In this letter, a novel method of reducing mutual coupling is proposed and it used on a modified compact broadband antipodal Vivaldi antenna (AVA) array for future 5G mmWave communication application. The proposed structure consists of eight antenna elements which are fed by a 1-to-8 power divider. In order to reduce the mutual coupling between AVA array elements, multiple notch structures are added on the ground plane. Thus, the isolation between the antenna elements can achieve a maximal additional 37.3 dB enhancement, impedance bandwidth is extended slightly from 24.65-28.5 GHz to 24.55-28.5 GHz, and the gain is improved simultaneously. To verify the designed method, the proposed AVA arrays were fabricated and measured. And they show an overall size of 28.823 mm $\times$ 60 mm $\times$ 0.787 mm. The measured gain of the modified AVA array is 6.96-11.32 dB in the frequency band of future 5G mmWave communication, which is higher than the initial AVA array, whose gain is 5.34-8.5 dB.

In this paper, a compact substrate-integrated waveguide (SIW) cavity-backed slot antenna array with high gain, broadband, and dual-polarization performances is proposed for 60-GHz applications. An enhanced 17.1% impedance bandwidth was achieved by cutting semi-circle edges on the conventional slot radiator. A simplified SIW feed network is aperture-coupled vertically and constructed on a double-layered structure to implement the dual-polarization operation. By adopting innovative techniques on both radiating element and double-layered SIW feed networks, a high-gain, broadband, and dual-polarized 8 × 8 antenna array was designed on three-layered printed circuit board that allows for mass production. This configuration also resolves the trade-off between the bandwidth and gain of the existing 60-GHz dual-polarized antenna array. Its feasibility is proved by obtaining a measured gain in the range of 19.7-22.3 dB and an enhanced impedance bandwidth of 17.1% over 55.7-66.1 GHz for both horizontal and vertical polarizations. With advantages of high-gain, broadband, and dual-polarization performances in a low-cost low-profile structure, the proposed antenna array is a promising candidate for millimeter-wave wireless systems.

A single-fed dual-band dielectric resonator antenna (DRA) with orthogonal circular polarizations (CPs) in K - and Ka -bands is proposed for satellite communications on unmanned aerial vehicle (UAV). The antenna overcomes the challenges of dual-band dual-CP operation, narrow axial-ratio bandwidth (ARBW) of single-fed antennas, and limited payload and space of UAVs. A shared-aperture merged-structure technique of DRA and slot-dipole antenna is proposed for dual-band dual-CP radiation, thus enabling full-duplex operation with compact size for high isolation systems. The orthogonal CPs in two frequency bands can be controlled independently by a phase compensation method. Besides, broadened ARBW and enhanced gain are attained from the stacked DR, from which high capacity and reliability communication can be achieved. A prototype operating at right-handed CP (RHCP) in the lower band, whereas left-handed CP (LHCP) in the upper band has been designed and measured. It features 10-dB impedance bandwidths of 6.4% and 12.8%, and 3-dB ARBW of 5.2% and 4.1% in the lower and upper bands, respectively. The antenna provides a low cost solution for high isolation, high throughput, and small payload full-duplex UAV satellite systems.

The function of passive wide-angle beam scanning is desired by base station antenna to provide “green” cellular services. In this paper, such function is realized by designing a compact phase-controlled pattern-reconfigurable Dielectric Resonator Antenna (DRA). The proposed DRA has a compact structure with side length of 0.38λc, and excites fundamental TE and TM modes by diverse ports. By assigning phase between diverse ports, E-plane tilted patterns are synthesized with ±66° scan angles. Its pattern-reconfigurable capability makes contributions for increasing array beam scanning angle and minimizing gain fluctuation. A passive four-element array is verified to have an enhanced beam scanning angle of ±81° with gain fluctuation of 1.25 dB. The maximum gain of the scanning beam is located on the off-axis angle of ±66°, and achieves a wide 3 dB scan coverage of ±105°. Good agreements have been shown between measured and simulated results. The proposed phase-controlled pattern reconfigurable DRA and DRA array have impedance bandwidth of 3.33% (2.95-3.05 GHz) for Sub-6GHz wireless system. They enable the wide-angle beam scanning for base station antenna, and provide a cost-effective passive system for “green” communications.

In this communication, a rectangular dielectric resonator antenna (DRA) is integrated with a backed cavity to enlarge the DRA side length by 1.8 times. The backed cavity also reduces the sensitivity of the DRA resonance to the DRA size, resulting in a relaxed fabrication tolerance. Based on the enlarged DRA design, a stacked DRA (sDRA) is proposed to improve the bandwidth from 8.7% to 15% and enhance the realized gain by an average of 1.5 dB. The proposed mechanisms are verified by fabricating a 4x4 sDRA array with an enlarged DRA side length of 1.8 mm (0.40λ), an improved bandwidth of 62.7-73.9 GHz (16.4%) and an enhanced measured gain of up to 17.2 dBi. The enlarged DRA dimension permits a higher DRA operating frequency without reducing the DRA size. The proposed millimeter-wave (mmW) sDRA array provides a wide bandwidth and high-gain solution for 67 GHz unlicensed band communications.

3D printing of antennas on removable fingernail for on-body communications at microwave and millimetre waves is proposed. Aerosol Jet technology, a fine-feature material deposition solution, has been used to directly print microstrip patch antennas on an acrylonitrile butadiene styrene (ABS) removable finger nail substrate. Two antennas have been printed and assessed, one operating at 15 GHz and the other at 28 GHz. Nanoparticle conductive silver ink has been employed to create the microstrip patch antennas and corresponding transmission line using an Optomec machine. The inks are then cured using a PulseForge machine. A further copper layer is added to the millimeter wave antenna via an electroplating process. The antennas have been simulated and measured off-the-finger and on-the-finger. Simulated and measured reflection coefficients (S11) and radiation patterns are found to be in good agreement. The proposed on-body antennas can find application in the Internet of Things (IoT) where large amount of sensing data can be shared at the microwave and millimetre wave spectrum of future 5G communications. The removable finger nails could include other electronic devices such as on-body sensors, computational, storage and communication systems.