromagnetically coupled to the driven element. The dielectric constant and dimensions of the parasitic element are quite similar to the driven dielectric resonator. The phase shift between elements is adjustable by changing the reactive loading on the parasitic DRs. The reactive loadings are two small capacitors inserted between the microstrip lines and ground plane. The scan coverage of the phased array antenna is \pm 30~degrees at 2.8 GHz. Across the entire scan angle range, the array return loss is less than 10 dB across a bandwidth of 130 MHz. [ABSTRACT FROM AUTHOR]