A millimeter-wave high-gain dual-polarized antenna array with an enhanced bandwidth is presented. An innovative air-filled differential feeding cavity loaded with a short-ended cross-shaped waveguide is investigated to serve as the feed network and the mode splitter simultaneously of the $2\,\,\times2$ dual-polarized subarrays. Wideband characteristics and a compact planar size that are desirable for the wideband array design are achieved. Moreover, a wideband dual-polarized waveguide-fed magnetoelectric (ME) dipole antenna with a lightweight self-support geometry and wideband H-plane parallel feed networks with modified dual-layered configurations are proposed, which are convenient to connect with the differential feeding cavity directly. With the use of a commercial metallic 3-D printing facility, the proposed radiating elements, feeding cavities, and feed networks can be combined successfully in a whole piece with a lightweight geometry. The printed $8 \times 8$ array prototype operating in the Ka-band confirms a wide bandwidth of about 30%, a gain of up to 28.5 dBi, and stable unidirectional radiation patterns for the two polarizations. Benefitted from the advantages of the promising wideband dual-polarized radiations and convenience of fabrication, the proposed antenna array would be attractive for millimeter-wave polarization diversity applications.

A specially designed millimeter-wave high-gain wideband magneto-electric (ME) dipole antenna array based on metallic three-dimensional (3D) printing technology is presented. In order to shorten the printing duration of the array that is related to the fabrication costs, components with novel self-supporting geometries in the printing process, including a waveguide fed ME-dipole radiating element, a 1-to-4 power divider acting as the subarray feed, and a full-corporate E-plane waveguide feed network, are investigated. Benefitted from these components, the entire array configuration can be fulfilled by employing a timesaving printing scheme, which leads to a 15% reduction in the printing duration for an 8 × 8 array, and the reduction can be further increased to 40% for a 16 × 16 design in comparison with the reported 3D printed Ka-band arrays with same sizes that were fabricated by using the traditional printing scheme. Simultaneously, excellent operating characteristics, including a wide bandwidth of 32.4%, a maximum gain of 27.1 dBi, and stable unidirectional radiation, are also confirmed experimentally by an 8 × 8 prototype of the proposed array. This work offers a method to effectively reduce the printing time of the 3D printed large-size antenna arrays with attractive performance, which would be of importance to the practical cost-effective large-scale applications in the emerging millimeter-wave wireless communications.

A three-dimensional (3-D) substrate integration method by using both the planar dimensions and the vertical dimensions in multilayered substrates for millimeter-wave devices and circuits design is presented in this article. The vertical substrate-integrated groove gap waveguide (SIGGW) is studied first, whose multilayered geometry without metal contact between stacked substrates and wide operating band supporting the single quasi-TE ₁₀ mode with stable propagation features enables it to be a promising vertical waveguide structure with ease of realization. By simultaneously utilizing the vertical and planar SIGGWs, a fully 3-D substrate-integrated orthomode transducer (OMT) consisting of E-plane power dividers, U-shaped connections, and a turnstile junction that are difficult to fulfill in previous works is successfully implemented in the Ka-band. Its compact geometry and significantly performance improvement demonstrate the merits of the proposed method. After that, the OMT is used for feeding a dual-polarized pyramidal horn antenna also with a 3-D substrate-integrated configuration. The overall multilayered antenna module with experimentally confirmed wide bandwidths, high isolations, and stable radiation patterns can still be fabricated conveniently by employing the standard single-layered printed circuit board (PCB) facilities. Taking the advantages of the flexible design freedom and satisfying operating characteristics, the presented design method and devices are valuable to advanced millimeter-wave applications.

An innovative approach to design millimeter-wave wideband high-gain large-scale antenna arrays is proposed with the use of waveguide T-junctions with multiple reflection nulls for building an H-type full-corporate feed network. By collaboratively optimizing the properties of the reflection nulls, the undesirable in-phase superposition of small reflections in the feed network can be weakened, and thus improving the bandwidth of the array. The method of synthesizing wideband iris-loaded H-plane stepped waveguide T-junctions with three reflection nulls is investigated. A 16 × 16 horn array in the Ka-band is designed based on the presented approach and manufactured by employing metallic three-dimensional (3D) printing technology. Excellent performance, including a wide bandwidth of 48.4%, a gain of up to 34.5 dBi, and symmetrical and stable radiation patterns in both the E- and H- planes, are experimentally verified. This work is feasible and convenient for the implementation of high-gain wideband antenna arrays, which is valuable to emerging millimeter-wave applications.

A one-time-reflection equivalent model of the full-corporate waveguide feed networks is investigated to propose a novel approach to bandwidth enhancement of millimeter-wave large-scale antenna arrays. Theoretical analysis reveals that the in-phase superposition phenomenon of multiple small reflections at specific frequencies caused by the topology of the feed network is also a significant factor to affect the achievable bandwidth of the large-scale arrays, apart from the bandwidth performance of the individual power dividers and radiators composing the array. In order to weaken the undesirable effects on bandwidths caused by the small reflections, a full-corporate waveguide feed network with an X-type topology is then presented. Air-filled waveguide X-junctions and waveguide-fed horn sub-arrays are designed to fulfill new three-dimensional (3D) printed V-band antenna arrays. Excellent performance, including an improved bandwidth of about 40%, a gain of up to 27.8 dBi, and stable unidirectional radiation patterns with cross polarization of less than −32 dB, are confirmed experimentally by an $8 \times 8$ prototype. The theoretical model and the bandwidth enhancement scheme in this paper are valuable to realize the high-gain wideband antenna arrays for emerging millimeter-wave applications.

A novel wideband high-gain air-filled waveguide fed antenna array is presented for millimeter-wave applications. A design scheme based on the optimized multistage phase cancellation with low complexity is investigated, which is able to weaken the undesirable in-phase superposition of small reflections in the array geometry, and thus significantly improving the achievable bandwidth of the large-scale array. The phase delay required for the proposed design method is obtained by introducing U-shaped bended waveguides in the feed network. Wideband 1 × 2 sub-arrays and E-plane waveguide T-junctions are also designed to build the array. A 16 × 16 array in the Ka-band is manufactured by employing metallic three-dimensional (3D) printing technology, which realizes excellent operating characteristics, including a bandwidth of 51.5%, a gain of up to 34.6 dBi, and stable unidirectional radiation patterns with cross polarization of less than -40 dB. The operating band of the proposed array covers multiple bands for 5G simultaneously, including n257, n258, n260 and n261. The proposed design method and antenna array would be attractive for emerging millimeter-wave applications.