This paper presents a wideband circularly polarized millimeter-wave (mmw) antenna design. We introduce a novel 3-D-printed polarizer, which consists of several air and dielectric slabs to transform the polarization of the antenna radiation from linear to circular. The proposed polarizer is placed above a radiating aperture operating at the center frequency of 60 GHz. An electric field, E, radiated from the aperture generates two components of electric fields, Ex and Ey . After passing through the polarizer, both Ex and Ey fields can be degenerated with an orthogonal phase difference which results in having a wide axial ratio bandwidth. The phase difference between Ex and Ey is determined by the incident angle φ, of the polarization of the electric field to the polarizer as well as the thickness, h, of the dielectric slabs. With the help of the thickness of the polarizer, the directivity of the radiation pattern is increased so as to devote high-gain and wideband characteristics to the antenna. To verify our concept, an intensive parametric study and an experiment were carried out. Three antenna sources, including dipole, patch, and aperture antennas, were investigated with the proposed 3-D-printed polarizer. All measured results agree with the theoretical analysis. The proposed antenna with the polarizer achieves a wide impedance bandwidth of 50% from 45 to 75 GHz for the reflection coefficient less than or equal -10 dB, and yields an overlapped axial ratio bandwidth of 30% from 49 to 67 GHz for the axial ratio ≤ 3 dB. The maximum gain of the antenna reaches to 15 dBic. The proposed methodology of this design can apply to applications related to mmw wireless communication systems. The ultimate goal of this paper is to develop a wideband, high-gain, and low-cost antenna for the mmw frequency band.

The coexistence of microwave and millimeter-wave technologies becomes the inexorable trend of future wireless communication systems. The corresponding components of the system are required to cover these two frequency bands simultaneously. However, it is difficult for the existing dual-band antenna configurations to achieve a frequency ratio larger than 3. In this paper, a novel topology is proposed to solve this problem. For the desired dual-band operation, a signal routing approach is proposed to guide the microwave/millimeter signals to the specific elements, respectively. The classical aperture coupling mechanism is deliberately utilized to block the millimeter-wave signal from feeding to the microwave antenna element and route the millimeter-wave signal into the millimeter-wave antenna element. Meanwhile, the substrate- integrated waveguide (SIW)-based millimeter-wave antenna element has the high-pass nature to reject the microwave signal. Therefore, the antenna elements for microwave and millimeter-wave bands can be designed separately with a high flexibility. First, a dual-band antenna was implemented to support 5.8 and 30 GHz simultaneously by integrating an annular-ring antenna element and an SIW slot antenna element. Furthermore, different radiation properties at the two bands can be easily realized owing to the high flexibility of the proposed approach. For validation, these two antennas were fabricated and measured.

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.

Active meta polarizers based on phase-change materials have recently led to emerging developments in terahertz devices and systems for imaging, security, and high-speed communications. Existing technologies of adaptive control of meta polarizers are limited to the complexity of external stimuli. Here, we introduce an active terahertz polarizer consisting of a single layer of large array patterns of vanadium dioxide material integrated with metallic patch matrix to dynamically reconfigure the polarization of the terahertz waves. The proposed active polarizer is simple in structure and can independently manipulate the polarization of the incident THz waves in two orthogonal directions. In addition, the device can also be performing as a highly efficient reflector at the same frequencies. We demonstrate that efficient and fast polarization changes of THz waves can be achieved over a wide operating bandwidth. Compared with other active polarizers using mechanical, optical and thermal controls, it can be conveniently manipulated with DC bias without any external actuators, intense laser source or heater. Therefore, with the advantages of high efficiency, compact size, low loss, low cost and fast response, the proposed polarizer can be highly integrative and practical to operate within adaptive terahertz circuits and systems.

This paper presents a novel wideband circularly polarized dielectric rod waveguide (DRW) antenna for millimeter-wave applications. The rotated tapering rod that consists of a matching taper and a radiation taper is the first time adopted to realize circular polarization in the DRW antenna design. The circular polarization is realized by generating two orthogonal electric fields through rotating the radiation taper to an angle of φ relative to the matching taper. The proposed antenna achieves a wide impedance bandwidth throughout the whole Ka-band as well as a wide 3 dB axial ratio bandwidth (ARBW) of 37% from 27.5 to 40 GHz. The main advantages for this antenna design are its wide impedance bandwidth, 3 dB ARBW, simple structure, and easy fabrication.

A new kind of multiport power-combining patch antenna in multiple polarization states is proposed in this paper. The proposed antenna consists of a ground, a stacked patch, and a driven patch fed by four centrally symmetric ports. Based on the S-parameter analysis of the multiport antenna, six polarization states (0°, 90°, 45° linear polarization, and left-handed and right-handed circular polarization) with stable reflection coefficients and radiation pattern can be realized by controlling the input phases of four ports. In this way, it is not necessary to use extra feeding network to realize the multiple polarization states. Moreover, in addition to radiating electromagnetic energy just like conventional antennas, the proposed multiport antenna can also realize on-antenna power combining without the need of power combiner. As a result, the losses and size caused by extra power combiner and feeding network can be avoided. For verification, the four-port patch antennas in different polarization states are designed and compared. Moreover, a four-port antenna integrated with four power amplifiers is fabricated and measured. The results show that both on-antenna power-combining and multiple polarization states can be realized without the need of power combiner and polarization feeding network.