High‐gain omnidirectional patch antenna for conformal application based on near‐zero‐index metamaterials

An investigation of novel techniques in the designing of a low profile, horizontally polarized omnidirectional (HPO) patch antenna with omnidirectionality in the H-plane using a defected ground structure is presented in this study. The HPO patch antenna is designed by sequentially etching four rectangular and four open diagonal slots symmetrically on the patch and the antenna's ground plane. It creates four quarterwavelength open stubs that produce an in-phase circulating current on both the ground and the patch. Narrow bandwidth is achieved by using the four quarter-wavelength open stubs and by printing sequential slots only on the ground. Another set of four quarter-wavelength shorted stubs is achieved by sequentially etching four rectangular and open diagonal slots on the patch to resonate with another frequency and to increase the bandwidth by merging these two resonance frequencies. Combining these two resonance frequencies covers the applications of 2.39–2.52 GHz WiFi bands. The overall dimension of the proposed antenna structure is 0.32 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.32 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.006 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> with 5.51% bandwidth and moderate gain of 2.2dBi and roundness within 1 dB in the azimuth plane.

In this paper, a beam switching antenna with a novel active frequency selective surface (AFSS) is proposed at 5.2 GHz. The antenna is composed of an omnidirectional patch antenna and AFSS. The AFSS is made up of 6 columns, each with 2 unit cells, which are placed vertically around a patch antenna to form a hexagonal wall. To steer beam of the antenna, high frequency pin diodes are precisely inserted into the AFSS to reconfigure electromagnetic (EM) response of surfaces. The reflection and transmission characteristics of the proposed AFSS unit cell are investigated. The simulation results show that the transmission and reflection bands of AFSS unit cell can be changed by setting diodes on and off. This new AFSS can be used to implement a sweeping radiation pattern at all azimuth angles. The antenna can sweep the entire azimuth plane in six steps and effectively operate over a bandwidth of more than 500 MHz.

A high gain omnidirectional antenna with low profile is proposed and is investigated numerically and experimentally. Based on the conventional center-fed circular epsilon-negative (ENG) zeroth-order resonator (ZOR) antenna, dendritic structure negative permeability metamaterial (NPM) is used as the substrate to enhance the gain of the omnidirectional antenna. The experimental results show that the gain of a center-fed circular ENG ZOR antenna with NPM substrate is enhanced about 2.2 dB, and the efficiency is enhanced about 38%, in the whole broad operating bandwidth as compared to that of the antenna without NPM substrate, which can be used to improve the reliability of wireless communications.

For the first time, the rectangular dielectric resonator (DR) operating in higher-order TE3δ1 mode is investigated and used as a magnetic-dipole driver to design quasi-Yagi antenna with high gain. For further enhancing the antenna gain, a near-zero-index (NZI) metamaterial (NZIM) is proposed instead of the traditional directors and put in the front of DR driver. It is a simple structure and composed of a set of the parallel metallic lines printed on a substrate along the end-fire direction. Benefiting from the higher-order mode operation of the DR and NZIM, the realized gain of the proposed antenna can reach 10.3 dBi, including the gain improvement of 2 dBi resulting from the employed NZIM. To verify the design concept, the prototype of quasi-Yagi DR antenna with NZIM is fabricated and characterized. The measured results agree very well with the simulated results.

This research proposes a circularly polarized (CP) single-fed omnidirectional dipole antenna operable in 2.45 GHz frequency for the industrial, scientific, and medical (ISM) radio band applications. The proposed antenna consisted of bisectional dipole core, a pair of quarter-wave baluns, and four diagonally adjoined parasitic braces. The bisectional dipole core was utilized to improve the antenna gain and realize omnidirectional radiation pattern, and the quarter-wave baluns were to symmetrize the current on the bisectional core. The four parasitic braces collectively generated circular polarization. In the study, simulations were conducted using CST Microwave Studio and a prototype antenna fabricated. To validate, experiments were carried out, and simulation and experimental results compared. The finding revealed good agreement between the simulation and experimental results. Essentially, in addition to achieving an antenna gain of 2.07 dBic, the proposed CP single-fed omnidirectional antenna is suited to ISM frequency band applications.

In this paper, a high gain patch antenna using a near-zero-index metamaterial (NZIM) coating is presented for operating at 4.35 GHz. The proposed NZIM unit-cell is investigated and analyzed by both theoretical and numerical methods. It is shown that the designed NZIM unit-cell has a near refraction index characteristic at 4.25–4.45 GHz, which overlaps with the operating bands of the reference antenna. By covering a single layer NZIM coating with 4×4 cells over a conventional microstrip antenna, a gain enhancement of 2.8 dBi is achieved in comparison with the original antenna.

ABSTRACTIn this article, a wideband near-zero-index metamaterial (NZIM) unit cell, for gain improvement of a broadband microstrip fractal patch antenna is proposed and designed. The near-zero refractive index characteristics of metamaterial superstrate is used, which gathers the radiated waves from the source antenna and collimates them toward the normal direction. The reference fractal patch antenna operates at a relatively wide frequency range covering from 2.38 to 3.61 GHz, corresponding to a 40% fractional bandwidth. In order to effectively enhance the broadside gain of the antenna, a proposed unit cell is optimized using invasive weed optimization (IWO) algorithm to have the widest bandwidth at the required frequency band, in which the refractive index is less than unity (approaches zero). A prototype of the antenna was fabricated and tested. Measured results are in good agreement with the simulation. The measured −10 dB relative impedance bandwidth for the loaded antenna with NZIM is found to be 31%. The maximum measured broadside gain is about 3.1 dB higher than that of the reference antenna without NZIM, which corresponds to 86% aperture efficiency.

In this paper, an omni-directional high gain collinear antenna array is proposed, which can show omnidirectional high gain in Ku band. The antenna array is composed of six low gain dipole elements to achieve high gain. The element is arranged in common axis to obtain omnidirectional radiation characteristics. The antenna was processed and measured, and the test results were basically consistent with the simulation results. The test data showed that the omnidirectional antenna array could realize VSWR<; 2 within 12.2GHz to 13.7GHz (the frequency difference of acceptable operation is 11.58% of the center frequency of the bandwidth). The horizontal pattern roundness is less than 0.5dB, the antenna gain in operating bandwidth is greater than 8dB, and the maximum gain is 9.3dB. The measured results show high gain and omnidirectional feature, which agree well with the simulated results.

This paper proposes an omnidirectional high-gain slot array antenna for mobile phone base station. The advantages of this proposed antenna are low profile, light weight, and easy fabrication and installation. Moreover, it provides not only the moderately high gain but also the omnidirectional pattern, which more appropriate for mobile phone base station. The half-power beamwidths in E-plane is around 24 degrees, while its radiation pattern is similar to the circle or omnidirection. The paper also presents the design procedures of a 1×4 array antenna using slot antennas associated with two side-wings for increasing its gain. A Computer Simulation Technology (CST) software has been used to compute the reflection coefficient (S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> ), radiation patterns, and gain of this antenna. The bandwidth, at S <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</inf> (−10 dB), is which can be well utilized for 3G base station, with a gain around 9 dB.

A low-profile and broadband metasurface antenna is proposed for circular polarization radiation. The metasurface is an array of subwavelength square patches. The modal behaviors of the proposed metasurface are investigated by using the characteristic mode theory. Two characteristic modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes. Furthermore, a hybrid feed system consisting of a cross-slot and a microstrip line is employed to excite the two orthogonal modes having a 90° phase difference to obtain circular polarization radiation. Based on these concepts, an antenna with low profile of 0.07λ <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 the free-space wavelength at an operation frequency of 5.5GHz) is designed. The measurement results show that the proposed antenna has -10 dB impedance bandwidth of 4.8-6.35 GHz and 3 dB axial-ratio bandwidth of 4.85-6 GHz. Moreover, the antenna gain is 6.8-9.7 dBic in the whole axial-ratio bandwidth.

Two types of circular-polarized smart patch antenna arrays, namely patch antenna with seven hexagonal elements (PASHE) and patch antenna with seven circular elements (PASCE) for indoor mobile wireless computing are investigated. A comparison between simulated and measured reflection coefficient was made with consistent results. The finite element method (FEM) and optimization using a gradient algorithm was carried out to optimize these patch antennas' physical structures on a finite ground plane to achieve optimal directivity in elevation plane and antenna gain at 2.4GHz operating frequency. Switched parasitic technique enables the two patch antennas to steer a directional beam through six locations in azimuth with elevation of approximately 65/spl deg/ for the former and 70/spl deg/ for the latter respectively. The low profile and low cost characteristics along with the simplistic beam control system of these smart patch antennas are ideal prototypes for commercialization.

There is a dilemma for omnidirectional antennas between a narrow beam on the elevation plane and a low-profile antenna configuration. In this communication, an annular loading of parasitic elements mechanism is proposed to circumvent the difficulty. A study for the proposed analytical model shows that the radiation from the parasitic elements can sufficiently cancel the original one in unwanted directions and thus reduce the beamwidth sufficiently. This array-based mechanism is validated for an omnidirectional circular patch antenna. With a proper design of the coplanar parasitic elements, a beamwidth reduction of 50° for the maximum radiation toward the ground plane and 73° for the maximum radiation toward the direction of 45° above the ground plane has been achieved, respectively. Both antennas have a simple configuration, and the total antenna thicknesses are only 0.06 and 0.01 guide wavelength, respectively.

The antenna gain of the omnidirectional cylindrical dielectric resonator antenna (DRA) is enhanced by using its higher-order TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">015</sub> mode. For demonstration, a prototype was designed and fabricated, which is operated at 5.82 GHz for WLAN applications. The reflection coefficient, radiation pattern, and antenna gain were studied and reasonable agreement between the measured and simulated results is observed. The simulated peak gain of the higher-order-mode DRA is 4.06 dBi, which is 2.3 dB higher than that of the fundamental TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> -mode reference DRA.

A wideband omnidirectional patch antenna with filtering response is investigated in this paper. The circular patch antenna is centrally fed by a probe, with its TM01, TM02, and TM03 modes simultaneously excited. Two ring slots are meticulously introduced into the patch and ground plane to merge the three modes of a kind, realizing a wide omnidirectionally radiating passband. The introduction of the slots also generates two radiation minimums at the lower and upper band-edges, leading to an enhanced suppression level in the stopbands. Hence, a compact wideband filtering patch antenna with quasi-elliptic bandpass response is obtained, without using any extra circuit. The proposed antenna has a low profile of $0.027~\lambda _{0}$ , a 10-dB impedance bandwidth of 19.5%, an average gain of 7.5 dBi within passband, and an out-of-band suppression level of over 23 dB within stopband.

In this article, a seven-band omnidirectional rectenna is proposed for the first time to harvest RF energy. The designed rectenna operates in the following practical and up-to-date frequency bands: GSM1800 (1.8 GHz), LTE (2.1 GHz), WLAN/Wi-Fi (2.4 and 5.8 GHz), and 5G bands (2.6, 3.5, and 4.9 GHz). To obtain the multiband rectenna, a novel seven-band rectifier is introduced and composed of three optimized single shunt diode rectifiers in parallel. Overall RF-to- dc conversion efficiencies as high as 44.4% @ 1.84 GHz, 43.9% @ 2.04 GHz, 45.4% @ 2.36 GHz, 43.4% @ 2.54 GHz, 36.1% @ 3.3 GHz, 32.4% @ 4.76 GHz, and 28.3% @ 5.8 GHz are achieved at an input power level of −10 dBm. Moreover, a broadband omnidirectional monopole antenna is further codesigned with elaborate impedance matching to the rectifier. The antenna can harvest RF energy in the bandwidth of 1.67–5.92 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}_{\mathbf {11}}$ </tex-math></inline-formula> no more than −10 dB) with stable omnidirectional radiation patterns. By integrating the rectifier and the monopole antenna in a low profile, a prototype of the rectenna was manufactured and tested. The experimental results demonstrate that the proposed rectenna has competitive performance in terms of RF-to- dc conversion efficiency and band coverage, indicating enormous potential for numerous battery-free or low-power-needed applications in the real world.