End-fire Antenna Array Research Articles

38-GHz Phased Array Transmitter and Receiver Based on Scalable Phased Array Modules With Endfire Antenna Arrays for 5G MMW Data Links

This article presents the 38-GHz phased array 32-element Tx and 16-element Rx with 2-GHz IF and 5-GHz LO for fifth-generation (5G) millimeter-wave (MMW) communications. The Tx and Rx beamformers and upconverters/downconverters are fabricated in 65-nm CMOS. The PAs and LNAs near antenna ends are fabricated in 0.15- $\mu \text{m}$ GaAs pHEMT. The eight-element Tx and four-element Rx phased array printed circuit board (PCB) modules integrated with multiple integrated circuits (ICs) and endfire antennas are implemented as unit cells. Four pieces of Tx modules are vertically stacked to construct an $8\times {4}$ brick array (planar array), while four Rx modules are to construct a $4\times {4}$ array. According to 38-GHz over-the-air (OTA) measurements, the 32-element Tx shows 47.5-dBm equivalent isotropic radiated power (EIRP) at OP $_{\mathrm {1 ~dB}}$ with −35.2-dB image rejection ratio (IMRR) and −37.4-dB $\times 8$ LORR. The 16-element Rx at 38 GHz shows −4-dBm OP $_{\mathrm {1~dB}}$ with −28-dB IMRR and −36.6-dB LORR. The Tx and Rx support the beam scanning around ±60° azimuth and ±30° elevation planes. The Tx-to-Rx wireless data link demonstrates 64 quadrature amplitude modulation (QAM)/400 M-BR, 256 QAM/200 M-BR, and 512 QAM/100 M-BR in 20 m. To the best of our knowledge, this work is the first 5G 37-/39-GHz phased array Tx/Rx using the scalable brick array configuration and demonstrating competitive performances compared with previous works.

PCB-Based Design of a Beamsteerable Array With High-Gain Antennas and a Rotman Lens at 28 GHz

This letter presents a low-cost single-layer printed circuit board (PCB) design of a Rotman lens and an eight-element Yagi–Uda antenna array suitable for radio frequency (RF) beamsteering at 28 GHz. The antenna array realizes 19 dBi gain due to the guiding parasitic elements of each antenna element and a shaped ground plane surrounding the array. The array radiates in a direction parallel to the PCB enabling the possibility for two-dimensional beamsteering by stacking the PCBs. Integrated with an RF switch network, the design has seven switchable beams to the directions $-\text{30}^\circ$ , $-\text{20}^\circ$ , $-\text{10}^\circ$ , 0 $^\circ$ , 10 $^\circ$ , 20 $^\circ$ , and 30 $^\circ$ . The measured realized gain is still as high as 4–10 dBi including losses of the Rotman lens and the RF switches, thanks to the high-gain antenna array design. The array works wideband across 25.5–28.5 GHz where broadside beam gains are better than 8 dBi. This is the first letter in the literature introducing an experimentally verified design of a PCB endfire antenna array at 28 GHz including all necessary components for RF beamsteering, i.e., a Rotman lens and a switch network.

A Wideband Dual-Polarized Endfire Antenna Array With Overlapped Apertures and Small Clearance for 5G Millimeter-Wave Applications

In this article, an endfire dual-polarized phased antenna array with small ground clearance is proposed for the fifth-generation (5G) millimeter-wave (mmW) applications with a wide bandwidth. In this array, each antenna element consists of a dipole fed by a microstrip line for horizontal polarization and an H-plane horn using substrate-integrated waveguide (SIW) for vertical polarization. To achieve a wide bandwidth for vertical polarization, two metal vias are added at the aperture of the horn antenna. Then, a four-element antenna array is designed by partially overlapping the aperture of each horn element. A prototype has been fabricated using multilayer printed circuit board (PCB) process. The measured results agree well with the simulated ones. The antenna is with an impedance bandwidth of |S11| <; -10 dB from 24.4 to 29.5 GHz for both polarizations. The maximum gains of vertical and horizontal polarizations are 9.16 and 9.27 dBi, with the scanning angle from -34° to 33° for both polarizations with gain deterioration less than 3 dB. The proposed antenna is a promising solution for 5G mmW cellphones or antenna-in-package applications.

Dual-Polarized mm-Wave Endfire Antenna for Mobile Devices

This article presents a dual-polarized millimeterwave endfire antenna array for mobile devices. The antenna array is integrated into a metal-framed mobile phone and radiates through a 20 × 3.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> window in the metal frame. The measurement results show a realized gain above 6 dBi for the frequency band of 28-33 GHz for a three-element array. Beam-steering up to ±40° is possible. The array is physically offset from the metal frame, thus minimizing the capacitive loading effect on the sub-6 GHz antennas. Moreover, due to the lack of mechanical contact between the frame and the antenna module, the antenna is robust against external impacts or hits to the phone. The design of the antenna module facilitates integration in mobile devices for mm-wave operation.

Dual-Polarized mm-Wave Endfire Chain-Slot Antenna for Mobile Devices

This article describes a dual-polarized endfire antenna array for millimeter-wave (mm-wave) frequencies. The antenna consists of a chain-slot-shaped pattern on a mobile phone metal frame. The antenna is fed using a transmission line, which would cause only a negligible capacitive loading of the sub-6 GHz antenna realized on the same metal frame and, therefore, would not significantly degrade its performance. This makes colocating the sub-6 GHz and mm-wave antennas in the same, shared volume possible. Measurements indicate that a four-element array placed within a mobile phone provides a realized gain between 8 and 12.6 dBi for both polarizations across the entire band from 24.5 to 29.5 GHz. The total efficiency of a single element is better than -2 and -3 dB for the whole band for horizontal and vertical polarizations, respectively.

Circularly‐polarised end‐fire antenna and arrays for 5G millimetre‐wave beam‐steering systems

This study presents a circularly-polarised substrate-integrated waveguide end-fire antenna and four-antenna arrays for 5G beam-steering mobile devices at 28 GHz. Polarisation is achieved through implementation of a substrate-integrated waveguide notched-septum polariser. It is then loaded with a dielectric lens to improve gain, axial ratio bandwidth, and circular polarisation (CP) purity. To suppress the mutual coupling between array elements, vias are extended on either side of the lens. It also improves the single-element axial ratio and front-to-back ratio. The antenna's performance is found to be resilient to typical manufacturing tolerances for the lens and via extensions. The element and arrays are manufactured and measured. The prototypes demonstrated an impedance bandwidth of 11.4% with a maximum array gain of 10.5 dBi and a steering range of up to ± 35 ° (with reduced performance when steered to ± 45 ° ). Within this range, the antenna array demonstrates a gain variation of up to 3 dB and very good CP purity within the radiation half-power beamwidths (HPBWs). A wide single-element elevation HPBW of 95 ° is also demonstrated. Given its performance and ease of manufacture in a printed circuit board process, the proposed antenna could be a strong candidate for 5G millimetre-wave beam-steering systems.

A Method for Optimising Superdirectivity of Coupled Meta-Atoms via Planar Directivity Evaluation

We propose a simple and rapid way of optimising directivity in metamaterial-inspired endfire antenna arrays with strong inter-element coupling. We introduce, in addition to the traditional 3D directivity, also its planar equivalents defined as the ratio of the power density in the desired endfire direction to the average power density calculated either in the horizontal (azimuthal) or vertical (elevation) plane. Using dimers of magnetically coupled split-ring resonators with only one element driven by an external source, we derive conditions that must be satisfied in order to realise superdirective current distributions. The superdirective conditions link the quality factor of the resonators and their coupling constant to the array size and the operating frequency. We demonstrate that a rapid measurement in the azimuthal plane can be used as a reliable indicator for whether the superdirective conditions for the 3D directivity are satisfied. Analytical calculations are verified by CST simulations in the MHz frequency range for meta-atoms of circular and square shape. Our method can be extended to arrays comprising larger number of meta-atoms of various shape and would enable rapid prototyping of 3D-printed meta-atoms with desired radiation properties.

End-Fire Vivaldi Antenna Array With Wide Fan-Beam for 5G Mobile Handsets

In this paper, we present a portable end-fire antenna array design for the fifth-generation (5G) mobile handsets that exploits a Vivaldi antenna and shows a wide fan-beam on the elevation plane. We make the proposed antenna array more efficient by printing on a 10-layer printed circuit board (PCB) lamination in a vertical direction of the ground plane edge. Using the proposed Vivaldi antenna array design, the radiation characteristics of 4 × 1 linear arrays are fabricated. To validate the feasibility, we perform simulations and experiments. Simulation results show that the total efficiencies of the antenna array are higher than about 8.16 - 9.46 dBi for the scanning range between 0° to 60°. Measurement results display that the antenna has S11 reply less than -10 dB in the frequency area of 27.5 to 28.5 GHz and wide beamwidth (130.8° in elevation plan, 21.35° in azimuth plan). There is a high accord between the calculated and measured results and we consider that the results in this study can be well achieved by designers who design the wide beamwidth high-speed antennas of 5G mobile terminals.

A Bidirectional Same Sense Circularly Polarized Endfire Antenna Array With Polarization Reconfigurability

In this communication, a bidirectional same sense circularly polarized (Bi-SSCP) endfire antenna array with reconfigurable polarization is proposed and implemented. First, a circular polarization (CP) reconfigurable endfire antenna element is realized by adopting two pairs of switchable electric dipoles, which have a 180° phase difference inherently. Along with the fixed magnetic dipole, the endfire antenna element can work at two CP states, i.e., left-hand CP (LHCP) and right-hand CP (RHCP) by switching the states of the two electric dipoles. Then, a Bi-SSCP endfire antenna array with polarization diversity is developed by using two identical endfire antenna elements placed back-to-back with a single feeding probe. For verification, prototypes of the designed endfire antenna element and Bi-SSCP endfire antenna array are fabricated and measured. The measured results show reasonable agreement with the simulated ones. The measured overlapped bandwidth for 10 dB return loss and 3 dB axial ratio of the Bi-SSCP endfire antenna array is from 5.7 to 5.9 GHz for the two CP states.

Endfire Antenna Array Using Microstrip-Fed Cavity-Backed Slot Elements

In this communication, an endfire antenna array using series-fed cavity-backed slot elements is proposed with low profile and high gain properties. By adopting the cavity-backed slot element as the radiating element, the antenna array can be partly embedded under the ground plane, which reduces the profile. Fed by an air–substrate microstrip line, the antenna array achieves a moderate phase constant, which leads to an endfire radiation pattern. By optimizing the coupling level between the cavity-backed slot elements and microstrip line, the aperture distribution of the antenna array is improved to enhance the endfire gain. With the overall length of 3.75 wavelength at 4 GHz, the proposed antenna array obtains a measured endfire gain of 11.5 dBi. Compared with the low-profile endfire antennas mounted on the metallic plane, the proposed antenna array has lower profile and higher endfire gain.

V-Band Wideband Circularly Polarized Endfire Multibeam Antenna With Wide Beam Coverage

A V -band wideband circularly polarized (CP) endfire multibeam antenna array with the wide beam coverage is presented in this letter. First, a wideband compact endfire CP element with the wide axial ratio (AR) beamwidth is proposed. The design procedure and working principle of the element are discussed in detail. Besides, connected holes are used to reduce the mutual coupling and improve the AR performance. After that, a wideband substrate integrated waveguide Butler matrix is designed to feed the antenna array. Finally, the multibeam antenna is fabricated, measured and investigated. The measured results demonstrated that the proposed multibeam antenna provides a wide −10 dB impedance bandwidth of 28.5% (55.5 to 74 GHz) and a wide 3 dB AR bandwidth of 24.6% (57 to 73 GHz). Additionally, a wide beam coverage ranging from 45°–66° is achieved. Good agreement achieves between measured results and simulated ones.

A Broadband and High-Gain Endfire Antenna Array Fed by Air-Substrate Parallel Strip Line

A broadband and high-gain endfire antenna array fed by an air-substrate parallel strip line is proposed in this communication. It has a simple and planar structure consisting of multiple dipole radiating elements and one parallel strip line. By utilizing the center-fed dipole working between the first and third resonances as the radiating element, the antenna array could obtain stable radiating capability over a broad bandwidth. Fed by an air-substrate parallel strip line working on the TEM mode, the antenna array achieves a moderate phase constant, which is helpful for realizing stable endfire radiation. The radiating element separation is optimized to eliminate the high-order spatial harmonics, ensuring single beam radiation. Fabricated by thin copper plates, the merits of the antenna array include lightweight, low cost, and easy fabrication. According to the measured results, the antenna array has a good match and a stable endfire radiation pattern over the operating band from 4 to 10.5 GHz with the measured gain varying from 10.1 to 13.5 dBi.

Broadband Endfire Magnetoelectric Dipole Antenna Array Using SICL Feeding Network for 5G Millimeter-Wave Applications

A broadband endfire antenna array is investigated for 5G millimeter-wave applications. First, an improved magnetoelectric (ME) dipole with a defected ground structure is proposed, which is excited by a planar L-probe. This proposed ME-dipole antenna shows stable radiation during the relative bandwidth of 53.0%. Next, a 16-way substrateintegrated coaxial line (SICL) feeding network is presented. Its bandwidth is 109.5% for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ -15 dB and insertion loss is less than 13.4 dB. This full-corporate SICL feeding scheme is utilized to construct the broadband antenna array. Finally, the proposed antenna array is fabricated and its performance is evaluated. Considering the impedance bandwidth for |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ -10 dB, the 3 dB gain bandwidth, and the radiation efficiency, the overall measured operating bandwidth is 50.7%, which covers two main candidate frequency bands of 28 and 39 GHz. The cross-polarization level is less than -19.0 dB and the front-to-back ratio is better than 20.0 dB in the whole operating bandwidth. Additionally, a 4 × 4 2-D multibeam array is also simulated to verify the beamforming potential of the proposed antenna array.

Reduction of Main Beam-Blockage in an Integrated 5G Array With a Metal-Frame Antenna

In this paper, a novel technique is introduced to reduce the handset metal-frame blockage to the main beam of a millimeter-wave (mm-wave) endfire antenna array. The metal-frame blockage to mm-wave antennas with different polarizations is investigated first. It is found that the blockage is more severe for horizontal polarization than for vertical polarization. The effect of the metal bezel on an mm-wave array with horizontal polarization can be significantly decreased if two-tilted layers of coupled metal strips are placed at the borders of the frame. Furthermore, these metal strips are shown not to disturb the mm-wave antennas with vertical polarization. Different detailed design considerations are studied. To further demonstrate the idea, a 5G Vivaldi array (with horizontal polarization) is designed and integrated with a metal frame. The frame functions as a low-frequency antenna, operating in two frequency bands of 865–990 and 1358–2786 MHz. The mm-wave array with four elements operates at the frequency band 24.25–27.5 GHz and can scan ±60° in endfire direction, with a realized gain higher than 7 dBi in most of the frequency range.

Integrated Millimeter-Wave Wideband End-Fire 5G Beam Steerable Array and Low-Frequency 4G LTE Antenna in Mobile Terminals

In this paper, a novel technique of collocating a millimeter-wave end-fire 5G beam steerable array antenna with a low-frequency planar inverted-F antenna (PIFA) is presented. In this technique, the low-frequency antenna can be transparent by using some grating strips between the low- and high-frequency antennas. A quad-element mm-wave array with end-fire radiation patterns operating in 22–31 GHz is integrated with a dual-band low-frequency PIFA in a mobile terminal. The novelty of this paper is the collocation of a high-frequency end-fire 5G antenna array with an old-generation low-frequency antenna, such as 4G in small space in the mobile terminal, without interfering with the radiation pattern and impedance matching of both low- and high-frequency antennas. The proposed 5G antenna covers 22–31 GHz and can scan ±50° with the scan loss of better than 3 dB. The coverage efficiency of the proposed mm-wave 5G antenna is better than 50% and 80% for a minimum gain of 4 and 0 dBi in 22–31 GHz, respectively. The gain of the high-frequency antenna array is better than 9.5 dBi at 28 GHz. The low-frequency antenna covers some practical 4G LTE bands from 740–960 MHz and 1.7–2.2 GHz bands. The measured results in both low and high frequencies agree well with the simulations.

Superdirectivity from arrays of strongly coupled meta-atoms

We explore the possibility of achieving superdirectivity in metamaterial-inspired endfire antenna arrays relying on the good services of magnetoinductive waves. These are short-wavelength slow waves propagating by virtue of coupling between resonant meta-atoms. Magnetoinductive waves are capable of providing a rapidly varying current distribution on the scale of the free space wavelength. Using dimers and trimers of magnetically coupled split ring resonators with only one element driven by an external source, we introduce an analytical condition for realising superdirective current distributions. Although those current distributions have been known theoretically for a good 60 years, this is the first time that a recipe is given to realise them in practice. Our key parameters are the size of the array, the resonant frequency and quality factor of the elements, and their coupling constant. We compare our analytical results for coupled magnetic dipoles with numerical results from CST simulations for meta-atoms of various shapes. The calculated bandwidth of 5 MHz for a dimer operating at 150 MHz indicates that, contrary to popular belief, superdirective antennas exist not only in theory but may have practical applications.

Compact Quad-Mode Planar Phased Array With Wideband for 5G Mobile Terminals

In this paper, a quad-mode endfire planar phased antenna array with wide scan angle and 1.2 mm clearance is proposed for 5G mobile terminals. The proposed antenna can obtain over 8 GHz of impedance bandwidth. In this paper, it is suggested to efficiently combine a multimode array element with different radiation patterns for each mode into a phased antenna array. In the array, similar and wide embedded radiation patterns are obtained for the all four modes. Furthermore, a coaxial to differential stripline transition is designed in this paper. The differential feeding structure is very compact and utilizes only MMPX connector and vias. The total scan pattern and coverage efficiency of the measured and simulated phased array antenna are calculated in the range from 25 to 33 GHz, and good agreement between measured and simulated results is observed. The mean coverage efficiency along the frequency range is very similar, but minor difference in variance of coverage efficiency is observed in the measurements. The coverage efficiency of around 50% for the threshold gain of 5 dBi is achieved in the chosen frequency range.

A Cavity-Backed Endfire Dipole Antenna Array Using Substrate-Integrated Suspended Line Technology for 24 GHz Band Applications

This paper presents a 1 × 4 cavity-backed endfire dipole antenna array based on substrate-integrated suspended line (SISL) platform. A double-side SISL (DSISL) self-packaged feeding network with irregular boundaries is designed for the array. By utilizing the DSISL feeding network, the radiation loss and substrate loss of the feed line are effectively decreased, thus efficiency of better than 91% is achieved. Instead of the conventional metallic cavity, the proposed cavity structure is realized by multiple substrate layers. A predominantly TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> aperture field is obtained by adjusting the sizes of the backing cavity. Measured results show that the proposed dipole antenna array has narrow beam widths in the E-plane and obtained 10 dB impedance bandwidth of 19.7%, i.e., from 22.77 to 27.75 GHz which can cover the 24 GHz automotive radar band (24.25-26.65 GHz). Moreover, front-to-back ratio of better than 26 dB, high gain of better than 14.1 dBi, and low sidelobe level of better than -15 dB are achieved over the automotive radar frequency band.

Synthesis of Large Endfire Antenna Arrays Using Convex Optimization

An innovative approach utilizing convex optimization to simultaneously conduct pattern synthesis and improve the matching of large-scale endfire antenna arrays is proposed in this paper. A fast full-wave analysis tool facilitates the computation of the necessary data for running the optimization routine and enables analysis on arrays with dimensions $100\lambda \times 6\lambda $ for the highest simulated frequency. Simulated results are provided for various array configurations of bowties, and the results show that improved matching can be obtained while maintaining a clear endfire far-field pattern analogous to the pattern obtained with the classical Hansen–Woodyard excitation. The spatial dependence on the amplitude of the optimized input waves in the antenna ports indicates that a considerable fraction of the input power is fed to the antennas at the array’s front, in the direction in which the main lobe is launched.

A Dual Linearly Polarized End-Fire Antenna Array for the 5G Applications

A dual linearly polarized antenna array with end-fire radiation of the 60-GHz band is proposed by combining two types of magneto-electric dipoles (ME-dipole), which operate in vertical polarization (V-pol) and horizontal polarization (H-pol), respectively. Based on the substrate integrated waveguide structure, two kinds of ME-dipole are placed closely by sharing the same metallic post wall between them, achieving an element space of 0.77λ0. Besides, mutual coupling between the close elements is numerically analyzed and then suppressed by making modifications to the antenna structure. The proposed dual-polarized element achieves bandwidths of 26% and 32% (|S11| <; -14 dB) for the V-pol and H-pol, respectively. A 1×8 element array is designed, fabricated, and measured. Good agreement is achieved between the measurement and simulation. For the V-pol excitation, a bandwidth of 21% is obtained and gain is up to 16.1 dB. For the H-pol excitation, the bandwidth is 18% and peak gain is 15.1 dB. Radiation patterns are stable over the operating frequencies with cross polarizations below -30 dB for both polarizations. The port isolation is very high above 45 dB. With all these advantages of dual polarization, end-fire radiation, stable gain, and high port isolation, the proposed array is a potential candidate for the future 5G applications.