4-bit Phase Research Articles

A High Linearity +44.5-dBm IP $3~C$ -Band 6-Bit Digital Phase Shifter Using SOI Technology for Phased Array Applications

A 6-bit digital phase shifter in 0.18- $\mu \text{m}$ silicon-on-insulator (SOI) process is presented. It operates over a 4–7-GHz frequency band and provides 360° of phase coverage with 5.625° resolution using 64 phase states. The SOI phase shifter has a compact size of $1320\,\,\mu \text{m}\,\,\times 780\,\,\mu \text{m}$ . Compared to a state-of-the-art 0.15- $\mu \text{m}$ pHEMT-based product design, the SOI IC design is five times smaller in size with 2–6 dB higher IP3 and power handling capability. To the best of authors’ knowledge, this is the highest IP3 of phase shifter using commercial SOI technology. These SOI monolithic microwave integrated circuit (MMIC) phase shifter characteristics are attractive for military radar and commercial phased array communication systems where cost, size, weight, and power (C-SWAP) and high linearity are required.

A 40-GHz 4-Bit Digitally Controlled VGA With Low Phase Variation Using 65-nm CMOS Process

A 40-GHz variable gain amplifier (VGA) with 4-bit digital gain control and low phase variation is designed and fabricated on the 65-nm CMOS process. The digital gain control mechanism is achieved using the presented digital version current steering topology. The measured gain of the VGA is between 22 and 6 dB at 40 GHz with 16 different linear-in-decibel gain states. Using the proposed two-stage digital version current steering VGA phase compensation technique, the measured phase variation is 3.18° within a 16-dB gain control range (GCR) and the root mean square (rms) phase error is 0.89° at 40 GHz.

Broadband terahertz reconfigurable metasurface based on 1-bit asymmetric coding metamaterial

Terahertz metasurface has always aroused extensive attention for many years. However, terahertz reconfigurable metasurface is still a significant challenge. The broadband terahertz reconfigurable metasurface based on 1-bit asymmetric coding metamaterial is presented in this paper. The asymmetric metamaterial breaks the charge balance and provides multiple resonances, which is conducive to expanding the operating bandwidth. Conventional coding metamaterials change phase by varying the shape or size of the patch. The proposed metamaterial only disconnects or connects the metal lines in the metamaterial to obtain 1-bit phase information, which is beneficial for designing reconfigurable coding metasurface. Both simulated and experimental results show that the asymmetric metamaterial efficiently reflects the normal incident waves at 0.34–0.49 THz with a relative bandwidth of 36%, and the reflection coefficients are measured to exceeds 80%. Furthermore, the simulation and experimental results of the metasurface show that the normal incident wave is reflected as a double beam of the expected angle by configuring metamaterials with different coding sequences. This work provides important potential applications for the development of valuable dynamic terahertz beam scanning devices.

Linear Retro-Beam Scanning Array System

A unique beam scanning array, neither applying spherical-to-plane wave transformation like a reflect array nor utilizing corporate feed network like a Butler matrix, is proposed and investigated in this paper. The governing equations of a common retro-directive array are revisited and generalized to fulfill a linear array having retro-beam scanning without using heterodyne technique. In the proposed scheme, the progressive phase difference between the adjacent antenna elements is controlled not only by the interconnecting line in-between but also by an extra phase term introduced by a newly added phase shifter. According to the theoretical prediction, the main beam of the retransmitted wave can be steered to an arbitrary direction irrespective of the direction of arrival (DOA) of the incident wave. A linear four-element quasi-Yagi array, controlled by 4-bit phase shifters, is applied as a preliminary proof-of-concept. An automated retro-beam scanning system integrated with a DOA estimation network and a low-cost microcontroller was then experimentally demonstrated to validate its capability to steer and re-transmit a randomly incoming oblique wave within ±30° from the normal incidence to a preset targeted direction without any manual control. The theoretical background, formulation, experimental results, and potential application scenarios are carefully discussed.

Design of Diffusive Modified Chessboard Metasurface

In this letter, the design of ultrathin diffusive modified chessboard metasurface at microwave band is presented. Each quadrant of the conventional 2 × 2 chessboard is replaced by a small size 1-bit reflectarray exhibiting an optimized diffusive 1-bit quantized phase distribution. Furthermore, the proposed chessboard metasurface is designed in such a way to also have 180° phase shift between any adjacent quadrants (reflectarrays). A subwavelength-spaced cross-polarization rotating anisotropic unit cell, which can rotate the polarization of a linearly polarized incident wave to its orthogonal (cross polarized) component with 99% polarization conversion efficiency from 7 to 16 GHz, is used to compose a two small size 1-bit reflectarrays. The proposed unit cell and its mirror image are used to provide the required 1-bit phase states (“0°” and “180°”) of the 8 × 8 unit cells reflectarrays. The proposed diffusive metasurface is composed of four reflectarrays and has an aperture dimensions of 160 × 160 × 3.04 mm3. Both simulation and measurement results show that the proposed metasurface can diffuse the incident electromagnetic wave regardless of the polarization of the incident wave and under wide angle of incidence (up to 60°) with 10 dB radar cross reduction when compared to a PEC plate of same size.

Design of 3-Bit Digital RF Phase Shifter for Wireless Communication

In this paper, a 3-bit digital phase shifter based on switched transmission line technique using coplanar waveguide is proposed. The design has the resonant frequency of 10 GHz which can be used in wireless communication applictaions. Recent developments in radio frequency components development has raised as a significant way for constructing low loss phase shifters. MEMS phase shifters whose insertion loss is low and high isolation uses minimum power. This helps to bring low cost and light weighted phased array antennas. The transmission line length and wavelength decides the characteristics of phase shift. The phase shifter design consists of coplanar waveguides having center conductor width of 100µm and the gap of 14 µm on a FR-4 epoxy substrate with thickness of 1.6mm. The design is simulated using ADS to yield phase shift of 45, 90 and 180. The benefits of digital phase shifters include achieving flat phase over a wide bandwidth as well as having higher power handling and linearity with uniform performance. The phase shifters are used in different fields which includes microwave devices, feeder of radio system, phased array antenna, coherent radio system, etc.

Design of 3-Bit Digital RF Phase Shifter for Wireless Communication

In this paper, a 3-bit digital phase shifter based on switched transmission line technique using coplanar waveguide is proposed. The design has the resonant frequency of 10 GHz which can be used in wireless communication applictaions. Recent developments in radio frequency components development has raised as a significant way for constructing low loss phase shifters. MEMS phase shifters whose insertion loss is low and high isolation uses minimum power. This helps to bring low cost and light weighted phased array antennas. The transmission line length and wavelength decides the characteristics of phase shift. The phase shifter design consists of coplanar waveguides having center conductor width of 100μm and the gap of 14 μm on a FR-4 epoxy substrate with thickness of 1.6mm. The design is simulated using ADS to yield phase shift of 45, 90 and 180. The benefits of digital phase shifters include achieving flat phase over a wide bandwidth as well as having higher power handling and linearity with uniform performance. The phase shifters are used in different fields which includes microwave devices, feeder of radio system, phased array antenna, coherent radio system, etc.

Three-Bit DMTL Phase Shifter for Phased Array Antennas

RF MEMS phase shifter is a device that is used to modify the transmission phase of RF signal and provide signal control. Phase shifters are high-value components used in phased array antenna architectures. In phased array antenna the phase shifter is used to provide reliable electronic beam steering. The proposed 3-bit distributed MEMS transmission line (DMTL) phase shifter is designed using elevated coplanar waveguide (ECPW) transmission line for the first time, which results in better return loss of [Formula: see text]14.23[Formula: see text]dB and an average insertion loss of [Formula: see text]1.46[Formula: see text]dB. This paper discusses the development of ECPW-based 3-bit DMTL phase shifter designed to operate at 15[Formula: see text]GHz.

Multi-functional coding metasurface for dual-band independent electromagnetic wave control.

Multi-functional metasurfaces have exhibited powerful abilities of manipulating electromagnetic (EM) wave in predetermined manners, largely improving their information capacities. However, most works are implemented with EM functions controlled by one of the intrinsic properties of EM wave, such as polarization, frequency, etc. Herein, we propose a coding scheme to design a broadband and high-efficient multi-functional metasurface independently controlled by both frequency and polarization. To achieve this goal, we design anisotropic coding particles to realize independent phase functions and polarization-selectivity in the microwave region. Meta-atoms are finally optimized to exhibit 2-bit phase responses insensitive to incident polarization in the X-band while showing a 1-bit phase shift sensitive to incident polarization in the Ku-band. As a proof of concept, a metasurface is configured as an isotropic lens in the X-band, whereas the metasurface is designed as an anisotropic beam deflector in the Ku-band with or without polarization-conversion functionality dependent on the input polarization. The measured results, which agree well with the simulated ones, show excellent performances in the designed dual bands. Such a multi-functional coding metasurface may provide a flexible and robust approach to manipulate EM wave of multiple frequencies, as well as to integrate diverse functionalities into a single flat device.

A Millimeter-Wave Partially Overlapped Beamforming-MIMO Receiver: Theory, Design, and Implementation

This paper presents an analysis and design of a partially overlapped beamforming-multiple-input multiple-output (MIMO) architecture capable of achieving higher beamforming and spatial multiplexing gains with lower number of elements compared to conventional architectures. As a proof of concept, a four-element beamforming-MIMO receiver (RX) covering 64-67-GHz frequency band (the FCC’s newly allocated 64–71-GHz frequency band for high-speed wireless links between small cells) enabling two-stream concurrent reception is designed and measured. By partitioning the RX elements into two clusters and partially overlapping these clusters to create two three-element beamformers, both phased array (coherent beamforming) as well as MIMO (spatial multiplexing) features are simultaneously acquired. 6-bit phase shifters with 360° phase control and 5-bit VGAs with 11-dB range are designed to enable steering of the two RX clusters toward two arbitrary angular locations corresponding to two users. Fabricated in a 130-nm SiGe BiCMOS process, the RX achieves a 30.15-dB maximum direct conversion gain and a 9.8-dB minimum noise figure across 548-MHz IF bandwidth. S-parameter-based array factor measurements verify spatial filtering of the interference and spatial multiplexing in this RX chip.

A 7.5–9 GHz GaAs Two-Channel Multi-Function Chip

Based on the 0.5 μm GaAs enhancement/depletion (E/D) Pseudomorphic High Electron Mobility Transistor (pHEMT) process, a 7.5–9 GHz two-channel amplitude phase control multi-function chip (MFC) was developed successfully. The chip was integrated with a 6-bit digital phase shifter, a 6-bit digital attenuator, and a single pole single throw (SPST) switch in each channel. A design for the absorptive SPST switch is deployed to optimize the return loss and control channel array calibration. In the 8 dB and 16 dB attenuation bit, a switched-path-type topology is employed in order to obtain a good flatness of attenuation characteristic and achieve low additive phase shift. A 27-bit serial-to-parallel converter (SPC) was introduced to decrease the control lines and pads of the chip, and the power consumption was less than 70 mW. The measurement result shows that the insertion loss is less than −13 dB and the return loss is better than −19 dB. In both channels, the 64-state root mean square (RMS) errors of the phase shifter is less than 2° and the RMS parasitic amplitude error is less than 0.2 dB. The RMS attenuation error is less than 0.45 dB and the RMS parasitic phase error is less than 2.4°. The size of the chip is 3.5 mm × 4.5 mm.

Efficient Constant Envelope Precoding With Quantized Phases for Massive MU-MIMO Downlink Systems

This study considers a generalized constant envelope-based precoding design problem in massive multiuser multiple-input multiple-output systems, in which the output signals of digital-to-analog converters are restricted to $M$ -ary phase-shift keying signaling to facilitate the use of low-cost and power-efficient power amplifiers at a base station. We aim to jointly optimize the precoding vector and the precoding factor to minimize the mean-squared error between the transmitted and the estimated symbols. However, the considered precoding problem is nonconvex and challenging to solve because the precoding vector and the precoding factor are coupled together. To address this problem, we apply the alternating minimization (AltMin) framework to decouple the considered problem into two problems: the precoding factor design problem and the precoding vector design problem. The former has an analytical solution, while the latter requires solving a difficult combinatorial problem, which we address by proposing a simple yet efficient gradient projection (GP)-based algorithm to find an approximate precoding vector. Simulation results demonstrate that the proposed GP-based AltMin algorithm achieves the same or higher BER performance than state-of-the-art algorithms while requiring lower complexity. In addition, when higher order modulations are employed, the error floor experienced by the existing algorithms can be substantially mitigated by the proposed GP-AltMin algorithm through increasing the number of phase bits.

Low‐loss 7‐bit S‐band CMOS passive phase shifter with digital control

SummaryThis paper presents the design and implementation of a 7‐bit S‐band digital passive phase shifter using Complementary Metal‐Oxide‐Semiconductor (CMOS) 65‐nm technology in 2.6‐ to 3.2‐GHz frequency band. New switched delay network topology has been used for 5.625° and 2.8°, and modified switched filter topology has been used for implementation of other phase bits to achieve 7‐bit performance with low insertion loss and better isolation. The measured results of the fabricated chip show 7‐bit performance with an average insertion loss of 11 dB, average root mean square (RMS) phase error of less than 2.0°, average RMS amplitude error of less than 0.6 dB, input matching (S11) better than −7.5 dB, and output matching (S22) better than −14.5 dB across the target frequency band at 50Ω input/output impedance.

A 5G 28-GHz Common-Leg T/R Front-End in 45-nm CMOS SOI With 3.7-dB NF and −30-dBc EVM With 64-QAM/500-MBaud Modulation

This paper presents a 28-GHz common-leg phased-array front-end in 45-nm CMOS silicon on insulator with transmit and receive capabilities. The design alternates cascode amplifiers with passive switched- $LC$ phase-shifter cells to result in 5-bit phase control with an rms phase and gain error <4° and <0.8 dB, respectively, at 24–30 GHz, over 32 phase states. The front-end has 2- and 3-bit variable gain amplifiers with 7.5-dB total gain control, without affecting the system noise figure (NF). Two low-loss high-linearity single-pole double-throw switches are used to switch between transmit and receive modes. In the receive (Rx) mode, the measured gain, NF, input 1-dB compression point (P1dB), and input third-order intercept point are 16 dB, 3.7 dB, −15 dBm, and −7 dBm, respectively, with 54-mW dc power consumption. In the transmit (Tx) mode, measurements show 16.5-dB gain, an output P1dB of 8 dBm, and an output IP3 of 16 dBm with 100-mW dc power consumption. The error-vector magnitude and adjacent-channel-power-ratio measurements demonstrate quadrature phase-shift keying, 16-quadrature amplitude modulation (QAM), 64-QAM, and 16-QAM orthogonal frequency-division multiplexing modulations with several symbol-rates reaching up to 8 Gb/s data-rate for both the Rx and Tx modes at 2- and 5-dB back-off. The application areas are in fifth-generation phased arrays requiring high-linearity receivers and using external front-end modules for added transmit power.

Versatile Conical Conformal Array Antenna Based on Implementation of Independent and Endfire Radiation for UAV Applications

This paper proposed an integrated conical conformal array antenna (CCAA) for versatile application to the unmanned aerial vehicles. The CCAA consists of five flexible linear gradient subarrays with a uniform circumferential arrangement around the conical surface. It is also embedded with a pyramid reflective back-cavity (PRBC) within the conical carrier. The implementation for the three different elements of the linear gradient subarray toward impedance match and high isolation was investigated, and their identity resonant frequency (9.8 GHz) principle was developed and demonstrated. Furthermore, the PRBC was presented to improve the radiation null of the elements. A numerical 5-bit phase shifter manipulating phase difference of 72° was then combined with an 8-way power divider to obtain a fixed beam with a half power bandwidth (HPBW) of less than 24°, which indicated the backward endfire direction ( $\theta = 180 ^{\circ }$ ) in terms of three circumferential arrays (R#X). Finally, the measurements with the aid of the designed phase shifter and power divider (model SHPDW4-040140S) were conducted. The experimental results show one omnidirectional coverage (360°) in the $H$ -plane through the switching working mode of the elements with a wide scanning solid angle ( $\geqslant 72^{\circ }$ ) when these elements of the subarray hold an identity resonant frequency and exhibit a uniform performance in the point-to-point communication. The measurements of a narrow HPBW of less than 27.5° and the gain over 10.7 dBi in the endfire direction of the three circumferential arrays show great potential in backward blind space detection simultaneously.

Phase quantized quasi-Sierpinski carpet reflector for OAM beam generation

This work proposes a quasi-Sierpinski carpet type reflecting surface. The reflector incorporates remodeled Jerusalem type sub-wavelength elements. The element arrangement ensures a 3-bit phase quantized encoding for the reflected beam. Microstrip antenna feed illuminates this reflector. We start with EM simulation of a broadband unit-cell reflector. We assume that the final reflector based on such unit-cell shall show broadband characteristic. The simulated beam from the reflector, due to spatial arrangements of the unit-cells, showed the fundamental mode of orbital angular momentum vortex beams. Experimental verification of fabricated prototype shows good agreement with simulated far-field results at 9.5 GHz, 10 GHz, 10.5 GHz, and 11 GHz which indicate a broadband characteristic.

1.4 GHz Low-Cost PIN Diode Phase Shifter for ${L}$ -Band Radiometer Antenna

A 1.4 GHz 4-bit positive intrinsic negative (PIN) diode phase shifter with compact reflective loads for an L-band soil moisture measuring radiometer phased array antenna has been successfully designed. Unlike conventional PIN diode phase shifters using PIN diodes as switches, the designed PIN diode phase shifter adopting the low-cost PIN diodes with poor isolation as equivalent lumped components corresponding to the forward and reverse bias states. First, the PIN diode is fully characterized for its equivalent circuit models at on- and off-states, and, then, the reflective load is designed with only one inductance in parallel with the diode models to obtain the desired phase shift. The phase shifter consists of four individual bits in cascade, providing 16 states of phase shifts. Each bit is constructed with a meander branch-line 90° coupler and two identical PIN diode reflective loads. Thus, the novel design yields a highly compact phase shifter at L-band. The phase shifter is theoretically analyzed, fabricated, and measured. The measured results show good agreement with analysis and calculations. The insertion loss of the 4-bit phase shifter is less than 2 dB within 25 MHz radiometer bandwidth and less than 2.3 dB from 1.37 to 1.43 GHz. The input and output return losses are larger than 16 dB within the 1.37 to 1.43 GHz frequency band. The root mean square (RMS) phase error is just less than 1° at the center frequency of 1.4 GHz and less than 3° within the radiometer bandwidth. The phase shifter is controlled with switching electronics and a microcontroller and integrated within the beamforming network of an L-band 4×4-element radiometer phased array antenna for soil moisture measurement.

4-Bit Optimized Coding Metasurface for Wideband RCS Reduction

In this paper, a 4-bit reflective coding metasurface with the polarization-insensitive unit cell is designed for wideband radar cross section (RCS) reduction. The metasurface unit has rotational symmetry; therefore, it produces the same electromagnetic scattering response for both xand y-polarizations. To attain 4-bit phase response, the dimensions of the unit cell are optimized so that a phase difference of 22.5° is realized between respective digital elements and the magnitude of reflection is more than 0.95 from 15 GHz to 40 GHz. Therefore, 16 digital elements have phases of θ, θ + 22.5°, θ + 45°, θ + 67.5°, θ + 90°, θ + 112.5°, θ + 135°, θ + 157.5°, θ + 180°, θ +202.5°, θ +225°, θ +247.5°, θ +270°, θ +292.5°, θ +315°, and θ + 337.5°. Discrete water cycle algorithm (DWCA) is applied to the array factor to get the optimal coding sequence matrix for better RCS reduction. The coding metasurface can achieve more than 10 dB RCS reduction from 15 GHz to 40 GHz as compared with the same size of a copper sheet. The simulation and experiment results validate the ability of proposed coding metasurface for robust control of EM-wave and wideband RCS reduction.

Use of Subarrays in Linear Array for Improving Wide Angular Scanning Performance

The scanning performance of wide-angular scanning linear arrays is primarily degraded by the limited angular profile of the employed elements' patterns. This paper introduces an innovative strategy for compensating this degradation by using subarrays. Our design uses a uniform linear array with half-wavelength spaced elements, supplemented by subarrays that are symmetrically placed at its edges. The employed subarrays have controlled patterns, favoring some directions for effective scan-loss compensation (SLC) and suppressing other directions for lowering the sidelobes level (SLL). Two types of feeding configurations, making use of fixed power dividers in combination with 1-bit phase switch, are used for producing the desired patterns. The complete array design and physical validation, starting from the elements, continuing with the subarrays and ending with the system integration are also discussed in detail. The integration of the subarrays yields notable performance improvements at large scanning angles when compared with uniform linear arrays. The peak and first SLL of -14.1 dB, and the SLC of 2 dB are obtained when the array with CUP antennas as elements is scanned to the maximum scan angle direction.

1-bit Phase Shifters for Large-Antenna Full-Duplex mmWave Communications

Millimeter-wave using large-antenna arrays is a key technological component for the future cellular systems, where it is expected that hybrid beamforming along with quantized phase shifters will be used due to their implementation and cost efficiency. In this paper, we investigate the efficacy of full-duplex mmWave communication with hybrid beamforming using low-resolution phase shifters. We assume that the self-interference can be sufficiently cancelled by a combination of propagation domain and digital self-interference techniques, without any analog self-interference cancellation. We formulate the problem of joint self-interference suppression and downlink beamforming as a mixed-integer nonconvex joint optimization problem. We propose LowRes, a near-to-optimal solution using penalty dual decomposition. Numerical results indicate that LowRes using low-resolution phase shifters perform within 3% of the optimal solution that uses infinite phase shifter resolution. Moreover, even a single quantization bit outperforms half-duplex transmissions, respectively by 29% and 10% for both low and high residual self-interference scenarios, and for a wide range of practical antenna to radio-chain ratios. Thus, we conclude that 1-bit phase shifters suffice for full-duplex millimeter-wave communications, without requiring any additional new analog hardware.