Center Operating Frequency Research Articles

Compact and high isolated microstrip patch antenna system for full-duplex/MIMO applications

This paper presents a two-port microstrip patch antenna system with compact size and high isolation for full-duplex and multiple-input-multiple-output (MIMO) applications. The proposed miniaturization approach is to employ compact microstrip patch antenna and decoupling network as well. Here, two quarter-wavelength patch antennas are arranged in the H-plane coupled configuration with element spacing of about 0.008 λ at the center operating frequency. Besides, a defected ground structure is chosen as the decoupling network, which doesn't require any additional space and contributes to significantly reducing the overall antenna dimensions. The final antenna design with compact size of 0.49 λ × 0.37 λ × 0.01 λ has operating band from 2.45 to 2.48 GHz, in which isolation is better than 30 dB and the maximum isolation is 42 dB. Besides, the proposed antenna also achieved comparable gain of 3.8 dBi and good diversity performance. In comparison with other related works, the proposed design has smallest overall size with extremely small element spacing while obtaining comparable isolation enhancement.

Satellite Onboard Transmitter Design With Spread Spectrum MIMO Antenna for 5G Wireless Networks

AbstractThe 5G new era implements standalone satellite communications that support wireless networking systems for future mobile communications by locating multiple satellites in low Earth orbit to provide global coverage of the entire Earth's surface. In this research, a newly found model of a satellite onboard transmitter using a uniform circular array multiple‐input multiple‐output antenna was designed to operate at a carrier frequency of 12 GHz and derived theoretical equations compared to the real‐time scenario. The integration of spread spectrum with multiple‐input multiple‐output antenna provides an advantage for higher capacity. It has a higher percentage of gain amplification on improving the transmission of electromagnetic power to meet the bandwidth requirement of center operating frequency, and this can transmit over a bandwidth of 1.28 GHz. The proposed satellite onboard transmitter model design aims to minimize the components, increase the speed of operations for higher bandwidth, and transmit large amounts of information to a large group of users. The transmitter can operate for the speed of 1.28 Gbps using pseudo‐random code, direct‐sequence spread spectrum, quadrature phase shift keying modulation, bandwidth separated in bands for 64 symbols using 128 Chebyshev‐type bandpass filter for transmission using 128‐element uniform circular array multiple‐input multiple‐output antenna. The satellite transmitter antenna produces a maximum gain of 14.526 dBi, and a maximum directivity of 17.986 dBi, and the efficiency at 12 GHz is 45.1% for the radiated power at 0.93 mW. This satellite transmitter will interconnect 5G wireless networks for the application of mobile communications complement terrestrial‐dependent networks.

A Wideband Circularly Polarized Dipole Antenna with Compact Size and Low-Pass Filtering Response.

This paper presents a compact wideband circularly polarized cross-dipole antenna with a low-pass filter response. It consists of two pairs of folded cross-dipole arms printed separately on both sides of the top substrate, and the two dipole arms on the same surface are connected by an annular phase-shifting delay line to generate circular polarization. A bent metal square ring and four small metal square rings around the cross-dipoles are employed to introduce new resonant frequencies, effectively extending the impedance and axial-ratio bandwidth. Four square patches printed on the middle substrate are connected to the ground plane by the vertical metal plates in order to reduce the antenna height. Thus, a compact wideband circularly polarized antenna is realized. In addition, a transmission zero can be introduced at the upper frequency stopband by the bent metal square rings, without using extra filter circuits. For verification, the proposed model is implemented and tested. The overall size of the model is 90mm×90mm×33mm (0.37λ0×0.37λ0×0.14λ0; λ0 denotes the center operating frequency). The measured impedance bandwidth and 3 dB axial-ratio (AR) bandwidth are 53.3% and 41%, respectively. An upper-band radiation suppression level greater than 15 dB is realized, indicating a good low-pass filter response.

Ni-Co Complex Ionic Synergistically Modifying Octahedron Lattice of Cordierite Ceramics for the Application of 5G Microwave-Millimeter-wave Antennas.

In this work, phase-pure Mg1.8(Ni1-xCox)0.2Al4Si5O18 (0 ≤ x ≤ 1) ceramics were synthesized by a high-temperature solid-state method. On the basis of Rietveld refinement data of X-ray powder diffraction and Phillips-Vechten-Levine theory, the atomic ionicity, lattice energy, and bond energy of the compound were calculated to explore their influence on the microwave dielectric properties of ceramics. The Mg1.8Ni0.1Co0.1Al4Si5O18 (x = 0.5) ceramic exhibited the best microwave dielectric properties: εr = 4.44, Qf = 73 539 GHz@13 GHz, and τf = -23.9 ppm/°C. (Ni1-xCox)2+ complex ionic doping, compared with only Ni2+ or Co2+, is beneficial for improving the symmetry of [Si4Al2O18] hexagonal rings and reducing distortion. Subsequently, 8 wt % TiO2 was added to Mg1.8Ni0.1Co0.1Al4Si5O18, resulting in a near-zero τf and high Qf values for the composite ceramic, with εr = 5.22, Qf = 58 449 GHz@13 GHz, and τf = -2.06 ppm/°C. Finally, a 5G millimeter-wave antenna with a central operating frequency of 25.52 GHz was designed and fabricated using the Mg1.8Ni0.1Co0.1Al4Si5O18-8 wt % TiO2 ceramics. Operating in the 24.7-26.0 GHz range, it demonstrated favorable radiation characteristics with a simulated efficiency of 85.2% and a gain of 4.58 dBi. The antenna's performance confirms the high potential of the cordierite composite for application in 5G communication systems.

Miniaturized wideband metasurface antenna loaded with H‐slot based on characteristic mode analysis

AbstractAn H‐slot loaded metasurface (MTS) structure has been developed for the purpose of constructing a miniaturized wideband metasurface antenna (MTSA). The MTS is composed of an array of 3 × 3 rectangular small metal patches, each of which is loaded with an H‐slot. The inclusion of the H‐slot significantly lengthens the current path on the small metal patch, resulting in a small antenna size. Since the direction of the effective total current does not change, the radiation performance of the antenna is almost unaffected. To excite the MTS resonance and generate a stable radiation pattern while decreasing the backward radiation, an L‐probe with an intact ground is employed. Characteristic mode analysis (CMA) is applied to reveal the miniaturization mechanism of the MTS and guide modal excitation. The prototype is fabricated and measured within a compact radiation aperture size of 0.35λ0 × 0.29λ0 (λ0 is the free‐space wavelength at the center operating frequency). The measured −10 dB impedance bandwidth is 20.16% (5.22–6.39 GHz), with a peak gain of 6.28 dBi and a front‐to‐back ratio is larger than 20 dB.

A compact co-aperture dual-sense circularly polarized antenna for simultaneous transmit and receive systems.

This paper proposes a compact design of dual-sense circularly polarized (CP) antenna for simultaneous transmit (Tx) and receive (Rx) communication systems. The primary radiating aperture of the proposed antenna is a 2 × 2 unit-cell metasurface (MS). The MS is excited by the asymmetric patch in the center, which acts as the CP source of the whole antenna structure. By properly tuning the feeding positions, dual-sense CP with high isolation can be achieved. For verification, an antenna prototype with compact dimensions of 0.36λ × 0.36λ × 0.02λ (λ is the free-space wavelength at the center operating frequency) is fabricated and measured. The measured operating bandwidth is 1.6% (2.45-2.49 GHz), in which the reflection and transmission coefficients are less than-10 dB and the axial ratio is lower than 3 dB. Within this band, the maximum isolation value is 39 dB, and the peak gain is 5.7 dBi.

An Inverted Doherty Power Amplifier Insensitive to Load Variation With an Embedded Impedance Sensor in Its Output Power-Combining Network

This article presents an inverted Doherty power amplifier (IDPA) made load insensitive up to 2:1 voltage standing wave ratio (VSWR) across its fractional bandwidth with a very compact wideband impedance sensor embedded in its output power-combining network (OPCN). To correct for load variation, a low-loss tunable resonator (TR) is used to ensure ohmic loads to the main and peaking stages at the center frequency of operation. At off-center frequencies, TR is used to present an ohmic load for the main stage, while a digitally adjustable phase shifter is used to (re)align the main and peaking stage’s current summation in the OPCN. For ohmic load deviations, the main and peaking stage supply voltages and input drives are adjusted to maintain the ideal Doherty’s output power and efficiency profile related to nominal 50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\Omega}$</tex-math> </inline-formula> loading across the bandwidth. To implement the control of the formerly mentioned technique, a wideband impedance sensor is proposed, which uses the orthogonality of incident and reflected waves and requires only four peak detectors. As proof of principle, a prototype 850–950-MHz IDPA featuring the proposed correction technique, the impedance sensor, and the control loop has been implemented as a printed circuit board (PCB) demonstrator. Measurement results show that the IDPA can maintain constant output power with a tolerance of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\pm}$</tex-math> </inline-formula> 0.2 dB while improving the drain efficiency and linearity across the entire fractional bandwidth (11 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\%}$</tex-math> </inline-formula> ) for a VSWR range of 2:1.

A novel defected ground structure for high-isolation circularly polarized MIMO patch antenna

ABSTRACT This paper introduces a method to reduce mutual coupling in a two-element multiple-input multiple-output (MIMO) antenna, which is a significant challenge due to the need for high isolation over a wide frequency range with close element spacing. Previous works typically achieved high isolation within a narrow bandwidth. The paper presents a novel defected ground structure (DGS) with a modified I-shaped slot, which effectively minimizes mutual coupling in a dual-sense MIMO circularly polarized (CP) antenna over a broader bandwidth than the previous approaches. The fabricated 2-element prototype with an overall size of 0.98λ × 0.71λ × 0.05λ and an edge-to-edge spacing of 0.08λ at the center operating frequency has a measured bandwidth of 2.5% (5.2–5.33 GHz). Across this band, the isolation is always better than 35 dB and the gain is higher than 4.8 dBi. The MIMO parameters are also investigated, which proves the good diversity performance of the proposed design.

Two closely spaced microstrip patches with high isolation for full-duplex/MIMO applications.

This paper shows an effective method to significantly enhance the isolation of a closely spaced two-port patch antenna, which can be deployed for full-duplex transceivers as well as multiple-input-multiple-output (MIMO) systems. Two rectangular microstrip patches are arranged in the E-plane configuration. To achieve high isolation, a grounded stub is positioned between the radiating patches. For validation of the proposed concept, an antenna prototype is fabricated for measurements. The measured data demonstrates that the port-to-port mutual coupling can be suppressed to -50 dB, which is useful in self-interference cancellation for full-duplex communication systems. Compared with the coupled design, the isolation is significantly enhanced by 43 dB with an inter-element spacing of 0.034λc, where λc is a free-space wavelength at the center operating frequency. Regarding MIMO metrics, the antenna also shows good MIMO diversity performance based on an envelope correlation coefficient and a diversity gain.

Computer-aided design of quadra-ridged waveguide transformers for full-band matching of half-height rectangular waveguides

A quadra-ridged waveguide transformer (QRWT) is proposed for full-band matching between a standard waveguide and a half-height waveguide, which meets the need for compact waveguide components and the need for multiple sections of irregular transmission lines for better matching in wider operation bands. Unlike conventional matching circuits with monotonically changing impedances, QRWTs form abrupt cross-section changes between transmission line steps. The initial configuration of QRWT is built by CST MICROWAVE STUDIO, a system-level electromagnetic compatibility and general high frequency passive device simulation software, according to the basic electromagnetic (EM) concept and then is optimized by optimization functions from an advanced EM simulator, during the optimization, releasing restrictions as many as possible. To explain the concept, a sample QRWT is designed to match a standard rectangular waveguide WR34 to a half-height waveguide. The reflection coefficient is less than −24 dB in the full operation bandwidth, from 21.7 to 33 GHz. The optimized QRWT has a length of 3.088 mm, 0.218 times the waveguide wavelength at its center operation frequency of 27.35 GHz. For comparison, a two-stage quarter-wave transformer matching circuit is optimized. For similar reflection coefficients in the same bandwidth, the QRWT has a length 57% shorter than the conventional one, and it has an easier manufacturing method using wire-electrode cutting. To verify the design, a back-to-back matching circuit was fabricated using brass material without extra dielectric material. Its measured reflections are less than −16.6 dB, and the insertion loss is less than 0.2 dB.

Ultra-Miniature and Circularly Polarized Ferrite Patch Antenna

This paper describes the development, the design and the measurement of a circularly polarized ultra-miniature antenna. The modelled device takes advantage of the magnetic properties of ferrite materials to achieve the desired specifications. Indeed, the antenna is operating at a frequency where the effective permeability is greater than 1 and the permeability has a negative real part, i.e. in the zone between the μ and μ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</i> resonances of the ferrite. The dimensions of the designed antenna are about λ0/23.6×λ0/20.7×λ0/29.4 at 2.42GHz and a good circular polarization is achieved at the central operating frequency of the device, with a boresight axial ratio of 1.6dB. This paper is based on the modal study of a ferrite cavity which will be presented and detailed in a first step. The physical properties of the antenna and related material (dimensions, ferrite internal magnetic field, the saturation magnetization, etc.) will be deduced from this modal study and from the resolution of the wave equation inside a cylindrical ferrite cavity. All the antenna performances in terms of impedance matching, axial-ratio and radiation pattern are reported and commented. This concept is finally validated by the measurement of a prototype.

Metasurface-Covered Planar Endfire Antenna With Vertical Polarization

A trapped wave-based solution to design compact planar vertically-polarized (VP) endfire antennas is proposed in this paper. By placing a four-element series-fed magnetic dipole array with an inter spacing of half wavelength within a dual-layer metasurface and loading shorting pin arrays at two edges of the metasurface, the VP radiation is realized in a wide impedance band. In addition, the antenna profile can be further reduced by half according to the electric field distribution within the metasurface. Finally, a VP endfire antenna with a reflection bandwidth of 4.3 ~ 5.4 GHz, a peak gain of 9.8 dBi and a low total profile of 0.065λ <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 the center operation frequency) is designed for the validation. The proposed antenna can be used for some wireless communication systems on or near the ground plane, such as the car roof-mounted terminal for vehicle-to-roadside unit/base station communications.

Non-reciprocal transmission of coupled LC resonators through parity-time symmetry breaking

Non-reciprocal devices that allow a signal to be transmitted only in one direction are important for full-duplex communications. Due to the requirements of miniaturized systems, there has been an increase interest in non-magnetic non-reciprocal devices in recent years. Based on parity-time (PT) symmetric inductors-capacitors (LC) resonators, this paper has proposed non-reciprocal transmission configurations by PT-symmetry breaking. In the configuration, the coupled capacitance between the two coupled LC resonators can be adjusted so that the transmission frequency is tunable. At the same time, the resonant frequency and transmission frequency have been discriminated to optimize the non-reciprocal transmission. The configuration has been implemented by utilizing discrete components on a printed circuit board (PCB). It demonstrates that the center operation frequency of 14.05 MHz with the bandwidth 4 MHz, the insertion loss 0.32 dB, and the isolation 11 dB is adjusted to the center operation frequency of 14.95 MHz with the bandwidth 4.6 MHz, the insertion loss 0.716 dB, and the isolation 14.5 dB.

All-Metal Phased Array With Full Polarization Reconfigurability

An all-metal phased array with full polarization reconfigurability is presented in this article. Septum polarizers as phased array elements are first used to achieve left-handed and right-handed circular polarizations (LHCP and RHCP), and arbitrary linear polarizations (LPs) can be further synthesized. Two pairs of metal ridges are loaded into the septum polarizer to reduce the profile and aperture size so that the spacing between the two adjacent array elements can be constrained to about half of the free-space wavelength at the center operating frequency. Phased arrays of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> 8 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times $ </tex-math></inline-formula> 8 elements covering 25.5–27 GHz are designed to demonstrate the 1-D and 2-D beam scanning performance with different polarizations. For demonstration, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times $ </tex-math></inline-formula> 8 element phased array is implemented. Experimental results show that the array exhibits stable beam scanning performance for both circular polarizations (CPs) and LPs. The synthesized beam scanning range is up to ±55° with a gain-reduction of 4.7 dB for all polarizations. Under beam scanning, the axial ratio (AR) remains below 3.1 dB for the LHCP and RHCP, and the maximum gain variation during polarization reconfiguration is less than 0.8 dB.

Novel Synthesis Method for Reconfigurable Filtering Phase Shifter With Frequency-Dependent Coupling Using Optimization Technique

A novel optimization technique is proposed for reconfigurable filtering phase shifter with frequency-dependent coupling in this brief. It incorporates both the coupling matrix entries and the circuit elements into optimization process. With the proposed technique, it can not only obtain desired insertion phase at the center frequency, align the phase slope between different phase states to be same, but also maintain satisfactory return loss in the passband and have multiple transmission zeros in the stopband. The proposed method well suits the reconfiguration application scenario where frequency-dependent coupling is adopted between adjacent resonators. To validate the proposed idea, a microstrip prototype is fabricated and measured. Experimental results show that the operating center frequency can be tuned from 0.6 GHz to 0.71GHz, with a continuously tunable phase shifting range of larger than 175° at each frequency state.

High-Gain Transmissive Array Antenna with Broadband Cross-Polarisation Isolation

A transmissive metal unit working in the range of 18 GHz-29 GHz is designed in this paper. This is a three-layer metal circular slit unit with promising cross-polarization isolation properties. A planar lens antenna with a center operating frequency of 28 GHz is designed based on the unit utilizing a phase compensation algorithm. The numerical simulation results show that the antenna can improve the gain of the horn antenna from 22.9 dB to 25.6 dB, which can effectively advance the development of 5G communication technology.

Engineering Designs of Dual-Polarized Antennas With Reduced Profile and Mutual Coupling for 5G Microcell Application

In this letter, a miniaturized, low profile and low mutual coupling antenna array with stable radiation pattern for fifth-generation microcell is presented. The antenna element contains three parts, folded dipole radiator, vertical feeding baluns, and reflector. Four striplines with end connections and stepped slots etched on the main radiator are adopted to enhance the impedance bandwidth and miniaturized the antenna's aperture in the low-profile configuration. While folded stripline structure is applied to reduce the mutual coupling in dual-polarized antenna. The height of proposed antenna is only 0.1 λ <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 referring to the center operation frequency) and the antenna's aperture is only 0.4 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.4 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . Measured results show that the antenna array has good performances, exhibiting low voltage standing-wave ratio (VSWR < 1.5), high isolation (> 30 dB), and wide bandwidth (3.2–3.9 GHz, 20%). Stable radiation patterns are measured across the operating bandwidth.

Substrate-Integrated Coaxial Line (SICL) Rotman Lens Beamformer for 5G/B5G Applications

High-band allocations in the millimeter-wave (mm-Wave) frequency spectrum offer high-capacity wireless information transmission as required by fifth generation (5G) communication standards. Among different beamforming structures, the Rotman lens (RL) is an attractive passive-microwave-lens-based beamforming network due to its low fabrication cost, reliability, design simplicity and wide-angle scanning capabilities. Conventionally, the RL is implemented using microstrip line (MSL) technology for which there are inherent radiation losses that become severe when operating in mm-Wave 5G frequency bands. In this context, a novel substrate-integrated coaxial line (SICL)-based RL is designed, fabricated and tested, for accurate beamforming with extremely low feed line insertion loss. This article presents a complete design, development and performance analysis of an SICL-based RL beamformer. By using an SICL, isolation of up to 15 dB is achieved between the input beam ports of the RL, while the mutual coupling is kept at less than 20 dB. The SICL design shows a −10 dB insertion loss between the array and beam ports when compared to the same RL developed using MSL technology having an insertion loss of −15 dB. Due to the use of low-loss SICL technology, a realized gain of up to 14.2 dBi is achieved with an excellent scanning capability of −30 to 30 degrees, verifying for the first time the beamforming capabilities associated with SICL technology. The operational frequency band is 20–45 GHz, while the center operating frequency is 26 GHz making it appropriate for above 6-GHz 5G New Radio (NR) operating bands n257 (26.5 GHz to 29.5 GHz), n258 (24.25 GHz to 27.5 GHz), n261 (27.5 GHz to 28.35 GHz) and n260 (37 GHz to 40 GHz). Owing to the low-loss and stable beamforming performance, the SICL RL is suitable for mm-Wave 5G and is extendable to B5G applications.

Design, Fabrication, and Measurement of Efficient Beam-Shaping Reflectors for 5G Applications

An optimization procedure to design passive metallic reflectors for the fifth-generation (5G) mobile network applications, as well as fabrication and measurement of the designed reflectors, are presented. These reflecting surfaces can be used as passive repeaters in both indoor and outdoor applications to change field coverage by redirecting incident beams into desired directions with relatively controllable power distributions. The design procedure involves an efficient combination of a heuristic optimization method [based on genetic algorithms (GAs)] and a full-wave electromagnetic solver [based on the multilevel fast multipole algorithm (MLFMA)]. The optimized geometries are realized using a 3-D printing method that enables low-cost and adaptive fabrication. During optimizations, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\lambda $ </tex-math></inline-formula> by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10\lambda $ </tex-math></inline-formula> compact and efficient reflectors are implemented as reference designs, and they are fabricated to have 18 GHz center frequency of operation. Measurements in a free-space setup are in good agreement with simulations, demonstrating the success of both the design procedure and the designed reflectors as potential 5G components.

Low Profile Reflective Polarization Conversion Metasurface With High Frequency Selectivity

In this article, a multilayer reflective polarization conversion metasurface with both high-frequency selectivity and low profile is proposed. The frequency selective polarization conversion metasurface (FSPCM) is composed of four metal layers separated by three substrates. The cross-shaped patch on the top layer is connected to the folded microstrip line on the bottom layer with two via holes through the circle slots inside two ground layers, which converts the linearly polarized electromagnetic incident wave into cross-polarized wave after reflection. The second-order response can extend to the third-order response by introducing a coupled half-wavelength microstrip resonator on the bottom metal layer, which achieves high-frequency selectivity with a transmission zero and high polarization conversion rate (PCR) without increasing the thickness. The equivalent circuit analysis, structure simulation, and experimental demonstration are conducted in detail; the frequency selectivity of the fabricated FSPCM at the lower and upper band edge is 94 and 192 dB/GHz, respectively; PCR is more than 97% from 4.85 to 5.12 GHz, and the thickness is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.028\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free space wavelength at the center operating frequency. Our findings pave a new way for enhancing the anti-interference capability and electromagnetic compatibility in applications of communication system, microwave imaging, and stealth technology.