Dipole Elements Research Articles

Robust 2-D DOA Estimation in a Polarization Sensitive Single User Environment

Apart from the conventional parameters (such as signal-to-noise ratio (SNR), array geometry and size, and the number of samples), several other factors (e.g., alignment of the antenna elements, polarization parameters) influence the performance of direction of arrival (DOA) estimation algorithms. When all the antenna elements are aligned in the same direction, the polarization parameters uniformly affect the steering vectors, which is the underlying assumption of almost all conventional DOA algorithms. Unfortunately, in this case, for a given set of DOA angles, there exists a range of polarization parameters resulting in a very low SNR across all the antenna elements in the array and vice versa. To avoid this type of unwanted event, different antenna elements must be aligned differently. However, this fact will make almost all commonly used DOA estimation algorithms inoperable since the steering vectors are contaminated unevenly by the polarization parameters. To the best of our knowledge, no work in the literature handles this issue using simple hardware and signal processing techniques even for a single user environment. In this paper, that line of inquiry is pursued. We consider a circular array with the minimum number (i.e., 4) of short dipole antenna elements and propose an antenna alignment scheme. This ensures that at any given point no more than one element will suffer significantly from low SNR due to the contribution of polarization. A thresholding technique to isolate the antenna element after being seriously contaminated by the polarization parameters is developed and analyzed. Two algorithms that are suited for operating reliably in all possible DOA and polarization environments are addressed. The first algorithm follows the working principle of the popular MUSIC algorithm after cleaning the polarization contributions from the non-signal subspace. The other one, which is found as a byproduct of the process of cleaning the non-signal subspace, can estimate the DOA angles in a closed form manner. The implementations of the above algorithms for an arbitrary number of antenna elements greater than or equal to 4 are also presented. Finally, a thorough performance and complexity analysis are illustrated for those two algorithms considering various polarization and DOA scenarios.

Pattern Reconfigurable Dual-Polarized Dipole Antenna With Staggered Parasitic Elements

This paper presents a pattern reconfigurable dual-polarized dipole antenna with staggered parasitic elements operating in 3.5 GHz band. The proposed antenna is designed by assembling two linearly polarized antennas to be orthogonally polarized, and each antenna includes two parasitic elements and a single dipole element. A circuit including a varactor is inserted into each parasitic element, and the current phase of the parasitic element changes according to the capacitance of the varactor. Each antenna has a beam steering range of about ±30° in the E-plane, and the beamwidth and gain are maintained uniformly regardless of the steering angle due to the angled parasitic element. Also, because of the continuously changing characteristic of the varactor, the beam of the proposed antenna is steered continuously, and only four varactors are used. The size of the fabricated dual-polarized antenna is 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.47λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , and the measured results confirm that the antenna has an average gain of around 6 dB with 0.3 dB gain variation.

Comparison of Frequency‐Domain Electromagnetic Responses at Different Offsets Based on Exact Calculation of Grounded‐Wire Source

AbstractSubsurface geoelectric structures and resources can be detected based on the propagation of the electromagnetic field. Near‐source electromagnetic methods have recently become the most popular survey mode. However, calculation of the electromagnetic field in the near‐source region with artificial sources has always been performed based on far‐source dipole approximation. Owing to the introduction of artificial sources in the near‐source region, it is challenging to obtain accurate solution of the electromagnetic field based on the relationship between the observation point and the source, thereby affecting the detection accuracy. Specifically, the main problem lies in the position vector of the transmitting source, which is generally neglected in the response calculation based on the plane‐wave theory. Moreover, only far‐source data can be observed in the plane‐wave theory. However, near‐source data have been collected in a near‐source survey, with the dipole approximation resulting in a large error. We introduce a point charge element to decrease or eliminate the error caused by the dipole approximation. The non‐homogeneous Helmholtz equation is first solved using the Green's function. Then, the response expression of the real source, including the source position vector, is obtained by integrating the response of the harmonic point charge element. The substitution of the dipole elements with the point‐charge elements not only reduces the dipole approximation errors but also displays the electromagnetic characteristics of the entire zone, which are verified by the forward modeling and field survey results. The near‐source (offset is 0.8 of the target depth) survey can be realized based on the point charge element.

Performance Improvement of Substrate Integrated Cavity Fed Dipole Array Antenna Using ENZ Metamaterial for 5G Applications.

This paper exhibits a high-gain, low-profile dipole antenna array (DAA) for 5G applications. The dipole element has a semi-triangular shape to realize a simple input impedance regime. To reduce the overall antenna size, a substrate integrated cavity (SIC) is adopted as a power splitter feeding network. The transition between the SIC and the antenna element is achieved by a grounded coplanar waveguide (GCPW) to increase the degree of freedom of impedance matching. Epsilon-near-zero (ENZ) metamaterial technique is exploited for gain enhancement. The ENZ metamaterial unit cells of meander shape are placed in front of each dipole perpendicularly to guide the radiated power into the broadside direction. The prospective antenna has an overall size of 2.58 and operates from 28.5 GHz up to 30.5 GHz. The gain is improved by 5 dB compared to that of the antenna without ENZ unit cells, reaching 11 dBi at the center frequency of 29.5 GHz. Measured and simulated results show a reasonable agreement.

A Compact Log Periodic Planar Dipole UHF Array Sensor for Partial Discharge Measurements

A compact log periodic planar dipole UHF array antenna from 500 MHz to 2.2 GHz for partial discharge measurement in power transformers is presented in this paper. The compactness of the designed antenna is achieved by shaping the arms and tuning selected dipole elements of the array to fill the unoccupied areas. Shaped dipole arrangement results in additional capacitance between the antenna elements enhancing the bandwidth. The designed antenna achieves a fractional bandwidth of 126% and the size is ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.495\lambda _{0} \times 0.63\lambda _{0} \times 0.0144\lambda _{0}$ </tex-math></inline-formula> ) at center frequency of 1.35 GHz. The proposed antenna is experimentally validated on FR4 3.2 mm thickness substrate. The measured gain of antenna is 4 ± 0.5 dBi over 800 MHz to 2.2 GHz which provides lower variation in measured partial discharges. The effective antenna height of the proposed antenna is measured to be over 15 mm. The measured return loss is better than 10 dB over the frequency range. Moreover, partial discharge measurements with oil filled test objects demonstrate that the designed antenna can receive partial discharge signals effectively.

새로운 6-단자 급전 회로망을 이용한 이중 직교 원형 편파를 갖는 소형 고이득 GPS 안테나

In this study, the design, fabrication, and performance of a small high-gain global positioning system (GPS) antenna that generates dual orthogonal circular polarization using a novel six-terminal feeding network is presented. The proposed six-terminal feeding network has two input quadrature terminals and four output terminals having the same amplitude and 0° or 180° phase. Therefore, it is suitable for feeding the four radiating elements with linear polarization characteristics. To realize a dual orthogonal circular polarization antenna with miniaturization and high gain characteristics, the six-terminal power supply network is positioned in the center of the antenna, and the four radiating elements are arranged on the outside. The radiating element selected after considering the limited space is a three-dimensional printed dipole element with linear polarization characteristics which is rotated by 90°. The antenna size designed optimally in the GPS L1 band (1,575.42±12 MHz) is less than 130 mm (0.68 λ0) in diameter (D) and 40 mm (0.21 λ0) in height. The antenna’s input return loss and port isolation characteristics measured with a vector network analyzer are excellent within the band at 17.1 dB and 18.0 dB or more, respectively. In addition, the antenna gain, and efficiency measured in the anechoic chamber are 8.69 dBi (@bore-sight) or more and 83 % or more, respectively. Furthermore, it can be seen that the axial ratio characteristics of the dual orthogonal circular polarization wave are very good, with less than 0.2 dB (@bore-sight) and less than 1.8 dB (@ 3 dB beam width).

A nine-channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna.

The purpose of this study is to introduce a new antenna element with improved transmit performance, named the nonuniform dielectric substrate (NODES) antenna, for building transmit arrays at ultrahigh-field. We optimized a dipole antenna at 10.5 Tesla by maximizing the -SAR efficiency in a phantom for a human spine target. The optimization parameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simulations as well as phantom experiments to compare the transmit/receive performance of the proposed NODES antenna design with existing coil elements from the literature. Single NODES element showed up to 18% and 30% higher -SAR efficiency than the fractionated dipole and loop elements, respectively. The new element is substantially shorter than a commonly used dipole, which enables z-stacked array formation; it is additionally capable of providing a relatively uniform current distribution along its conductors. The nine-channel transmit/receive NODES array achieved 7.5% higher homogeneity than a loop array with the same number of elements. Excitation with the NODES array resulted in 33% lower peak 10g-averaged SAR and required 34% lower input power than the loop array for the target anatomy of the spine. In this study, we introduced a new RF coil element: the NODES antenna. NODES antenna outperformed the widely used loop and dipole elements and may provide improved transmit/receive performance for future ultrahigh field MRI applications.

Research on W‐band high‐gain magneto‐electric dipole antenna based on double‐sided gap waveguide

AbstractIn this paper, a W‐band magneto‐electric (ME) dipole antenna fed by double‐sided gap waveguide (DSGWG) feeding network is presented. The ME dipole antenna element is designed based on the end‐fire DSGWG and extended ridge with pins. The end‐fire open slot of DSGWG radiate as a magnetic dipole, and the metallic pins in extended ridge radiate as electric dipoles. Taking advantage of this DSGWG structure, the antenna element achieves with high gain and wide bandwidth performances. The antenna element is fabricated and measured with an impedance matching bandwidth of 85–110 GHz for |S11| &lt; −10 dB, and maximum realized gain of 9.2 dBi. A four‐way feeding network based on the DSGWG is designed and connected directly to the ME dipole antennas. The antenna array with ease integration and fabrication properties is designed to validate the performance of antenna elements. The measured average realized gain of the antenna array reaches up to 15.3 dBi over the bandwidth of 88–110 GHz.

Low Cost Printed Dipole Array Antenna for 5G Sub-6GHz Base Stations Implementing Beam-tilting, Ground-backing, and Series-Feeding

ABSTRACT An antenna array dedicated to wideband 5 G sub-6 GHz base station applications is presented. It combines several features to arrive at a very effective and low-cost topology. Printed dipole elements printed on both sides of a single substrate are used to reach a sufficient −10 dB bandwidth of 25.3%. The eight dipole elements are series-fed, which is ideal to realize down-tilt beam shaping in the E-plane. Ground-backing makes the antenna unidirectional with a peak realized gain of more than 9 dBi over the entire band, with a maximum of 12 dBi at 3.5 GHz. The array has a half-power beamwidth (HPBW) varying between 35° and 47° in E plane and between 82° and 86° in H-plane, respectively. The antenna is compared to similar designs in literature and reaches a superior performance.

Conditions for a pure toroidal dipole source

Recently, the physical significance of dynamic toroidal multipoles in the context of electrodynamics has been put under discussion. Indeed, the latter can be shown to arise simply from a Taylor series of the exact source (Cartesian) multipole moments. The split into elementary and toroidal parts was demonstrated to lead to an unphysical result were forbidden components of the momentum transform of the current could radiate into free space. In this contribution, we elaborate the conditions that a current distribution must necessarily satisfy to be considered a ‘pure’ toroidal dipole source. We demonstrate for the first time that symmetry prevents such current distribution to radiate as an elementary electric dipole moment, without leading to an unphysical result. Thus, while both elementary electric dipole and toroidal dipoles are indistinguishable outside the source, they display topologically distinct characteristics within the smallest spherical surface enclosing the source itself and have different physical origin. Based on our results, a pure ‘toroidal’ source can be designed. We believe the outcome of our investigations will help clarify further the formal meaning of the toroidal multipoles.

New distributed beamforming techniques based on optimized elliptical arc geometry for back lobe cancellation of linear antenna arrays

The presence of array back lobe is a major source of interference, power loss, and degrades the signal-to-interference ratio (SIR) in wireless communication systems. In this paper, new distributed beamforming techniques based on an optimized elliptical arc geometry (EAG) are proposed for back lobe cancellation of linear antenna arrays (LAA). The optimized EAG allows for flexible control of the elements' locations and initial transmission phases of their radiations, allowing them to add constructively towards the main beam direction and add destructively towards the back lobe direction. Firstly, two EAG based beamforming techniques are introduced using either a single ellipse-EAG (SE-EAG) or double ellipses-EAGs (DE-EAG). In these techniques, the back lobes are minimized by optimizing both the minor axes of the elliptical arcs and the elements' angular distributions using the particle swarm optimization (PSO) technique. While the elements' transmission energies are kept the same as that of the original LAA. For further back lobe minimization, the double ellipses-EAG with optimized energies (DE-EAG-WOE) beamforming technique is introduced, where both elements' transmission energies and positions are optimized. To verify the superiority and the possibility of practical validation of the proposed techniques, the proposed distributed array configurations based on the DE-EAG-WOE are realized using the CST Microwave Studio software package using dipole elements.

Research and Modeling of Digital Antenna Arrays with Directional Elements on Azimuth-Elevation in VHF Terrain and Vegetation Multipath Propagation Situations

In the paper the problem of using digital antenna arrays equipped with dipole and directive elements simultaneously in the azimuthal and elevation planes is discussed. In particular, they are investigated for communication channels of the VHF range below 1 GHz. This range is characterized by the fact that it has found wide distribution. However, its application is fraught with many difficulties, such as attenuation, reflection from rough surfaces, etc. One of the solutions to these problems can be azimuth-elevation digital beamforming. The paper presents the simulation results for the propagation of signals in the VHF range in free space, two-ray ground-reflection and foliage models. It is assumed that a symmetrical dipole is used on the transmitting side, and a directional Yagi antenna on the receiving digital antenna array (DAA) also equipped with a dipole. The circular (CAA) and hemi-dodecahedron shapes of the arrangement of elements of the receiving digital antenna array are simulated. The bit error rates (BER) depending on the distance between the transmitter and the receiver are estimated for the three above mentioned cases.

Design and Development of Dipole Array Antenna for Wi-Fi Applications

This paper illustrates the design and development of the series-fed two-dipole-array antenna (STDA) for Wi-Fi applications. The proposed antenna consists of two dipole elements of different lengths, which are serially joined by the coplanar strip line. The design incorporates a coaxial/probe feeding technique with balun as an alternative feeding mechanism. The main goal of this paper was to create a high-gain antenna with an array configuration for Wi-Fi applications. For STDA array configurations, antenna performance parameters such as return loss, radiation pattern, gain, and directivity are investigated. It operates at 2.4 GHz and has a high gain of 21.6 dBi when used with a reflector. In order to improve overall gain, the STDA was analyzed for different array configurations in the formation of 1 × 4, 1 × 8, and 2 × 8 STDA arrays. The proposed antenna is made of a FR-4 substrate with a dielectric constant of 4.4 and a loss tangent (tan) of 0.007 and a thickness of 1.6 mm. An antenna measures approximately 105 mm × 80 mm in size. The proposed antenna meets the requirements for a 2.4-GHz antenna with a bandwidth of 200 MHz, and thus, it is found to be suitable for Wi-Fi applications.

Instantaneous radiated power of brain activity: application to prepulse inhibition and facilitation for body dysmorphic disorder

BackgroundGlobal measures of neuronal activity embrace the advantage of a univariate, holistic and unique description of brain activity, reducing the spatial dimensions of electroencephalography (EEG) analysis at the cost of lower precision in localizing effects. In this work, the instantaneous radiated power (IRP) is proposed as a new whole-brain descriptor, reflecting the cortical activity from an exclusively electromagnetic perspective. Considering that the brain consists of multiple elementary dipoles, the whole-brain IRP takes into account the radiational contribution of all cortical sources. Unlike conventional EEG analyses that evaluate a large number of scalp or source locations, IRP reflects a whole-brain, event-related measure and forces the analysis to focus on a single time-series, thus efficiently reducing the EEG spatial dimensions and multiple comparisons.ResultsTo apply the developed methodology in real EEG data, two groups (25 controls vs 30 body dysmorphic disorder, BDD, patients) were matched for age and sex and tested in a prepulse inhibition (PPI) and facilitation (PPF) paradigm. Two global brain descriptors were extracted for between-groups and between-conditions comparison purposes, namely the global field power (GFP) and the whole-brain IRP. Results showed that IRP can replicate the expected condition differences (with PPF being greater than PPI responses), exhibiting also reduced levels in BDD compared to control group overall. There were also similar outcomes using GFP and IRP, suggesting consistency between the two measures. Finally, regression analysis showed that the PPI-related IRP (during N100 time-window) is negatively correlated with BDD psychometric scores.ConclusionsInvestigating the brain activity with IRP significantly reduces the data dimensionality, giving insights about global brain synchronization and strength. We conclude that IRP can replicate the existing evidence regarding sensorimotor gating effects, revealing also group electrophysiological alterations. Finally, electrophysiological IRP responses exhibited correlations with BDD psychometrics, potentially useful as supplementary tool in BDD symptomatology.

On the steerability of phased array EMATs: The dipole element

Shear wave phased array EMATs have a range of properties that make them a desirable solution compared to their piezoelectric counterparts: They do not require direct contact with the specimen and they can operate at elevated temperatures. Shear wave phased array EMATs do not need a Perspex wedge or couplant, making them easy to deploy across industrial applications even at elevated temperatures. Nonetheless, they are not commonly used because of concerns over the strength of signal excitation and lack of knowledge about potential changes in the emitted wavefields as a result of changes in the magnetic properties of the inspected material. In this work, a shear wave phased array EMAT designed to induce shear waves into paramagnetic, diamagnetic, ferromagnetic and ferromagnetic and magnetostrictive metals without compromising its angle coverage or steerability is proposed. The phased array EMAT was designed based on a dipole element wave generation source. The proposed dipole element source is formed by the interaction of the bias magnetic field of the PA EMAT and the electromagnetic field induced by the race-track coils of the PA EMAT. For each race-track coil this results in a combined source that consists of two parallel and slightly separated shear line sources of opposite polarity. A detailed study of the wave generation based on the surface loads induced by the dipole element is presented. The surface loads of the three excitation mechanisms involved in the EMAT transduction -Lorentz force, magnetisation force and magnetostriction force-were estimated in a 2D finite element model. The waves generated by the induced surface loads were estimated in a second 2D finite element model. A shear wave steerability analysis of the phased array EMAT on different metallic materials based on the 2D finite element results is presented in combination with an experimental evaluation on Aluminium 6082 (diamagnetic), mild steel EN1A (ferromagnetic), stainless steel 316 (paramagnetic), stainless steel 304 (paramagnetic) and nickel 201 (ferromagnetic and magnetostrictive). The experimental results showed good agreement with the simulation study. The simulation and experimental results concluded that the angle coverage of the phased array EMAT is almost insensitive to the inspected metallic material.

An ultrawide‐angle scanning tightly coupled dipole array with double‐layer double‐sided frequency selective surface superstrate

In this article, we present an ultrawide-angle scanning tightly coupled dipole array (TCDA). The impedance match issue is a major challenge in the design of ultrawide-angle scanning TCDA. To overcome this issue, we employ a multi-stage wideband balun and design the balun synergistically with the dipole element to improve impedance match performance. A double-layer double-sided (DLDS) superstrate is exploited to further improve scanning performance in the H plane. The capacitance of the DLDS Frequency Selective Surface (FSS) superstrate is used to counteract the inductance at the upper face of the antenna array to improve impedance match at different scanning angles. The DLDS FSS superstrate has similar performance with the equivalent double-layer dielectric superstrate, but with advantages of light weight, low cost, and low cross-polarization level at high frequencies. Consequently, the proposed TCDA has a bandwidth of 2.4:1 (2.1–5 GHz) with VSWR<3, while scanning up to 80° in the E plane, 70° in the H plane, and 75° in the D plane, respectively. A 16 × 16 prototype was fabricated and measured, showing good agreement with the simulated results.

A wide‐band all‐metal and high‐gain omnidirectional antenna with simple prototype

An all-metal dipole two-element array antenna is proposed to achieve a wide-band impedance bandwidth and an omnidirectional radiation pattern. The concept of this antenna derives from a quarter-shorted magnetic dipole structure. The proposed antenna consists of an air-filled metallic parallel bi-plate and two dipole elements. The dipole elements are perpendicularly fabricated at the open end of the bi-plate. Fed by a single coaxial SMA connector in the center of this structure, a quasi-TEM mode in the bi-plate can be excited similar to the parallel waveguide. Based on the multiple resonances and line-array effect, the proposed antenna can achieve a wide-band working bandwidth and a stable omnidirectional pattern. Simulated and experimental results confirm that this antenna has a peak gain of 4.16 dBi and a relative impedance bandwidth of 72% (0.8–1.7 GHz). The proposed antenna can be used in UAV (unmanned aerial vehicle) application.

Stability and increased radio communication coverage of sea area infrastructure measurement antennas

This research presents a modified method of signal amplification over layered surfaces of absolutely thin ice over marine waters on condition of stable operation of communication networks, necessary for deployment of Big Information Management Communication Systems and the concept of E-Navigation development. The method was first tested when deploying a GMSSB(b) network in the Azov-Black Sea region. Peculiarity of radio wave behavior during propagation over thin layered ice is that mutual phase ratios make a part of field energy “sticking” to the surface and propagating along it, thus creating a surface wave effect. At that, attenuation function is above one, and the field may increase with distance, even above design limits, breaking the proportionality law of reduction with distance. There are several details requiring clarification and adjustments to local conditions.In the MF and LF radio bands, solid surface and sea water are good conductors of electromagnetic flow. Thus, antenna fields for radio communications are located immediately above the surface for reception and transmission of vertical polarization signals, while field calculations are conducted with an elementary dipole.

A Planar Wideband Millimeter-Wave Antenna Array With Low Sidelobe Using ‘±1’ Excitations

A new method is proposed to suppress the sidelobe level (SLL) of antenna array. Different from the conventional amplitude-tapered excitation method, ‘±1’ excitations are used to feed the antenna array and achieve low SLL. The SLL is first optimized by using a modified binary particle swarm optimization algorithm with ideal ‘±1’ excitations. Then, the ideal ‘±1’ excitations are replaced with microstrip line feed and aperture-coupled magnetoelectric (ME) dipoles. The ‘+1’ excited ME dipoles are fed from the default direction, while the ‘−1’ excited ME dipoles are fed from the direction physically reversed. According to the optimized array configuration, combining the ME dipole elements with a 256-way parallel power divider, a planar <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16\times16$ </tex-math></inline-formula> millimeter-wave antenna array is designed, fabricated, and measured. An overlapped working bandwidth of 38% (24.1–35.4 GHz) is obtained with an SWR less than 2.4 and SLL lower than −17.2 dB. The gain is up to 26.3 dBi. The new binary concept paves a new way for SLL suppressing.

60 GHz dual‐polarized magneto‐electric dipole antenna array with hybrid gap waveguide feeding network in low temperature co‐fired ceramic technology

AbstractA 60 GHz 8 × 8 dual‐polarized aperture‐coupled magneto‐electric (ME) dipole antenna array in low temperature co‐fired ceramic (LTCC) technology is proposed. Taking advantage of the LTCC technology of high integration, the antenna array is composed of three parts, including the wideband ME dipole elements, dual‐polarized strip‐line series feeding network and low‐loss gap waveguide (GWG) feeding network. The ME dipole antenna element is fed by aperture coupling with 45° rotation. Two separate orthogonal strip lines are located right below the aperture to realize dual polarization performance. The simulated −10 dB impedance bandwidth of the dual‐polarized antenna element is 50–66.5 GHz with an isolation lower than −20 dB for two input ports. By employing the proposed radiating element, a 4 × 4 wide‐band dual‐polarized antenna subarray is realized by using strip‐line series‐feed technology. A compact hybrid low‐loss feeding network is realized by combing the GWG technology with the strip‐line series feed technology. For demonstration, one prototype was fabricated. The measured impedance bandwidth is 14.2% and 16.7% respectively for dual polarizations with |S11| &lt; −8 dB, and the port isolation is lower than −20 dB over the entire frequency band of interest.