Low-profile Wideband Research Articles

Low-profile wideband phased array antenna radiator with wide-angle beam scanning

Low-profile wideband phased array antenna radiator with wide-angle beam scanning

Wideband Dual-Feed Dual-Polarized Reflectarray Antenna Using Anisotropic Metasurface

In this letter, an anisotropic metasurface is proposed for independent phase control upon orthogonal linearly-polarized waves, and is then applied to implement a low-profile wideband dual-polarized reflectarray antenna (RA) operating in Ku-band by integrating the metasurface with two Vivaldi feed sources. This RA can collimate both primary beams into one narrow beam along broadside direction with dual-linear polarizations or circular polarization. The prototype is fabricated and the measured results indicate that it achieves peak gain of 24.5 dBi, peak aperture efficiency of 37.4%, 1-dB gain bandwidth of 15% for fixed broadside direction for both Vivaldi feed sources. The proposed method may have potential uses in applications of the multiplexing, demultiplexing, and full-duplex antennas.

High gain, high isolation, and low‐profile two‐element MIMO array loaded by the Giuseppe Peano AMC reflector for wireless communication systems

A low-profile printed dipole antenna (PDA) backed by a broadband Giuseppe Peano fractal artificial magnetic conductor (AMC) is introduced for wireless communications. A suggested PDA with a pair of microstrip dipoles excited by an E-shaped microstrip feedline is used to expand the bandwidth range of 5.5–6.96 GHz (S11 ≤ −10 dB). Then, the suggested Giuseppe Peano fractal AMC surface as a reflector of the antenna is inserted into the PDA to improve radiation efficiency. The PDA with the 4 × 4 Giuseppe Peano AMC array exhibits −10 dB measured impedance bandwidth from 4.25 to 7.10 GHz (50.2%) for the wireless local area network and worldwide interoperability for microwave access (WiMAX) applications. The suggested PDA with AMC compared to the PDA without AMC exhibits a size reduction of 50.5%, enhanced gain up to 8.2 dBi, and excellent impedance matching (at least −19 dB) with uni-directional radiation patterns. The novel AMC unit cell is realized based on the Giuseppe Peano fractal patch to operate at 6.10 GHz with an AMC bandwidth of 5.15–7.10 GHz (32%). Besides, by loading a 4 × 8 AMC reflector into the two-element array with diverse polarisations, a low profile wideband printed structure with enhanced radiation properties is achieved. The measured results show the broad bandwidths from 4.3 to 7.05 GHz for two elements with enhanced gains and good isolations between the elements (more than 28.5 dB) for multiple-input multiple-output (MIMO) systems.

Low-Profile Wideband Four-Corner-Fed Square Patch Antenna for 5G MIMO Mobile Antenna Application

A low-profile wideband four-corner-fed square patch antenna for fifth-generation (5G) multiple-input–multiple-output (MIMO) mobile antenna application is presented. The proposed antenna uses a single square patch to generate four uncorrelated waves over a wide band to cover 3.3–4.2 GHz (5G N77 band) with a low profile of 2.4 mm (0.03 λ at 3.75 GHz). Wideband operation is obtained by generating the half-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode and the quarter-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,1/2</sub> mode for each port. The half-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode is created by embedding two diagonal linear slots in the square patch. By further placing shorting pins along the patch's two centerlines, a square two-edge-shorted quarter-patch for each port to support the quarter-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,1/2</sub> mode is created, which combines with the half-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode to form a wide operating band. Details of the proposed antenna including the experimental results are presented.

Wideband Gain Enhancement of an AMC Cavity-Backed Dual-Polarized Antenna

A novel low-profile wideband antenna is proposed with high-gain, high-isolated, and dual-polarized properties. It consists of two mutually-orthogonal bowtie-shaped dipole radiators, four rectangular parasitic elements, and a cylindrical artificial magnetic conductor (AMC) cavity. By introducing parasitic elements, additional resonance is generated, and the bandwidth is widened. The gain is mainly improved by the cylindrical metallic wall and wideband AMC of the cavity. The AMC operates in ±90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> reflection phase band-gap bandwidth of 2.35-4.25 GHz, and its equivalent circuit model is developed to understand the working mechanism. The orthogonal placement of two dipole radiators ensures polarization diversity and high isolation. The impacts of various environmental conditions on antenna performance are investigated. To verify the concept of design and demonstrate its excellent performance features, a prototype is fabricated and measured. The proposed wideband antenna has a height of 0.18 wavelength at the center frequency. The measured -10-dB impedance bandwidth is from 2.16 to 3.96 GHz, where the realized gain is 8.34-10.96 dBi and the radiation efficiency is more than 81.8%. High isolation of > 28.65 dB and low envelop correlation coefficient (ECC) of < 2.74 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> are also achieved between antenna elements. It can be used in the base station for intelligent Internet of Vehicle (IoV) applications, covering the bands of WLAN, WiMAX, Bluetooth, LTE, and 5G sub-6 GHz.

A low profile wideband horizontally polarized omnidirectional printed loop antenna

This article presents a low profile horizontally polarized omnidirectional antenna in S-band. The antenna adopts a printed coupling loop structure which consists of an inner ring radiator, an outer ring radiator and an 8-channel power divider. The inner ring radiator is composed of eight symmetrical arc-shaped branches, which are excited by power divider with constant amplitude and phase. Hence, these branches produce a uniform current in the same circumferential direction. The bandwidth of the antenna is broadened by loading an outer ring radiator which is feed by energy coupling. The outer ring is also divided into eight segments to ensure the same current direction as the inner ring. Measured results show that the frequency range for |S11| < −10 dB is from 2.17 to 2.86 GHz (27.4%), and the gain variation in azimuthal angle is less than 2.7 dB in the same band. Meanwhile, the height of the antenna is only 0.025λ0.

Low‐profile wideband patch antenna with pattern diversity using custom‐designed feeding schemes

A low-profile wideband patch antenna with pattern diversity is proposed in this paper. In our design, custom-designed feeding schemes are utilized to substitute for conventional power dividers beneath the ground plane, thus selectively generating the broadside or conical beam and introducing additional resonant modes. Then, by placing two novel feeding schemes orthogonally to realize pattern diversity, a new resonant mode is successfully excited, which fully makes use of the configuration of the two-port antenna. Moreover, for reallocating radiating modes, an array of four shorting pins is introduced to push up the resonant frequency of each first desired resonant mode, which enhances the overlapped impedance bandwidth. Finally, the proposed antenna is designed, fabricated, and measured. The measured results show that the antenna achieves a broad overlapped impedance bandwidth of around 28.5% ranging from 2.11 to 2.81 GHz. Meanwhile, the peak-measured gain is 7.0 dBi for the conical beam and 9.9 dBi for the broadside beam, while an isolation of 23 dB is also realized. Most importantly, novel feeding schemes still maintain the low-profile property of around 0.066 λ0 (λ0 is the free-space wavelength at 2.46 GHz).

Low-Profile Wideband Millimeter-Wave Circularly Polarized Antenna With Hexagonal Parasitic Patches

A low-profile wideband circularly polarized (CP) millimeter-wave (mm-Wave) L-shaped dipole antenna with hexagonal parasitic patches is presented in this letter. Two types of hexagonal parasitic patches are placed round the rotationally symmetrical L-shaped dipole to enhance the impedance and axial ratio (AR) bandwidth. Based on this antenna element, a substrate integrated waveguide-fed 2 × 2 subarray with sequential rotate feeding technique is designed to further improve AR bandwidth. Finally, a 4 × 4 CP array is designed to further enhance the gain. The measurement shows the proposed array can achieve the impedance bandwidth of 27.7%, the AR bandwidth of 28.5%, and the peak gain of 17.85 dBic while maintaining a lower profile. Therefore, the design scheme will be suitable for 5G mm-Wave communications and satellite communication systems.

Novel Metasurface Lens-Based RF Sensor Structure for SAR Microwave Imaging of Layered Media

In this article, a novel low profile wideband highly directive gradient refractive index (GRIN) metasurface (MS) lens is designed to improve the gain of the X-band waveguide-based RF sensor system for the microwave imaging application. The proposed GRIN MS lens consists of several layers comprising the core layers at the centre and the impedance matching layers around both sides of the core layers. The core layers and the impedance matching layers of the proposed lens are based on a novel three-layer unit cell, wherein a single rectangular ring and two C-shaped strips are printed on both sides of the middle layer. The cross-sectional dimensions of the proposed unit cell varying across the lens aperture to realize the refractive index profile gradually varying from 1.5 at both edges to 7 at the centre. After designing the GRIN MS lens, an attractive microwave technique using a combination of piecewise synthetic aperture radar (PW-SAR) scheme and a time-domain algorithm for imaging of layered media is proposed. The use of a noniterative time-domain technique in the present situation basically helps to retrieve the electrical and physical properties of each layer, which are inherently required for the SAR algorithm to obtain a focused image of the target object buried in the layered media. The experimental results show that the integration of the proposed GRIN MS lens with the RF waveguide sensor improves the overall gain by the maximum value of 10.5 dB, thereby enhancing the spatial resolution of the target object in a layered media using the modified SAR imaging scheme.

Design and experimental validation of a low-profile wideband metamaterial absorber by characteristic modes analysis

A wideband microwave metamaterial absorber (MMA) with a relative absorption bandwidth of 127.3% and the actual thickness of only 0.084λL at the lowest operating frequency is presented in this paper. Compared with other MMAs, the characteristic modes theory is proposed to guide our design and shows an excellent performance with wider bandwidth, lower profile, and fewer modes. Characteristic modes analysis (CMA) shows a wideband modal significance (MS) over 0.707 (MS > 0.707) by exciting one mode from 1.38 GHz to 6.44 GHz, suggesting that the MMA achieves a wideband absorption performance by exciting only one mode. According to the surface current distributions, the natural modes’ current under the normal direction has the same direction with modal current shows that the mode has been successfully excited. The input impedance also illustrates a wideband match characteristic with free space. A prototype has been designed, fabricated, and measured. Measurements and simulation results show a wideband absorption with a high absorption rate of over 90% range from 1.44 to 6.32 GHz. Our design demonstrates that CMA is an effective method to design absorbers.

High-gain low-profile circularly polarized patch antenna for universal RFID reader application

It is known that for a microstrip antenna, if the height of the antenna is strictly limited, then the bandwidth is narrow. A way to solve this problem is to combine two modes. However, for almost all the two-mode resonant patch antennas reported, the height of the antenna conflicts with the frequency ratio of the two modes. The smaller the frequency ratio is, the higher the antenna. In this paper, a detailed mode analysis is performed, and a comprehensive mode shift design method is established. A dual resonant patch antenna with any frequency ratio can be designed. Guided by this method, a low-profile wideband patch antenna with a size of only 0.6λ0 × 0.6λ0 × 0.05λ0 for the universal RFID reader (840-960 MHz) is designed. The simulated and measured results show that a low-profile is achieved for universal RFID reader antennas.

Development of a wideband hexagonal SIW cavity-backed slot antenna array

In this paper a novel wideband hexagonal cavity-backed slot antenna array using two sots including Resonant Narrow Slot (RNS) and Non-Resonant Wide Slots (NRWS) based on Substrate Integrated Waveguide (SIW) is proposed. First, a single element low profile wideband linearly polarized cavity-backed antenna using two slots is designed and analyzed. The antenna bandwidth is increased by NRWS, which makes both hybrid modes of TM110 and TM210 close to each other to be excited. Then, to improve antenna gain, an array of two elements cavity-backed slot including is designed and investigated. Moreover, in order to match the input impedance over the operating bandwidth, a special power divider using tapered line is introduced. The proposed single element and antenna array is made and successfully tested. The simulation and measurement results are in a good agreement for both single and antenna array. The measured gain and impedance bandwidth are 12 dBi and 14% respectively for the designed array.

A Low-Profile Wideband Microstrip Antenna With Pattern Diversity Based on Composite Right/Left-Handed Transmission Lines

A low-profile wideband microstrip antenna is proposed based on the structure of composite right/left-handed transmission lines (CRLH TLs). The dimensions of the proposed antenna are 64 × 64 × 4 mm. The impedance matching bandwidth is 5.05-5.92 GHz (16.5%). The unit cell of the CRLH TLs is a mushroom structure. Several different resonant modes with different radiation patterns are excited to obtain the pattern diversity. Particularly, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> modes are merged to realize a wideband performance with broadside radiation pattern, whereas the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode is used to realize a conical radiation pattern. The simulations and measurements are in good agreement, and the envelope correlation coefficient shows that the proposed antenna owns an excellent diversity performance.

Low-Profile Wideband Millimeter-Wave Antenna-in-Package Suitable for Embedded Organic Substrate Package

An antenna-in-package solution is proposed based on embedded organic substrate package. RF front-end module is integrated with an antenna considering the electrical and thermal performance, dimensions, manufacturing as well as cost. A millimeter-wave low-profile wideband antenna is designed, analyzed, and verified experimentally. The radiator of the proposed antenna consists of three groups of patches with different dimensions and it is fed by a stripline through an aperture etched on a ground plane. Input impedance analysis is utilized to accurately explore resonance characteristics of the aperture-coupled radiator. As a comparison, characteristic mode (CM) analysis is applied to calculate CMs of the source-free radiator. Different results obtained by two methods are analyzed. Over the operating band, three resonance modes, respectively, dominated by quasi-TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode of different patches are excited in turn, which contributes to wideband performance. Measured results demonstrate that the proposed antenna with only 0.039λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is wavelength of 28 GHz in free space) substrate thickness achieves an impedance bandwidth ( |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | ≤ -10 dB) of 37.5% (22.8-33.3 GHz). The peak gain is up to 10.7 dBi and 3 dB gain bandwidth is 23.7% (25.7-32.6 GHz), while 6 dBi gain bandwidth is 33.6% (23.5-33 GHz).

Wideband Beam-Switchable Antenna Loaded With Dielectric Slab for 5G Applications

A novel low-profile wideband beam-switchable antenna for 5G applications is proposed in this letter. The antenna consists of two parts: a crossover with slots based on the substrate integrated waveguide (SIW) and a dielectric slab with a high dielectric constant. Four centrosymmetric slots are etched on the top layer of the SIW crossover. A crossed dielectric slab is overlaid on the SIW forming a dielectric image slab waveguide, which is well excited by the slots to transmit TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> modes (or surface wave) due to the high similarity of the electric field distribution, which generates the tilted radiation beam. Owing to the novel crossover configuration and four antenna ports, there are four transmission directions of the electromagnetic waves, which result in four tilted beams. The antenna operating mechanism and the design procedure are illustrated in detail. Measured results show a -10 dB impedance bandwidth of 31% from 4.25 to 5.82 GHz and a gain of 6.2-9.1 dBi over the operating band. The antenna shows a stable and switchable pattern. The overall antenna size is 1.134 × 1.134 × 0.085 λ (λ is the free space wavelength at 4.25 GHz). The proposed antenna features a novel working principle, a low profile, good radiation performance, which is well suited for 5G NR indoor applications.

Bandwidth enhancement of low-profile slot antennas using theory of characteristic modes

In this article, we have presented a novel design of wideband slot antennas using theory of characteristic modes and theory of mode coupling. First, the narrow slot antenna, etched in a finite ground, is investigated with combined characteristic modes. While most of resonant slot antennas show narrowband operation, the modification of modal properties using structural manipulations is studied in detail and this analysis helps in the design of low-profile wideband slot antennas. Characteristic mode analysis explains the physical insight of resonance and radiation mechanism of proposed wideband slot antennas. Bandwidth enhancement techniques of these slot antennas are presented and validated with measured results of wideband slot antennas. This approach gives a large fractional bandwidth of >35% and high gain of >3 dB.

Low profile wideband circular patch antenna surrounded by mushroom‐type structure

A novel low profile wideband circular patch antenna is proposed for millimetre-wave applications. Seven mushroom units are uniformly placed along with the edge of the circular driven patch. Two resonant modes, TM 10 mode and quasi-TM 30 mode, are generated by the driven patch and mushroom-type structure, respectively. These two modes will move in proximity to each other by optimising the size and location of mushroom-type structure, resulting in wideband performance. Compared with our previous work, the proposed antenna owns the advantage of low profile and rotational symmetric structure. Therefore, the radiation performance is improved. Measured results show that the impedance bandwidth of 26.4% from 12.2 to 15.9 GHz is obtained with a low profile less than 0.047 λ 0 .

Low‐profile millimetre‐wave wideband microstrip antenna with parasitic patch arrays

A millimetre-wave low-profile wideband microstrip antenna is proposed. To widen impedance bandwidth and achieve stable large gain simultaneously, coplanar parasitic patch arrays are arranged on both sides of a microstrip patch fed by a coaxial probe. Double slots are etched on the microstrip patch to reduce H-plane cross-polarization levels. Zero-phase-reflection analysis with Floquet-port model is proposed to predict resonant frequency of the parasitic patch arrays. Resonance modes excited is verified according to input impedance with an ideal probe. Two adjacent broadside resonances respectively dominated by the quasi-TM10 mode of the microstrip patch and quasi-TM30 of the parasitic patch array are excited in turn. The proposed antenna with a dimension of 1.06 × 1.06 × 0.024 λ03 (λ0 is the wavelength of 29 GHz in free space) realizes 15% (27–31.35 GHz) impedance bandwidth for |S11| ≤ −10 dB. Realized peak gain is up to 9.26 dBi and 2-dB gain bandwidth is 15.7%. H-plane cross-polarization levels within 3-dB beamwidth are less than −14 dB, and back radiation levels are less than −17.9 dB.

Low-Profile Wideband Omnidirectional Antenna for 4G/5G Indoor Base Station Application Based on Multiple Resonances

A novel low-profile antenna with monopole-like radiation characteristics is proposed for 4G/5G indoor micro ceiling base station applications. The proposed antenna consists of a top loading disk, two polygonal copper sheets, which are orthogonally intersected, and a circular printed circuit board (PCB), which serves as the ground. A prototype is fabricated and measured. The proposed antenna has a very low profile of 0.057λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is the free-space wavelength at the lowest frequency of the operating band. A fractional bandwidth of 85.3% ranging from 1.6 to 3.98 GHz with |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -10 dB is achieved, which covers the 4G LTE band and 5G N78 band. The proposed antenna demonstrates consistent monopole-like radiation pattern in the whole working band, which is very suitable and well designed for indoor ceiling base station applications.

A Wideband Pattern Diversity Antenna With a Low Profile Based on Metasurface

In this letter, a low-profile wideband pattern diversity antenna based on metasurface (MTS) is proposed. Initially, based on the theory of characteristic mode (TCM), the two adjacent intrinsic modes, which correspond to the broadside and conical radiation pattern, respectively, are exploited to realize a wideband pattern diversity characteristic under a low profile. Then, by analyzing the modal current distribution on the MTS, the optimal locations, orientations and relative phases of the four L-shaped feeding probes are determined to excite the above two modes. However, the in-band high-order modes (HOMs) introduced by the feeding structure will deteriorate the radiation pattern. Therefore, chamfering corners on the MTS is used to suppress the HOMs for radiation pattern improvement. Finally, by combining TCM and MTS, the modes are manipulated to achieve a pattern diversity antenna with an extremely low profile of 0.06 λ0 (the free-space wavelength at the center frequency) and an isolation of better than 38 dB, which also maintains an operating bandwidth of 20.24%. Based on these excellent performances, the proposed antenna is an attractive solution for pattern diversity applications requiring low profile, especially in unmanned aerial vehicle communications.