A broadband multibeam endfire dual-circularly polarized (CP) antenna array using dielectric-loaded stepped slot antennas for millimeter-wave (mmWave) applications is proposed. First, a dual-CP endfire antenna element is designed for broadband mmWave applications. Additional loaded dielectric is utilized to improve the interelement isolation, the polarization purity, and the gain performance. Second, a substrate integrated waveguide (SIW) feeding network is designed for multibeam array applications. The broadband $4\times 4$ SIW Butler matrix, interconnections, and transitions are designed and applied in the antenna array. Third, mutual coupling and its influence on the array performance are investigated. Additional air gaps between elements are designed for axial ratio performance enhancement. Finally, the proposed multibeam array is designed, fabricated, and measured. The fabricated prototype achieves wide impedance bandwidth of 29.3% with the interbeam isolation greater than 15 dB, and a wide axial ratio bandwidth of 22.5%. The proposed multibeam endfire dual-CP antenna array would be a very attractive candidate for 5G mmWave wireless applications.

Millimeter-Wave Multibeam Endfire Dual-Circularly Polarized Antenna Array for 5G Wireless Applications

A novel compact dual-band cavity-backed substrate integrated waveguide (SIW) array antenna using high-order radiation modes has been proposed in this paper. The first high-order hybrid mode (superposition of TM310 and TM130) and the second high-order mode (TM320) of K-band in the SIW cavity are excited by an inductive window for dual-band application. The operation mechanism of high-order modes is analyzed and then verified through simulations by inserting metallic vias in different positions of the resonant SIW cavity. The designed subarray antenna has the advantages of high gain, high front-to-back ratio, and low cross-polarization level. To further validate the design idea, a dual-frequency band $2 \times 2$ array antenna has been fabricated and measured including reflection coefficients, realized gains, and radiation patterns. The measured results show that the 10-dB impedance bandwidths at resonant frequencies of 21 and 26 GHz are 800 MHz (3.7%) and 700 MHz (2.6%), and the realized gains at boresight direction are around 16 and 17.4 dBi, respectively. Moreover, the proposed array antenna also possesses both advantages of metallic cavity-backed antennas and planar patch antennas, such as low cost, easy fabrication with the printed circuit board technology, and integration with other planar circuits.

Substrate Integrated Waveguide Cavity-Backed Slot Array Antenna Using High-Order Radiation Modes for Dual-Band Applications in $K$ -Band

A novel planar end-fire circularly polarized (CP) complementary Yagi array antenna is proposed. The antenna has a compact and complementary structure, and exhibits excellent properties (low profile, single feed, broadband, high gain, and CP radiation). It is based on a compact combination of a pair of complementary Yagi arrays with a common driven element. In the complementary structure, the vertical polarization is contributed by a microstrip patch Yagi array, while the horizontal polarization is yielded by a strip dipole Yagi array. With the combination of the two orthogonally polarized Yagi arrays, a CP antenna with high gain and wide bandwidth is obtained. With a profile of $0.05\lambda _{\mathrm{0}}$ (3 mm), the antenna has a gain of about 8 dBic, an impedance bandwidth ( $\vert S_{11}\vert dB) of 13.09% (4.57–5.21 GHz) and a 3-dB axial-ratio bandwidth of 10.51% (4.69–5.21 GHz).

A Broadband and High-Gain Planar Complementary Yagi Array Antenna With Circular Polarization

This paper presents a low-profile log-periodic monopole array antenna with end-fire radiation and vertical polarization. It consists of 15 monopole elements and a conductor-backed coplanar strip line as the feeding line. The monopoles are of the same height but loaded with top hats of different sizes to achieve the required resonant frequencies. A wideband transition from coaxial line to conductor-backed coplanar strip line is designed for the antenna feed. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 1.5 to 6.8 GHz (4.53:1) for $\text{VSWR { and a gain better than 4.5 dBi over the same operating frequency band are obtained while the antenna has a very low profile of only $0.047\;\lambda_L$ ( ${{{\lambda}}_L}$ is the free-space wavelength at the lowest operating frequency).

Low-Profile Log-Periodic Monopole Array

Anisotropic crystals have recently attracted considerable attention because of their ability to support polaritons with a variety of unique properties, such as hyperbolic dispersion, negative phase velocity, or extreme confinement. Particularly, the biaxial crystal $\ensuremath{\alpha}\ensuremath{-}{\mathrm{MoO}}_{3}$ has been demonstrated to support phonon polaritons, light coupled to lattice vibrations, with in-plane anisotropic propagation and unusually long lifetime. However, the lack of theoretical studies on electromagnetic modes in biaxial crystal slabs impedes a complete interpretation of the experimental data, as well as an efficient design of nanostructures supporting such highly anisotropic polaritons. Here, we derive the dispersion relation of electromagnetic modes in biaxial slabs surrounded by semi-infinite isotropic dielectric half-spaces with arbitrary dielectric permittivities. Apart from a general dispersion relation, we provide very simple analytical expressions in typical experiments in nano-optics: the limits of short polaritonic wavelength and/or very thin slabs. The results of our study will allow for an in-depth analysis of anisotropic polaritons in novel biaxial van der Waals materials.

/pdf/analytical-approximations-for-the-dispersion-of-1wbzsav3ov.pdf

Analytical approximations for the dispersion of electromagnetic modes in slabs of biaxial crystals

This paper presents the design of a compact and wideband surface wave antenna that exhibits very low profile and can be flush-mounted on a conformal platform. The proposed antenna comprises a tapered grounded ceramic slab, a unidirectional surface wave launcher, and a tapered impedance transition. The ceramic slab is smoothly tapered to transform the guided surface wave into radiated space wave over a wide frequency range. The surface wave launcher employs a probe-fed parallel plate waveguide with a modified parabolic reflecting wall and a metallic post, which are critical for effectively transforming the cylindrical waves to a unidirectional plane wave within a broad frequency range. Simulated results show that the proposed surface wave antenna achieves a wide operation bandwidth from 6.1 to 18 GHz with a thickness of only ${\bf 0}.{\bf 12}{\lambda _0}$ at the center frequency. Acceptable gain values with stable and quasi end-fire radiation beams are obtained over the entire frequency band. A prototype of the proposed antenna is fabricated and tested. Measured results are in good agreement with simulated ones.

https://dr.ntu.edu.sg/bitstream/10220/38458/1/Wideband%20flush-mounted%20surface%20wave%20antenna%20.pdf

Wideband Flush-Mounted Surface Wave Antenna of Very Low Profile

A planar helical antenna is presented for achieving wideband end-fire radiation of circular polarization while maintaining a very low profile. The helix is formed using printed strips with straight-edge connections implemented by plated via-holes. The currents flowing on the strips and along via-holes of the helix contribute to the horizontal and vertical polarizations, respectively. Besides, the current on the ground plane is utilized to weaken the strong amplitude of the horizontal electric field generated by the one on the strips. Thus, a good circular polarization can be achieved. Furthermore, a tapered helix and conducting side-walls are employed to broaden the axial ratio (AR) bandwidth as well as to improve the end-fire radiation pattern. The designed antenna operates at the center frequency of 10 GHz. Simulated results show that the planar helical antenna achieves wide-impedance bandwidth ( $\vert S_{11} \vert ) from 7.4 to 12.8 GHz (54%) and 3-dB AR bandwidth from 8.2 to 11.6 GHz (34%), while retaining a thickness of only $0.11{{{\lambda }}_0}$ at the center frequency. A prototype of the proposed antenna is fabricated and tested. Measured results are in good agreement with simulated ones.

/pdf/planar-helical-antenna-of-circular-polarization-93m75d5xky.pdf

Planar Helical Antenna of Circular Polarization

A compact endfire slot antenna is presented in this letter, which employs two thin substrates on both the top and bottom broad walls of a metallic cavity Three slots with different lengths at suitable positions etched out of the cavity walls are utilized to enhance the bandwidth and achieve endfire radiation with supergain The designed antenna operates at the center frequency of 58 GHz Simulated results show that the slot antenna has an impedance bandwidth ( dB) from 551 to 608 GHz (98%) and a maximum gain of 84 dB in the endfire direction The gain ripple is 09 dB over the bandwidth of interest A prototype of the proposed antenna with an integrated rat-race feeding balun is fabricated and tested Measured results are in good agreement with simulated ones

A Compact Cavity-Backed Endfire Slot Antenna

A planar low-profile log-periodic antenna based on cavity-backed slot is proposed in this letter. The slot element is made of a microstrip patch on a large ground plane with three edges shorted and one edge open. It is excited by a probe protruding into the cavity from the back of the ground. Through choosing different length and width, each slot element of the array can resonate at different frequency with a same height. A meandered microstrip line on the bottom is used to feed the array, achieving endfire radiation with wide bandwidth. The proposed antenna has been fabricated using printing technology. Measured results show that an operating frequency band from 6.9 to 17.4 GHz (2.52:1) for VSWR λL at the lowest operating frequency are obtained. The proposed array has a good overall performance of wide bandwidth, low profile, and planar structure with easy printing fabrication process, which may be useful for the demand of endfire radiation with low profile.

A Planar Low-Profile Log-Periodic Array Based on Cavity-Backed Slot

A conformal supergain slot antenna is presented in this paper, which comprises a thin substrate on the top broad wall of a shallow metallic cavity Three slots with different lengths are etched out at suitable positions of the cavity wall to enhance the bandwidth as well as to achieve the supergain A large ground is employed to obtain the near-end-fire radiation pattern The proposed conformal antenna operates at the center frequency of 10 GHz Simulated results show that a fractional bandwidth of 15% and maximum gain of 91 dB can be obtained for the three-slot conformal structure, the maximum radiation pattern tilts 38° from the end-fire direction A prototype of the proposed antenna is fabricated and tested Measured results are in good agreement with simulated ones

Zhuozhu Chen

Papers

Wideband Flush-Mounted Surface Wave Antenna of Very Low Profile

Planar Helical Antenna of Circular Polarization

A Compact Cavity-Backed Endfire Slot Antenna

A Planar Low-Profile Log-Periodic Array Based on Cavity-Backed Slot

A conformal cavity-backed supergain slot antenna