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A phased array usually suffers from severe gain drop when its beam steers in a wide range. In this article, an alleviating technique based on a gain-compensating approach is proposed. Isolated element pattern (IEP) and array factor are jointly considered. When calculating the array factor, mutual couplings between antennas in an array are also included. The IEP is optimized in such a way that the element gain is nearly inversely proportional to the peak gain of the array factor. As a result, the peak gain of the overall array beam can be kept almost the same in a wide scanning range. As an example, a cylindrical dielectric resonator antenna (DRA) array is investigated. In such a design, a dip is introduced to the top of the element pattern so that the top peak in the array factor envelope can be compensated. This idea is demonstrated by using an X-band cylindrical DRA, with its beam shaped by using a loading peripheral metal ring and two top dielectric slabs. This shaped-beam DRA element is used to construct a nine-element H-plane linear phased array. The element and array prototypes were fabricated and measured, and reasonable agreement between the measured and simulated results is observed. The measured 3-dB beamwidths of the DRA element are 172° and 149° in the E- and H-planes, respectively. It is found that the H-plane main beam of the DRA array can scan from $- \mathrm{72}^{\circ }$ to $+ \mathrm{72}^{\circ }$ with a small gain fluctuation of less than 0.9 dB. [ABSTRACT FROM AUTHOR]

A novel decoupling method based on the superposition principle is proposed for compact multi-input–multi-output (MIMO) antenna systems in this work. A dielectric block is introduced to encompass all radiators in a compact MIMO system and works as a decoupler when the block is appropriately designed. Owing to the presence of dielectric–air boundary (DAB) introduced by the dielectric block, scattered paths show up for electromagnetic (EM) waves inside the block. For any two encompassed primary radiators, mutual couplings via the direct and scattered paths are superposed one on another. Because the scatted wave paths can be controlled by changing the shape and dimension of the DAB, mutual coupling between two encompassed primary radiators can be minimized with a properly designed DAB. To illustrate this decoupling principle, the electric field distribution of a basic Hertzian dipole wrapped in a dielectric decoupler is first studied. Results show that this method can generate several field valleys inside the dielectric block and can lead to good isolation when a second radiator is placed at a valley. A dual-port antenna wrapped in a dielectric decoupler is then proposed for demonstration. By optimizing the DAB shape, this antenna can realize a measured 20 dB isolation bandwidth of 12.6%, covering the whole 3.3–3.7 GHz 5G frequency range 1 (FR1) band. Furthermore, a quad-port decoupled antenna is studied to show the generality of the proposed decoupling method. Using a hollow rectangular dielectric block, isolations among four ports of more than 21.5 dB can be obtained in the 3.3–3.7 GHz band with a 20-dB isolation bandwidth of 18%. The envelope correlation coefficients (ECCs) and calculated ergodic channel capacity (CC) results show that the proposed compact dual-port and quad-port antennas are competitive for MIMO applications. [ABSTRACT FROM AUTHOR]

A new method powered by an artificial neural network (ANN) is studied for resonant-mode recognitions of a rectangular dielectric resonator antenna (DRA). Different rectangular DRAs were simulated with ANSYS HFSS to generate a large dataset for training the model. Their resonance frequencies, dimensions, and 3-D electric fields are input to the ANN. The output end is a 12-element array representing the corresponding probabilities of 12 different resonant modes. Using this trained ANN model, the mode recognition accuracy can reach 96.74%. Apart from identifying the resonant modes, our proposed approach can suggest how to modify a rectangular DRA to improve the purity of a resonant mode for better antenna performance. [ABSTRACT FROM AUTHOR]

A dual-fed dual-frequency shared-aperture antenna array with a large frequency ratio is investigated. Its unit cell consists of a microwave ground-surrounded patch antenna and a millimeter-wave substrate-integrated 2 × 2 slot antenna subarray. The former is excited in the fundamental TM10 mode, whereas the slot elements are excited in their fundamental mode. Based on the dual-frequency antenna unit, a dual-frequency antenna array is designed. To demonstrate the idea, a prototype that consists of a C-band 2 × 2 patch antenna array and a Ka-band 8 × 8 slot antenna array was designed, fabricated, and tested. Its matching and radiation characteristics are studied for both bands. Reasonable agreement between the measured and simulated results is observed. Excellent measured intraband isolations of over 32 dB are obtained. [ABSTRACT FROM AUTHOR]

A novel wideband circularly polarized (CP) horn antenna with a pair of twisted ridges is investigated in this communication. The wide impedance bandwidth is obtained by adapting a pair of exponential-shaped ridges, whereas the wide axial ratio (AR) bandwidth is achieved by twisting the ridges. The impedance matching and AR can be tuned easily and independently, which is an attractive feature of the design. An $X$ -band right-hand circular polarization (RHCP) design was simulated with CST Microwave Studio. Its metal-printed prototype was fabricated to validate the simulation. The measured 15 dB impedance and 3 dB AR bandwidths are 53% (7.43–12.80 GHz) and 65% (7.63–15.00 GHz), respectively, with an overlapping bandwidth of 51% (7.63–12.80 GHz). The measured peak antenna gain is between 8.0 and 10.1 dBic in the operating band. [ABSTRACT FROM AUTHOR]

A circularly polarized (CP) broad-beam parallel-plate (PP) antenna is investigated. The difference between the phase velocities of two PP orthogonal modes is used to obtain CP fields. The two orthogonal modes are excited by an inclined slot fabricated on the ground plane that connects the two PPs. By tuning the slot length, the impedance can be easily matched. To reduce the cross-polarized fields, a modified CP PP antenna with semicircular plates is introduced. ANSYS HFSS was used to simulate the antennas and prototypes were fabricated to verify the simulations. Both the original and modified CP PP antennas have an overlapping antenna bandwidth of ~13.0% and an antenna gain of ~8 dBic. As compared with other broad-beam antennas, the two PP antennas have simpler and larger structures, easing their fabrications especially at millimeter-wave frequencies. A design guideline is developed. [ABSTRACT FROM AUTHOR]

A broad-beam spherical open resonator (OR) antenna (SORA) is proposed for wireless mobile communications at millimeter-wave bands. The presented SORA, mainly composed of two opposite spherical reflecting surfaces, is excited by an L-probe. The formula for calculating its resonance frequency is given to facilitate the design. The antenna was designed, fabricated, and measured, with reasonable agreement between the measured and simulated results. The measured 10 dB impedance bandwidth and maximum gain are about 4% and 9 dBi, respectively. The SORA is compared with the cylindrical and planar counterparts, and it is found that the OR antenna performance is more stable by adapting the spherical reflectors. [ABSTRACT FROM AUTHOR]

A broadbeam cross-dipole antenna with improved low-elevation gain for global positioning system (GPS) applications is reported. The cross-dipole consists of two perpendicular dipoles, which are printed on two separate substrates that are vertically placed inside a cylindrical back cavity. Circularly polarized fields are generated by applying two quadrature signals with equal amplitude to the dipoles. To enhance the low-elevation gain, circular dipoles, curved ground planes, and corrugated back cavity are deployed in our design. A prototype operating in GPS L1 band (1.575 GHz) was designed with ANSYS HFSS, and measurement was done to verify the simulations. The reflection coefficient, axial ratio (AR), radiation pattern, antenna gain, and antenna efficiency are studied. It is found that the antenna has a wide 3 dB AR beamwidth of over 230° and a 3 dB gain beamwidth of 150°. The measured and simulated antenna gains at \theta = 85^\circ are 0.11 and 0.68 dBic, respectively, which are higher than those of existing designs. [ABSTRACT FROM PUBLISHER]

A new omnidirectional circularly polarized (CP) cylindrical dielectric resonator (DR) antenna (DRA) is excited by four open-ended logarithmic spiral slots in the ground plane. Radiated E\theta and E\phi components are obtained from the TM 01\delta mode of the DR and the slotted ground plane, respectively. Omnidirectional CP fields can be obtained when E\theta and E\phi are equal in magnitude but different in phase by 90°. This CP technique does not require any special shape or treatment of DR, greatly facilitating the design. To demonstrate the idea, a prototype using a glass DR was fabricated. It is a dual-function DRA that also serves as the cover of light sources. The prototype has a measured bandwidth of ~6.2%, covering the entire 2.4-GHz WLAN band. [ABSTRACT FROM PUBLISHER]

The quasi-isotropic dielectric resonator antenna (DRA) is investigated for the first time. It uses a small ground plane which also serves as an electric dipole. The electric dipole combines with the equivalent magnetic dipole of the DRA to generate quasi-isotropic fields. A choke (balun) is connected to the outer conductor of the coaxial cable to suppress stray radiation. ANSYS HFSS was used to simulate the antenna, and a prototype operating at 2.4-GHz WLAN band was fabricated to verify the simulation. Results show that the difference between the measured maximum and minimum radiation power densities is 5.6 dB over the entire pseudo spherical radiating surface. By using a narrower ground plane and a higher dielectric constant, the gain difference can be reduced to 3.4 dB, approaching the theoretical limit of 3 dB. [ABSTRACT FROM PUBLISHER]

The differential Fabry–Perot resonator (FPR) antenna is investigated for the first time. It has advantages of suppressing the cross polarization and enabling integration with differential circuits. Its basic structure consists of two vertical parallel metal plates, which are connected by a horizontal ground plane. The differential FPR antenna is fed by a pair of differential L-probes protruding from the ground plane. It is found that the basic differential FPR antenna has considerable sidelobes in the E-plane. To suppress the sidelobes, a modified differential FPR antenna is proposed which has a pair of ridges at each side-opening of the parallel plates. In addition, a second modified differential FPR antenna is also proposed to reduce undesirable backward radiation. The second modified antenna has a pair of ridges placed at the top of each metal plate. It is found that all of the basic and modified antennas have low cross polarizations. The two modified differential FPR antennas were fabricated and measured, and the measurements agree reasonably well with HFSS simulations. The first and second modified antennas have calibrated measured gains of 14.2 dBi and 15.4 dBi, respectively, with measured 10-dB impedance bandwidths of \sim 2.4\%. [ABSTRACT FROM PUBLISHER]

A new Fabry-Perot resonator (FPR) antenna fed by an L- probe is proposed for mobile applications that require relatively low antenna gains. The proposed antenna consists of two parallel metal plates that are perpendicular to the ground plane. Its resonance frequency can be controlled by changing the separation between the parallel plates, as similar to that of the FPR. A probe resonance near the FPR mode is utilized to widen the impedance bandwidth. To reduce the cross polarization, a groove is introduced to each parallel plate. Ansoft HFSS was used to simulate the antenna, and a prototype operating in K-band was fabricated to verify the simulation. Reasonable agreement between the measured and simulated results is observed. The prototype has a 10-dB impedance bandwidth of 5% and the maximum gain of 11.1 dBi. The proposed antenna is simple and, more importantly, not too tiny to fabricate even at millimeter-wave frequencies. [ABSTRACT FROM PUBLISHER]

The rectangular dielectric resonator antenna (DRA) centrally fed by a probe is investigated. Its operating mode is analogous to the TM011 mode of a cylindrical DRA. The DRA radiates like an electric monopole, generating omnidirectional linearly polarized (LP) fields. Based on this LP design, a novel omnidirectional circularly polarized (CP) DRA is studied for the first time. Slots are introduced to the sidewalls of the DRA, exciting a degenerate mode for the generation of CP fields. To demonstrate the idea, an omnidirectional CP DRA was designed for WLAN (2.4–2.48 GHz) applications. The reflection coefficient, axial ratio (AR), radiation pattern, and antenna gain are studied, and reasonable agreement between the measured and simulated results is observed. [ABSTRACT FROM PUBLISHER]