Showing papers on "Wideband published in 2018"

Spatial- and Frequency-Wideband Effects in Millimeter-Wave Massive MIMO Systems

Abstract: When there are a large number of antennas in massive MIMO systems, the transmitted wideband signal will be sensitive to the physical propagation delay of electromagnetic waves across the large array aperture, which is called the spatial-wideband effect. In this scenario, the transceiver design is different from most of the existing works, which presume that the bandwidth of the transmitted signals is not that wide, ignore the spatial-wideband effect, and only address the frequency selectivity. In this paper, we investigate spatial- and frequency-wideband effects, called dual-wideband effects in massive MIMO systems from the array signal processing point of view. Taking millimeter-wave-band communications as an example, we describe the transmission process to address the dual-wideband effects. By exploiting the channel sparsity in the angle domain and the delay domain, we develop the efficient uplink and downlink channel estimation strategies that require much less amount of training overhead and cause no pilot contamination. Thanks to the array signal processing techniques, the proposed channel estimation is suitable for both TDD and FDD massive MIMO systems. Numerical examples demonstrate that the proposed transmission design for massive MIMO systems can effectively deal with the dual-wideband effects.

Faceting for direction-dependent spectral deconvolution

Abstract: The new generation of radio interferometers is characterized by high sensitivity, wide fields of view and large fractional bandwidth. To synthesize the deepest images enabled by the high dynamic range of these instruments requires us to take into account the direction-dependent Jones matrices, while estimating the spectral properties of the sky in the imaging and deconvolution algorithms. In this paper we discuss and implement a wideband wide-field spectral deconvolution framework (ddfacet) based on image plane faceting, that takes into account generic direction-dependent effects. Specifically, we present a wide-field co-planar faceting scheme, and discuss the various effects that need to be taken into account to solve for the deconvolution problem (image plane normalization, position-dependent Point Spread Function, etc). We discuss two wideband spectral deconvolution algorithms based on hybrid matching pursuit and sub-space optimisation respectively. A few interesting technical features incorporated in our imager are discussed, including baseline dependent averaging, which has the effect of improving computing efficiency. The version of ddfacet presented here can account for any externally defined Jones matrices and/or beam patterns.

Propagation Measurement System and Approach at 140 GHz-Moving to 6G and Above 100 GHz

Abstract: With the relatively recent realization that millimeter wave frequencies are viable for mobile communications, extensive measurements and research have been conducted on frequencies from 0.5 to 100 GHz, and several global wireless standard bodies have proposed channel models for frequencies below 100 GHz. Presently, little is known about the radio channel above 100 GHz where there are much wider unused bandwidth slots available. This paper summarizes wireless communication research and activities above 100 GHz, overviews the results of previously published propagation measurements at D-band (110–170 GHz), provides the design of a 140 GHz wideband channel sounder system, and proposes indoor wideband propagation measurements and penetration measurements for common materials at 140 GHz which were not previously investigated.

A Dual-Band Metasurface Antenna Using Characteristic Mode Analysis

Abstract: A compact metasurface-based antenna is proposed for dual-band operations. The proposed metasurface is designed on a single-layered substrate including an array of modified $3 \times 3$ squared patches. Each of the four corner patches is split into four fractional patches while the four edge patches are evolved into Malta crosses and the center patch is scaled. A substrate integrated waveguide-based Y-junction cavity-fed dual slot drives the metasurface with multiple impedance resonances. Based on the predicted modal behaviors of metasurface using a characteristic mode analysis (CMA), as an example, an antenna operating at three resonant modes at 28, 33, and 36 GHz, respectively is designed for the dual-band operation for the coming 5G. The proposed design shows that the measured impedance bandwidths (return loss larger than 10 dB) are 23.7–29.2 GHz and 36.7–41.1 GHz with the achieved gain of 4.8–7.2 dBi and 8.9–10.9 dBi, respectively. The proposed dual-band antenna features the advantages of low profile and wideband, suitable for the coming dual-band 5G applications.

A Reconfigurable Broadband Polarization Converter Based on an Active Metasurface

Abstract: We propose an active metasurface whose functionalities can be dynamically switched among linear-to-linear, linear-to-elliptical, and linear-to-circular polarization conversions in a wideband. The active metasurface is composed of butterfly-shaped unit cells embedded with voltage-controlled varactor diodes. By controlling the bias voltage of the varactor diodes, the electromagnetic responses of the proposed metasurface can be tailored, leading to reconfigurable polarization conversions. The simulation results reveal that with no bias voltage, the proposed metasurface is able to reflect linear-polarization waves to cross-polarization waves in the frequency range from 3.9 to 7.9 GHz, with a polarization conversion ratio of over 80%; however, at the bias voltage of −19 V, the metasurface is tuned to be a circular polarization converter in a wideband from 4.9 to 8.2 GHz. Moreover, two equivalent circuits along the $x$ - and $y$ -directions are developed to elucidate the tunable mechanism. The experimental results are in a good agreement with the simulation results obtained from commercial software and from the equivalent circuit model.

Wideband Gain Enhancement and RCS Reduction of Fabry–Perot Resonator Antenna With Chessboard Arranged Metamaterial Superstrate

Abstract: The simultaneous improvement in radiation and scattering performance of an antenna is normally considered as contradictory. In this paper, wideband gain enhancement and radar cross section (RCS) reduction of Fabry–Perot (FP) resonator antenna are both achieved by using chessboard arranged metamaterial superstrate (CAMS). The CAMS is formed by two kinds of frequency-selective surfaces. The upper surface of CAMS is designed to reduce RCS based on the phase cancellation principle, and the bottom surface is used to enhance antenna gain on the basis of FP resonator cavity theory. Both simulation and measured results indicate that compared with primary antenna, the gain of the proposed FP resonator antenna is enhanced by 4.9 dB at 10.8 GHz and the 3 dB gain bandwidth is from 9.4 to 11.1 GHz (16.58%). Meanwhile, the RCS of the proposed FP resonator antenna is reduced from 8 to 18 GHz, with peak reduction of 39.4 dB. The 10 dB RCS reduction is obtained almost from 9.6 to 16.9 GHz (55.09%) for arbitrary polarizations. Moreover, the in-band RCS is greatly reduced, owing to the combined effect of CAMS and FP resonator cavity.

Wideband Metasurface-Based Reflective Polarization Converter for Linear-to-Linear and Linear-to-Circular Polarization Conversion

Abstract: A wideband reflective polarization converter based on metasurface is proposed in this letter. This converter can transform a linearly polarized (LP) incident electromagnetic (EM) wave into its orthogonal LP reflection wave in a lower band, and a circularly polarized (CP) reflection wave in a higher band. The unit cell of this converter is comprised of two meander lines and one cut wire printed on a dielectric substrate, backed with metallic ground sheet. The simulation results show that the y / x -polarized incident EM wave can be converted to the x/y -polarized reflected wave over a fractional bandwidth of 59.6% from 6.53 to 12.07 GHz with a polarization conversion ratio over 0.88. Besides, the y / x -polarized incident EM wave is converted to a CP reflected wave from 13.70 to 15.60 GHz (a fractional bandwidth of 13.0%). To verify the polarization conversion performance, a sample consisting of 30 × 30 unit cells is fabricated and measured. The experimental and simulation results obtained are in a reasonable agreement, which verifies the properties of the design.

A Method of Suppressing Higher Order Modes for Improving Radiation Performance of Metasurface Multiport Antennas Using Characteristic Mode Analysis

Abstract: A method is proposed to suppress the unwanted higher order modes (HOMs) of the metasurfaces in multiport antenna systems for improving the radiation performances using characteristic mode analysis (CMA). The proposed method is to control the modal currents under consideration by loading the unit cells of the metasurface with slots and vias. The positions of loads are determined with the aid of CMA of the metasurface. For proof of concept, the proposed technique is applied to a compact wideband four metasurface antenna (MA) systems operating at 5 GHz Wi-Fi bands. With the suppression of HOMs, the split and tilted radiation patterns of the MAs are significantly improved. The concept is experimentally validated for potential compact multiport antenna applications.

Advanced RF and microwave functions based on an integrated optical frequency comb source.

Abstract: We demonstrate advanced transversal radio frequency (RF) and microwave functions based on a Kerr optical comb source generated by an integrated micro-ring resonator. We achieve extremely high performance for an optical true time delay aimed at tunable phased array antenna applications, as well as reconfigurable microwave photonic filters. Our results agree well with theory. We show that our true time delay would yield a phased array antenna with features that include high angular resolution and a wide range of beam steering angles, while the microwave photonic filters feature high Q factors, wideband tunability, and highly reconfigurable filtering shapes. These results show that our approach is a competitive solution to implementing reconfigurable, high performance and potentially low cost RF and microwave signal processing functions for applications including radar and communication systems.

A Low-Profile Dual-Polarized Dipole Antenna Using Wideband AMC Reflector

Abstract: A low-profile dual-polarized dipole antenna using wideband artificial magnetic conductor (AMC) reflector with stable radiation pattern for use in 2G/3G/4G base stations operating from 1.7 to 2.7 GHz is presented. The antenna consists of a pair of crossed-dipoles and a wideband AMC reflector which consists of an AMC surface, a metallic ground plane, and the air substrate between them. The AMC is designed to operate with 90° reflection-phase bandwidth of 1.64–2.88 GHz (54.8%). Compared with using perfect electric conductor reflector, the profile height of the dual-polarized dipole antenna using AMC reflector is reduced by half from 36 to 18 mm, resulting in the lowest-profile 2G/3G/4G base station antenna. Six metallic ground walls are used to stabilize the radiation pattern, and the resulted half-power beamwidths are around 68±3° and 81±3° in the H- and V-planes, respectively, across the operating band. More measured results show that wide impedance bandwidths of 1.67–2.98 and 1.64–3.05 GHz for the two input ports, isolation of more than 25 dB, and cross-polarization of less than −20 dB are achieved.

Broadband Polarization-Insensitive Tunable Frequency Selective Surface for Wideband Shielding

Abstract: In this paper, a low-profile broadband frequency selective surface (FSS) is presented for wideband shielding. The FSS consists of periodic patterns of circular loops connected among themselves through varactor diodes, which exhibit tunable operation. The novelty of the proposed design lies in its wideband tuning, where the bandstop response can be varied from 0.54 to 2.50 GHz under the reverse bias voltage, thereby exhibiting a tunable range of 363%. Moreover, the structure exhibits a wide 1.28 GHz stopband (fractional bandwidth of 152%), which is maximum as compared to other wideband FSSs. Additionally, the design is polarization-insensitive and angularly stable for both TE and TM polarizations. A prototype of the proposed structure has been fabricated where the varactor diodes are biased through a novel biasing technique. The sample is measured using parallel-plate waveguide setup as well as the free-space technique, where the measured results show good agreement with the simulated responses.

Channel Measurement, Simulation, and Analysis for High-Speed Railway Communications in 5G Millimeter-Wave Band

Abstract: More people prefer to using rail traffic for travel or for commuting due to its convenience and flexibility. As the record of the maximum speed of rail has been continuously broken and new applications are foreseen, the high-speed railway (HSR) communication system requires higher data rate with seamless connectivity, and therefore, the system design faces new challenges to support high mobility. Millimeter-wave (mmWave) technologies are considered as candidates to provide wideband communication. However, mmWave is rarely explored in HSR scenarios. In this paper, channel characteristics are studied in the 5G mmWave band for typical HSR scenarios, including urban, rural, and tunnel, with straight and curved route shapes. Based on the wideband measurements conducted in the tunnel scenario by using the “mobile hotspot network” system, a 3-D ray tracer (RT) is calibrated and validated to explore more channel characteristics in different HSR scenarios. Through extensive RT simulations with 500-MHz bandwidth centered at 25.25 GHz, the power contributions of the multipath components are studied, and the dominant reflection orders are determined for each scenario. Path loss is analyzed, and the breakpoint is observed. Other key parameters, such as Doppler shifts, coherence time, polarization ratios, and so on, are studied. Suggestions on symbol rate, sub-frame bandwidth, and polarization configuration are provided to guide the 5G mmWave communication system design in typical HSR scenarios.

Chaotic optical communications over 100-km fiber transmission at 30-Gb/s bit rate.

Abstract: For the first time, to the best of our knowledge, we experimentally demonstrate a successful 30-Gb/s signal transmission of a duobinary message hidden in a chaotic optical carrier over 100-km fiber. Thanks to the duobinary modulation format with high spectral efficiency, the 30-Gb/s signal can be encrypted by a 10-GHz-wide chaotic carrier. A digital signal processing technique can be used to convert duobinary data into binary data on the receiver side. This proposal lowers the requirement for wideband chaos generation and synchronization in high-speed long-distance chaotic optical communications, and fiber dispersion compensation can also be simplified, which has potential to be used in high-speed long-distance secure optical communications.

Spatial-Wideband Effect in Massive MIMO with Application in mmWave Systems

Abstract: Massive MIMO, especially in the millimeter- wave frequency bands, has been recognized as a promising technique to enhance spectrum and energy efficiency, as well as network coverage for wireless communications. Most research in massive MIMO just uses the extended conventional MIMO channel model by directly assuming that the channel dimensionality becomes large. With massive numbers of antennas, however, there exists a non-negligible propagation delay across the large array aperture, which then causes a transmitted symbol to reach different antennas with different delays, thereby rendering conventional MIMO channel models inapplicable. Such a phenomenon is known as the spatial-wideband effect in the areas of array signal processing and radar signal processing, and introduces the beam squint effect in beamforming. However, the spatial-wideband effect and the related beam squint issue are seldom studied in massive MIMO communications. To design a practical massive MIMO system, it is important to understand when the spatial-wideband effect appears and how it affects signal transmission, how the spatial-wideband effect interacts with the frequency-wideband effect (frequency selectivity), especially for multi-carrier modulations such as orthogonal frequency- division multiplexing (OFDM), and how we should re-design the transceiver. In this article we suggest a new massive MIMO channel model that embraces both the spatial- and frequency- wideband effects, and discuss these issues.

Towards Realistic High-Speed Train Channels at 5G Millimeter-Wave Band—Part I: Paradigm, Significance Analysis, and Scenario Reconstruction

Abstract: The upcoming fifth-generation (5G) mobile communication system is expected to support high mobility up to 500 km/h, which is envisioned in particular for high-speed trains. Millimeter wave (mmWave) spectrum is considered as a key enabler for offering the “best experience” to highly mobile users. Despite that channel characterization is necessary for the mmWave system design and validation, it is still not feasible to directly do extensive mmWave mobile channel measurements on moving high-speed trains (HST) at a speed up to 500 km/h in the present. Thus, rather than conducting mmWave HST channel sounding directly with high mobility, this study proposes a viable paradigm for realizing the realistic HST channels at the 5G mmWave band. We first propose the whole paradigm. Then, we define the scenario of interest and select the main objects and materials. Afterwards, the electromagnetic and scattering parameters of the materials are measured and estimated between 26.5 GHz and 40 GHz. With this information, the most influential materials are determined through significance analysis. Correspondingly, we reconstruct the three-dimensional mmWave outdoor HST and tunnel scenario models. Through extensive ray-tracing simulations, we determine the main propagation mechanisms in these two scenarios, the channel models based on that are validated by measurements. This verifies the whole paradigm proposed in this paper.

A Wideband Variable Gain LNA With High OIP3 for 5G Using 40-nm Bulk CMOS

Abstract: This letter presents a CMOS wideband variable gain LNA for 28-GHz 5G integrated phased-array transceivers preserving high third-order intercept point (OIP3) at all gain settings. The prototype LNA has three stages providing digitally controlled gain optimized for higher IIP3 at lower gain. The stages are coupled together using double-tuned transformers for maximum group delay flatness. Fabricated in a 40-nm CMOS process, it achieves 18–26 dB gain at 1-dB gain step with 12–14.5 dBm OIP3 and 3.3–4.3 dB noise figure, while consuming 21.5–31.4 mW across 26–33 GHz frequency range. The root-mean-square error of the gain steps is less than 0.38 dB.

Beyond the Bode-Fano Bound: Wideband Impedance Matching for Short Pulses Using Temporal Switching of Transmission-Line Parameters.

Abstract: Impedance matching is one of the most important practices in wave engineering as it enables one to maximize the power transfer from the signal source to the load in the wave system. Unfortunately, it is bounded by the Bode-Fano criterion which states that, for any passive, linear, and time-invariant matching network, there is a stringent trade-off between the matching bandwidth and efficiency, implying severe constraints on various electromagnetic and acoustic wave systems. Here, we propose a matching paradigm that overcomes this issue by using a temporal switching of the parameters of a metamaterial-based transmission line, thus revoking the time-invariance assumption underlying the Bode-Fano criterion. Using this scheme we show theoretically that an efficient wideband matching, beyond the Bode-Fano bound, can be achieved for short-time pulses in challenging cases of very high contrast between the load and the generator impedances, and with significant load dispersion, situations common in, e.g., small antenna matching, cloaking, and with applications for ultrawideband communication, high resolution imaging, and more.

A Comparison of Hybrid Beamforming and Digital Beamforming With Low-Resolution ADCs for Multiple Users and Imperfect CSI

Abstract: For 5G, it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidirectional coverage with a similar effective antenna aperture compared to state-of-the-art cellular systems, an antenna array is required at both the mobile and base station. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front end of the receiver with a large number of antennas becomes especially power hungry. Two main solutions exist to reduce the power consumption: hybrid beam forming and digital beam forming with low resolution Analog to digital converters (ADCs). In this paper, we compare the spectral and energy efficiency of both systems under practical system constraints. We consider the effects of channel estimation, transmitter impairments, and multiple simultaneous users for a wideband multipath model. Our power consumption model considers components reported in the literature at 60 GHz. In contrast to many other works, we also consider the correlation of the quantization error, and generalize the modeling of it to nonuniform quantizers and different quantizers at each antenna. The result shows that as the signal-to-noise ratio (SNR) gets larger the ADC resolution achieving the optimal energy efficiency gets also larger. The energy efficiency peaks for 5-b resolution at high SNR, since due to other limiting factors, the achievable rate almost saturates at this resolution. We also show that in the multiuser scenario digital beamforming is in any case more energy efficient than hybrid beamforming. In addition, we show that if mixed ADC resolutions are used, we can achieve any desired tradeoff between power consumption and rate close to those achieved with only one ADC resolution.

A 2.5-D Angularly Stable Frequency Selective Surface Using Via-Based Structure for 5G EMI Shielding

Abstract: A novel broadband bandpass frequency-selective surface (FSS) designed for fifth generation (5G) EMI shielding is proposed in this paper. This new design employs the vertical vias into the 2-D periodic arrays, and such a single 2.5-D periodic layer of via-based structure is demonstrated to produce a highly stable angular response up to 60° for both TE and TM polarizations. By cascading two layers of such 2.5-D periodic arrays, the proposed FSS is able to obtain a broad passband as well as the wide out-of-band rejection. Moreover, it has a quite sharp band edge between the passband and the specified stopband. A corresponding equivalent circuit model (ECM) is further developed for better analysis of the operating principle. Finally, a prototype working at the center frequency of around 28 GHz is fabricated and measured. The main novelty of this paper is introducing the 2.5-D concept into designing a wideband FSS, and further reduce the unit size as well as improve the angular stability. Favorable agreement is achieved among the 3-D full-wave simulation, ECM and measurement. All these results demonstrate that the proposed FSS is a good candidate for 5G EMI shielding.

140 GHz High-Gain LTCC-Integrated Transmit-Array Antenna Using a Wideband SIW Aperture-Coupling Phase Delay Structure

Abstract: This paper presents the complete design of a wideband transmit-array (TA) antenna with high gain and high efficiency for D-band applications based on the low-temperature co-fired ceramic technology. The proposed unit cell is composed of a pair of wideband magnetoelectric dipoles as the receive/transmit elements, together with a substrate-integrated waveguide (SIW) aperture-coupling transmission structure for independent phase adjustability. A 360° phase coverage is obtained by the proposed phasing element, and its phase response curves are nearly parallel within a broad frequency band, which indicates a wideband performance. To verify the design, the fabricated prototype is measured by using a vector network analyzer in a terahertz compact-range anechoic chamber. The measured peak gain is 33.45 dBi at 150 GHz with the aperture efficiency of 44.03%, and the measured 3 dB gain bandwidth is 124–158 GHz (24.29%). The good radiation performance ensures that the proposed SIW aperture-coupling TA antenna is a promising candidate for D-band applications.

Digital Predistortion for Multi-Antenna Transmitters Affected by Antenna Crosstalk

Abstract: In this paper, a digital predistortion (DPD) technique for wideband multi-antenna transmitters is proposed The proposed DPD compensates for the combined effects of power amplifier (PA) nonlinearity, antenna crosstalk, and impedance mismatch The proposed technique consists of a linear crosstalk and mismatch model block shared by all transmit paths and a dual-input DPD block in every transmit path By avoiding the use of multi-input DPD blocks in every transmit path, the complexity of the proposed technique is kept low and scales more favorably with the number of antennas than competing techniques It is shown that all blocks can be identified from measurements of the PA output signals using least-squares estimation Measurement results of a four-path transmitter are presented and used to evaluate the proposed DPD technique against existing techniques The results show that the performance of the proposed DPD technique is similar to those of existing techniques, while the complexity is lower

Design of a Wideband Omnidirectional Antenna With Characteristic Mode Analysis

Abstract: A low-profile horizontally polarized (HP) omnidirectional metasurface-inspired antenna is presented. To realize HP omnidirectional radiation pattern, the theory of characteristic mode is utilized to facilitate the analysis of three antenna structures. Then, by properly exciting the desired characteristic mode, the antenna with a wide bandwidth and good omnidirectionality, which is based on the modification of the standard patch antenna, is obtained. The simulated results show that the proposed antenna not only can obtain a low profile of 0.06 λ 0 (where λ 0 is the free-space wavelength at 5.2 GHz), but also has a wide operating bandwidth of 16.6%. Finally, the metasurface-inspired antenna is manufactured and the error analysis between the simulated and measured results is also provided. The antenna can be applied to 5G wireless local area network systems.

Wideband Phase Shifter in Groove Gap Waveguide Technology Implemented With Glide-Symmetric Holey EBG

Abstract: A wideband phase shifter in $U$ -band realized in groove gap waveguide (GGWG) technology is presented as a good solution to be integrated in antenna feed structures. The GGWG is implemented by glide-symmetric holes to reduce manufacturing complexity. The design is also proposed to be mechanically variable by changing the height of the dielectric slab used to change the phase. Experimental results evidence the potential of this solution.

A mmWave Wideband Slot Array Antenna Based on Ridge Gap Waveguide With 30% Bandwidth

Abstract: A wideband $8 \times 8$ element slot antenna array based on ridge gap waveguide feeding network has been proposed for mmWave applications. The antenna subarray consists of four radiating slots which are excited by a groove gap cavity layer. Compared with previously published works, the proposed planar antenna array has quite wide impedance bandwidth. The antenna covers a wideband of 50–67.8 GHz with 30% impedance bandwidth (VSWR < 2). Also, the antenna has only 2.5 dB gain variation over the entire bandwidth which implies also good radiation characteristics for the proposed antenna. The maximum measured gain value is about 27.5 dBi with a total efficiency of 80% for the proposed antenna within the band of interest. With this performance, the proposed antenna array is a promising candidate for mmWave communication systems.

Connected-Slot Array With Artificial Dielectrics: A 6 to 15 GHz Dual-Pol Wide-Scan Prototype

Abstract: In this communication, we report on the design, manufacturing, and testing of a dual-polarized array of connected slots radiating in the presence of an artificial dielectric superstrate. The prototype array consists of 512 elements, i.e., $16\times 16$ connected slots for each of the two polarizations. The antenna array is realized with a single multilayer printed circuit board (PCB), which represents an advantage in terms of cost and complexity with respect to the typical configuration based on multiple vertically arranged PCBs. The performance is investigated in terms of simulated and measured matching characteristics and radiation patterns. The proposed structure achieves active voltage standing wave ratio lower than 3.1 over about an octave bandwidth (6–15 GHz), within a wide scan range (±60° in the H-plane and ±80° in the E-plane).

Compact Planar Multistandard MIMO Antenna for IoT Applications

Abstract: A novel compact single-substrate planar multiband five-element multiple-input multiple-output (MIMO) antenna system is presented in this paper. The tunable two-element folded meandered MIMO antenna covers the long-term evolution frequency bands below 1 GHz (687–813 MHz) and radio frequency identification bands centered around 2.4 and 5.8 GHz. The other two-element compact MIMO antennas operate over 754–971 MHz, 1.65–1.83 GHz, 2–3.66 GHz, and 5.1–5.6 GHz frequency bands. Furthermore, the proposed antenna elements are integrated with a wideband sensing antenna for the spectrum sensing in 0.668–1.94 and 3–4.6 GHz, which also acts as the ground plane for the MIMO elements in the cognitive radio application environment. The antenna is fabricated on a 65 mm $\times \,\, 120$ mm $\times \,\, 1.56$ mm low-cost FR-4 substrate. The antenna’s radiation characteristics are experimentally verified, and the results are in agreement with the full-wave simulation. The 3-D radiation pattern-based envelope correlation coefficient of the MIMO antennas is also experimentally verified which is below the desired value of 0.5. Finally, to show its utility at the Internet-of-Things platform, the antenna is tested in the realistic application environment.

Wideband acoustic wave resonators composed of hetero acoustic layer structure

Abstract: A plate wave resonator illustrated in Fig. 1 (a) has attractive features such as large electromechanical coupling factor (k2) and high phase velocity. For example, 0-th shear horizontal (SH0) mode plate wave has k2 larger than 50% in a LiNbO3 (LN) plate thinner than 0.1λ around an Euler angle of (0o, 120o, 0o).1) In our previous study,2, 3) an SH0 mode plate wave resonator exhibited a large bandwidth (BW) of 22%. Ladder filters for a TV white space cognitive radio4) were also prototyped using the plate wave resonators, and extremely wide passband at 6 dB attenuation of 41 to 51%, which was enough to fully cover digital TV band in Japan, USA and EU, was obtained.3) On the other hand, the ultra-thin LN plate thinner than 0.1λ was more fragile than expected, which must be addressed for practical application. To solve the problem, a lot of attentions are recently paid to a new type of acoustic wave device, “Hetero Acoustic Layer (HAL) SAW device,” which has a single crystal piezoelectric thin plate solidly supported with a substrate, as shown in Fig. 1 (b).5-10) Our previous papers reported SH type LN HAL SAW resonators with a high velocity of 6,000 m/s or a wideband of 20%, but the measured impedance ratio was smaller than expected.6,8) In this study, we achieved a very high impedance ratio of 83 dB using a 3.5 μm thick LN plate. This paper reports the finite element method (FEM) simulation, fabrication and characterization of the HAL SAW resonator.

A High-Gain Circularly Polarized Fabry–Perot Antenna With Wideband Low-RCS Property

Abstract: In this letter, a low radar cross section (RCS) and the high-gain circularly polarized (CP) antenna using a novel linear-to-circular polarization converter is presented. A simple linearly polarized patch antenna rotated 45° relative to x -axis is used as the primary source. The polarization converter is an asymmetrical metastructure composed of different metal patterns printed on the two sides of a dielectric substrate, which can transmit a CP wave. The top-side metallic pattern is an absorbing surface to realize the RCS reduction, while the bottom-side one is a partially reflective surface (PRS). A CP Fabry–Perot resonance cavity is constituted by the PRS and the anisotropic high-impedance surface (HIS) plane to obtain the gain enhancement. The simulation and measured results demonstrate that the proposed antenna exhibits good circular polarization performance in the operating frequency. In addition, the gain of the proposed antenna can be improved by about 3.2 dB at 10.7 GHz, and the RCS can be reduced significantly over a wideband ranging from 4 to 13 GHz for both polarizations, compared with the conventional patch antenna.

Characteristic Mode Design of Wide Band Circularly Polarized Patch Antenna Consisting of H-Shaped Unit Cells

Abstract: This paper proposes a general characteristic mode-based design procedure of simple three steps for wideband circularly polarized (CP) antenna design. First of all, the characteristic mode analysis is carried out to understand the different modes of a proposed antenna geometry without feeding network. Second, modal currents and their corresponding modal fields (radiation patterns) are studied for choosing modes to shape the required radiation pattern. Finally, a suitable feeding structure is chosen to excite the desired modes at the same time owns a good impedance matching. As an example, a CP patch antenna fed with cross-shaped aperture is proposed and designed following the design procedure. Patch consisting of H-shaped unit cells is used as the radiator. Characteristic mode method is applied to analyze the modes of the proposed antenna and explains the property of wide band circular polarization. It is revealed that higher order modes of the patch can be used to achieve circular polarization over a wideband of frequency. The antenna is fabricated using printed circuit techniques. The return loss and radiation properties are measured and compared with simulation results. With the highly coupled units, a wide impedance bandwidth of 38.8% is obtained. Besides, a wide 3-dB axial ratio bandwidth of 14.3% is achieved.

A Low-Profile Dual-Polarized High-Isolation MIMO Antenna Arrays for Wideband Base-Station Applications

Abstract: A low-profile dual-polarized high-isolation multiple input multiple output (MIMO) antenna array for wideband base-station applications is presented in this paper. The proposed dual-polarized antenna element has the advantage of lower profile ( $0.067\lambda $ ) by utilizing artificial magnetic conductor structure. The antenna array consisting of four elements is working within the frequency band from 2.4 to 3 GHz. Furthermore, decoupling branches among the elements are introduced to improve the isolation by about 10 dB. Both simulation and measured results indicate that the proposed dual-polarized antenna element has a good isolation over 28 dB. Moreover, the beamwidth of the antenna array can be effectively broadened by the adjustment of phase distributions of corresponding artificial material plane. Finally, a larger MIMO system is also investigated, and the simulation and measured results prove that dual-polarized dipole antenna MIMO array has good system performance.