A wideband and wide-angle linear-to-circular polarization converter (LCPC) based on a single-layer dielectric substrate is proposed. The converter element consists of a metal strip cross backed by a strip horizontally and centrically located on the other metallic layer. The vertical arm of the strip across the whole surface performs as a high- pass filter with a wide passband above a low cutoff frequency. Meanwhile, the horizontal strip resonates at a high out-of-band frequency and also offers a wideband response below the resonant frequency. Another two short strips vertically and horizontally placed around the crosses increase the phase shift caused by the crosses and improve both the passbands. Using equivalent circuit models and ANSOFT HFSS, an example of LCPC is designed with the overall element size of only $0.11\lambda _{0}\times 0.21\lambda _{0}$ for a 90° phase difference and wide-angle stability over the wide operation band. The prototype shows the simulated / measured axial ratios (ARs) below 3 dB over the bandwidth of 69%/74% for a normal incidence wave and 54% for the oblique incident angle of 55° in yz plane, respectively. With the insertion loss of less than 3 and 2 dB, the measured 3 dB AR bandwidth keeps 70% and 55%, respectively.

Wideband and Wide-Angle Single-Layered-Substrate Linear-to-Circular Polarization Metasurface Converter

A novel circularly polarized (CP) complementary source antenna with endfire radiation is proposed in Ka-band. With the existence of two antipodal notches etched at the edges of the two broad walls of an open-ended substrate-integrated waveguide, two orthogonal electric field components radiated from the equivalent magnetic current, and the electric currents separately can be excited simultaneously. The magnitude and phase differences between the two filed components can be controlled effectively by properly tuning the dimensions of the notches. The operating mechanism and the design procedure of the antenna are analyzed in detail. Wide −10 dB impedance and 3 dB axial ratio bandwidths of 64% and 51%, a gain varying from 3.1 to 6.4 dBic, and the symmetrical radiation pattern are obtained. In order to further increase the gain and front-to-back ratio (FTBR) of the antenna, a dielectric rod structure is then integrated with the antenna. An overlapped operating bandwidth of 41%, an improved gain up to 12 dBic and the stable radiation pattern with an FTBR close to 20 dB are verified by a fabricated prototype. The antenna presented in this paper provides a new mean to design the wideband endfire CP antenna with a simple configuration, which would be attractive for future millimeter-wave wireless systems.

Millimeter-Wave Wideband Circularly Polarized Planar Complementary Source Antenna With Endfire Radiation

In this paper, a novel 3-D printed circularly polarized (CP) modified Fresnel lens antenna operating at 300 GHz is introduced By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG) The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the terahertz CP lens The measured results show that the axial ratios (ARs) of the fabricated antenna prototype are smaller than 3 dB from 265 to 320 GHz Moreover, the modified Fresnel lens has a maximum gain of 274 dBic, which is 09 dB larger than that of the conventional Fresnel zone plane antenna (FZPA) These validate the concept, the design, and the fabricated prototype

3-D Printed Circularly Polarized Modified Fresnel Lens Operating at Terahertz Frequencies

In this communication, a W-band substrate-integrated waveguide (SIW) magnetoelectric (ME) dipole array antenna is reported with a wide operating bandwidth. By combing a longitudinal slot, which is functioned as a magneto dipole, on the top surface of the SIW, and a loaded short-circuited patch functioned as an electric dipole, an SIW ME dipole is designed. Thus, both merits of the low-loss character of the SIW and the wideband performance of the ME dipole are utilized. The proposed technique is capable of designing a large planar array with a wide operating bandwidth. As a demonstration, a W-band $4\times 8$ SIW array antenna is designed and fabricated by using a low-cost printed circuit board technology. The experimental results show that the 10 dB impedance bandwidth of the designed prototype is 13.89%, i.e., from 78.4 to 90.1 GHz. Stable radiation patterns, high radiation efficiencies, and low cross-polarization levels are achieved within a wide operating frequency band. In addition, a stable gain of 19.6±0.7 dBi is obtained as well. The proposed antenna is a good candidate for the millimeter-wave wireless system.

Wideband $W$ -Band Substrate-Integrated Waveguide Magnetoelectric (ME) Dipole Array Antenna

An endfire circularly polarized (CP) complementary antenna array is proposed for 5G applications. The proposed antenna is realized using a single-layered printed circuit board (PCB) with plated-through-hole technology and metal blocks. The antenna element consists of an open-ended substrate-integrated waveguide (SIW), an electric dipole, a double-sided parallel-strip line (DSPSL), and two metal blocks. It is simple in configuration and can achieve wide impedance and axial ratio (AR) bandwidths, stable gain and radiation patterns, and low back radiation. To increase the gain, a $1 \times 8$ antenna array is formed by integrating eight antenna elements with a planar 1–8 SIW feed network. The measurement results show that the proposed array can achieve an overlapping impedance and AR bandwidth of 23.8% from 56.3 to 71.5 GHz with an endfire left-handed CP (LHCP) gain from 14 to 15.3 dBic. The proposed array possesses all the salient features of the complementary source in symmetric and stable radiation patterns, low back radiation, and wide bandwidth.

An Endfire Circularly Polarized Complementary Antenna Array for 5G Applications

A circularly polarized (CP) antenna based on the complementary source technique is designed for 60-GHz applications. The proposed antenna is composed of a strip dipole, a slot, and a cavity, and it is realized by plated-through-hole and printed-circuit technologies. Experimental results show that the proposed antenna can present an overlapping bandwidth of 21.9% from 53.6 to 66.8 GHz, within which the right-handed CP gain varies from 5.3 to 8.6 dBic and all radiation patterns are relatively symmetric and stable.

A Complementary Circularly Polarized Antenna for 60-GHz Applications

Funding information Research Grants Council of the Hong Kong SAR, China, Grant/Award Number: T42-103/16-N Abstract Based on a simple and effective calculation method, two free-space measurement setups are employed to investigate the dielectric properties of various materials at terahertz (THz) frequencies. One setup involves THZ time-domain spectroscopy (THz-TDS) at a frequency range of 0.4 to 1 THz. The other setup comprises a vector network analyzer (VNA) with pairs of VAN extenders (VNAXs) and diagonal standard gain horns (SGHs) at a frequency range of 0.22 to 1.1 THz. The calculation method is verified for the THz-TDS system and employed in the VNA system for the first time. Dielectric properties, including refractive indices, power absorption coefficients, relative permittivities, and loss tangents, are calculated from measured transmission data. Several materials, including printed circuit boards and 3D printing materials, are characterized to verify the calculation method and compare the measurement setups.

Terahertz free‐space dielectric property measurements using time‐ and frequency‐domain setups

A circularly polarized (CP) differentially fed magnetoelectric dipole (ME-dipole) array is proposed for fifth-generation applications. The proposed transmission-line-excited antenna, fabricated on a printed circuit board, can achieve wide impedance and axial ratio (AR) bandwidths and high gain. The antenna consists of a $2 \times 2$ ME-dipole array enclosed by a circular cavity. It is modified from our previous work on linearly polarized (LP) array with its element orientation selectively rotated by ±45° with respect to the differentially fed transmission line and the use of sequential rotation technique to generate CP radiation. A differential feed network is utilized to feed the prototype for experiments. Experiments show that the antenna can present an overlapping impedance and AR bandwidth of 32.2% from 52.2 to 72.2 GHz with a broadside left-handed CP gain from 10.2 to 11.8 dBic. The proposed CP antenna retains all the salient features of our previously proposed LP antenna in symmetric and stable radiation patterns and relatively low back radiation levels.

A Circularly Polarized Differentially Fed Transmission-Line-Excited Magnetoelectric Dipole Antenna Array for 5G Applications

A differentially driven transmission-line-excited magnetoelectric dipole (ME-dipole) is designed for fifth generation applications. The proposed antenna, realized using a single-layered printed circuit board with the plated-through-hole technology, is simple in configuration yet can achieve wide bandwidth and high gain. The antenna is composed of a $2 \times 2$ ME-dipole array surrounded by a rectangular cavity. A differential feed waveguide network based on an E-plane tee is also introduced to feed the prototype for measurements. Measurements show that the proposed antenna with the differential feed network can present an impedance bandwidth of 29.2% from 52.6 to 70.6 GHz with a broadside gain from 10.9 to 13.7 dBi. The proposed antenna retains all the salient features of ME-dipole in symmetric radiation patterns and relatively low cross-polarization and back radiation levels. The radiation patterns are mostly stable with the sidelobes that increase toward the higher end of the operating band.

Xuexuan Ruan

Papers

An Endfire Circularly Polarized Complementary Antenna Array for 5G Applications

A Complementary Circularly Polarized Antenna for 60-GHz Applications

Terahertz free‐space dielectric property measurements using time‐ and frequency‐domain setups

A Circularly Polarized Differentially Fed Transmission-Line-Excited Magnetoelectric Dipole Antenna Array for 5G Applications

A Differentially Fed Transmission-Line-Excited Magnetoelectric Dipole Antenna Array for 5G Applications