Miniaturization of patch antenna using metasurface

A low-profile high-gain patch antenna is proposed using the double-layer metasurface (MS). The proposed MS plays the role of frequency selective surface to improve the gain of the patch antenna. With the help of the MS, the antenna gain is improved by 8.5 dBi at 5.9 GHz. At the same time, the MS is only 0.1 wavelength away from the patch antenna in the free space. With the use of the metasurface, the patch antenna obtains peak broadside gain of 11 dBi at 5.9 GHz.

To overcome the narrow axial ratio (AR) bandwidth inherent in conventional linearly to circularly polarised converters, this research proposes a metasurface (MS) with a diamond‐shaped configuration that can mitigate the effect of surface wave (SW) along the MS edge and achieve a wider 3 dB AR bandwidth. The diamond‐shaped MS structure is realised by slanting a square MS by 45°, and it consists of constituent unit cells of rectangular and arbitrary shapes. The rectangular unit cells are positioned 45° to the square dielectric substrate, and the unit cells along the MS edge are partially cut into arbitrary shape to be perfectly aligned along the edge. The 3 dB AR bandwidths and degradation of the MS are characterised by SW and magnetic current distribution. Simulations are carried out and an MS prototype is fabricated to verify the results. The effects of partially cut unit cells (PCUCs) along the MS edge on the SW are characterised. The simulation and measured 3 dB AR bandwidths of the diamond‐shaped MS are 37.6 and 28.8%, respectively. The novelty of the proposed diamond‐shaped MS polarisation converter lies in the implementation of arbitrary‐shaped PCUCs and the use of the diamond‐shaped configuration in place of conventional square geometry to realise wider AR bandwidth.

A novel metasurface (MS)-based method for broadband radar cross section (RCS) reduction of circularly polarized (CP) patch antennas is proposed. The RCS reduction is achieved in a much broader band than the operational band of the antenna. The simple technique is based on MS units on a grounded substrate in a checkerboard-like configuration. The broadband RCS reduction is achieved by combining two different destructive interference principles. In the high-frequency region, for a normal incident wave, the RCS is reduced by the phase cancellation generated by the MSs and the grounded substrate. In the low-frequency region, the RCS is reduced by the polarization conversion property of the MS. In this case, the fields reflected by two MS sections are in counter phase for a normal incident wave. The MS is combined with a CP patch antenna. It concerns a traditional corner-truncated square patch and four sequentially rotated surrounding MS cells. This dedicated MS allows two things: an additional resonant mode is excited resulting in a 3 dB AR bandwidth extension from 4.2% to 15.9% and a broadband RCS reduction of over 6 dB from 4.95 to 15.73 GHz (104.25% bandwidth) for both x- and y-polarized incident waves.

A metasurface (MS) antenna that allows polarization reconfigurability is proposed. The MS antenna is formed by a MS and source antenna, separated by a small air gap. The MS consists of 16 identical unit cells on a substrate, where each unit cell used is a corner truncated square patch. A microstrip fed slot antenna (MFSA) is used as the source antenna. The MS converts the linearly polarized (LP) signal generated by the MFSA into a circularly polarized (CP) signal with wider return loss bandwidth(RLBW). By rotating the MS relative to the MFSA, different polarizations could be achieved. For verification of simulation results, the MS antennas are fabricated and measured. Simulated and measured results show good agreements. The MS antenna has an operating frequency of 2.4 GHz, suitable for WLAN applications.

Based on classic electromagnetic Huygens' Principle and the concept of modern metamaterials, metamaterial Huygens surface, namely, metasurface (MTS) is presented to be the two-dimensional analogues of metamaterials. With the dense arrays of electrically small unit cells, the MTS can control electromagnetic waves and fields in either usual or unusual ways. Such unique electromagnetic properties greatly offer additional opportunities to innovate new antennas. This paper updates the latest progress in the MTS based antenna at microwave bands. First, the concept of the MTS is briefly introduced with a summary of applications of the MTS in microwave antenna design. After that, three of selected MTS based antenna techniques are elaborated with design examples. Finally, the promising applications of the MTS in antenna engineering are commented.

SummaryIn this paper, a 4 × 4 MIMO (multiple‐input multiple‐output) antenna with metasurface (MS), which is composed of dual circularly polarized (CP) patch antennas, is proposed for 5G (sub‐6 GHz) applications. The MIMO antenna consists of four microstrip patch antennas. In order to improve the isolation of the MIMO antenna, parasitic elements are placed on the MS and layer of patch antennas. In addition, a substrate‐integrated waveguide (SIW) structure is used at the center of the MIMO antenna for this purpose. The proposed MIMO antenna is fabricated for validation tests. The antenna has overall dimensions of 115 mm × 115 mm × 3.2 mm (1.219 × 1.219 × 0.033, where is the free space wavelength at the lowest operating frequency in 10‐dB impedance bandwidth). The MIMO antenna has 10‐dB impedance bandwidth (IBW) from 3.3 to 3.8 GHz (14.08%), 3‐dB axial ratio bandwidth (ARBW) from 3.42 to 3.69 GHz (7.59%), and 6.36‐dBi peak gain. The isolation is greater than 28.14 dB in the n78 frequency band (3.3–3.8 GHz).

A miniaturized high‐performance metasurface (MTS) antenna with cross‐shaped strips is designed, which can be applied to wireless communication systems. The resonant frequency of the main mode of the proposed MTS is reduced by embedding a 2 × 2 cross‐shaped strip array in the gaps of the 3 × 3 circular MTS array, resulting in a lower operating frequency and miniaturization. The main mode of the MTS and the probe mode are excited simultaneously by the L‐probe structure, resulting in a dual‐mode resonance for a broadband performance. The entire design mechanism of the antenna is explained analytically through characteristic mode analysis (CMA) method. Additionally, the cross‐polarization levels in H‐plane are effectively suppressed by a metal via positioned at the MTS center. Measured results show a wide impedance bandwidth of 32.6% (reflection coefficient ≤ −10 dB) with an MTS size of 0.44λ0 × 0.39λ0 (where λ0 is the free‐space wavelength of 6.6 GHz). The achieved peak gain is 7.1 dBi, with a 2 dB gain bandwidth of 36% (5.25‐7.55 GHz) and a low cross‐polarization level below ‐20 dB.

A frequency-reconfigurable slot antenna designed using metasurface (MS) is proposed and studied. The proposed antenna is composed of a simple circular slot antenna and a circular MS with the same diameter of 50 mm and implemented using planar technology. The MS is placed directly atop the slot antenna, making the proposed antenna very compact. The MS consists of rectangular-loop unit cells placed periodically in the vertical and horizontal directions. Frequency reconfigurability of the antenna is achieved by rotating the MS around the center with respect to the slot antenna. The antenna with MS is studied, designed and optimized to operate at around 3 GHz using computer simulation. The simulated performances in terms of frequency reconfigurability and radiation pattern are presented.

A dual-polarized dual-band antenna with a simple bifunctional metasurface (MS) is proposed. Previous studies often require various elements to design MSs, and most monofunctional MSs are designed to control one intrinsic property of electromagnetic wave. In contrast, the proposed MS uses only one type of element to realize dual functions. In the lower frequency band, the MS helps to excite the TM leaky-wave mode and together with the slot mode to obtain a wide bandwidth of 25.8%. In the higher frequency band, the MS functions as a frequency selective surface to enhance the antenna gain by 6 dB and decreases the distance between the MS and the patch antenna to 0.1 wavelength. By composing the antenna with a pair of stub-loaded slots and a rectangular patch sharing the same ground and diamond-shaped MS, dual bands and dual polarizations are obtained. The MS antenna is first simulated, and then fabricated and measured. The proposed antenna demonstrates the operating bands of 2.12–2.75 GHz (0.63 GHz, 25.8%) for Port 1 and 5.69–5.91 GHz (0.22 GHz, 3.8%) for Port 2, with peak boresight gains of 7.9 dBi at 2.7 GHz and 11.7 dBi at 5.75 GHz.

In this paper, a high gain, aperture efficient, low profile compact, near zero index (NZI) metasurface (MS) lens antenna with enhanced radiation characteristic is proposed. A high‐performance transmissive MS is designed by using modified double circular ring resonator as unit cell with measured 3 dB transmission band from 8.80 to 11.90 GHz. It is observed that a triple layer stacked MS lens has the maximum ability to converge the electromagnetic radiation. The focusing mechanism of multiple stacked MS is studied by using measured E‐ and H‐plane radiation pattern plot and H‐Field distribution. A high gain low profile antenna is designed by placing the proposed small single surface NZI MS lens over a microstrip patch antenna acting as a microwave source. The proposed NZI MS lens is found to increase the measured gain of E‐ and H‐plane by 10.70 dB in boresight direction at operating frequency 10.15 GHz. The front to back ratio is improved by 8 and 3 dB in E‐ and H‐plane, respectively. The proposed MS lens antenna is able to achieve a broadside gain of 97.50% of the maximum gain achieved due to ideal effective radiation surface.

The compact Multi-Port Power Divider is presented based on the microstrip patch resonator. To explicate its mode of operation, the resonant property of the circular microstrip antenna is illustrated for multi-port power divider operation. This MPPD is constructed with two aligned patch resonators with a meta surface to control the radiation parameters. In this paper, the functional description of the power divider along with the meta surface can be exemplified by the field distributions of the resonating ports. The FR4 epoxy substrate material, with a dielectric constant of 4.4 and a thickness of 1.6, is used for the antenna to operate at a 2.4 GHz resonating frequency, with an antenna size of 0.4 λ0 ×0.48 λ0 ×0.128 λ0 , also having a bandwidth of 2.2GHz to 2.6GHz with a gain of 5dBi, along with an axial ratio below 3dB at the reflection coefficient of -40dB. The presence of meta surface in microstrip antenna increases the bandwidth and valued gain at certain extent, it further improves the functionality of the overall system. The performance of the proposed antenna was analyzed with the E and H planes of the radiation pattern, with improved gain obtained in the presence of a meta surface-based microstrip antenna. The meta surface appeared in the form of a mesh type of structure, fed by a microstrip antenna revealing a good agreement with the simulated one. The measured result shows that the proposed antenna has the perfect axial ratio along with a 10dB impedance bandwidth achieved with a valued gain of 5to 11dBi.

In this article, a metasurface (MS) is placed as superstrate to counteract the effect of mutual coupling in linear antenna array in X-band. The metasurface is single layered and consist of single split ring resonator (SRR) and two I-shaped structures. The proposed metasurface can curb the interactions between adjacent antenna elements by collimating the electric field and reduce horizontal magnetic field interactions due to its negative refractive index and mu-near-zero property. The functioning of metasurface is tested by placing it above a 1×3 patch antenna. The experimental measurement shows an isolation below -25 dB in the 5.12% operational bandwidth with maximum isolation of -38.2 dB for an edge-to-edge distance of only 0.16λo. The active radiation pattern indicates an improved cross-polarization levels to below -30 dB, in both the orthogonal planes. The performance of MS is further tested for a 1×7 linear array where a 9.2 dB reduction in coupling value is observed. On placing the MS on the array there is no change in the operational bandwidth indicating that no modifications is needed in the antenna array geometry making it a preferable and easily transferrable solution to already existing antenna array.

High gain and efficiency dual-band antenna using meta-surface

This study proposes a metasurface (MS) based high performance antenna in which the radiating patch is embedded with split ring resonators in its square slots. The slotted corner cut rectangular patch antenna with defected ground plane and the MS are placed together in the same plane. The designed prototype operates over dual frequencies with impedance bandwidths (S11 < −10 dB) of 4.02% and 28.24% at 9.20 and 11.65 GHz respectively. The antenna possesses a maximum return loss of 42 dB at 11.65 GHz over 11.23–14.5 GHz band while the measured realized gain of 10.66 dBi has been obtained at 14.44 GHz. The antenna exhibits unidirectional far‐field radiation characteristics and the radiation efficiency of 67% has been achieved at 14.44 GHz. The antenna prototype has been fabricated on FR4 dielectric substrate, having an electrical size of 1.16λ0 × 1.82λ0 × 0.06λ0, where λ0 is the free‐space wavelength at 11.65 GHz. This makes the proposed antenna single‐layer, broad impedance bandwidth, high gain and ease of fabrication in nature. The measured results are in good agreement with the simulated ones. The designed antenna can be applicable in defense and military, satellite communication, medical analysis for determination of radio waves and numerous communication fields.

A planar polarization-reconfigurable metasurfaced antenna (PRMS) designed using metasurface (MS) is proposed. The PRMS antenna consists of a planar MS placed atop of and in direct contact with a planar slot antenna, both having a circular shape with a diameter of 78 mm (0.9 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\lambda_{0}$</tex></formula> ), making it compact and low profile. By rotating the MS around the center with respect to the slot antenna, the PRMS antenna can be reconfigured to linear polarization, left-hand and right-hand circular polarizations. An equivalent circuit is used to explain the reconfigurability of the antenna. The PRMS antenna is studied and designed to operate at around 3.5 GHz using computer simulation. For verification of simulation results, the PRMS antenna is fabricated and measured. The antenna performance, in terms of polarization reconfigurability, axial-ratio bandwidth, impedance bandwidth, realized boresight gain and radiation pattern, is presented. Results show that the PRMS antenna in circular polarizations achieves an operating bandwidth of 3.3–3.7 GHz (i.e., fractional bandwidth 11.4%), a boresight gain of above 5 dBi and high-polarization isolation of larger than 15 dB. While the PRMS antenna in linear polarization achieves a gain of above 7.5 dBi with cross-polarization isolation larger than 50 dB.