High Isolation Level Research Articles

High selectivity wideband two‐channel bandpass filter for 5G microwave communication systems

AbstractA two‐channel high‐selectivity, wideband bandpass filter has been presented. This is based on a microstrip mixed‐impedance resonator and defected ground structure with the mixed coupling strategy. Two pairs of peripheral stepped‐impedance resonator (SIR) structures are used as stubs, achieving TZs at the immediate lower and upper cut‐off sides of the passband and control the bandwidth, while the other two transmission zeros on the upper cut‐off side are yielded through the defected ground structure, and the coupling between the SIR and uniform‐impedance resonators components, respectively. A prototype of the circuit is fabricated and measured for validation. The measured results exhibited insertion and return losses better than 1.1 and 20.5 dB, respectively, and high isolation levels exceeding 19 dB. In total, four transmission zeros are achieved. The designed filtering circuit realized a 3‐dB fractional bandwidth of 58.1%. There is a 0.95f0 stopband at the upper cutoff. The fabrication of the prototype shows good agreement between the simulated and measured performance.

Wide stopband QMSIW diplexer with large frequency ratio and flexible specification

AbstractIn this letter, a wide stopband quarter‐mode substrate‐integrated waveguide (QMSIW) diplexer is proposed. By using coupling feeding lines and QMSIW cavities, the two passbands of the diplexer can be controlled independently by their respective QMSIW bandpass filters. In comparison to other counterparts, the proposed diplexer provides flexible passband specification, compact size, and high isolation. The design exhibits a wide 20‐dB stopband up to 3.2f0, a frequency ratio of 1.6, and a high isolation level larger than 42.2 dB across the passbands.

Design of a Crossed Dielectric Resonator-Loaded, Dual-Band Dual-Polarized Differential Patch Antenna with Improved Port Isolation and Gain

To meet the urgent requirement for more channel capacity in modern wireless communication systems, antennas with more operation bands are demanded. However, large amounts of antennas suffer from low radiation gains and low port isolation levels. In view of this, a differentially fed, dual-wideband, dual-polarized patch antenna is proposed in this paper. Compared with conventional crossed-feeding structures, the proposed crossed dielectric resonator (CDR) can provide extra resonances with improved isolation levels and radiation gain. Further, four shorting pins are introduced to the radiating patch to help improve the impedance-matching performance. In addition, the proposed antenna also has a very compact size of 0.46λ × 0.46λ × 0.12λ. Finally, a prototype of the proposed antenna is fabricated to validate the design concept. The measured results show that the proposed antenna generates dual wide bands of 1.86–2.52 GHz and 3.26–3.72 GHz for |S11| < −10 dB. High radiation gains of 8.9 ± 0.9 dBi and 10.8 ± 1.2 dBi are also obtained, as well as high port isolation levels of better than 38.4 dB and 36.2 dB at the two bands. The excellent performance of the proposed antenna makes it a promising candidate for 4G/5G wireless communication systems.

A Differential Slot-type Dual-polarization Ultra-wideband Antenna

A differentially fed dual-polarization slotted antenna with an ultra-wide bandwidth and low cross polarization is presented in this paper. The antenna is composed of a radiation patch and a ground plane, both of which are printed on the top of the dielectric substrate. The ground is extended toward the radiation patch to form a slotted coplanar structure. In order to expand the bandwidth, a cross-shape symmetrical slotted structure is loaded into the radiation patch. Differential feed is adopted to realize 0∘/90∘ linear polarizations and suppress the cross polarization. Simulation and measurement results show that the proposed antenna with dimensions of 0.53λ0× 0.53λ0 × 0.0135λ0 (λ0is the wavelength at 4 GHz) has a differential mode impedance bandwidth of 82.25% (2.27-5.56 GHz), a differential feed port isolation of higher than 28 dB, and a cross polarization level of less than −30 dB, which achieves the characteristics of ultra-wideband, high isolation, and low cross polarization level.

Substrate Integrated Waveguide-Based Dual-Polarized Self-Diplexing Antenna Array

Substrate Integrated Waveguide (SIW) cavity backed self-diplexing slot antenna array is proposed with dual-polarized capability. The antenna array is composed of four linearly placed full-duplex elements operating at 3.5 and 4 GHz independently. The antennas are designed inside a Half Mode SIW (HMSIW) cavity, and two capacitive slots adjust the resonant frequencies. Furthermore, two 1 by 4 power dividers all including 50-ohm transmission lines are designed to feed the radiators, thus resulting in a single layer antenna array integrated with feeding networks. Upon evaluating the simulated and measured results, the minimum reflection coefficients of -25 dB were observed at both operating frequencies. In addition, the data showed that the suggested structure brings about a high isolation level of more than 23 dB between two bands. It is also worth expressing that maximum gains of 10 and 11.5 dBi are obtained at 3.5 and 4 GHz, respectively. And, the radiation efficiencies are 0.78 and 0.9 for the low and high frequency bands.

A Survey of Five Generations of MIMO Multiband Base Station Antennas

AbstractAs telecommunication systems evolve, there is an increasing demand for multi‐band MIMO base‐station antennas. Antenna arrays are generally used to support multiple frequencies with multiple ports in a compact size. However, this can result in significant degradation in scattering patterns and return loss/port isolation due to the close proximity of the radiation from the array. Various techniques have been proposed in the literature to address these issues. This paper presents an overview of the challenges faced by base station antennas (BSAs) over time and their general solutions. With the technological advancements of communication systems, accompanied by high data rates, high‐frequency antenna designs and MIMO operations have been introduced at the base station level. Base station antennas encountered design challenges, including broad bandwidth, high isolation levels, stable half‐power beam width, beam squint reduction, high cross polarization discrimination (XPD), gain improvement, beam steering, compact size, and cost reduction. This survey provides information on the solutions adopted by researchers over time for each design challenge, with citations. Additionally, the authors discuss techniques developed to overcome these challenges, demonstrating the evolution of BSAs from the first to the fifth generation of telecommunication systems.

A Self-Decoupling Method for MIMO Linear and Planar Dielectric Resonator Antenna Arrays Based on Transmission Characteristics of Feeding Structure

In this paper, a novel self-decoupling method for the multi-input multi-output (MIMO) dielectric resonator antenna (DRA) arrays is investigated. This method is based on the transmission characteristics of the conformal strip that feeds the DRA. It is found that when the strip-fed DRA operates in the higher-order mode, e.g., TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">113</sub> mode, the E-field coupled to the metal strip of the adjacent passive DRA presents a standing wave distribution. By appropriately adjusting the dimensions of the feeding strip, the E-field can form a node with zero amplitude at its bottom where a coaxial probe is connected, preventing the energy from getting into the receiving port and hence achieving a high isolation level without requiring any extra decoupling structure. This self-decoupling method is applicable not only to one-dimensional (1-D) H- and E-plane coupled MIMO linear arrays but also to two-dimensional (2-D) MIMO planar array. To verify its feasibility, a prototype of 2 × 2 MIMO planar DRA array is simulated, processed, and tested. The results show that a usable bandwidth (|S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ii</sub> | < -10 dB and |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ij</sub> | < -20 dB) of 10.8% is achieved, and the maximum isolation is over 40 dB within the passband.

Isolation Improvement Using the Field-Circuit Combined Method for In-Band Full-Duplex MIMO Antenna Arrays

This paper proposes a field-circuit combined decoupling method for co-polarized in-band full-duplex multiple-input multiple-output (MIMO) antenna arrays. The proposed field-circuit combined method is composed of decoupling network and neutralization-based decoupling. An in-band full-duplex antenna with high isolation and low cross-polarization level is designed and extended to a 1 × 4 linear array. The decoupling network and ADS are applied for the array to alleviate the mutual coupling by rebuilding the neutralization wave paths in the circuit and field domains. Thus, low coupling (&lt; −25 dB) among the transmitting/receiving antennas and high isolation (&gt; 47 dB) between the transmitting and receiving antennas are achieved at 2.6 GHz, exhibiting a superior decoupling performance.

Capsule Endoscopic MIMO Antenna With Radiation Pattern and Polarization Diversity

This article presents a novel compact dual-element capsule endoscopic multiple-input-multiple-output (MIMO) antenna at a 915 MHz industrial, scientific, and medical (ISM) band. Both radiating elements of the MIMO antenna system are circularly polarized (CP) at the desired frequency band (915 MHz). In fact, Antenna- 1 operates at left-handed CP (LHCP) and Antenna- 2 operates at right-handed CP (RHCP), enabling polarization diversity at 915 MHz. Moreover, the radiating elements radiate in two opposite directions; thus, they enable pattern diversity. The performance of the proposed antenna system is analyzed in a realistic human phantom. Reactive slots in the patch antennas are incorporated to achieve compactness ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi \times $ </tex-math></inline-formula> (4.7) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\mathrm{ 2}}\,\,\times0.13$ </tex-math></inline-formula> = 9.01 mm3) and CP characteristics. Furthermore, a rectangular slot on the ground plane is introduced to reduce the mutual coupling between the radiating elements. The proposed antenna has compact dimensions of 9.01 mm3, a peak realized gain of −24.6 dBiC, and a high isolation level of 29.7 dB within the whole band. The specific absorption rate (SAR), link margin (LM) and main MIMO channel parameters are investigated which show good results. The key features of this antenna are its compact size, high isolation level between the antennas, and polarization and pattern diversity.

Design of MIMO Antenna with Double L-Shaped Structure for 5G NR

To satisfy the demand for 5G communication to smartphone terminal antennas in element quantity and isolation, an eight-element wideband MIMO antenna set of high isolation level is proposed. Each antenna element in the array is a double-L antenna consisting of an L-shaped slot and an L-shaped 50 Ω microstrip line. The L slot is formed by adding an I-shaped open circuit directly to the side of the rectangular slot. In addition, the antenna arrays are located on the long bezels on both sides of the mobile phone motherboard, and the coupling feed is made in the frequency range of 3.6–4.7 GHz through the L-shaped microstrip line, so as to cover the 5G NR band (N77/N78/N79). Finally, the four element pairs (8 components) achieve isolation of greater than 11 dB, the performance frequency range is 3.6–4.7GHz, the return loss is −6 dB, the total efficiency is greater than 85%, and the envelope correlation coefficient is less than 0.08. Other MIMO performances are also calculated, the design process is discussed in detail, and one-handed grip mode and two-handed grip mode are discussed to demonstrate their stabilities in real-world applications.

Design of Self-Decoupling Dielectric Resonator Antenna With Shared Radiator

The method of mode cancellation to design a two-port dielectric resonator antenna (DRA) for an in-band full-duplex (IBFD) application is investigated in this communication. The whole antenna structure is straightforward, only composed of a single DRA element, a pair of feeding lines, and a pair of metallic probes. Attributing to the features of different modes used in this design, mutual coupling between the exciting port and the passive port can be suppressed to an extremely low level without using an extra decoupling structure. A prototype is fabricated and measured for verification. The measured results demonstrate that the proposed antenna has broad bandwidth and high isolation level can be achieved throughout the whole working band.

A Mutual-Coupling-Suppressed Dual-Band Dual-Polarized Base Station Antenna Using Multiple Folded-Dipole Antenna

An interleaved shared-aperture dual-band dual-polarized base station array antenna is proposed in this article. The lower-band (LB) element is realized by using a multiple folded-dipole antenna (MFDA) and four parasitic loops. To interpret the working principle of the MFDA, a double folded-dipole antenna (DFDA) is firstly analyzed by using the transmission line (TL) model. Then, by combining two bended DFDAs and introducing four parasitic loops, a low cross-band scattering LB element with a high out-of-band rejection level of 16 dB is obtained to cover 2.3–2.7 GHz. The higher-band (HB) element with a wide impedance bandwidth of 42.5% (3.0–4.6 GHz), a high roll-off rate (RoR) of 249.2 dB/GHz, and a high out-of-band rejection level of 17 dB is obtained by introducing a meander line loop (MLL), a rectangular loop (RL), and V-shaped strips (VSS) near the dipole arms. By combining the proposed low-scattering low-pass LB element and the high- RoR high-pass HB element, a novel interleaved shared-aperture dual-band dual-polarized array antenna with a small frequency ratio of 1.46 and a high cross-band isolation level of 25 dB is realized. Due to the low-scattering characteristic and filtering response of the LB element, the radiation patterns of the wideband HB sub-arrays are almost unaffected.

A 3D-Printed DRA Shared-Aperture Array for Low Cost Millimeter-Wave Applications

In this article, a K-/Ka-band shared-aperture array with high isolation is proposed using 3D-printed dielectric resonator antennas (DRAs). The design procedure with DRAs enables flexibility while implementing shared-aperture arrays. Furthermore, DRAs as nonmetallic radiators are attractive for millimeter-wave (mm-wave) applications due to the absence of ohmic loss. In addition, 3D-printing technology facilitates the design of complex shapes with high-dimensional accuracy. The K- and Ka-bands DRAs are orthogonally oriented to provide improved isolation and cross-polarization level. Meanwhile, the corresponding feeding networks are implemented using the substrate integrated coaxial line (SICL) and the substrate integrated waveguide (SIW). Thus, further isolation improvement is provided by using two different feeding mechanisms for the K- and Ka-bands radiators. Moreover, the SICL network is shared with the SIW wall to efficiently utilize the feeding aperture. As a proof-of-concept, the 3D-printed shared DRAs are designed and fabricated. The standard printed circuit board (PCB) technology is used for the fabrication of the antenna boards. The measurement data agree with the simulations, realizing high isolation and cross-polarization level. The proposed array features low profile, ease of integration, and wideband operation, which makes it viable candidate for mm-wave applications.

Isolation Enhancement of a Two-Monopole MIMO Antenna Array with Various Parasitic Elements for Sub-6 GHz Applications.

In this paper, a high-isolation multiple-input/multiple-output (MIMO) microstrip monopole antenna array is investigated. To reduce the mutual coupling between antenna elements, a novel composite parasitic element constituted by a T-shaped ground branch and an isolated branch was designed and analyzed. The proposed composite parasitic element is capable of generating a unique three-dimensional weak electric field, which can effectively suppress the mutual coupling between the antenna elements. To give an intuitive illustration about the design principle and decoupling strategy of the proposed antenna, the antenna design procedure was ingeniously divided into four steps, and three types of decoupling structures during the antenna evolution were meticulously analyzed at both the theoretical and the physical level. To validate the proposed decoupling concept, the antenna prototype was fabricated, measured, and evaluated. The reflection coefficient, transmission coefficient, radiation pattern, and antenna gain were studied, and remarkable consistency between the measured and simulated results was observed. The simulations showed that the antenna has a peak gain of 3.5 dBi, a low envelope correlation coefficient (ECC &lt; 0.001), and a high radiation efficiency (radiation efficiency &gt; 0.9). Parameters of the proposed MIMO antenna including electrical dimension, highest isolation level, and 20 dB isolation bandwidth were evaluated. Compared with the previous similar designs, the proposed antenna exhibits attractive features including compressed dimension (0.55λ0 × 0.46λ0), extremely high isolation level (approximately 43 dB), fabulous 20 dB isolation bandwidth (3.11-3.78 GHz, 19.4%), a high diversity gain (DG &gt; 9.99 dB), an appropriate mean effective gain (-3.5 dB &lt; MEG &lt; -3 dB), and low design complexity.

A broadband dual‐polarized antenna with quasi‐trapezoidal patches for 5G base station application

A differential dual-polarized patch antenna with broadband, high isolation, and low cross-polarization level for 5G base station is presented. The antenna is composed of the radiating element, feeding structure, and reflector. The radiating element is designed with four identical smaller quasi-trapezoidal patches to achieve a wider bandwidth, which is capacitively driven by two trapezoidal feeding patches. Impedance matching of antennas can be adjusted by tuning the size of quasi-trapezoidal patches in the feeding portion. Finally, a prototype antenna is fabricated based on the simulated model. The measured bandwidth of the proposed antenna is about 27.8% (3.19–4.22 GHz) with VSWR<1.5, and the port isolation is better than 39.5 dB over the whole operating band. Furthermore, the proposed antenna has a stable gain of 8.55 ± 0.8 dBi and a low cross-polarization level (<−33 dB) within the operating band.

Electrically small, low‐profile, full‐duplex Huygens dipole filtenna

AbstractAn electrically small, full‐duplex Huygens dipole filtenna (HDF) is realized as a dense array of two HDF elements consisting of Egyptian axe dipole and capacitively‐loaded loop near‐field resonant parasitic (NFRP) elements. The dual‐band HDF elements operate at two very nearby frequency bands and are physically separated by only 0.12 λLB. Benefitting from the HDF element's good out‐of‐band rejection performance characteristics, high isolation levels between the lower‐band (LB) and higher‐band (HB) ports are obtained without any decoupling structure. The measured results, in good agreement with their simulated values, demonstrate that the entire system is electrically small (ka = 0.975) and low‐profile (0.041 λLB). The measured isolation levels at its LB (HB) port is, respectively, over 33.9 (29.2) dB. When the LB (HB) port is excited, its fractional bandwidth, broadside realized gain, front‐to‐back ratio, and overall efficiency values are, respectively, 0.86% (0.77%), 2.1 (2.31) dBi, 8.1 (9.6 ) dB, and 62.1% (62.8%).

Optimized Super-Wideband MIMO Antenna with High Isolation for IoT Applications.

A compact, low profile, multiple-input–multiple-output (MIMO) diversity antenna with super-wideband (SWB) characteristics has been proposed. The proposed antenna comprises four symmetric monopole-radiating elements printed on low-cost FR4 substrate with the slotted ground plane. The single antenna of a monopole structure and a quad-port MIMO antenna, with the dimensions of 30 × 20 mm2 and 60 × 55 mm2, respectively, are ideal for IoT and high-speed data applications. The proposed MIMO antenna has a high diversity gain and low envelope correlation coefficient (ECC) within the frequency range. Simulated results demonstrate the performance of the MIMO-SWB antenna, which operates from 2.3 to 23 GHz, with a high isolation level over 20 dB in the achieved frequency band. Moreover, the proposed MIMO antenna has been investigated with mirror fashion and orthogonal structure. Both structures provide similar results except for mutual coupling performance. The orthogonal adjustment for high isolation achieves better results with the proposed model. Further, the prototype of the proposed antenna is fabricated and measured effectively. Simulated and measured results show good agreement for super-wideband applications.

Design of an isolation improved MIMO antenna using metasurface based absorber for wireless applications

The paper intends to present a design of isolation improved MIMO (multiple-input and multiple output) antenna with two elements achieving operating band from 4.04 GHz to 5.48 GHz for wireless applications. The MIMO configuration is comprised of two antenna elements that are maintained at two extreme edges of substrate having dimension of 100 × 50 × 0.8 mm3. The incorporation of metasurface based isolator between MIMO antenna elements provide exceptional isolation (< −23 dB) for practical mobile and wireless application. The mutual coupling of unwanted field between MIMO antenna elements acts as major deterrent to exploit the optimum performance for MIMO antenna. The work focus on design and development of MIMO elements with metasurface based isolator (acting as absorber) clearly with an intention to provide high order optimum isolation levels between two antenna elements. The surface current distribution mechanism provide insight to the high isolation level achieved through incorporation of metasurface based isolator in MIMO setup. The display of spatial/pattern diversity with the attainment of suitable values of envelope correlation coefficient clearly testify its suitability for MIMO based mobile application in microwave regime.

Design of a Compact High Isolation 4-Element Wideband Patch Antenna Array for GNSS Applications

This work presents a compact (125 mm diameter) wideband four-element antenna array with a high isolation level for Global Navigation Satellite System (GNSS) anti-jamming applications. The array consists of four identical right hand circularly polarized (RHCP) single feed rectangular patch antennas that can cover BeiDou B1 band (1559.05 – 1563.15 MHz), GPS L1 band (1563 – 1587 MHz), Galileo E1 band (1559 – 1591 MHz), and GLONASS G1 band (1593 – 1610 MHz). The proposed array has a wide frequency bandwidth of 100 MHz (1.55 – 1.65 GHz) with an axial ratio of less than 3 dB. The patch antenna elements are designed on a substrate that has a high dielectric constant to achieve a compact size. The size of each patch element is only 32 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 32\times5.08$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . These patches are placed along the circumference of a circular aluminium ground plane of 125 mm diameter and 1.5 mm thickness in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 2$ </tex-math></inline-formula> symmetrical arrangement. The edge-to-edge distance between the opposite patch elements is only 48 mm while for the adjacent elements the separation is only 27 mm. A microwave absorber material is employed to achieve an extremely low mutual coupling level over a wide frequency range (1.55 – 1.65 GHz) within a compact form factor. The proposed design achieves a mutual coupling of less than −20 dB within a compact overall form factor of 125 mm diameter over the entire band of interest. The simulated and measured results of reflection coefficient, mutual coupling, null steering, null depth, and radiation pattern show that the proposed antenna array is an excellent choice for multiband GNSS applications.

A Low Phase-Noise Dual-Frequency Oscillator Based on Filter Switching Technique

This letter presents a parallel-feedback dual-frequency oscillator (DFO) with low phase noise. It is achieved based on the filter switching technique. By using four switches to control two oscillator loops with a common active device, the oscillation frequency of the proposed DFO can be switched from one to another. Due to the high isolation level of the employed switches, the two oscillator loops almost operate independently. Thus, there is no intermodulation (IM) spurs generated in the output spectrum of the proposed DFO. In the meantime, to improve the phase noise performance of the DFO, each oscillator loop utilizes a high frequency-selectivity bandpass filter with high group delay (GD) as a frequency selective element. In this way, the low phase-noise DFO is developed. For demonstration, the DFO is designed, fabricated, and tested. As seen from the measurement results, the oscillator can oscillate at 2.04 or 3.092 GHz by controlling the four switches. At 100 kHz and 1 MHz frequency offset from the carrier frequency, the phase noises are −108.5 and −129.7 dBc/Hz for 2.04 GHz, while −112.7 and −135.7 dBc/Hz for 3.092 GHz.