Broadside Radiation Research Articles

Miniaturization and Cross-Polarization Reduction of Quarter-Wave Microstrip Antennas Based on Magnetic Currents Reconstruction

In this work, a simple method is proposed to simultaneously reduce the size and cross-polarization level (XPL) of quarter-wave microstrip antennas by reconstructing the magnetic currents along the radiation edges. A design example of five shorted elements is given with a comparison of the quarter-wave microstrip antennas at 1.88 GHz. Measured results show an over 64% size reduction and 17-dB cross-polarization suppression enhancement for the proposed scheme as compared with the conventional one. Moreover, the proposed scheme exhibits good broadside radiation patterns with a gain of 5.4 dBi and the half-power beamwidths of about 104° in the E-plane and 84° in the H-plane.

Anisotropic Complementary Metantenna for Low Sidelobe Radiation and Low In-Band Co-Polarized Scattering Using Characteristic Mode Analysis

An anisotropic complementary metantenna (ACMA) is proposed for the integration of low sidelobe radiation and low in-band co-polarized (IBCP) scattering with the aid of characteristic mode analysis (CMA). With the guidance of CMA, the proposed ACMA evolving from a conventional metantenna (MTA) not only generates a coding phase distribution for low scattering but also restores broadside radiation modes like a uniform MTA. With the IBCP conditions set to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarization and the band around 9 GHz, the ACMA is constructed by mixing two types of double-layer anisotropic complementary metasurface (MTS) unit cells. Two desired characteristic modes of ACMA are simultaneously excited by a substrate integrated waveguide (SIW) cavity through dual bow-tie slots. Both the simulation and experiments demonstrate that the proposed ACMA achieves both the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -polarized broadside radiation with sidelobe level below −18.9 dB and IBCP scattering levels below −17.8 dB over the frequency range from 8.87 to 9.78 GHz.

Frequency reconfigurable dielectric lens antenna with graphene nano-antenna feed for THz applications

This paper proposes a frequency reconfigurable dielectric lens antenna (DLA) to compensate high attenuation due to atmospheric losses in the THz region. An aperture coupled graphene plasmonic nanoantenna has been designed and used to feed DLA. Frequency tuning has been introduced by varying the chemical potential of graphene. A lumped elements equivalent circuit for graphene-based feed antenna has also been proposed. The values of the lumped elements are obtained using the vector fitting algorithm. The proposed DLA has high gain, narrow beamwidth, broadside radiation pattern and stable input impedance. Directivity achieved through simulation is up to 7.3 dBi with radiation efficiency of 70 % and 21.2 dBi with radiation efficiency of 65 % for feed antenna and DLA respectively. The performance of DLA has also been studied as the function of feed element, relative permittivity of lens material, radius of lens and off-axis displacement tolerances.

Circularly polarized directive hybrid patch/horn antenna for upper band 5G applications

AbstractA circularly polarized high gain hybrid rectangular patch/horn antenna with chamfered corners is presented in this paper. The measured impedance bandwidth of the proposed design extends from 26.7 to 28.7 GHz. The suggested design antenna exhibits circular polarization propagation over the working band, which is achieved by introducing chamfered corner overlapped patch antennas surrounded by the truncated pyramidal horn. The main purpose of this horn is to enhance the overall gain without any deterioration of other antenna characteristics (more than 4 dB over the operating band when compared to the patch antenna). The maximum measured gain of the hybrid antenna is 10.9 dBi. The radiation patterns of the hybrid antenna show directive broadside radiation with stable performance over the whole frequency band. The suggested antenna is analyzed and designed applying both the numerical simulator (CSTMWS and HFSS).

A Design Method for a Leaky-Wave System With Uniform Field Coverage and Broadside Radiation for a Vacuum-Tube Ultra-High-Speed Train

The communication system for vacuum-tube ultrahigh-speed trains faces great challenges from unstable signal coverage and severe Doppler effects as a result of long running distances and ultrahigh speeds. This communication presents a possible solution for a communication system in a vacuum-tube high-speed train system that operates using a leaky waveguide. The design method for the leaky waveguide is demonstrated in detail. The developed leaky waveguide consists of periodic metal posts and longitudinal slots in a staggered arrangement, and it can achieve the properties of uniform field coverage and broadside radiation. Therefore, the performance of long-distance transmission with stable signal quality can be realized, and the Doppler effect in the scenario of ultrahigh-speed rail can be mitigated. Leaky waveguides with lengths of 5, 10, and 20 m are designed as verifications of the method. A 5 m leaky waveguide is fabricated and measured. The measured results are consistent with the simulated results, demonstrating that a uniform field distribution and broadside radiation can be achieved using the developed leaky waveguide.

A Compact Wideband Filtering Antenna on Slots-Loaded Square Patch Radiator Under Triple Resonant Modes

In this article, a compact microstrip patch antenna (MPA) with enhanced bandwidth and filtering response is proposed and implemented solely by loading pairs of slots on the conventional square patch radiator. Initially, the dominant mode TM10 of the square patch radiator is theoretically investigated, revealing its broadside radiation pattern and its current flows in the consistent direction. After that, based on the regularities of field distribution, two pairs of slots are etched in the square patch so as to generate two extra modes without destroying both resonant and radiating properties of TM10 mode. By virtue of these two excited modes, two extra resonances are produced in proximity to its dominant one, so as to widen the bandwidth under triple resonant modes. Meanwhile, owing to the inverse equivalent magnetic currents (EMCs) along the radiation edges of the patch and the out-of-phase electric fields at the two sides of each slot under these two excited modes, radiation cancellation toward broadside direction and efficiency reduction occur simultaneously. Hence, radiation nulls are achieved in all direction, and particularly, the radiation null toward broadside direction is deeper than others. After our intensive investigation is done on the entire slots-loaded patch radiator, a wideband filtering MPA with three in-band resonances and two out-of-band radiation nulls has been finally constructed. For demonstration, a prototype antenna at a center frequency of 3.5 GHz is designed, fabricated, and measured. The measured results are found in good accordance with the simulated ones, demonstrating an impedance bandwidth of 9.14% with stable broadside realized gains as well as two radiation nulls at 3.12 and 3.83 GHz, respectively, in addition to its low profile of 0.029 free-space wavelength. Notably, the presented antenna has occupied the almost same area as the conventional square MPA, maintaining its good size compactness.

A D-Band Magnetoelectric Dipole Antenna-in-Package (AiP) Implemented on BT-Based Organic Substrate

A high gain, wide bandwidth (BW), and low-profile <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band magnetoelectric dipole antenna-in-package (AiP) is proposed in this article. The unit antenna with a cavity backed slot is first evaluated by a substrate integrated waveguide (SIW) feed structure. The simulated impedance BW of the unit antenna covers 27 GHz from 132 to 159 GHz with stable broadside radiation patterns. Then, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> 2 array based on the proposed unit antenna is designed and verified on a four layer BT-based organic substrate. The array design is composed of an isolation, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 subarray, a two-way SIW power divider, and a probe pad to SIW transition. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 subarray is realized by a four-way broad wall coupler with a V-junction design in particular. Tested by probing on substrate in the direct far-field chamber, the measured impedance BW covers 23.4 GHz from 135.4 to 158.8 GHz with a peak gain of 14.1 dBi at 150 GHz. The average of measured gains within the 130–160-GHz band is 12 dBi. Modeled with the dimensions of structural analysis results from optical microscope (OM) and cross-sectional scanning electron microscope (SEM) inspection, the post-simulation result shows a good agreement with the measurement result, including impedance BW, radiation patterns, and gains. This article demonstrates that the proposed AiP using the low-cost BT-based substrate manufacturing technology can be a good candidate for the future <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band applications.

Low-Profile Patch Antenna Pair With Pattern Diversity Using Common and Differential Modes for MIMO Systems

We propose a low-profile hexagonal patch antenna pair with pattern diversity by using a single shared radiator. More specifically, both equivalent circuit and full wave simulation results show that the common mode and the differential mode of the grounded hexagonal patch could be excited with similar resonant frequencies, and then the coupling-feed method is employed to extend the impedance bandwidth. Simulation and measurement results demonstrate that such antenna pair, featuring a better decoupling performance, could be capable of generating both of the apple-shaped radiation pattern and the broadside radiation pattern in a wide band with the shared patch size of 0.2 <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}$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \times\, 0.37\, \lambda _{0}$</tex-math></inline-formula> and the profile height of 0.05 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \lambda _{0}$</tex-math></inline-formula> . The proposed design should pave the way for the development of more compact multiple-input–multiple-output (MIMO) systems.

Dual‐band full‐duplex antenna with high isolation using differential fed and dual‐polarization

AbstractThis study proposes a new design approach for a dual‐band full‐duplex antenna to achieve high interport isolation using the differential fed technique. It consists of a single radiating patch, a differential fedline, and a direct fedline. A slotline‐based balun is used in the design to implement the differential fed, which offers minimum phase and magnitude imbalances to the patch of the antenna. The differential fed and direct‐fed lines are orthogonally connected to the radiating patch to realize dual polarization. Both the dual‐polarization and differential fed techniques help to improve the interport isolation of the antenna. It offers an interport isolation of more than 51 and 53 dB over the entire lower and higher operating bands, resonating at 3.22 and 4.1 GHz with 84 and 110 MHz bandwidths. To validate the proposed antenna, a prototype has been fabricated on an FR‐4 substrate with the dimensions of (1.79 × 1.79 × 0.017)λg (λg is the guided wavelength in the substrate at the lower frequency f1), with measured results consistent well with simulations. The far‐field measurement exhibits that the proposed antenna provides a unidirectional broadside radiation pattern and achieves a minimum cross‐polarization of less than −38 dB in all directions and less than −42 dB in the direction of the main lobe in both E‐ and H‐planes at the resonant frequencies. The antenna has insignificant backward radiation with the front‐to‐back ratio 20 dB when port1 is active and the front‐to‐back ratio 30 dB when port2 is active. Moreover, the proposed antenna design is simple and easy to fabricate as the differential fed is implemented using the slotline‐based balun within the same general purpose FR‐4 substrate layer. This eliminates the need for any additional and separate circuits for differential fed and minimizes the overall volume of the antenna.

Conformal Array Antenna for Applications in Wide-Scanning Phased Array Antenna Systems

A dipole with four branches, fed by Marchand balun, is designed to be conformal with wing of an unmanned aerial vehicle. With the help of branches, the proposed dipole element achieves a better impedance matching performance. Meanwhile, the metallic coupled strip is added to move the scanning blindness out of the operating frequency band, without deterioration at broadside radiation. Besides, the beamwidth in the vertical plane, i.e., the H-plane of the dipole, can be effectively compressed by loading three metallic strip directors, and the element gain increases as well. Based on the dipole element, a 12-element linear phased array is designed and simulated. The simulated results show that the array achieves ±60° scanning range in the horizontal plane, with the voltage standing wave ratio lower than 2.5 in the operating band of 2.4∼3 GHz. Moreover, the 3 dB beamwidth in the H-plane is 81° at the center frequency of 2.7 GHz. The measured results of the fabricated antenna prototype agree reasonably well with the simulated ones, which verify the feasibility of the wing-conformal linear phased array design.

Novel Cavity-Backed Filtering Antennas Based on Radiant Metal Block Structure

In this article, a radiant metal block structure is proposed for designing reduced-size cavity-backed filtering antenna. The method of characteristic mode analysis is used to investigate the characteristic current modes of the cubic metal block, one of which can maintain a high inherent radiation capacity over a wideband. In addition, the radiation quality factor of the utilized mode is described in detail. Based on this characteristic current mode, metal block antennas with different bandwidths can be designed to realize broadside radiation. The proposed metal block antenna element can maintain stable radiation characteristics in the passband and the realized gain is greater than 9 dBi. To design the filtering antennas, the proposed metal block is cascaded with traditional resonant cavities. A third-order metal block filtering antenna array is fabricated for verification. The measurement results are basically consistent with the simulated ones. The maximum measurement gain is 12.85 dBi and the gain in the passband is flat.

Extremely Low-Profile Periodic 2-D Leaky-Wave Antenna: An Optimal Solution for Antenna-Frontend Integration

We investigate and present a very low-profile, high-efficiency, and high-gain 2-D leaky-wave antenna (2DLWA) implemented on a high permittivity substrate operating in the millimeter-wave range, paving the way for the seamless integration of a high-gain and high-efficiency antenna with a frontend. In contrast to the typical air-filled 2DLWA, where a perturbation of the first higher-order mode (TE1/TM1) results in highly directed broadside radiation, in the proposed antenna, the propagation and leakage of a quasi-TEM (Q-TEM) mode results in an extremely low-profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> ), high-gain (~15 dBi) antenna. In this scenario, the transverse resonance condition for a Q-TEM mode is established by employing a capacitive partially reflective surface (PRS) in a thin ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.065\lambda _{0}$ </tex-math></inline-formula> ) substrate with a relative permittivity of 10.2. The proposed periodic 2DLWA, unlike the conventional uniform/quasi-uniform air-filled counterparts, radiates based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbf {n}=-\mathbf {1}$ </tex-math></inline-formula> space harmonic operation. Due to a strong mutual interaction between the PRS and ground plane, conventional design and analysis approaches are no longer relevant in this low-profile architecture. Instead, we employ the Floquet modal expansion theory to create an equivalent circuit model (ECM) for the PRS that takes into account the contributions and mutual interactions of the Floquet harmonics as well as the ground plane effect. By employing reflecting boundaries realized with edge truncation (air trenches) in a high permittivity substrate, we show that the aperture efficiency is enhanced by 15% compared to conventional counterpart.

Printed leaky‐wave antenna with stable gain and reduced cross polarization

AbstractA printed leaky‐wave antenna with stable gain and reduced cross‐polarization level is presented in this letter. The proposed antenna has the property of continuous backward‐to‐forward beam scanning with symmetrical scanning. The proposed antenna's unit cell consists of two unequal inclined stubs connected to a microstrip line. The angle between the stubs and their dimensions is designed optimally to obtain improved antenna performance. The antenna provides stable gain with peak gain 14.4 dBi and gain variation 2.55 dBi in the operating band 9.5–15 GHz. The maximum value of cross‐polarization level along the main beam is −30 dB. The design gives a scanning angle of 73° from −36° to +37° through broadside. Another important feature of the proposed antenna is that there is no gain reduction at the broadside radiation.

Dual-Frequency Microstrip Leaky-Wave Antenna for High-Gain Broadside Radiation

This article presents a resonator-fed dual-frequency dual-mode bidirectional leaky-wave antenna to provide attractive high-gain broadside radiation at dual desired frequencies. First, by analyzing the dispersion diagrams of the first (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) and third (EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) higher order modes of a microstrip line, it is theoretically verified that these two modes can both be suitably employed for bidirectional leaky-wave antenna design. In addition, it is also determined that the ratio between these two operation frequencies can be handily controlled by appropriately loading periodical shorting pins along the nodal lines of the EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modal field. As such, the dual-frequency operation principle is thoroughly investigated and determined. Afterward, to effectively excite the desired modes and suppress any unwanted modes of the microstrip line, a dual-frequency resonant-fed strategy is adopted. More specifically, the introduced feeding resonator is first fed by a pair of differential probes, and then, the microstrip EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modes are excited through the coupling gap. In this way, the desired pure EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> modes are successfully excited. As an example, a dual-frequency bidirectional microstrip leaky-wave antenna is designed to work at 3.6 and 4.9 GHz, and its prototype is simulated, fabricated, and tested. The obtained far-field radiation patterns from simulations and measurements show a reasonable agreement, and the concerned high-gain radiation at the broadside is well achieved at both frequencies.

A new compact ultra-wideband frequency selective surface with angular stability and polarization independence for antenna radiation enhancement in microwave imaging application

A new compact, rudimental, uni layered frequency selective surface (FSS) is proposed to work in the commercial ultra-wideband (UWB) spectrum with its application in enhancing broadside radiation of an UWB antenna. The overall unit cell dimension (length × width × thickness) of the proposed UWB FSS is 0.15λL × 0.15λL × 0.016λL only where λL represents the wavelength corresponding to lowest band edge in the 3.04 to 10.88 GHz (∼112.6 %) spectrum with transmission coefficient less than −10 dB. Moreover, the proposed FSS provides certain degree of angular stability of 45° in both TE and TM planes of polarization. The proposed FSS is well suited for antenna gain augmentation as it offers linearly decreasing reflection phase profile. A compact ultra-wideband U-shaped CPW fed antenna with the dimension of 32 × 26 × 0.8 mm3 is designed that covers a bandwidth from 2.7 to 12.76 GHz (130 %). The proposed FSS is integrated with the U-shaped antenna to exhibit an improved and steady gain profile of 5.1–6.8dBi in the 2.82–12.92 GHz (128.34 %) impedance band. Maximum gain augmentation of 3.62 dBi is achieved at 9.5 GHz along with steady gain profile in the entire operating band of “antenna-FSS”, linear S21 response and flat group delay variations which implies the applicability of proposed antenna-FSS in various UWB communication purposes that comprise impulse radar, through wall imaging, microwave imaging, short range indoor communication etc. The applicability of UWB ‘antenna-FSS’ is established by ground coupling microwave imaging test in proximity of soil test bed where the fundamental characteristics of ‘antenna-FSS’ is found to be unaltered.

Novel method for reshaping TM 00 mode radiation patterns of rectangular patch antenna by using characteristic mode analysis

Based on characteristic mode analysis (CMA), a novel method for reshaping the TM00 mode of the rectangular patch antenna (RPA) is presented. Initially, the RPA loaded by periodic shorting vias, as the basic structure for generating the TM00 mode, is investigated by CMA. The nonbroadside pattern of TM00 mode is revealed to be caused by the vertical currents on the shorting vias. And it can be transformed into a broadside direction by replacing the vertical vias with a new shorting structure possessing strong horizontal currents. Moreover, to further verify the feasibility of the proposed method, a compact CPW-fed aperture-coupled RPA for the WLAN application is designed. By simultaneously exciting a reshaped TM00 mode, a fundamental TM10 mode, and a slot mode, the proposed RPA can achieve dual-band performance with broadside radiation features. Finally, the proposed antenna is fabricated and tested. The results illustrate that the fabricated antenna can achieve good impedance matching and broadside radiation characteristics in 2.4–2.46 GHz and 5.1–5.6 GHz bands.

Design of a broadband U-slot loaded E-shaped patch antenna using characteristic mode analysis

This article introduces a characteristic mode analysis (CMA) based broadband and high gain microstrip patch antenna by embedding U-slot into an E-shaped patch in a single-layer radiating structure. The design and analysis of the antenna utilize the CMA to obtain the inherent modal currents induced in the E-shaped radiator. Out of possible radiating intrinsic modes, an undesired higher-order mode (HOM), adjacent to the upper band of the E-shaped patch, is efficiently excited with a secondary radiating slot (U-slot) to increase the bandwidth. Additionally, the U-slot creates another HOM with proper polarization and broadside radiation. Consequently, the overlapping of these new excited modes with the primary operating band of the E-shaped patch exhibits a broader bandwidth of 64.7% (4.7–9.2 GHz) and a peak gain of 10.6 dBi with an overall dimension of 1.4λ0×1.4λ0×0.1λ0 (λ0 being the free-space wavelength at a centre frequency of ≃ 7 GHz). The fabricated prototype agrees well with the simulation results, and the radiation patterns remain consistent over the entire bandwidth. Due to planar and broadband features, the proposed antenna is suitable for low-cost WLAN, Wi-Max, Wi-Fi 6E, and sub-6 GHz applications.

A Pillbox Based Dual Circularly-Polarized Millimeter-Wave Multi-Beam Antenna for Future Vehicular Radar Applications

In this paper, a dual circularly-polarized (CP) multi-beam antenna is proposed for future vehicular radar applications. The antenna is composed of two pillbox reflector beamforming networks (BFNs) and a series-fed microstrip line based dual CP leaky-wave antenna (LWA) array, which has a symmetrical structure and can obtain both left hand circular polarization (LHCP) and right hand circular polarization (RHCP) by switching the exciting current direction of the microstrip line. Besides, a shorted stub is loaded in the LWA to suppress the open-stop band (OSB), and thus achieve the broadside radiation and good impedance matching of the LWA. To realize the dual-polarized radiation characteristic with low-cost passive beam scanning capability, two pillbox BFNs are connected at both sides of the LWA to share the LWA aperture. The two different BFNs can excite different CP radiation patterns. A prototype of the proposed antenna is fabricated in the frequency band 23.5–24.5 GHz, and the measured results approve that the proposed antenna can realize ±36° beam scanning range with −4.0 dB crossover level, and the gain is higher than 17.7 dBi in the operating band. The advantages of the proposed antenna, including low-profile, low-cost, passive beam scanning ability, and dual circular polarization, make it an attractive choice for low-cost millimeter-wave radar applications.

Mutual coupling reduction between the cylindrical dielectric resonator antenna using split ring resonator based structure

In this work, the design of a compact Multiple Input Multiple Output (MIMO) Cylindrical Dielectric Resonator Antenna (CDRA) with an efficient technique for mutual coupling reduction is investigated and validated experimentally. Two cylindrical dielectric resonators (CDR) are excited by the microstrip line through the rectangular slot underneath the CDRAs. Isolation between the CDRAs is improved by a separator wall loaded with Split Ring Resonator (SRR) placed in between the elements. A maximum improvement of isolation up to 40 dB is achieved over the frequency band 7.40–7.80 GHz centered at 7.56 GHz. Broadside radiation patterns at both the principal planes justify the use of the proposed MIMO antenna for commercial applications.

A beam‐formed leaky‐wave antenna array with power‐recycling feeding network

A substrate integrated waveguide leaky-wave antenna array using power-recycling feeding network to achieve beamforming radiation pattern is investigated in this article. The antenna array consists of three elements represented by An1, An2, and An3 on two kinds of radiation mechanism. An1 and An2 are working on the -1th spatial harmonic mode with broadside and backward radiation directions, respectively, and An3 is working on the fundamental wave mode with forward radiation direction. The open-stopband due to broadside radiation design in An1 is suppressed by arranging two similar slots in one radiation unit. By using power-recycling feeding network, the traveling wave directions in An2 and An3 are opposite, which partially compensates the opposite radiation directions of these two elements. Therefore, by adjusting the sizes of radiation slots appropriately, the proposed antenna array can achieve a cosecant–distribution radiation pattern within the range from 0° to 50°.