This letter presents a novel transmission metasurface to achieve orbital angular momentum (OAM) waves at the X-band. The unit cell of the proposed metasurface consists of three dielectric layers and four metallic layers, where the metallic layer is composed of an outer metallic ring and a center quasi-snow patch. A good transmission coefficient of the unit cell is obtained at the operating frequency. Meanwhile, a full 360° phase shift can be achieved by changing the length of the quasi-snow patch. The method of generating OAM waves is studied and analyzed. Based on this method, a metasurface producing a +1-mode OAM wave is designed and simulated. To verify this concept, one prototype is fabricated, assembled, and measured. The measured results agree well with the simulated ones, showing that the +1-mode OAM wave can be generated successfully with a high gain of 14.5 dBi. Moreover, a narrow divergence angle of +/-9° is achieved in the produced OAM wave.

A compact low-profile all-textile multiband antenna operating in the 2.45/5.8 GHz ISM bands, mobile WiMAX IEEE 802.16 2005 (3.3–3.4 GHz), and 5G sub-6 NR frequency band n77 (3.85–4.0 GHz) is proposed for wireless body-area network (WBAN) applications. Good broadside radiations are achieved by properly activating the inherent TM ₁₁ , TM _21, and TM ₃₁ modes of a circular patch antenna. An elliptical slot and a C-shaped slot are employed to tune the three modes to the desired operating frequencies. A rectangular slot is used to reduce undesirable depression in the 5.8 GHz radiation pattern. The proposed antenna is fabricated from a conductive fabric layer integrated onto a single layer of denim, making it extremely low-profile and suitable for wearable applications. It has an overall size of 60 × 60 × 1.17 mm (0.64 λ_g × 0.64 λ_g × 0.0125 λ_g at 2.45 GHz). The measured maximum realized gains and bandwidth at the four frequencies are −0.81, −2.81, −1.16, 2.83 dBi, and 90, 190, 230, 570 MHz, respectively. Test results show that when the antenna is placed on and bent around a human arm model, the reflection coefficient has only slight influence. Since the antenna adopts full ground plane structure, the SAR values are far below the EU standard of 2 W/kg limit. With merit characteristics, the proposed design indicates a promising candidate for WBAN applications.

This communication proposes a novel method to design a dual-band circularly polarized (CP) transmitarray (TA) antenna with a linearly polarized feed. By using this method, a shared-aperture dual-band TA is developed, which forms independent beams with right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) in two frequency bands with a single linearly polarized feed antenna. Four different CP TA prototypes operating at 12 GHz and 14.2 GHz with different senses of CP and different beam directions are designed, and two of the prototypes are fabricated to validate the design concepts. A good agreement is obtained between the radiation patterns, gain curves, polarizations, and cross polarization levels measured and computed in both frequency bands. The proposed single-source dual-band CP TA design has advantages of simple structure, lightweight, easy fabrication, low cost, and high performance, making it a good candidate for varied applications.

A wideband high-efficiency millimeter-wave (mm-wave) circularly polarized (CP) array which is constituted by novel planar SIW-fed S-dipoles is presented in this paper. The proposed mm-wave CP S-dipole consists of two rotational symmetric curved arms and is fed differentially through aperture coupling, which features simple configu-ration and excellent performance. Detailed analysis is given to explain the operating principles of this element. It is noted that superior element performance including a wide impedance bandwidth of 43%, a wide 3-dB axial ratio (AR) bandwidth of 36% and 1-dB gain bandwidth of 38% is achieved by the planar SIW-fed S-dipole. By feeding 64 in-phase S-dipole elements through a full-corporate SIW feeding network, a planar wideband highly efficient mm-wave 8 × 8 CP array is realized. To verify the design concept, a prototype operating at Ka-band is fabricated and measured. Measurement results indicate that the proposed array achieves a wide overlapped bandwidth of 27.6%, a high antenna gain of 25.2 dBic and a high aperture efficiency of 89.9%. Attributed to the planar and robust array structure as well as its excellent performance, the presented array is a good candidate for various mm-wave applications.

Low-terahertz (Low-THz, 100 GHz-1.0 THz) technology is expected to provide unprecedented data rates in future generations of wireless system such as the 6th generation (6G) mobile communication system. Increasing the carrier frequencies from millimeter wave to THz is a potential solution to guarantee the transmission rate and channel capacity. Due to the large transmission loss of Low-THz wave in free space, it is particularly urgent to design high-gain antennas to compensate the additional path loss, and to overcome the power limitation of Low-THz source. Recently, with the continuous updating and progress of additive manufacturing (AM) and 3D printing (3DP) technology, antennas with complicated structures can now be easily manufactured with high precision and low cost. In the first part, this paper demonstrates different approaches of recent development on wideband and high gain sub-millimeter-wave and Low-THz antennas as well as their fabrication technologies. In addition, the performances of the state-of-the-art wideband and high-gain antennas are presented. A comparison among these reported antennas is summarized and discussed. In the second part, one case study of a broadband high-gain antenna at 300 GHz is introduced, which is an all-metal model based on the Fabry–Perot cavity (FPC) theory. The proposed FPC antenna is very suitable for manufacturing using AM technology, which provides a low-cost, reliable solution for emerging THz applications.

This paper proposes a novel dual-band full-duplex antenna/array for intelligent transport systems (ITS) applications. Different from traditional single-port single-band antennas, the two ports of the antenna are highly isolated and designed to operate at different frequency bands simultaneously. Such a property could support the full-duplex operation-mode, which significantly simplifies the complexity of the RF frontend subsystem. The other contribution of this work is that multiple functions such as filtering, duplexing and radiation are combined into one single device, resulting in a simplified RF frontend. This co-design multifunctional device could also remove the separate filters, duplexers and interfaces between them, resulting in the reduction of the size, weight and cost. In addition, cross-coupling is investigated and employed to generate additional transmission zeros so as to improve the channel isolation and out-of-band interference. To verify the concept, an antenna element and two 2 × 2 arrays at C-band are designed, prototyped and tested. All the measurements agree well with the simulations, showing two full-duplex channels of 4.58 - 4.83 GHz and 5.86 - 6.2 GHz for transmitting and receiving, respectively. The proposed antennas also exhibit excellent performance in terms of channel isolations, frequency selectivity, out-of-band rejections and gains.