Phase Shift Network Research Articles

An OAM-Mode Reconfigurable Array Antenna With Polarization Agility

An Orbital angular momentum (OAM) antenna with both mode reconfigurability and polarization agility is proposed in this paper. The proposed antenna is designed based on a four-element uniform circular array with a phase-shifting reconfigurable feed network. To reduce its dimensions and complexity, the feed work is constructed with two stages of single-pole double-throw switches and a stage of 90° phase-shifting power dividers, partially of which can be shared among the chosen operating states. Moreover, the use of a small amount of p-i-n diodes as binary switches allows low insertion loss and low component cost. By varying the ON/OFF status of the diodes strategically, the resultant array can be reconfigured to horizontal polarization (HP) or vertical polarization (VP), along with OAM mode $l = -1$ or +1 achieved for each polarization. The antenna performance is evaluated in terms of reflection coefficients, near-field distributions and far field radiation patterns. According to the measured results, the antenna exhibits an overlapped frequency band ranging from 2.29 to 2.59 GHz among the different operating states. Meanwhile, stable radiation patterns as well as high cross-polarization discrimination can be obtained. Benefiting from the above features, the antenna could help to improve the signal quality and increase the channel capacity in wireless communications.

Developing the First mmWave Fully-Connected Hybrid Beamformer With a Large Antenna Array

Millimeter wave (mmWave) systems with effective beamforming capability play a key role in fulfilling the high data-rate demands of current and future wireless technologies. Hybrid analog-to-digital beamformers have been identified as a cost-effective and energy-efficient solution towards deploying such systems. Most of the existing hybrid beamforming architectures rely on a subconnected phase shifter network with a large number of antennas. Such approaches, however, cannot fully exploit the advantages of large arrays. On the other hand, the current fully-connected beamformers accommodate only a small number of antennas, which substantially limits their beamforming capabilities. In this article, we present a mmWave hybrid beamformer testbed with a fully-connected network of phase shifters and adjustable attenuators and a large number of antenna elements. To our knowledge, this is the first platform that connects two RF inputs from the baseband to a $16\times 8$ antenna array, and it operates at 26 GHz with a 2 GHz bandwidth. It provides a wide scanning range of 60°, and the flexibility to control both the phase and the amplitude of the signals between each of the RF chains and antennas. This beamforming platform can be used in both short and long-range communications with linear equivalent isotropically radiated power (EIRP) variation between 10 dBm and 60 dBm. In this article, we present the design, calibration procedures and evaluations of such a complex system as well as discussions on the critical factors to consider for their practical implementation.

Generating Tunable Orbital Angular Momentum Radio Beams With Dual-Circular-Polarization and Dual-Mode Characteristics

In this paper, a mode and circular-polarization (CP) simultaneously reconfigurable patch array antenna for orbital angular momentum (OAM) beams generation is presented and experimentally investigated. The array antenna simply consists of a 1:4 power divider and four antenna elements, each of which is fed with two switchable ports and a quadrature phase shift. Besides, the four elements are arranged using an orthogonal configuration. In this manner, switchable CPs are generated for each element, and switchable ±90° phase differences are obtained between adjacent elements. By strategically varying the ON/OFF status of the p-i-n diodes loaded as switches, the antenna could operate among left-hand CP (LHCP) with OAM-mode +1 or −1 and right-hand CP (RHCP) with OAM-mode +1 or −1. Without additional phase-shifting networks, the design method can be easily extended to large-scale antenna arrays. According to the measured results, an overlapped operational band of 2.39 to 2.64 GHz is obtained among the four states. In addition, both far-field and near-field distributions are performed to verify the design. Owing to its flexibility of OAM mode and polarization reconfigurablity as well as symmetrical and simple configuration, the antenna could be a promising application in future OAM-based communications system.

Hybrid Transceivers Design for Large-Scale Antenna Arrays Using Majorization-Minimization Algorithms

Hybrid analog-digital (A/D) transceivers are an appealing solution to reduce the transceiver hardware complexity and power consumption for the millimeter wave (mmWave) communication and more general large-scale antenna array (LSAA) systems. In contrast to fully digital conventional multiple-input-multiple-output (MIMO) systems, the baseband precoding operation splits into a lower-dimensional digital precoder followed by a network of analog phase shifters. In this paper, we consider the hybrid precoder design as a constant modulus constrained matrix factorization (CMCMF) problem for the most common types of hybrid architectures namely, the fully and the partially connected ones. Two lines of algorithms based on the majorization-minimization (MM) and the minorization-maximization framework, respectively are proposed for these architectures. In particular, we present efficient algorithms scalable for LSAA systems with provable convergence guarantees to a stationary point. We also consider the hybrid postcoder design at the receiver end. Simulation results demonstrate that the proposed algorithms converge faster to a stationary point as compared to the state-of-the-art solutions that exist in literature. Furthermore, the solution tailored for the partially connected case achieves significantly improved performance in terms of the system spectral efficiency when compared to the existing solutions.

Subarray hybrid precoding with finite‐resolution PSs for massive MIMO capacity maximisation

The addition of analogue processing to the digital precoding, known as hybrid beamforming (HB), is an efficient solution for massive multiple-input multiple-output (MIMO) systems. The design of a phase shifter (PS) network plays an important role in the complete precoder operation because it necessitates accurate components for realising precise phases, and that can be costly. Finite resolution PSs are good alternatives because they need simpler hardware implementation than those with infinite resolution. However, the degradation of performance of a MIMO system with very low-resolution PSs is significant. Although recent studies suggest adding extra radio frequency (RF) chains to substitute for the accuracy of the PSs, it is complex, expensive and not energy efficient. This study demonstrates that HB with low-resolution PSs can realise a high performance without increasing the number of RF chains. The authors proposed solution relies on a proper selection of the weights of the RF beamformer, hence exploiting the structure of the multipath propagation channel to maximise the system capacity. They also show that separating antennas from each other by sufficient distance, results in a less correlated channel, and thus, a minimal loss in the capacity and the antenna gains are assured.

On the Power Leakage Problem in Millimeter-Wave Massive MIMO With Lens Antenna Arrays

The emerging millimeter-wave massive multiple-input multiple-output (MIMO) with lens antenna arrays, which is also known as “beamspace MIMO,” can effectively reduce the required number of power-hungry radio frequency (RF) chains. Therefore, it has been considered as a promising technique for the upcoming 5G communications and beyond. However, most current studies on beamspace MIMO have not taken into account the important power leakage problem in beamspace channels, which possibly leads to a significant degradation in the signal-to-noise ratio (SNR) and the system sum-rate. To this end, in this paper, we propose a beam-aligning precoding method to handle the power leakage problem. First, a phase shifter network (PSN) structure is proposed, which enables each RF chain in beamspace MIMO to select multiple beams to collect the leakage power. Then, a rotation-based precoding algorithm is designed based on the proposed PSN structure, which aligns the channel gains of the selected beams toward the same direction for maximizing the received SNR at each user. Furthermore, we reveal some system design insights by analyzing the sum-rate and energy efficiency (EE) of the proposed beam-aligning precoding method. In simulations, the proposed approach is found to achieve the near-optimal sum-rate performance compared with that of the ideal case of no power leakage, and obtains a higher EE than those of the existing schemes with either a linear or planar array.

Generation of Broadband High-Purity Dual-Mode OAM Beams Using A Four-Feed Patch Antenna: Theory and Implementation

A broadband four-feed circular patch antenna is demonstrated to generate high-purity dual-mode vortex beams carrying orbital angular momentum (OAM) for the first time. The electric field formula of the circularly polarized (CP) component is derived for analyzing radiation characteristics of different OAM modes, such as the CP property, phase and amplitude distributions. Theoretical calculation and numerical simulation results show that the four-feed patch antenna operating in the TMn1 mode can generate ±n OAM waves. A prototype of a four-feed circular TM21-mode patch antenna is fabricated and measured to verify the effectiveness of the theoretical analysis. The proposed antenna consists of a four-feed patch with an air-coupled parasitic patch and a four-way phase-shifting feeding network. Experimental results show that the proposed antenna can generate a left-hand CP OAM with mode l = +2 and a right-hand CP OAM with mode l = −2. The OAM beams are generated in a wide band from 5.50 to 6.50 GHz with a mode purity over 90%. The proposed method is very suitable for the generation of wideband, dual-mode and high-purity OAM beams in the microwave and millimeter wave bands.

Semiconductor Quantum Dots for Integrated Quantum Photonics (Adv. Quantum Technol. 9/2019)

The cover image shows an artistic impression of a fully on-chip quantum photonic circuit based on semiconductor quantum dots (QDs) as nonclassical light sources. The QDs are directly integrated within a network of waveguides, beam splitters and phase shifters for the passive and active manipulation of the quantum states of light. The integrated superconducting nanowire single-photon detectors make the on-chip detection of single photons feasible. For further information see the review by Stefan Hepp and co-workers, article number 1900020. (Image design by S. Kolatschek.)

A Broadband Electronically Mode-Reconfigurable Orbital Angular Momentum Metasurface Antenna

In this letter, a 2 × 2 low-profile broadband triple-mode orbital angular momentum (OAM) array antenna is presented, which can be dynamically controlled with electrostatic method. The antenna element consists of a 4 × 4 metasurface array, a 90° phase-shifting reconfigurable feed network (RFN), and a square driven patch with two switchable feeding ports (SWPs). With the computer-assisted micro-controller unit, the p-i-n diodes direct current (dc) bias voltage on the RFN, and SWPs, the OAM modes can then be dynamically switched between l = +1, l = − 1, and l = 0. The OAM beams of mode l = ±1 and mode l = 0 have been generated in the broad frequency with the impedance band of 4.9–6.5 GHz and 5.0–6.3 GHz, respectively. The experimentally measured peak gains of the triple-mode are 11.17, 11.05, and 15.19 dBi, respectively. Both the simulation and experiment demonstrate that the proposed antenna exhibits several advantages, such as mode-reconfigurable ability, broad frequency band, high directivity, and good helical phase front of the OAM waves.

Constant-${\epsilon}_{r}$ Lens Beamformer for Low-Complexity Millimeter-Wave Hybrid MIMO

It is well established that the utilization of unused millimeter-wave (mmWave) spectrum is inevitable due to unavailability of required bandwidth in the conventional RF band to support the high data demands of 5G. Large antenna arrays with beamforming capabilities are required to compensate for the high path loss at mmWave frequencies. We are at the verge of a massive mmWave radio front-end deployment, and low-complexity low-cost hardware beamforming solutions are required now at this stage than ever before. In this paper, one such solution is demonstrated and analyzed. A high-performance and low-complexity lens-based beamformer consisting of constant dielectric material ( $\epsilon _{r}$ ) with antenna feeds is presented for multibeam operation. A prototype is developed based on the classical synthesis approach, and in line with the requirements of mmWave hybrid multiuser multiple-input multiple-output (MU-MIMO) systems. A characterization at 28 GHz is performed wherein an uplink signal-to-noise ratio of user terminals is evaluated with the zero-forcing (ZF) baseband signal processing. Radiation performance of a single-source beamformer is measured in an anechoic environment, and end-to-end ergodic sum spectral efficiency performance is estimated based on the measured data. It is shown that the constant- $\epsilon _{r}$ -based beamformer solution is simple, yet significantly outperforms conventional antenna array beamformers with analog phase shifter networks, making it a promising candidate for future hybrid massive MIMO systems.

A Shared Aperture 1 Bit Metasurface for Orbital Angular Momentum Multiplexing

In this letter, a shared aperture 1 bit metasurface for orbital angular momentum (OAM) multiplexing is studied. A phased array antenna fed by the phase shift network is embedded on the reflective aperture of the 1 bit metasurface. The proposed device can work on reflectarray mode and phased array mode from 7.1 to 7.5 GHz and 7 to 7.5 GHz, respectively. Correspondingly, OAM vortex beam with topological charge l = −1 and 1 can be generated. The transmission coefficient between the two working modes is below −30 dB, and the envelope correlation coefficient is quite close to 0, which reveals the excellent isolation and diversity performance. A prototype of the proposed device is fabricated and tested. The measured S -parameters and radiation patterns agree well with the simulation results.

Inkjet printed array antennas with frequency controlled beamsteering and multi-angle receiving

This paper presents the first frequency scanning array on a flexible substrate constructed using printed electronics methods and systems. Devices were designed using a printed wide band stacked ellipsoid antenna and phase shifter network with 50 ohm matching power splitters which was developed using Ansys Electromagnetics. These devices were produced in both 1 × 4 and 1 × 8 antenna patch configurations. The resulting devices were then tested to demonstrate beam steering as a function of frequency at 4.35 GHz, 5.32 GHz, 6.27 GHz, and 7.2 GHz and compared. Additionally, bending tests were performed to demonstrate the usability of the devices in a flexible, internet of things oriented application. The demonstrated devices have a multibeam receiving and transmitting capability while being inexpensive and easy to produce in a flexible package.

A High-Precision Hybrid Analog and Digital Beamforming Transceiver System for 5G Millimeter-Wave Communication

In this paper, the development of a millimeter-wave hybrid beamforming (HBF) transceiver system for 5G millimeter-wave multiple-input-multiple-output (MIMO) communication is presented. The developed transceiver system is operated at 28-GHz band in the time division duplex (TDD) mode, with 500-MHz signal bandwidth. To implement high beamforming accuracy, a phased-array-based HBF transceiver with high-precision phase shifting network (PSN) at intermediate-frequency (IF)-paths is proposed. The designed PSN has 8-bit phase resolution within 360° range and 0.13-dB amplitude variation. With the use of such low-cost 8-bit PSN, this HBF transceiver system achieves 0.6° beam resolution and a good RF transceiver performance. In addition, under the over-the-air MIMO communication test with two data streams, the error vector magnitude (EVM) of the received signals at two user equipment (UE) is 2.58% and 2.34%. The high-data rate millimeter-wave communication and MIMO performance of this HBF are verified.

Analysis, Calibration, and Performance Evaluation of a Generalized <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math> </inline-formula>-Phase Quadrature Phase Shift Frequency Selective Receiver

In this paper, a new low-power and blocker-tolerant receiver architecture, the generalized N-phase quadrature phase shift frequency selective (QPS-FS), is proposed and analyzed that is suitable for radio frequency (RF) energy harvesting networks. A complete comparative analysis of the N-phase QPS-FS receiver with conventional N-path passive mixer (P-M) receiver is also provided. The QPS-FS receiver utilizes the impedance translation concept to improve the receiver selectivity but eliminates the need of an active multiphase clock generation circuit used in the conventional N-path P-M receivers. It uses a single clock signal source at the desired signal carrier frequency and a phase shift network in the RF path of the receiver for frequency downconversion and quadrature (I/Q) demodulation. The QPS-FS receiver requires a slower clock signal source, the frequency of which is equal to the desired band RF signal carrier frequency ( $f_{c})$ as opposed to at least N/2 times $f_{c}$ for the conventional N-path P-M receivers. Consequently, the lower frequency clock source requirement extends the frequency coverage of the receiver by a factor of at least N/2 for a given clock source with a fixed maximum frequency. Reduction of the operating frequency and elimination of the active multiphase clock generation circuit would also eventually reduce the overall power consumption for the whole receiver system as confirmed through measurements. A wideband receiver calibration approach provides less than 2% of error vector magnitudes between the transmitted and received constellation points for various modulated signals having bandwidths up to 4 MHz.

Independent control of harmonic amplitudes and phases via a time-domain digital coding metasurface

Harmonic manipulations are important for applications such as wireless communications, radar detection and biological monitoring. A general approach to tailor the harmonics involves the use of additional amplifiers and phase shifters for the precise control of harmonic amplitudes and phases after the mixing process; however, this approach leads to issues of high cost and system integration. Metasurfaces composed of a periodic array of subwavelength resonators provide additional degrees of freedom to realize customized responses to incident light and highlight the possibility for nonlinear control by taking advantage of time-domain properties. Here, we designed and experimentally characterized a reflective time-domain digital coding metasurface, with independent control of the harmonic amplitude and phase. As the reflection coefficient is dynamically modulated in a predefined way, a large conversion rate is observed from the carrier signal to the harmonic components, with magnitudes and phases that can be accurately and separately engineered. In addition, by encoding the reflection phases of the meta-atoms, beam scanning for multiple harmonics can be implemented via different digital coding sequences, thus removing the need for intricate phase-shift networks. This work paves the way for efficient harmonic control for applications in communications, radar, and related areas.

Hybrid Precoding for Millimeter Wave Communications With Fully Connected Subarrays

In this letter, we propose a novel hybrid precoding architecture for millimeter wave communications named fully-connected subarrays (FC-SA), wherein each radio frequency (RF) chain is connected to all subarrays through a FC phase shifter (PS) network, and each subarray contains several antennas each with an individual PS. Since PSs inside subarrays are shared by all RF chains, the beamforming gain of the entire array is utilized with much lower hardware complexity than the conventional FC structure. Moreover, we propose a hybrid alternating minimization precoding algorithm to handle the additional rank-one constraint on analog precoder. Performance comparisons between the proposed FC-SA architecture and existing FC and partially connected structures are presented in terms of spectral efficiency (SE) and energy efficiency (EE). Simulation results demonstrate that the proposed scheme approaches the SE of FC structure and achieves the highest EE with a moderate number of RF chain.

Low-Complexity Constant Envelope Precoding Using Finite Resolution Phase Shifters for Multiuser MIMO Systems With Large Antenna Arrays

The present study considers a constant envelope (CE) precoding design problem in massive multiuser multiple-input multiple-output systems, where CE precoding is implemented with a network of finite resolution phase shifters (PSs). Mathematically, such CE precoding design problem can be formulated as a discrete optimization problem whose optimal solution can be obtained through an exhaustive search. Unfortunately, an exhaustive search involves exponential complexity with numerous base station antennas ( $M$ ) and bits in PS resolution. We resolve the aforementioned concern by using a low-complexity algorithm developed from the iterative gradient descent (IGD) based algorithmic framework. However, unlike conventional IGD-based solvers, finite resolution PSs are considered directly in the optimization procedure of the proposed algorithm to improve performance. In addition, the proposed algorithm is roughly $M/2$ times less complex than the conventional IGD algorithm at each iteration. The simulation results reveal that the proposed algorithm has nearly the same performance as that of the unquantized version of the state-of-the-art IGD algorithm.

RF Lens-Embedded Antenna Array for mmWave MIMO: Design and Performance

The requirement of high data rate in 5G calls for utilization of the mmWave frequency band. Researchers seeking to compensate for mmWave's high path loss have proposed that mmWave MIMO systems make use of beamforming. Hybrid beamforming systems demonstrate promising performance in achieving high gain and directivity by using phase shifters. The actual implementation, however, is costly and complex. To reduce such cost and complexity, this article presents actual prototypes of the lens antenna to be used in 5G mmWave beamforming systems. Using a lens as a passive phase shifter enables beamforming without the heavy network of phase shifters, while gain and directivity are achieved by the energy-focusing property of the lens. Proposed in this article are two types of lens antennas, one for static and the other for mobile usage. The lens antennas' sizes are varied to also discuss the lens design. Their performance is evaluated using measurements and simulation data along with link- and system-level analysis. Results show the lens antenna yields high gain, directivity, and improved beam-switching feasibility compared to when a lens is not used.

Interferometric modulation of quantum cascade interactions

We consider many-body quantum systems dissipatively coupled by a cascade network, i.e. a setup in which interactions are mediated by unidirectional environmental modes propagating through a linear optical interferometer. In particular we are interested in the possibility of inducing different effective interactions by properly engineering an external dissipative network of beam-splitters and phase-shifters. In this work we first derive the general structure of the master equation for a symmetric class of translation-invariant cascade networks. Then we show how, by tuning the parameters of the interferometer, one can exploit interference effects to tailor a large variety of many-body interactions.

Energy Efficiency of mmWave Massive MIMO Precoding With Low-Resolution DACs

With the congestion of the sub-6 GHz spectrum, the interest in massive multiple-input multiple-output (MIMO) systems operating on millimeter wave spectrum grows. In order to reduce the power consumption of such massive MIMO systems, hybrid analog/digital transceivers and application of low-resolution digital-to-analog/analog-to-digital converters have been recently proposed. In this work, we investigate the energy efficiency of quantized hybrid transmitters equipped with a fully/partially-connected phase-shifting network composed of active/passive phase-shifters and compare it to that of quantized digital precoders. We introduce a quantized single-user MIMO system model based on an additive quantization noise approximation considering realistic power consumption and loss models to evaluate the spectral and energy efficiencies of the transmit precoding methods. Simulation results show that partially-connected hybrid precoders can be more energy-efficient compared to digital precoders, while fully-connected hybrid precoders exhibit poor energy efficiency in general. Also, the topology of phase-shifting components offers an energy-spectral efficiency trade-off: active phase-shifters provide higher data rates, while passive phase-shifters maintain better energy efficiency.