Dual-polarized Antenna Array Research Articles

Polarimetric Direction of Arrival Estimations Based on Adaptive Linear Time-Frequency Transforms

A spatially polarized time-frequency distribution (SPTFD) based on dual-polarized double-fed antenna arrays is adapted to deal with polarization-unstable signals. A linear time-frequency (TF) representation was used for an instantaneous frequency (IF) estimate, primarily due to its simplicity and immunity to cross-interference. Using a set of linear TF transformations using Gaussian windows and Fourier oscillation kernels, the IF estimated window widths of multiple unstable signals are obtained. This paper introduces a new method for estimating the direction of arrival (DOA) of polarized waves using adaptive linear time-frequency transforms. In this paper, a narrowband far-field point source on the receiving array is analyzed. The source signal is split into two orthogonally polarized components. The optimal window is determined by the first derivative of the IF; for this purpose, we take a simple algorithm for solving the derivative and optimize it. In developing TF-adaptive and fully automatic TF display technology, the first method is to use the time-adaptive window for minimizing the IF estimate mean square error (MSE) sum at each moment, while the second procedure is to adjust according to time and frequency and minimize estimate MSE sum at each position in the TF region. Due to its combination with signal polarization, the spatial time-frequency distribution (STFD) gains more freedom and thus perfects the phonon space estimation of noise and signal. On the SPTFD platform, polarized time-frequency multiple signal classification (PTF-MUSIC) is used for the estimation of signal direction of arrival, which outperforms conventional time-frequency MUSIC. Using the example of a synthesized signal, this method outperforms conventional techniques in DOA estimation.

Enhanced Angle-of-Arrival and Polarization Parameter Estimation Using Localized Hybrid Dual-Polarized Arrays.

The millimeter wave (mmWave) channel is dominated by line-of-sight propagation. Therefore, the acquisition of angle-of-arrival (AoA) and polarization state of the wave is of great significance to the receiver. In this paper, we investigate AoA and polarization estimation in a mmWave system employing dual-polarized antenna arrays. We propose an enhanced AoA estimation method using a localized hybrid dual-polarized array for a polarized mmWave signal. The use of dual-polarized arrays greatly improves the calibration of differential signals and the signal-to-noise ratio (SNR) of the phase offset estimation between adjacent subarrays. Given the estimated phase offset, an initial AoA estimate can be obtained, and is then used to update the phase offset estimation. This leads to a recursive estimation with improved accuracy. We further propose an enhanced polarization estimation method, which uses the power of total received signals at dual-polarized antennas to compute the cross-correlation-to-power ratio instead of using only one axis dipole. Thus the accuracy of polarization parameter estimation is improved. We also derive a closed-form expression for mean square error lower bounds of AoA estimation and present an average SNR analysis for polarization estimation performance. Simulation results demonstrate the superiority of the enhanced AoA and polarization parameter estimation methods compared to the state of the art.

A New Multi-Band Multi-Array Antenna Configuration With Scattering Suppression for Radiation Pattern Distortion Mitigation of Base Station

This communication presents a new multiband multiarray (MBMA) scattering suppression antenna configuration for a dual-band and dual-polarized antenna array with reduced radiation distortion. The proposed antenna array configuration consists of a low-band (LB) antenna element working in the 690–960 MHz band and four high-band (HB) antenna elements working in the 1.7–2.7 GHz band. The LB antenna introduces U-shape structures to the radiation element to neutralize HB scattering currents. On the other hand, the HB antenna involves an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonant structure between its radiation arm and feeding balun to suppress LB scattering currents. An antenna array using the proposed LB and HB elements is designed to achieve MBMA functions. Experimental results show that the radiation distortions in both LB and HB bands are improved significantly. The VSWR of less than 1.5, the isolation of more than 25 dB, and the symmetrical radiation pattern are obtained in both bands.

Flexible Dual-Polarized UWB Antenna Sensors for Breast Tumor Detection

Detection of breast cancer in its early stage is critical for reducing the death rate. In this paper, a compact and flexible breast tumor sensing system is designed using dual-polarized UWB antenna arrays. Each UWB unit is composed of two orthogonally placed circular monopoles, which are printed on flexible and low-profile Kapton polyimide. The antennas are fed by single-side coplanar waveguides for size reduction. A wide band from 3.9 GHz to 19 GHz is obtained, with an isolation of above 16 dB over the operating band. High fidelity factors are achieved at different solid angles, indicating little distortion of the signal and stable sensing ability. To obtain the image of the tumor, eight UWB units are employed surrounding the breast phantom. Using the reflected and scattered signals from the antennas, 3D images of the breast are reconstructed using delay-and-sum (DAS) algorithm. Attributed to the dual-polarized UWB antennas, accurate location and size of the tumors are retained with little clutter. Moreover, the proposed system can detect two tumors with an edge to edge distance of 15 mm. Experiments have been carried out on rotating platforms, with the tumor successfully detected in the measurement. The proposed tumor sensing system is suitable for wearable applications due to its compact size and flexibility.

Efficient Online Data-Driven Enhanced-XGBoost Method for Antenna Optimization

The tremendous progress in artificial intelligence promotes the wide application of machine learning (ML) technology in the field of electronic science. Recently ML-based antenna optimization provides a distinct candidate and attracts considerable attention. However, the large number of training samples generated through time-consuming EM simulations becomes a significant challenge. In this article, an efficient online data-driven enhanced-XGBoost (E-XGBoost) method for antenna optimization is proposed, which is mainly composed of two parts, i.e., an input variable filter module (IVFM) and an antenna optimization module (AOM). Specifically, IVFM serves as a variable sensitivity analyzer, which is accomplished by E-XGBoost to efficiently reduce the dimension of design variable and hence save the training samples. Next, the design variables obtained by IVFM are fed into AOM to find the near-optimal solution. In AOM, an online learning strategy is proposed to train a local E-XGBoost model to evaluate the population in the metaheuristic optimization algorithm (MOA). Compared to the global ML model that can mimic the entire design space, this local E-XGBoost model can further cut down the training samples. To verify the performance of the proposed method, several different antenna examples, i.e., U-slot patch antenna, Fabry–Perot resonant antenna, and dual-polarized cross dipole antenna and 5G MIMO antenna array, are simulated. Numerical results support the proposed method in terms of its superior performance and potential advantage of saving computational overhead.

Artificial magnetic conductor‐backed dual‐band shared‐aperture antenna array for base station applications

A low-profile dual-band dual-polarized base station antenna array is proposed. The dual-band array is backed by an artificial magnetic conductor (AMC) surface. The AMC achieves profile reduction to 0.159 λL0 in the low band (LB), but it acts as a bandpass metasurface in the high band (HB). The nested design of AMC unit cell creates two out-of-phase induced currents with lower intensities, enabling suppression and cancelation of HB scattered fields. The back cavities establish clear and independent radiating environments for the LB and HB antennas. They aid in further radiation pattern restoration and antenna profile reduction. The proposed antenna array was fabricated and experimentally measured. The simulated and measured results are presented. The operating principles of the proposed AMC and back cavities are also investigated.

Self-Decoupled Dual-Band Dual-Polarized Aperture-Shared Antenna Array

This communication presents a self-decoupled dual-band dual-polarized aperture-shared antenna array. The proposed dual-band array consists of a low-band (LB) antenna element interleaved into 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> high-band (HB) antenna array with compact elements spacing. To mitigate the blockage effect resulting from the LB element, shorted patches are loaded on the LB radiator for suppressing its scattering in the HB frequency range. In addition, high cross-band isolation between the closely spaced LB and HB elements is obtained due to their intrinsic filtering response. Moreover, the in-band mutual coupling between the HB elements is reduced by adding cross-shaped strips on them. As a result, the cross-band and in-band couplings and the antenna blockage effect can be simultaneously reduced without adding an extra decoupling component. A prototype of the proposed array operating in 1.71–2.17 GHz (LB) and 3.3–3.8 GHz (HB) is fabricated and measured. The radiation patterns of the LB and HB elements are almost unaffected by each other. Furthermore, all of the port-to-port isolations are higher than 20 dB. These merits make the proposed design suitable for the multiband base station.

Design of π-Shaped Decoupling Network for Dual-Polarized Y-Probe Antenna Arrays

In this letter, a simple decoupling method is proposed to improve the isolation in a dual-polarized patch antenna array that operates in the frequency range of 3.4–3.8 GHz. The method includes the decoupling network based on the π-shaped architecture of the transmission line and matching network. The distance of the two adjacent antenna elements is 0.48 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> . The cross-polarization isolation of the antenna element using Y-probes and differential feeding is higher than 35 dB in the operating frequency band. The proposed scheme is able to deal with the decoupling requirement and obtains 37 dB isolation at 3.6 GHz, which shows a significant improvement compared with the original antenna array. The measured results demonstrate that the proposed scheme is suitable for multiple–input–multiple-output (MIMO) systems.

Unequally Spaced Scalable dual-polarized Ultra-wideband Antenna Array with Slot Positioning for Large Scale Array

ABSTRACT article shows a splicable dual-pol. ultra-wideband array antenna used in large-scale arrays. An unequal-spaced metal bullet structure is used as the basic antenna element, and the gradual slot for radiation is spliced by the metal bullet radiator. The bullet structure is directly and vertically interconnected through elastic RF connectors. The antenna structure can be independently installed on the metal backplane and positioned through the slots on the metal backplane to ensure good electrical performance. Compared with the antenna structure processed by PCB technology, this type of antenna can effectively avoid the generation of surface wave modes, thereby ensuring that there is no VSWR singularity in the broadband. The proposed antenna array can realize ±45°scanning in azimuth plane and ±35°scanning in elevation plane within four octave bands. Based on the proposed antenna, a 10*10 prototype was tested. The measured results were consistent with the simulation results.

Study on Impact of Mutual Coupling on Performance of Dual Polarized Phased Array Antenna

This study involves the determination of the impact of mutual coupling between antenna elements on the performance of a dual-polarized, wide-angle scanning, phased array antenna for weather radar applications. Weather radars require dual linearly polarized antennas with low cross-polarization, and a narrow beam phased array for wide scanning angle. For this simulation-based study, a microstrip dual linearly polarized 2x20 phased array antenna operating at S-band (2.65 to 3.0 GHz) is designed. This antenna has been designed to have a cross-polarization level less than -45 dB at both polarizations and for the scan angle range of -55o to 55o, which is better than most of the existing dual-pol phased array antennas. This antenna has been used to analyze the impact of mutual coupling on cross-polarization, beamwidth, and antenna gain at various scan angles. Mutual coupling is studied in terms of antenna active element pattern and the corresponding cross-polarization value as well as the active reflection coefficient and impedance values for inter-element spacings of 0.4λ and 0.5λ. It has been found in this study that cross-polarization levels of the whole array (at various scan angles) are affected significantly because of mutual coupling between elements.

High-Gain and Low-Loss Dual-Polarized Antenna Array With Reduced Sidelobe Level Based on Gap Waveguide at 28 GHz

In this letter, a 16×16-element dual-polarized antenna array with a reduced sidelobe level is proposed at 28 GHz for fifth-generation (5G) communication systems. The dual linear polarization operation is carried out through cross-shaped waveguide slots and multilayer feeding networks. Low-loss gap waveguide technology and Taylor distribution are applied in the feeding networks. A ridge unequal power divider with flexible power ratio and phase difference is devised and applied in the gap waveguide feeding network to reduce the complexity of unequal power structural design. A prototype of the proposed dual-polarized antenna array is manufactured by milling technology. Measured results show that the realized gains are higher than 28 dBi over the operating frequency band of 27.4–28.6 GHz. Moreover, the sidelobe level is lower than −18.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> -direction polarization and −19.5 dB for the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> -direction polarization.

Tri‐band dual‐polarized base station antenna array with self‐decoupling ability

A tri-band dual-polarized antenna array for base station applications is presented. The proposed tri-band antenna array is devised by stacking the 1 middle-band (MB) + 4 high-band (HB) interleaved array above the low-band (LB) patch antenna. The MB antenna yields partial reflection to the HB subarrays, enabling cross-band and in-band decoupling abilities without introducing additional decoupling layer. With the aid of spatial cancelation and partition, transmission nulls are successfully generated in the in-band mutual coupling curves. Measured results show that good impedance matchings and polarization isolations are acquired in the operating bandwidths. The measured co- and cross-polarized in-band isolations in the HB are improved to >22.4 dB and >29.1 dB, respectively. The HB radiation patterns are well restored.

A high isolation dual-polarized antenna array with coplanar parasitic decoupling wall

A wideband dual-element dual-polarized stacked MIMO antenna array with high isolation is proposed using a coplanar parasitic decoupling wall (CPDW). The CPDW is constructed using a negative permittivity metamaterial array that works at the operating band of the antenna elements. Then, the CPDW is inserted between MIMO antenna elements to block the propagation of the coupling waves. The simulated and measured results are presented to verify the effectiveness of the CPDW. The devised wideband dual-element dual-polarized MIMO antenna array operates in the bandwidth of 4.2–4.9 GHz with high isolation of less than −25 dB, and its radiation patterns are almost unchanged without and with loading the CPDW.

Coplanar Dual-Band Dual-Polarized Shared-Aperture Antenna Array For 4/5G Base Station Applications

A novel dual-band dual-polarized shared-aperture antenna array is presented for fifth generation wireless communication application. This novel antenna array is a combination of a low-band antenna and four high-band antennas. In order to simplify the design model while achieving broadband, antenna working on low-band (from 0.68 to 0.99 GHz) and antenna working on high-band (from 3.3 to 5.1 GHz) are both loop-shape radiator fed by Y-shape feed. Coplanar, dual-band and shared-aperture are resolved by embedding four HB antenna elements in the LB antenna. From simulation, the proposed coplanar antenna array respectively achieves 43% (from 0.68 to 0.99 GHz) and 37% (from 3.3 to 5.1 GHz) impedance bandwidth in the low-band and high-band.

A 64-Element and Dual-Polarized SICL-Based Slot Antenna Array Development Applied to TDD Massive MIMO

This letter reports the concept, design, fabrication, and characterization of a novel 64-element, slot-based and substrate-integrated coaxial line (SICL)-fed dual-polarized antenna array (SICL-SAA) for fully digital massive multiple-input&#x2013;multiple-output (mMIMO) applications. The proposed array is composed of &#x00B1;45&#x00B0; polarized elements based on half-wavelength slots. Each slot has its own back cavity, acting as an individual reflector for enabling boresight radiation. The slot is fed using a SICL feeding line for shielding the propagating mode in the feeding network, aiming at low mutual coupling levels. Experimental results in excellent agreement with full-wave numerical simulations demonstrate up to 2 GHz bandwidth from 24.5 GHz to 26.5 GHz for all array elements. Furthermore, the mutual coupling between adjacent elements is kept lower than &#x2212;23 dB for the entire bandwidth, the radiating elements provide an 85&#x00B0; beamwidth in both planes (&#x03D5; &#x003D; 0&#x00B0; and &#x03D5; &#x003D; 90&#x00B0;) and 7.4 dBi gain.

Novel Decoupling Method Based on Coupling Energy Cancellation and its Application in 5G Dual-Polarized High-Isolation Antenna Array

A novel decoupling method by utilizing one <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times2$ </tex-math></inline-formula> subarray to provide a pair of phase-reversed coupling paths for coupling energy cancellation is proposed. The newly proposed decoupling approach is implemented by symmetrically loading several U-type, I-type, and cross strips around the antennas to change the original couplings, so that two elements in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1\times2$ </tex-math></inline-formula> subarray can form a pair of phase-reversed coupling paths into adjacent element in different subarray for coupling cancellation. Then, the couplings from the subarray to adjacent element are effectively suppressed, thus the isolations between different subarrays of the array are promoted. Moreover, the method can be also applied in improving the isolation between different polarizations in the same subarray. In addition, these strips not only have little influence on radiation characteristics of the antenna array, but also can be etched on the antenna layer without extra profile and process. For demonstration, one dual- polarized patch antenna array based on the new decoupling mechanism is designed. The results indicate that all the isolations between the subarrays of the proposed dual-polarized antenna array can achieve a very high level of over 25 dB in an operation band of 3.4–3.6 GHz. Compared with other decoupling methods, the proposed method can simultaneously improve complex multiple-port isolations among different subarrays and different polarizations to realize a very high isolation with less impact on antenna radiation. Due to above features, the proposed decoupling mechanism is expected to find potential applications in 5G dual-polarized multiple-input–multiple-output (MIMO) antenna array.

Wearable Dual Polarized Electromagnetic Knee Imaging System.

With the increasing uptake of sport activities, onsite detection of associated knee injuries at early stages is in high demand to avoid severe ligament tear and long treatment period. Portable electromagnetic imaging (EMI) systems have the potential to meet that demand, but there are challenges. For example, EMI is based on the contrast in the dielectric properties due to the accumulated fluid after knee injury. However, that fluid can be in any shape and orientation. Therefore, to capture enough data for processing, EMI should operate as a dual-polarized wearable system with compact antennas. Thus, the proposed system is a textile brace worn on the knee and consists of an 8-element dual-polarized aperture antenna array, which is matched with the knee. Each of the utilized antennas is fed by two orthogonal coaxial feed, occupies a small size of 36 ×36 ×3.1 mm3, and is backed by a full ground plane for unidirectional radiation. The antenna covers the band 0.7-3.3 GHz (130%), with front to back ratio of more than 10 dB. The textile wool-felt is used as the substrate to enable building flexible brace system. The system's capability to reconstruct knee images with different injuries is verified on realistic knee models and phantoms. The double stage delay, multiply and sum algorithm (DS-DMAS) is used to reconstruct those images, which demonstrate the efficiency of the dual-polarized system and its superiority over single-polarized systems.

Wideband Dual-Polarized Endfire Antenna Based on Compact Open-Ended Cavity for 5G Mm-Wave Mobile Phones

This article describes a compact dual-polarized endfire antenna array for fifth-generation (5G) millimeter-Wave (mm-Wave) mobile application. The dual-polarized endfire antenna element is constructed by a compact open-ended cavity with cavity mode for vertical polarization (VP) radiation and open-slot mode for horizontal polarization (HP) radiation. With the integrated design of VP and HP elements, the proposed antenna shows a much more compact size compared to existing schemes. To enhance the bandwidth of low-profile VP radiation, a slot is etched on the cavity to create a new mode for dual-resonance response, realizing a wide bandwidth of 24.5&#x2013;29.5 GHz for both polarizations. In addition, radiation pattern modification techniques are employed to achieve good endfire beams with a high front-to-back ratio for both polarizations, thus enabling a high peak gain of 10.3 and 11.3 dBi for VP and HP, respectively. A wide beam scanning range of &#x00B1;50&#x00B0; with realized gain above 7 dBi is realized at 27 GHz for both polarizations. In virtue of compact size, wide bandwidth, high gain, and good spatial coverage, the proposed design strategy is promising for future 5G mm-Wave mobile phones.

Broadband Dual-Polarized Differential-Fed Filtering Antenna Array for 5G Millimeter-Wave Applications

This article presents a novel broadband dual-polarized filtering patch antenna array using low-temperature cofired ceramic (LTCC) process for 5G millimeter-wave (mmW) applications. The filtering antenna element is implemented using a ± 45° polarized patch antenna fed by two pairs of differential L-type probes. An additional square ring and open strips are connected to each probe, resulting in radiation nulls and realizing the lower/upper stopband rejection level over 24 dB with skirt selectivity. The cross coupling among these structures not only introduces filtering responses, but also contributes to broadening the passband of 24.25–29.5 GHz covering 5G n257/n258/n261 bands. The antenna performance is validated by equivalent circuits based on transmission line models, which reveals clearly the principles of filtering antenna step by step and provides guidelines for further designs. The proposed filtering antenna element is expanded to a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 4$ </tex-math></inline-formula> filtering antenna array with shunt-fed feeding networks. The spacing between elements is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.48~\lambda _{0}$ </tex-math></inline-formula> . The measured results demonstrate that the array performs good filtering characters including high stopband rejection, high selectivity, and wide upper stopband up to 40 GHz, where the antenna efficiency (considering radiations from all the directions) is less than 5%. In addition, the differential feeds provide symmetric radiation patterns with low cross-polarized counterparts. Compared with other reported works, the proposed filtering antenna/array has excellent performances of wideband, high stopband rejection and wide upper stopband for potential 5G mmW applications.

Dual-Layer Superstrate Structure for Decoupling of Dual-Polarized Antenna Arrays

A new antenna decoupling structure by combining metal and dielectric superstrates is studied in this letter. The decoupling concept is elaborated in a 5-element antenna array. Afterwards, the decoupling performances are validated in a 3 × 3 staggered antenna array. The dielectric superstrate serves as magnitude and phase compensators. It achieves the tradeoff design to simultaneously improve decoupling bandwidth and matching in wideband decoupling issue. The E-plane and H-plane isolations are enhanced by at least 9 dB, reaching > 23 and > 27.2 dB in the operating bandwidth of 3.4–4.2 GHz. The radiation performances are also enhanced through decoupling.