A simple decoupling method of using metallic vias to improve the isolation of millimeter-wave multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) elements is investigated. The vias are vertically added to the DRA elements, at appropriate positions. By means of the interaction with the electromagnetic fields, the vias can potentially affect the filed distributions and further reduce the coupled fields effectively. The isolation between the MIMO DRA elements can, therefore, be enhanced substantially. As the vias are placed inside the DRA elements, no extra footprint is needed, making the entire antenna system very simple and compact. Two typical examples, including an H-plane and an E-plane, coupled $1\times2$ MIMO DRA arrays, have been designed, fabricated, and measured to demonstrate the feasibility and universality of this method. The results show that by using the vias appropriately, the isolation of the H-plane coupled MIMO DRA array can be enhanced from ~15.2 to 34.2 dB, while that of the E-plane array can be improved from ~13.1 to 43 dB at 26 GHz.

A two-port dual-frequency substrate-integrated antenna with a large frequency difference is presented. It consists of a differentially fed slot antenna and a substrate-integrated dielectric resonator antenna for low- and high-frequency radiation, respectively. The former is loaded by a hollow patch, whereas the latter is fabricated inside the hollow region of the patch by using air holes and metalized vias. Beneath the antenna substrate is a second substrate on which slot-coupled sources are printed to feed the two antennas. For demonstration, a two-port dual-frequency antenna working at 5.2-GHz WLAN band and 24-GHz ISM band was designed, fabricated, and measured. The S-parameters, radiation patterns, and antenna gains of the two antenna parts are reported. Reasonable agreement between the measured and simulated results is observed. Very good isolation of over 35 dB between the two antenna parts is observed.

The linearly polarized (LP) and circularly polarized (CP) filtering dielectric resonator antennas (DRAs) are presented. They have conducting loops inside them. Equivalent horizontal magnetic dipoles can be obtained from the HEM11δ mode of the DRA and the loop structure. When they are equal in magnitude but opposite in phase, the radiated fields can be canceled out and a good filtering response can be obtained. To demonstrate the idea, both the LP and CP filtering DRAs operating at 2.4 GHz were designed, fabricated, and tested. The reflection coefficient, axial ratio, radiation pattern, antenna gain, and antenna efficiency are studied, and reasonable agreement between the measured and simulated results is found. The LP and CP designs have measured peak realized gains of 5.86 dBi and 5.1 dBic, and out-of-band suppression levels of over 19 dB and 18 dB, respectively.

A singly-fed wideband circularly polarized (CP) substrateintegrated dielectric resonator antenna (SIDRA) is proposed for millimeter-wave (mm-wave) applications. The SIDRA consists of an inner cylindrical dielectric resonator (DR), an outer ring DR, and a substrate integrated waveguide (SIW) cavity. To generate CP fields, a cross-slot formed by two rectangular slots with different lengths is utilized to feed the DRA at its bottom. It has been found that owing to the embedded structure, the fundamental HEM11δ mode of the inner DR and the higher order HEM12δ+1 mode of the entire DR can be excited simultaneously, at adjacent frequencies. Moreover, owing to the different loading effects of the two feeding slots, the resonance frequencies of the nearly degenerate DR modes excited by the two slots are slightly different from each other. The two nearly degenerate modes lead to the wide impedance and axial ratio (AR) bandwidths of 34.6% and ∼ 30%, respectively. In addition, due to the surrounding SIW cavity, the directivity of the antenna is greatly improved as compared with that of the isolated counterpart, with the maximum gain given by 8.15 dBic.

This letter investigates dual-band and wideband designs of dual-polarized cylindrical dielectric resonator antennas (DRAs). These designs make use of the fundamental HEM₁₁₁ mode and higher-order HEM₁₁₃ mode of the DRA. The strip- and slot-fed excitation methods are used for Ports 1 and 2 of the antennas, respectively. For demonstration, a dual-band dual-polarized DRA for DCS (1.71-1.88 GHz) and WLAN (2.4-2.48 GHz) bands and a wideband version that covers the 2.4-GHz WLAN band were designed. The S-parameters, radiation patterns, antenna gains, antenna efficiencies, and envelope correlations of the two designs are studied. It was found that the dual-band and wideband designs have port isolations of higher than 36 and 37 dB, respectively. Good agreement between the measured and simulated results is observed.

This paper presents a compact dual-port dual-frequency planar shared-aperture antenna with large frequency ratio. It consists of a microwave magneto-electric (ME) dipole antenna and a millimeter-wave parallel-plate resonator antenna (PPRA). It has two vertical conducting walls that form an upper-band parallel-plate resonator and meanwhile provide a magnetic source to the lower-band ME dipole. The design is a shared-aperture structure and is therefore very compact. For demonstration, a dual-frequency antenna simultaneously covering the 5.9-GHz vehicle-to-vehicle (V2V) band (5.855–5.925 GHz) and the 28-GHz 5G band (27.5–28.35 GHz) was designed, fabricated, and measured. Good agreement between the measured and simulated results was found. The lower and upper bands have the measured 10-dB impedance bandwidths of 41.6% (5.30–8.08 GHz) and 6.66% (27.15–29.02 GHz), and measured peak antenna gains of 5.80 dBi and 8.46 dBi, respectively. The antenna can be used on vehicular platforms for providing V2V communications and 5G millimeter-wave connections simultaneously.