Wideband Hybrid Research Articles

Energy Efficiency Beamforming Design for UAV Communications With Broadband Hybrid Polarization Antenna Arrays

Stringent physical resource constraints in unmanned aerial vehicle (UAV) communications bring new challenges to energy efficient transmission. In this paper, we study energy efficient beamforming for UAV communications, where a wideband hybrid polarized antenna array with tapped-delay-lines (TDLs) structure is deployed on the UAV. By exploiting hybrid structured, TDLs, and polarized antenna arrays, the strict requirements of hardware size and cost on UAV can be satisfied. It is shown that the energy efficient beamforming with the adopted array can be formulated as a WMMSE-based parameter optimization problem, which however is still a challenging nonconvex problem due to unit modulus constraints in analog beamformer. To overcome the nonconvex nature, an iterative algorithm is proposed, in which the optimization problem is iteratively solved through three convex quadratic programming problems with convex equality or inequality constraints. Finally, the numerical results demonstrate that the proposed wideband beamforming algorithm can significantly improve the energy efficiency, compared with the gradient projection algorithm.

Low Complexity Hybrid Precoding for Multiuser Millimeter Wave Systems Over Frequency Selective Channels

We propose new hybrid precoding schemes for the downlink transmission in a multiuser millimeter wave (mmWave) system over frequency selective channels. In the system, the multiantenna base station employs the fully connected architecture and uses orthogonal frequency-division multiplexing to serve multiple mobile users. We first propose an alternating minimization based hybrid precoding scheme by transforming the wideband hybrid precoding problem to a narrowband hybrid precoding problem. We then propose a beamforming-based hybrid precoding scheme by exploiting the correlation of subchannels to profoundly reduce the computational complexity. Numerical results are presented to demonstrate the advantages of our proposed schemes relative to two existing schemes, as well as to examine the impact of system parameters on the achieved performance.

Bussgang decomposition-based sparse channel estimation in wideband hybrid millimeter wave MIMO systems with finite-bit ADCs

Both the hybrid architecture and low precision analog-to-digital converters (ADCs) are considered to alleviate the burden of high power cost and hardware implementation of millimeter wave (mmWave) communication system. Accordingly, the channel estimation issue in wideband mmWave system with finite-bit ADCs becomes even challenging. To address this issue, the non-linear mmWave channel estimation problem is reformulated into a linear sparse signal recovery problem by utilizing the Bussgang decomposition. Then, based on the equivalent linear sparse model, a Bussgang decomposition-based OMP (BD-OMP) algorithm is proposed to both exploit the inherent sparsity of wideband mmWave channel and alleviate the quantization error. Furthermore, we analyze that the actual noise of linear sparse model consists of combined noise and distortion noise, which is related to the number of quantization bits, antennas, and received signal power in a large scale regime. In addition, the terminal condition of BD-OMP algorithm is derived based on the residual difference of two consecutive iterations, where the expectation of residual difference is the variance of the actual noise. Simulation results demonstrate that the proposed approach can significantly reduce the training overhead for estimating wideband mmWave channel with finite-bit ADCs at the receiver.

Hybrid Precoding for Wideband Millimeter-Wave Systems With Finite Resolution Phase Shifters

In this paper, we study the hybrid analog-digital precoding for OFDM based-wideband millimeter wave (mmwave) communication systems. Since the analog precoding matrix is performed in the time domain and used for the entire bandwidth while the digital precoding matrices are performed on a per-subcarrier basis, the resulting wideband hybrid precoding problem becomes very complicated. Moreover, in practice phase shiftier (PS) usually has only finite resolution, which brings more difficulties. To solve the resulting difficult problem, we propose an efficient algorithm by leveraging the penalty decomposition method. Simulation results are finally provided to confirm the effectiveness and superiority of the proposed algorithm and show the performance improvement than the existing algorithm.

A wideband hybrid feeding circularly polarized magneto‐electric dipole antenna for 5G Wi‐Fi

AbstractA hybrid‐fed circularly polarized magneto‐electric (ME) dipole antenna is presented for 5G Wi‐Fi application. A single series feeding cross‐aperture coupled structure is used to stimulate the ME dipole antenna. Measurement shows that the ME dipole antenna has an overlapped bandwidth of 23.5% from 4.98 to 6.31 GHz for the standards of both |S11| < −10 dB and axial ratio < 3 dB. A measured gain of approximately 7.5 dBi is obtained and the fluctuation of the realized gain is <1 dB from the whole operating frequency band. Moreover, because of the advantages of ME dipole, the proposed design realized a stable radiation patterns and roughly coincide radiation patterns at x‐o‐z and y‐o‐z plane in the operating frequency band.

Performance Analysis of a Low Profile Hybrid Antenna for Broadband Applications

In this paper, a low profile dielectric resonator antenna (DRA) is proposed and investigated. To achieve the broad impedance bandwidth the proposed antenna geometry combines the dielectric resonator antenna and an underlying microstrip-fed slot with a narrow rectangular notch, which effectively broadens the impedance bandwidth by merging the resonances of slot and DRA. The physical insight gained by the detailed parametric study has led to find out a set of guidelines for designing the antennas for any particular frequency band. The design guidelines have been verified by simulating a set of antennas designed for different frequency bands. For validation, a prototype antenna is fabricated and tested experimentally. The measured results show that the proposed DRA offers an impedance bandwidth of about \(125.34\%\) from 1.17 to 5.1 GHz with reasonable gain between 3.5 and 5.7 dBi. The volume of the proposed DRA is \(0.16\lambda _{dr}^{3}\), where \(\lambda _{dr}\) is the wavelength at center operating frequency of the DR. A comprehensive study on bandwidth shows that the proposed DRA provides maximum bandwidth in terms of the DR volume (\(\hbox {BW}/V_{dr}\)) and the DR height (\(\hbox {BW}/h_{dr}\)) than the other similar reported work on hybrid wideband DRA designs.

Efficient energy localization for hybrid wideband hyperthermia treatment system

This article presents efficient energy localization approach for hybrid wideband system for hyperthermia treatment of cancer based on a transmission line (TL). A heterogeneous head phantom is built by incorporating frequency dependent tissue properties of head layers considering both electromagnetic and ultrasound treatment. Effective medium properties are derived and used to compensate signal phase and magnitude values based on TL model. The obtained field map results emphasize the feasibility of the developed approach to obtain system parameters that enhance energy localization and eradicate hotspots.

Dual-Band Circularly Polarized Antenna With Wide Axial Ratio Beamwidths for Upper Hemispherical Coverage

This paper presents a dual-band circularly polarized cross-dipole antenna with wide axial ratio beamwidths for full upper hemispherical coverage for GPS L1 and L2 bands. The antenna has curved radiating arms and a corrugated back cavity to enhance the beamwidth. A wideband hybrid coupler is used to feed the antenna at the two nearby frequency bands. Experimental results show that very wide 3-dB AR beamwidths of over 200° can be obtained, fully covering the upper hemisphere for the two GPS bands.

A Modified Hybrid RF Predistorter Linearizer for Ultra Wideband 5G Systems

The wide-bandwidth signal transmission is one of the requirements in upcoming 5G communication systems in its quest for high data rates. In this paper, a wideband hybrid RF/digital predistortion (HRF-DPD) linearization technique is reported to compensate for the nonlinearity of ultra-wideband power amplifier (PA) for 5G systems driven by carrier aggregated and wideband modulated signals. The proposed methodology is suitable for 5G PA design, since its power overhead and system bandwidth does not increase with an increase in signal bandwidth. Taking advantage of recent available digital signal processing solutions, the proposed method reduces hardware requirements of the conventional analog predistorter by alleviating the need of vector multiplier, branch line coupler, and delay lines. Such linear operations are controlled digitally, which provides flexibility in terms of digitally compensation of delay, gain and phase control of the signal. For establishing a proof of concept, HRF-DPD is implemented with ZX60V-82+ class AB PA and tested using a 100- and 50-MHz long term evolution-carrier aggregated (LTE-CA) signal at 2 GHz. Experimental results show that the wideband PA along with the proposed predistorter delivers an adjacent channel leakage ratio (ACLR) of −54 dBc with a cancellation of 30.6 dB for 100-MHz LTE-CA signal. With the proposed method PA, nonlinear distortion outside the 100-MHz band can be linearized leading to filter less architecture which provides 45-dBc ACLR performance.

Wideband Hybrid Coupler With Electrically Switchable Phase-Difference Performance

A wideband hybrid coupler with an adjustable output phase difference with equal power division is proposed. A compact, low-loss and low-cost reconfigurable transmission line with electrically switchable equivalent characteristic impedance and length is introduced and adopted in this design, which is based on a two-section quadrature hybrid structure. Additionally, only two bias points are needed in this hybrid coupler to operate six switches synchronously and provide three output phase differences; 90° and $90 \pm a^{\circ }$ ( $a \le 30^{\circ }$ has been verified). Good matching, isolation, and equal power division are obtained under all phase-difference possibilities. Two examples of $a = 15^{\circ }$ and 30° are fabricated and measured for 2.4-GHz applications. Testing results demonstrate satisfying properties including the notably stable phase difference with an error less than ±6° over 30% frequency bandwidth. The presented hybrid couplers would be appropriate for Butler matrices to increase the number of possible beams, which will be more than the number of ports.

Wideband Matching of Full-Wavelength Dipole With Reflector for Base Station

This communication introduces a wideband hybrid feeding method for full-wavelength dipole antennas with a reflector. A full-wavelength dipole is designed to cover the band from 698 to 960 MHz for cellular base station applications. Its matching circuit consists of a triple-tuned circuit and a quasi-quarter-wavelength impedance transformer. The proposed matching circuit can provide balanced feeding as a balun and has a compact size. The working mechanism and a complete design scheme of the proposed matching circuit are elaborated. The matching circuit is designed and optimized using a circuit theory model and then physically realized using microstrip lines based on full-wave simulation. The measured reflection coefficient $|S_{11}|$ is lesser than −14 dB across the entire band from 698 to 960 MHz, exhibiting a bandwidth of 32%. This is the first time that a wideband center-fed full-wavelength dipole is proposed.

Two Section Wideband 90° Hybrid Coupler Using Parallel-Coupled Three-Line

Two section wideband hybrid coupler with short-circuited coupled lines in the middle branch is demonstrated. The coupled lines are designed with a parallel-coupled 3-line, which has tight coupling and symmetric transmission phase over the center frequency. Without defected ground planes and a multilayer process, the proposed two-section coupler has the widest fractional bandwidth (FBW) than other two or even three section hybrid couplers modified from branch-line couplers. The designed wideband coupler has 55% FBW at the center frequency of 1.9 GHz. The bandwidth is limited by 1-dB power imbalance and the worst return loss, isolation, and phase imbalance within the bandwidth are 20.1 dB, 20.8 dB, and 3.2°, respectively.

A Compact Wide-Band Hybrid Dielectric Resonator Antenna with Enhanced Gain and Low Cross-Polarization

By loading two printed patches to the dielectric resonator antenna (DRA), a compact wide-band hybrid dielectric resonator antenna with enhanced gain and low cross-polarization is presented. The proposed antenna utilizes a combination of a rectangular dielectric resonator and two printed patches. Due to the hybrid design, multiple resonances were obtained. By adding two air layers between the dielectric resonator and the printed patches, the bandwidth has been significantly improved. Compared to the traditional hybrid dielectric resonator antenna, the proposed antenna can achieve wide bandwidth, high gain, low cross-polarization, and even small size simultaneously. The prototype of the proposed antenna has been fabricated and tested. The measured −10 dB return loss bandwidth is 25.6% (1.7–2.2 GHz). The measured antenna gains are about 6.3 and 8.2 dBi in the operating frequency band. Low cross-polarization levels of less than −28.5 dB and −43 dB in the E-plane and H-plane are achieved. Moreover, the overall dimensions of the antenna are only 67 × 67 × 34 (mm3). The proposed antenna is especially attractive for small base antenna applications.

Application of the Crank–Nicolson FDTD method for analysis of a wideband multi-section hybrid coupler

In this paper the Crank---Nicolson (CN) finite-difference time-domain (FDTD) method is applied for the analysis of a planar wideband hybrid coupler. The proposed method is applied for analysis of transmission lines. Stability issue is investigated for different cases, including lossless and lossy transmission lines. Sufficient conditions for unconditional stability are derived. As a practical problem, a wideband compact hybrid coupler working on 1---6 GHz frequency band is analyzed using the CN-FDTD method. Measurement results show that the proposed coupler provides coupling of 3 ± 0.8 dB with 90° ± 0.85° phase shift and demonstrate the return loss and isolation better than 16 dB over 1---6 GHz. To validate the accuracy of the method, the results of this scheme are compared with measurements and the conditional stable leap-frog (LF) FDTD method. It is observed that using the CN-FDTD, the temporal step-size can be increased up to 1500 time compared with the LF-FDTD method with still good agreement with the measured results.

Novel high gain and wide band hybrid amplifier designed with a combination of an EYDFA and a discrete Raman amplifier

In an optical communication network, over a broad range of spectrum, the gain of the amplifier must be flattened in order to increase the bandwidth utilization of the network. Here we analyze a novel approach of designing a hybrid amplifier with a combination of a single mode (SM) erbium ytterbium co-doped fiber amplifier (EYDFA) and a discrete Raman amplifier (RA) to flatten its gain over the optical spectrum of the C and L bands, which is about 90 nm of spectral width. This hybrid amplifier requires only 5 optimal pump signals in RA, and there is no need of any gain flattening filter in it. The performance of this simulated hybrid amplifier is analyzed with the help of 110*40 Gb/s non-return-to-zero dense wavelength division multiplexed (DWDM) signals as the input. They cover the entire C and L bands, and the presence of dense channels also ensures the accurate measurement of important parameters of the hybrid amplifier such as maximum gain, gain ripple, noise figure, and optical signal-to-noise ratio (OSNR). The five pump signals of RA are spaced equally, unequally, and semi-unequally in order to attain the objective. The least gain ripple is obtained for semi-unequal pump frequency spacing. The length of the SM EYDFA, the RA, the power of the pump signals, and the power of the DWDM input signals are optimized through the multi-parameter multi-target optimization tool of the Optisystem simulation software. The five pumping signals of RA are tested with forward, backward, and both forward and backward schemes in order to analyze the performance of the hybrid amplifier. Out of all the experiments, the SM EYDFA + RA forward pumping scheme offers superior performances such as maximum gain of 31.2 dB, very low gain ripple of 2.09 dB (6.7% of the maximum gain), maximum noise figure of 4.68 dB, and maximum OSNR of 34.23 dB. This new design of hybrid amplifier with superior gain flattening performance will be very much useful for cable television or community antenna television (CATV) and telecommunication networks.

Hybrid wide-band, low-phase-noise scheme for Raman lasers in atom interferometry by integrating an acousto-optic modulator and a feedback loop.

We report a hybrid scheme for phase-coherent Raman lasers with low phase noise in a wide frequency range. In this scheme, a pair of Raman lasers with a frequency difference of 3.04 GHz is generated by the ±1-order diffracted lights of an acousto-optic modulator (1.52 GHz), where a feedback loop is simultaneously applied for suppressing the phase noise. The beat width of the Raman lasers is narrower than 3 Hz. In the low-frequency range, the phase noise of the Raman lasers is suppressed by 35 dB with the feedback. The phase noise is less than -109 dBc/Hz in the high-frequency range. The sensitivity of an atom gyroscope employing the hybrid Raman lasers can be implicitly improved 10 times. Due to the better high-frequency response, the sensitivity is not limited by the durations of Raman pulses. This work is important for improving the performance of atom-interferometer-based measurements.

An Efficiency-Enhanced Hybrid Supply Modulator With Single-Capacitor Current-Integration Control

This paper presents a high-efficiency wideband hybrid supply modulator (HSM). We show that proper control of the average current from the class-AB linear amplifier (LA) and proper selection of the inductor value are essential to efficiency optimization. In line with the above criteria, a single-capacitor current-integration (SCCI) control method is proposed. Current integration is achieved by using a single capacitor, circumventing the need of the high-speed full-range current sensor required for conventional HSMs and reducing the design complexity greatly. The ripple current of the LA is controlled indirectly, and enhanced efficiency is achieved by enforcing the average output current from the LA to be around zero. A wideband LA is proposed to suppress the output voltage ripple. A proof-of-concept design using an inductor with an optimized value of 100 nH is fabricated in 130 nm CMOS technology. It switches at a peak frequency of 50 MHz, achieves up to 8% efficiency improvement when compared to recent works, and is able to track a $0.8\;{\text{V}}_\text{pp}$ sinusoidal signal with high fidelity up to 10 MHz. The measured output voltage ripple is reduced to below 8 mV. The peak conversion efficiency is 88.3% at the maximum output power of 23 dBm.

Optimisation of sensing time and transmission time in cognitive radio-based smart grid networks

ABSTRACTCognitive radio (CR)-based smart grid (SG) networks have been widely recognised as emerging communication paradigms in power grids. However, a sufficient spectrum resource and reliability are two major challenges for real-time applications in CR-based SG networks. In this article, we study the traffic data collection problem. Based on the two-stage power pricing model, the power price is associated with the efficient received traffic data in a metre data management system (MDMS). In order to minimise the system power price, a wideband hybrid access strategy is proposed and analysed, to share the spectrum between the SG nodes and CR networks. The sensing time and transmission time are jointly optimised, while both the interference to primary users and the spectrum opportunity loss of secondary users are considered. Two algorithms are proposed to solve the joint optimisation problem. Simulation results show that the proposed joint optimisation algorithms outperform the fixed parameters (sensing time and transmission time) algorithms, and the power cost is reduced efficiently.

Investigation of Resonant Modes in Wideband Hybrid Omnidirectional Rectangular Dielectric Resonator Antenna

In this paper, resonant modes of the hybrid omnidirectional rectangular dielectric resonator (DR) antenna (DRA) are investigated. It is found that the omnidirectional mode of the rectangular DR is a combination of the higher-order ${{TE}}_{{121}}^{{x}}$ and ${{TE}}_{{211}}^{{y}}$ modes. Omnidirectional patterns can be achieved by exciting the ${{TE}}_{{121}}^{{x}}$ and ${{TE}}_{0{211}}^{{y}}$ modes of a rectangular DRA, which has a square cross-section, with equal amplitude and phase. Thus, the dielectric waveguide model (DWM) method can be used to predict the resonant frequency and field distributions of the omnidirectional mode of rectangular DRA. In addition, the resonance of feeding probe is also studied. And a wideband hybrid design is achieved by merging resonances of the rectangular DRA and feeding probe. Full-wave simulations and experimental measurements were carried out to verify the proposed idea. Both the simulated and measured results agree well with the calculated results.

Design Investigation of Microstrip Patch and Half-Mode Substrate Integrated Waveguide Cavity Hybrid Antenna Arrays

In this paper two linear arrays including a linear 1×4 and a planar 2×2 of microstrip patch and half-mode substrate integrated waveguide (SIW) cavity hybrid antenna are introduced and investigated. These are simply implemented using low cost single layer printed circuit board (PCB) process. The array element consists of a rectangular microstrip patch with appropriate dimensions in the vicinity of a semi-cicular SIW resonator which are formed a wideband hybrid antenna. In both antenna arrays a microstrip feeding network including a quartur wave transformer matching circuit has been used to fed the array elements. The size of 1×4 linear array is 1.58λ0×2.87λ0 and planar 2×2 array size is 1.57λ0×1.37λ0. Array structure are numerically and experimentally investigated. The measured and simulated results including reflection coefficient, radiation patterns and gain of the both antenna arrays are reported.