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High isolation two-element MIMO antenna array based on embedded meta-material cells
... Embedding meta-materials in radiating structures is another well-traveled research avenue. Meta-materials have been used in arrays to reduce antenna coupling [19][20][21] and reduce the size of a linear array [22]. They have also been used in antenna designs to reduce the antenna size [23], increase its bandwidth [24], and alter its polarization [25]. ...
In order to take on arbitrary geometries, shape-changing arrays must introduce gaps between their elements. To enhance performance, this unused area can be filled with meta-material inspired switched passive networks on flexible sheets in order to compensate for the effects of increased spacing. These flexible meta-gaps can easily fold and deploy when the array changes shape. This work investigates the promise of meta-gaps through the measurement of a 5-by-5 λ -spaced array with 40 meta-gap sheets and 960 switches. The optimization and measurement problems associated with such a high-dimensional phased array are discussed. Simulated and in-situ optimization experiments are conducted to examine the differential performance of metaheuristic algorithms and characterize the underlying optimization problem. Measurement results demonstrate that in our implementation meta-gaps increase the average main beam power within the field of view (FoV) by 0.46 dB, suppress the average side lobe level within the FoV by 2 dB, and enhance the field-of-view by 23.5 ∘ compared to a ground-plane backed array.
A ±45°, dual-polarized, high-isolation, 1 × 2 multiple-input, multiple-output (MIMO) antenna array for wideband microbase-station application is presented in this article. The proposed antenna element incorporates two perpendicular magnetic coupling feeding (MCF) networks and an H-shaped slot in the ground plane to improve the port isolation. Simulation results indicate that it has an isolation of more than 38 dB. To suppress the mutual coupling between antenna elements, a dual wall consisting of a novel metasurface structure is introduced. When spatial-wave incidents occur, the isolation wall can restrain the electromagnetic wave propagation. The electromagnetic waves produce resonance on the wall surface, which scatters some of the resonance, while the rest is transmitted to the ground and weakened by the decoupling structure between two elements. The metasurface walls, which are inserted vertically between the antenna elements, improve the isolation by roughly 5.9 dB within the 2.5-2.7-GHz frequency band and reach a maximum of -22.8 dB at approximately 2.6 GHz. The proposed antenna has been fabricated, and the experimental results are near the simulation responses.
This paper proposes a compact dual band-notched UWB-MIMO antenna whose size is 26.5–30mm 2 . Two identical semicircle ring shaped monopole UWB antennas are designed and placed side by side. Two notched bands are realized by etching two L-shaped slots on the ground plane and inserting two "anchor" shaped stubs into the radiating patch to suppress the WiMAX and WLAN band interferences. Simulated results show that two notch bands and wide bandwidth are achieved. Furthermore, the proposed UWB-MIMO antenna can provide a high isolation which is better than −19.74 dB in most of the UWB band. Also, gain and radiation patterns are given to verify the effectiveness of the designed UWB-MIMO antenna.
A mutual coupling reduction method between microstrip antenna array elements is proposed by using periodic L-loading E-shaped electromagnetic band gap structures. Two identical microstrip patch antennas at 2.55 GHz are settled together and used to analyze the performance of the designed two-element antenna array. The two antenna elements are settled with a distance of about 0.26 λ . To reduce the mutual coupling, the L-loading E-shaped electromagnetic band gap structures are used between these antenna elements. The simulated and measured results show that the isolation of the antenna array reaches 38 dB, which has a mutual coupling reduction of 26 dB in comparison with the antenna array without the decoupling structures.
In this paper a multi-band/Ultra-Wideband (UWB) Multiple Input Multiple Output (MIMO) antenna, which is composed of two identical microstrip fed triple notch band UWB antennas and a Radial Stub Loaded Resonator (RSLR), is proposed and verified numerically and experimentally. The antenna is designed to meet the requirement of multi-band/UWB communication applications. A Defected Microstrip Structure (DMS) Band-Stop Filter (BSF) and an invert pi-shaped slot are employed to design the triple notch band UWB antenna. The resonance characteristics of the DMS-BSF and the band notch functions are presented to realize the proposed triple notch band UWB antenna. The isolation of the multi-band/UWB-MIMO antenna has been enhanced by inserting an RSLR loaded T-shaped stub between two identical triple notch band antennas. Both simulation and measurement results are presented to illustrate the performances of the proposed multi-band/UWB-MIMO antenna.
One-dimensional electromagnetic bandgap (1-D EBG) and split ring resonator (SRR) structures were inserted between two closely located monopole antennas to suppress mutual coupling. The 1-D EBG and SRR structures in these planar multiple antennas function as a reflector and wave trap, respectively. With the effect of these two structures, the mutual coupling between the two antennas is reduced by more than 42 dB and the back lobes are reduced by 6 dB. Thereby, the radiation efficiency of the antenna is also improved. The two fabricated antennas with 0.19λ 0 spacing exhibit mutual coupling (S 21 , S 12) of less than −30 dB from 2.43 to 2.54 GHz. A minimum correlation coefficient of 0.002 and maximum radiation efficiency of 82% are also demonstrated. Index Terms—Electromagnetic bandgap (EBG) materials, isolation technology, multiple-input multiple-output (MIMO) antennas, mutual coupling, split ring resonator (SRR).
A double-layer mushroom structure is proposed to enhance the interelement isolation of a four-element antenna system, wherein four closely positioned substrate-integrated cavity-backed slot (SICBS) antenna elements are configured for multiple-input multiple-output (MIMO) applications. A wall with a double-layer mushroom structure is positioned in between the four antenna elements. An antenna prototype with a ground plane size of ( is the free space-wavelength at 2.4 GHz) demonstrates an enhanced interelement isolation of 16 dB for parallel-directed antenna element pairs, while the isolation of the orthogonally directed antenna element pairs remains unchanged over the operating bandwidth () of 2.396 –2.45 GHz. With the enhanced isolation larger than 42 dB between each antenna element pair, the envelope correlation coefficient (ECC) is lower than 0.02 across the operating bandwidth. The simulated and measured results validate the good MIMO diversity performance of the proposed antenna system.
A metamaterial-based broadband low-profile mushroom antenna is presented. The proposed antenna is formed using an array of mushroom cells and a ground plane, and fed by a microstrip line through a slot cut onto the ground plane. With the feeding slot right underneath the center gap between the mushroom cells, the dual resonance modes are excited simultaneously for the radiation at boresight. A transmission-line model integrated with the dispersion relation of a composite right/left-handed mushroom structure is applied to analyze the modes. The proposed dielectric-filled mushroom antenna with a low profile of ( is the operating wavelength in free space) and a ground plane of attains 25% measured bandwidth with 9.9-dBi average gain at 5-GHz band. Across the bandwidth, the antenna efficiency is greater than 76%, and cross-polarization levels are less than 20 dB.
A wideband neutralization line is proposed to reduce the mutual coupling of a compact ultrawideband (UWB) MIMO antenna. With the introduced decoupling method, the designed UWB MIMO antenna covers the band of 3.1-5 GHz with an isolation of higher than 22 dB. The proposed wideband neutralization line is not necessarily placed in the clearance area between two MIMO elements and can be put above the copper ground. A small clearance (antenna area) of 35 mm × 16 mm is achieved. The designed UWB MIMO antenna is fabricated. S parameters, radiation patterns, total efficiency and realized gain of the prototype are measured and compared with the simulations.
Two closely spaced printed meander line antennas (MLAs) are developed by using metamaterial loading techniques with reduced mutual coupling. The antenna array built on the metamaterial substrate showed significant size reduction and less mutual coupling compared to similar arrays on conventional substrates. Demonstrated to have left-handed magnetic characteristics, the methodology uses elliptical split-ring resonators (E-SRRs) placed horizontally between the patch and the ground plane with a row of the same type between antenna elements. Measured return loss of the printed antenna with this technique is less than -10 dB from 5.1-5.9 GHz which covers the IEEE 802.11a (5.15-5.35 GHz and 5.47-5.725 GHz) American standard and HIPPER LAN/2 (5.15-5.35 GHz and 5.725-5.825 GHz) European standard. Also this antenna has an omnidirectional radiation pattern, high gain, and very good pattern stability over the operating band. It is shown to have great impact on the antenna performance enhancement in terms of high efficiency, low voltage standing wave ratio, good bandwidth and less mutual coupling between two antennas with a very close separation of about 0.073 λ0. Experimental data show a reasonably good agreement between the simulation and measured results.
Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer () with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit–patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented.
The reduction of mutual coupling between closely spaced antenna elements is attractive in the electromagnetic and antenna community. An efficient approach to suppress the mutual coupling between microstrip patch antennas is proposed using waveguided metamaterials. The waveguided metamaterials are designed and realized by crossed-meander-line slits, which exhibit magnetic resonances and further the band-gap property. By inserting the waveguided metamaterials between two H-plane coupled rectangular patch antennas with the edge-to-edge distance less than , about 6 dB reduction of mutual coupling throughout the 10-dB bandwidth has been achieved, which is verified by measurement results.
Utilization of electromagnetic band-gap (EBG) structures is becoming attractive in the electromagnetic and antenna community. In this paper, a mushroom-like EBG structure is analyzed using the finite-difference time-domain (FDTD) method. Its band-gap feature of surface-wave suppression is demonstrated by exhibiting the near field distributions of the electromagnetic waves. The mutual coupling of microstrip antennas is parametrically investigated, including both the E and H coupling directions, different substrate thickness, and various dielectric constants. It is observed that the E-plane coupled microstrip antenna array on a thick and high permittivity substrate has a strong mutual coupling due to the pronounced surface waves. Therefore, an EBG structure is inserted between array elements to reduce the mutual coupling. This idea has been verified by both the FDTD simulations and experimental results. As a result, a significant 8 dB mutual coupling reduction is noticed from the measurements.