Antenna Feed Research Articles

Design and Realization of Wearable Textile Slotted Waveguide Antennas.

The design of wearable antennas presents a challenge from multiple perspectives, as they must meet technical requirements and satisfy safety standards while also being suitable for integration into clothing and aesthetically pleasing. In recent years, the development of conductive fabrics has, in many ways, allowed for significant progress in the manufacturing of wearable antennas, and in previous work, we developed textile slotted waveguide antennas using conductive textiles and traditional sewing processes. However, various aspects of the design and realization of such antennas remain challenging. In particular, this work investigates the issue of using foam-based molds, which enables the realization of thin, flexible, wearable antennas, as well as the issue of antenna feed, specifically the transition from a classic coaxial transmission line to a waveguide. The design of the transition was focused on simplicity and robustness, due to which we limited the number of degrees of freedom in the design process in order to achieve a structure suitable for mounting on textile waveguide antennas. In addition, the antenna design procedure and the body-channel model were considered in order to optimize the performance of the antennas and the wireless body-centric system itself. Several prototypes of different kinds were developed in the 5.8 GHz ISM band, confirming the feasibility of the proposed concepts through experimental results.

A Low-Cost Multibeam Switching Antenna Using Reconfigurable Hybrid Metasurface for Beamforming Applications.

In this paper, we proposed a multibeam switching antenna based on a low-cost reconfigurable hybrid metasurface applied for beamforming systems. The antenna consists of two parts: a microstrip feed antenna and a transmission hybrid metasurface. The latter is composed of three types of units with different amplitude and phase responses to electromagnetic waves so as to control the beams of the feed antenna. Sixteen PIN diodes are arranged in the metasurface with a simple bias network. When two different direct-current voltages are applied to the PIN diodes, the antenna can dynamically switch between two beams and four beams. For demonstration, the proposed antenna is fabricated, and the measured results show that the antenna operates at 9.07-9.42 GHz (-10 dB bandwidth) with a total size of 1.80λ0 × 1.52λ0 × 0.22λ0 (λ0 corresponds to the wavelength of 9.28 GHz in free space). With the merits of a compact structure, low cost and good radiation performance, the proposed design is suitable for beamforming applications.

Compact 4-Port Wideband MIMO Antenna with Connected Ground, High Diversity Performance and Dual-Notched Filters

This paper reports multiband microwave access multiple-input-multiple-output (MIMO) four-port antenna for UWB-X (3.10–12.0 GHz) band applications radiating electromagnetic energy with dual notched bands and compact size of 0.68λo × 0.92λo. Two notched bands are introduced on the radiating patch of the antenna and microstrip feed line mitigating Wireless-Local-Area-Network (WLAN: 5.11–5.88 GHz) & Downlink-Uplink Satellite (DUS: 7.28–8.36 GHz) interference. The technology reported includes simulated results and is validated by comparing the measured results of the 4 × 4 MIMO antenna. The mutual coupling between the radiating patch is suppressed below −15.0 dB which is achieved by interconnecting the ground and placing a cross-shaped parasitic patch between the radiating elements. The proposed MIMO antenna offers maximum gain efficiency of 5.92dBi & 0.95 (95%) respectively. The diversity parameters (ECCmax = 6 × 10−4, DGmax = 9.99 dB, TARCmax = −27.0 dB, CCLmax = 0.015b/s/Hz, MEG−3.0 dB) are in the permissible range given by International Telecommunication Union (ITU) for information and communication technology.

Broadband inhomogeneous lens with conical radiation pattern

This manuscript presents a lens antenna with simultaneous broadside and conical beams. The lens is designed for the Ku band using the ray inserting method. The proposed conical radiation pattern is broadband due to good matching with the source and surroundings. The simulation is conducted using the CST microwave studio solver. Instead of complex antenna shapes used in other works, a simple circular patch ring and RF connector are used as the lens feed to generate broadside and omnidirectional conical patterns, respectively. To validate the performance of the designed lens and its two-port feed antenna, the lens structure is realized and fabricated using the 3D printing method. Polyethylene terephthalate glycol (PETG) plastic material is utilized for constructing the lens in this work. The electromagnetic characteristics of PETG in the Ku band are accurately measured. The results of simulations and experiments demonstrate the good performance of the designed lens over a wide frequency bandwidth. The advantage of this designed structure over other works is its high gain and broad bandwidth.

Beam Steering 3D Printed Dielectric Lens Antennas for Millimeter-Wave and 5G Applications.

Two types of cost-efficient antennas based on dielectric gradient index dielectric lens have been designed for 5G applications at 28 GHz. The first is a linearly polarized flat lens antenna (LP-FLA) for terrestrial 5G communications. The second is a novel circularly polarized stepped lens antenna (CP-SLA) for 5G satellite services. An efficient design method is presented to optimize and conform the lens topology to the radiation pattern coming from the antenna feeder. The LP-FLA is fed by a traditional linearly polarized pyramidal horn antenna (PHA). The CP-SLA is fed by an open-ended bow-tie waveguide cavity (BCA) antenna. This cavity feeder (BCA), using cross-sections with bow-tie shapes, allows having circular polarization at the desired frequency bandwidth. The two types of presented antennas have been manufactured in order to verify their performance by an easy, low-cost, three-dimensional (3D) printing technique based on stereolithography. The peak realized gain value for the flat (LP-FLA) and stepped (CP-SLA) lens antennas have been increased at 28 GHz to 25.2 and 24.8 dBi, respectively, by disposing the lens structures at the appropriated distance from the feeders. Likewise, using an array of horns (PHA) or open-ended bow-tie waveguide cavity (BCA) antenna feeders, it is possible to obtain a maximum steering angle range of 20° and 35°, for a directivity over 15 dBi and 10 dBi, in the planar and stepped lens antennas, respectively.

Examination of Mid-Infrared Photon Detection by Hot Electron Bolometer With Twin Slot Antenna

As a high-speed and sensitive mid-infrared (MIR) photon detector, we developed a MIR superconducting hot electron bolometer (MIR-HEB). The MIR-HEB consists of a twin-slot MIR-wavelength antenna and a small Nb/NbN superconducting strip located at the antenna's feeding point. To prevent the HEB from latching, a parallel shunt resistor was added. For detector evaluation, a continuous-wave quantum cascade laser with a wavelength of 4.57 μm was used as the source of MIR light. A constant bias current was applied near the HEB critical current during the detector operation. Upon illumination with MIR light, numerous voltage pulses with a width of approximately 4 ns were observed. Furthermore, it was demonstrated that the pulse count rates were nearly proportional to the incident power over a two-order magnitude range. We conclude that MIR-HEB achieved MIR photon detection based on this result. Also confirmed were the polarization dependences attributed to the antenna's operation.

Energy-Efficient Ground Base Station Antenna Array System for Wireless Back-Hauling and Two State Charging of Drone Base Stations

A ground base station (GBS) antenna array system (AAS) geometry and feed technique are proposed for 360 degree azimuth beam scan, elevation beam scan, azimuth beam-width control, elevation beam-width control, and in existing AASs these four capabilities do not coexist. Firstly, the results confirm that the number of active radio-frequency (RF) switches in the proposed AAS feed network is reduced by more than 99 %, and the AAS achieves a power consumption reduction of up to 50 % without fully connected (FC) architecture and 35 % with FC architecture compared to the existing AAS. Also, an independent GBS AAS azimuth and elevation plane beam-width control can be achieved from 65 to 0.01 degrees which makes it suitable for GBS-assisted wireless back-hauling plus wireless charging of unmanned aerial vehicle base stations (UAV-BSs), dynamic GBS sectorisation order control, and millimeter wave beam tracking. Also, a parallel concurrent UAV-BS battery charging configuration with power source swap capability is proposed to charge UAV-BS using the GBS back-haul and onboard power amplifier (PA) system as the power sources. The results show that the proposed charging configuration improves hovering time by 180.7 % compared to the existing onboard PA system configuration for battery charging. Furthermore, the proposed charging configuration can recharge the battery of the inactive state UAV-BS to increase the state of charge of two 16 Ampere hour batteries to 80 % in 180.13 minutes, and UAV-BS’s inactive state charging was not proposed in the existing onboard PA system configuration for UAV-BS’s battery charging.

Additively Manufactured Metal-Only Waveguide-Based Millimeter-Wave Broadband Achromatic Reflectarrays

This communication demonstrates additively manufactured metal-only waveguide-based tri-band and broadband reflectarray antennas. The unit cell (UC) is implemented by cascading two metal waveguide sections with different cut-off frequencies (fc1 and fc2 (fc1< fc2)). When illuminated with the feed antenna, the reflectarray provides different reflection paths to compensate for the spatial phase delay over triple bands, fl (fl<fc1), fm (fc1 <fm<fc2), and fh (fh>fc2). By tuning the length of the two waveguide sections and vertically adjusting the position of the UC, the phase-shifting over the triple bands can be independently controlled. In addition, because of the sharp selectivity of the waveguide, a reflectarray with the broadband achromatic feature can be achieved by properly selecting the tri-band’s frequency and the cut-off frequency of the waveguides. A tri-band reflectarray centering at 25 GHz (low-band), 32 GHz (middle-band), and 37 GHz (high-band) is designed firstly to demonstrate the independent beam shaping over triple bands. Then, two waveguide-based reflectarrays with the broadband achromatic feature are designed, which show stable performance from 22 GHz to 38 GHz with a relative bandwidth of 53.3%. The prototypes are conveniently fabricated using additive manufacturing, and their performance is experimentally verified.

Adaptive triple-fed antenna and thinned RF-chip integration into ultra thin flexible polymer foil

AbstractAttaching a wireless transmission system comprising a radio frequency (RF)-chip and a dipole antenna to dielectric material of largely different permittivity leads to strong variation of the antenna feed impedance. Due to the severe impedance mismatch between the RF-chip and the antenna, the performance of the system may deteriorate drastically. The proposed antenna provides three feed points, which show respective feed-point match to 100 Ohm balanced feeds for three different dielectric environments (free-space and half-spaces of permittivity 4 and 42, respectively). Thereby, the RF-chip incorporates three 100 Ohm balanced output ports that are connected to the antenna from whom only one can be selected to provide the output signal. The respective other two output ports are shorted by an internal switching circuit that is controlled by external DC voltages. The measurement of the reflection coefficient of the stand-alone antenna and the chip agree well with the simulations, allowing to interconnect these two components. Further, the radiation pattern of the whole system is measured for two different scenarios showing good functionalities.

A high‐performance dual‐polarized corrugated horn for a compact antenna test range system

AbstractA high‐performance dual‐polarized horn antenna for a 5G millimeter wave compact antenna test range system (CATR) is proposed in this article. The feed antenna is mainly composed of a double‐ridged waveguide junction orthomode transducer (OMT), mode converter, and corrugated horn antenna. Among them, the OMT is the key device for the feed antenna to achieve dual polarization characteristics, and adopts a modular design method to apply the multi‐section impedance transformer in the vertical and horizontal polarization channels with good transmission characteristics. The corrugated horn antenna generates a symmetrical radiation pattern mainly in six corrugated slots. The proposed dual‐polarized corrugated horn antenna impedance matching bandwidth (VSWR &lt; 2) is 24–50 GHz. Moreover, the measured gain is 10–12 dBi, and the measured cross‐polarization level is less than −30 dB within the operating frequency range. Meanwhile, the half‐power beamwidth radiation pattern in the whole operating band has a good symmetry and the beamwidth in both E‐ and H‐plane remains stable. As a practical application, the designed antenna is used as the feed of the CATR system. The measured results show that the amplitude distribution in the quiet zone (QZ) is within ±1 dB, the phase distribution is within ±8°, and the cross‐polarization isolation is better than 27 dB. The performance of the QZ is conducive to the use of the CATR system.

A Novel Wideband Tightly Coupled Dual-Polarized Reflectarray Antenna

In this communication, a novel tightly coupled dual-polarized reflectarray antenna is presented. The antenna consists of a dual-polarized feed antenna and a wideband dual-polarized reflecting surface. The reflecting surface is composed of dual-polarized tightly coupled unit cells. Each unit cell contains two types of elements, of which the polarizations are perpendicular. Each element contains a dipole and a delay line. For one polarization, the reflecting surface consists of 13 × 34 elements, while there are 26 × 11 elements on the reflecting surface for the other polarization. The feed antenna is a wideband dual-polarized horn antenna. The phase error distribution on the reflecting surface is analyzed as well. To verify the design, a prototypical tightly coupled dual-polarized reflectarray antenna operating from 3 to 8 GHz is simulated, manufactured, and measured. The simulated results are in good agreement with the measured results. In the working band, the radiation patterns of the proposed reflectarray antenna are stable.

Broadband, Low-Profile, Planar Reflectarray Antenna Based on an Achromatic Metasurface

This paper presents a broadband, low-profile, and planar reflectarray antenna based on an achromatic metasurface. The achromatic metasurface has advantageous broadband focusing capabilities compared to conventional reflectarrays. Six types of unit cells offering versatile phase responses are employed to design an achromatic metasurface optimized by a convolutional algorithm. A broadband achromatic reflectarray antenna with a diameter of 270 mm is simulated, fabricated, and tested. The test results agree well with the simulated results. Notably, the 3-dB realized gain of the reflectarray antenna reaches a fractional bandwidth of 58.2% at a range of 8.9 GHz to 16.2 GHz. Furthermore, the reflectarray antenna significantly enhances the feeding antenna’s gain from 7.3 GHz to 17 GHz. The reflecting metasurface also has a low profile of 0.11 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> is the wavelength in free space at 7.3 GHz. With excellent broadband performance, high gain, low profile and ease of fabrication, the developed reflectarray antenna serves as a promising device for long-distance integrated communication systems.

Triple-Mode Resonant Backfire Feed Antenna With Nearly Equal E-/H-Plane and Inverse Taper Patterns

A design approach to triple-mode resonant feed antenna is advanced for parabolic reflector antenna system. The antenna is composed of a slit-loaded 1.5-wavelength sectorial dipole, a primary corner reflector, and an auxiliary circular reflector. The corner angle of the primary reflector can be employed to properly narrow down the H-plane half-power beam width (HPBW), while with the E-plane one rarely affected, such that equal E-/H-plane characteristic can be yielded accordingly. Unlike traditional backfire antennas, high-order resonant modes are employed to generate inverse taper radiation pattern at the high frequency band. As is numerically demonstrated and experimentally validated, the corner angle of the primary reflector can be eventually determined as 45∘. The antenna exhibits an impedance bandwidth of up to about 79.7%, and a nearly equal E-/H-plane bandwidth of up to about 29.4%. Average HPBW of about 65∘, gain up to about 8.9 dBi with fluctuation of less than 1 dB can be achieved within the equal E-/H-plane bandwidth. The inverse taper radiation pattern at the high frequency band can provide effective edge illumination and uniform aperture field distribution in parabolic reflector antenna systems.

A Triple-Band Uni-Cavity Fabry–Perot Cavity Antenna With Hybrid Excitation Modes

A novel methodology realizing multiband Fabry-Perot-Cavity Antenna (FPCA) is proposed. Different from single transmission-mode (T-mode) or reflection-mode (R-mode) FPCA, the R+T-mode FPCA employs hybrid excitation modes to the same FPC, reducing the requirement for multiband high-quality feed antennas. To verify this methodology, a triple-band FPCA integrated by two R-mode ones, operating at the middle and the high bands, and a T-mode one working at the low band is designed. A triband partially-reflective-surface (PRS) offering bidirectional asymmetric transmission for middle and high bands, and partial reflection for the low band, is proposed. Meanwhile, a triband artificial magnetic conductor is designed to fulfill the in-phase bouncing condition in a low-profile uni-cavity for all bands. One inter-cavity feed and two external ones are utilized to complete the hybrid excitation of the FP cavity. Finally, a proof-of-concept prototype is fabricated showing -3 dB gain bandwidths of 7.0% (3.02-3.24 GHz), 16.9% (5.38-6.37 GHz), and 10.0% (10.31-11.40 GHz). Beam-scanning ranges of ±35° and ±30° are also obtained for the middle and the high bands. The proposed methodology may readily realize an FPCA of even more frequency bands with limited aperture size and a low-profile resonant cavity.

Design and analysis of Minkowski fractal antenna for wideband THz frequency tuning/multiband operation in a MIMO antenna system

The proposed Minkowski fractal antenna design achieves wideband and continuous frequency tuning in a multiple-input and multiple-output (MIMO) antenna system. By manipulating the fractal geometry of the unit antenna element, the resonance frequency of the antenna can be adjusted simply by changing its electrical length. The Minkowski fractal operator generates an increasing current path, resulting in a leftward frequency shift as the antenna side length increases with each iteration. In the first iteration, the proposed fractal antenna demonstrated a 97.9% continuous frequency shift from 0.204 to 0.404 THz with maximum return loss values of −31.23 and −21.6 dB, respectively. In the second iteration, a 38.6% continuous resonance frequency shift from 0.413 to 0.578 THz was achieved with return loss values of −18.22 and −40.47 dB, respectively. The maximum tunable bandwidths of the first and second iterations were approximately 0.2 and 0.16 THz, respectively. The proposed correlation between the dimensions of a single antenna and its resonance frequency provides the foundation for designing and implementing MIMO antenna systems in high-speed wireless devices, cognitive radio, and other multiband MIMO applications. A 2 × 2 MIMO antenna system has been designed from the results of the proposed single antenna to achieve multiband operation or frequency tuning through selective switching of the antenna feed.

A Fabry–Perot antenna using a frequency selective surface layer with wideband and Low RCS for Mm-wave applications

In this article, a Fabry-Pérot cavity antenna operating in the K-band is introduced, offering wideband, high gain with low RCS properties. The design consists of a patch antenna serving as a feed antenna and a bianisotropic frequency selective surface (FSS) layer incorporated to create a Fabry–Perot antenna for expanding the bandwidth, intensifying the gain, and minimizing radar cross-section (RCS). The proposed Fabry–Perot antenna is fabricated and measured, showing good agreement between simulated and measured results. The results show an impedance bandwidth of 23.6 % and a 3-dB gain of 14.1% at the center frequency of 28 GHz.

Metamaterial lenses for monostatic and bistatic 77 GHz radar systems

AbstractMetamaterial lenses are appealing thin alternatives to conventional dielectric lenses. In this contribution we describe their design and application in two exemplary 77 GHz automotive radar sensors operating in monostatic and bistatic modes. The frontends are built around commercially available MMICs and small feed antennas are used in coordination with the six-layer printed circuit board-based realizations of metamaterial lenses. The design follows the principles of dielectric lenses, while the required local phase shift is obtained from a set of metasurface bandpasses. Their design uses a novel interpolation procedure to extract layout parameters for a given phase shift. Despite the small structural sizes due to the high frequency, the fabricated frequency-selective surfaces show very good performance in the required frequency range. Verification measurements were conducted on single bandpasses as well as on metamaterial lenses mounted on the radar frontend. The results agree very well with the simulation and confirm the applicability of thin lenses operating at mm-wave frequencies for automotive radar applications.

Broadband high‐gain low‐temperature cofired ceramic substrate integrated cavity antenna array based on high‐order mode for W‐band applications

AbstractA broadband substrate integrated cavity (SIC) antenna array based on high‐order mode is proposed for low‐temperature cofired ceramic (LTCC) integrated systems in W‐band. To improve the gain of antenna element, a large SIC is adopted to work in high‐order mode, which also avoid using excessive vias and reduce the process complexity. Two parasitic patches are loaded on the high‐order mode SIC to remove the reverse E‐field in the open aperture, leading to a high‐gain broadside radiation. The high‐order‐mode SIC antenna element is fed by high‐order TE20‐mode substrate integrated waveguide (SIW), rather than regular TE10‐mode SIW. The simplified feeding network with TE20‐mode SIW is also designed with wideband performance, further enhancing the fabrication robustness of antenna array. To validate the proposed high‐order mode‐based antenna element and feeding network, a W‐band 2 × 4 antenna array is designed as an example using LTCC technology. The measured return loss is better than 10 dB from 81.1 to 98.1 GHz (19% bandwidth) with a maximum gain of 18.3 dB at 94 GHz. The proposed antenna array has great potential in millimetre‐wave and terahertz LTCC integrated applications.

A Fully Symmetrical Uni-Planar Microstrip Line Comparator Network for Monopulse Antenna

In this letter, a fully symmetrical uni-planar comparator network is proposed for monopulse antenna feeding. To break through the fundamental limitation of a conventional 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> coupler (crossing between input and output ports and amplitude imbalance), a novel symmetric ports coupler is designed by cascading two identical 90 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> couplers with two-phase delay lines, where the total phase delay of two lines is 180 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> . To realize in planar structure, a zero-phase delay planar crossover is designed to resolve signal crossing between two stage couplers in a comparator network. To verify our design concept, a prototype monopulse array operating at 5.7 GHz is designed, fabricated, and measured, and results are aligned well with simulation and theory.

Compact substrate‐integrated waveguide filtering multiple‐input multiple‐output magnetic dipole antenna with high selectivity and high isolation

AbstractA compact substrate‐integrated waveguide (SIW) filtering multiple‐input multiple‐output magnetic dipole antenna with high selectivity and high isolation is proposed. Each filtering antenna element contains a SIW cavity, a half‐mode SIW cavity, and a magnetic dipole antenna with backed ground. Meanwhile, the SIW cavity and the half‐mode SIW cavity are vertically connected through magnetic coupling, and second‐order filtering frequency responses can be obtained. Owing to the cross‐coupling between the feeding line and antenna, two radiation nulls can be created to realize high selectivity. Based on the radiation mechanism of the magnetic dipole antenna and polarization diversity, high isolation can be obtained. The measured isolation and the envelope correlation coefficient are greater than 24 dB and less than 0.004, respectively.