RF Phase Shifter Research Articles

A Survey of Phase Shifters for Microwave Phased Array Systems

ABSTRACTPhased Array Systems (PASs) are extensively used in radar and telecommunication systems for diverse applications, including military surveillance and wireless broadband communication. Besides, they are becoming increasingly indispensable in modern applications such as multi‐function phased array radars for weather monitoring and aircraft tracking or high‐throughput satellite systems, which aim to provide fast broadband connectivity in remote areas. Despite the numerous advantages of phased array systems with RF phase shift, including high signal‐to‐noise and signal‐to‐interference ratios, as well as low complexity, they present a few limitations, including high cost and large chip areas. The cost and size of PASs are mainly dependent on the RF phase shifters, which are essential to their operation. This article describes the different types of phase shifters (mechanical, ferromagnetic/magnetic, electromechanical, and electronic). It compares their performance metrics, highlighting that electronic phase shifters are the most common type used in modern PASs. In this regard, a comparative study of different subcategories of electronic phase shifters, such as the switched‐type, reflective‐type, loaded‐transmission line, and vector‐sum phase shifters, are explored along with their advantages, drawbacks and state‐of‐art techniques used to address their limitations. Therefore, this article may serve as a reference for research milestones on RF phase shifters.

GHz repetition rate tunable optical pulses generation using a SBS-based coupled optoelectronic oscillator

An optical pulse generator with a tunable repetition rate of GHz is proposed employing a coupled optoelectronic oscillator (COEO). The tunability is achieved with an equivalent tunable RF bandpass filter which is realized through phase modulation and stimulated Brillouin scattering (SBS) in a high nonlinear fiber. An injected seed laser is applied to stabilize the central wavelength of the mode-locked loop. The repetition rate of the generated optical pulses is the frequency difference between the Stokes wave and the seed laser. It is adjusted by changing the wavelength of the pump laser for SBS effect. In the experiments, optical pulse trains with a repetition rate of 7.3 GHz–9.3 GHz are generated, and RF oscillating signals at the corresponding frequency are simultaneously produced. The side-mode suppression ratios (SMSRs) of the generated RF signals are all higher than 50 dB, and the phase noise is lower than −80dBc/Hz @10-kHz offset frequency. The tunable range of the optical pulse rate is limited by the bandwidth of the used RF phase shifter in the oscillating loop.

Large Scale Optical Assisted Mm-Wave Beam-Hopping System for Multi-Hop Bent-Pipe LEO Satellite Networks

By introducing the arrayed waveguide router (AWGR) optical true time-delay (OTTD) architecture in bent-pipe satellite optical inter-link to optically assist the RF phased array in Low-earth orbit satellites will extend the multi-hop bent-pipe satellite beam-hopping protocol proposed in DVB-S2X. It solves the challenge of beam steering with the support of precise, broadband, and wide-range scanning. This architecture utilizes a subarray to combine the advantages of AWGR and a high-precision RF phase shifter to realize the beam pointing without an oblique view. Unlike the traditional digital and analog phased array architecture, the introduction of OTTD can solve the problem of beam squint and also ensure the high-precision scanning of the beam.

A novel digital transceiver module structure for multi-functional active phased array systems

This paper proposes a transceiver (T/R) module structure for the multi-functional active phased array (APA) systems (including radar and wireless communication systems). The proposed structure uses a full digital interface and applies a GaN supply-modulated power amplifier (SMPA) to improve the power efficiency. In particular, the paper proposes a solution that combines the direct digital synthesis (DDS) with IQ modulation to perform flexibly the functions of phase shifting and amplitude level controlling of the transmitted signals with high resolution for antenna beamforming and scanning. The proposed solution not only eliminates RF attenuator and phase shifter that are commonly used in antenna beamforming but also flexibly configures system functions. The experimental results of designing and manufacturing DDS and IQ modulation parts demonstrate the ability of the proposed structure to generate several common signal types used in radar and communication systems as well as verifies the ability to control the phase and the amplitude level of the transmitted signal.

Independent Amplitude and Phase Control of Two Orthogonal Linearly Polarised Light and Its Applications

A technique to provide independent control on the amplitude and phase of two orthogonal linearly polarised light is presented. It is based on operating a commercial dual-polarisation dual-drive Mach Zehnder modulator (DPol-DDMZM) in reverse direction that routes the input light in slow and fast axis into two different DDMZMs. The technique has the advantage of controlling the phase of the slow-axis light and the amplitude of the fast-axis light has no effect on the light travelling in the orthogonal polarisation state. It has applications in linearised microwave photonic links, frequency multipliers and microwave phase shifters. A new microwave photonic Hilbert transformer based on using the reverse operating DPol-DDMZM to alter the phase of an RF modulation sideband without affecting the orthogonally polarised optical carrier is developed. Experimental results demonstrate 24.3 dB attenuation in the fast-axis light with no change in the slow-axis light, and 0°–360° RF phase shift for only 3.3 V change in DC voltage. The new Hilbert transformer with less than 2.5° phase imbalance and 0.4 dB amplitude ripples over 4–18 GHz frequency range is also demonstrated.

Design and Simulation of Capacitive MEMS Switch for Ka Band Application

In this paper, RF MEMS switch with capacitive contact is designed and analyzed for Ka band application. A fixed‐fixed beam/meander configuration has been used to design the switch for frequency band 10 GHz to 40 GHz. Electromagnetic and electromechanical analysis of three‐dimensional (3D) structure/design has been analyzed in multiple finite element method (FEM) based full‐wave simulator (Coventorware and high‐frequency structure simulator). A comparative study has also been carried out in this work. The high resistivity silicon substrate (tanδ = 0.010, ρ > 8 kΩ − cm, εr = 11.8) with a thickness of 675 ± 25 μm has been taken for switch realization. The designed structure shows an actuation voltage of around 9.2 V. Impedance matching for the switch structure is well below 20 dB, loss in upstate, i.e., insertion loss >0.5 dB, and isolation of >25 dB throughout the frequency band is observed for the aforesaid structure. Furthermore, to increase the RF parameters, AIN dielectric material has been used instead of SiO2 resulting in capacitance in downstate that increases hence improved the isolation. The proposed switch can be utilized in various potential applications such as any switching/tunable networks phased‐array radar, reconfigurable antenna, RF phase shifter, mixer, biomedical, filter, and any transmitter/receiver (T/R) modules.

Beamforming Optimization for MIMO Wireless Power Transfer With Nonlinear Energy Harvesting: RF Combining Versus DC Combining

In this article, we study the multiple-input and multiple-output (MIMO) wireless power transfer (WPT) system so as to enhance the output DC power of the rectennas. To that end, we revisit the rectenna nonlinearity considering multiple receive antennas. Two combining schemes for multiple rectennas at the receiver, DC and RF combinings, are modeled and analyzed. For DC combining, we optimize the transmit beamforming, adaptive to the channel state information (CSI), so as to maximize the total output DC power. For RF combining, we compute a closed-form solution of the optimal transmit and receive beamforming. In addition, we propose a practical RF combining circuit using RF phase shifter and RF power combiner and also optimize the analog receive beamforming adaptive to CSI. We also analytically derive the scaling laws of the output DC power as a function of the number of transmit and receive antennas. Those scaling laws confirm the benefits of using multiple antennas at the transmitter or receiver. They also highlight that RF combining significantly outperforms DC combining since it leverages the rectenna nonlinearity more efficiently. Two types of performance evaluations, based on the nonlinear rectenna model and based on realistic and accurate rectenna circuit simulations, are provided. The evaluations demonstrate that the output DC power can be linearly increased by using multiple rectennas at the receiver and that the relative gain of RF combining versus DC combining in terms of the output DC power level is very significant, of the order of 240% in a one-transmit antenna ten-receive antenna setup.

Ultra-High Boron Doping of Si and Ge for Nanoelectronics and Photonics

In-situ boron doping of Si and Ge can be of use in various types of devices. Poly-Si:B gates can be integrated in p-type metal oxide semiconductor (pMOS) transistors. Monocrystalline Si:B layers can be used in p-i-n junctions for RF switches, attenuators, photo-detectors (PDs) or phase shifters. Ge:B layers can be integrated in the sources and drains of Ge pMOS transistors or as the p-type films in Ge p-i-n PDs. If the growth temperature is low enough, they can even be used in GeSn PDs or light emitting devices. We have explored here the boron-doping of Si and Ge with Si2H6 + B2H6 and Ge2H6 + B2H6. Such chemistries enable Si (Ge) epitaxy at temperatures lower than with conventional SiH4 (GeH4) precursors. Growth temperatures and pressures in our 200mm RP-CVD tool were 550°C, 20 Torr (Si) and 350°C, 100 Torr (Ge).X-Ray Diffraction (XRD) was used to convert the tensile strain in Si:B or Ge:B into substitutional B concentrations, as shown in Fig. 1 and Fig. 2, with layer peaks moving away from the Si(001) substrate or the Ge Strain-Relaxed Buffers (SRB) as the diborane flow increased. The presence of marked thickness fringes testified to the high crystalline quality of the films. Secondary Ions Mass Spectrometry (SIMS) gave us the atomic B concentration. X-Ray Reflectivity on Si0.5Ge0.5 / Si:B stacks yielded Si:B Growth Rates (GR). Finally, differential weighting gave us the thickness of Ge:B layers grown on Ge SRBs and other GR values.A huge Si:B GR increase, from 9.5 up to 40 nm min.-1, was evidenced when adding relatively small amounts of B2H6 to Si2H6, as shown in Fig. 3. This was due to the presence of B atoms on the surface which catalyzed H desorption, freeing sites for growth. Ultra-high substitutional and atomic boron contents were obtained in those Si:B layers (at most: 2.7x1020 and 1.1x1021 atoms cm-3), as shown in Fig. 4. Films became poly-cristalline for the highest F(B2H6)/F(Si2H6) Mass-Flow Ratios (MFRs) probed, without XRD peaks anymore and a boron ion concentration which was reduced compared to its peak value of 2x1020 cm-3. The good agreement between substitutional, atomic and ionic B concentrations for low to medium MFRs is to be underlined. By contrast, the growing discrepancy between XRD and SIMS for the highest diborane flows probed might partly be due to a SIMS artefact. Indeed, the Relative Sensistivity Factor used to convert the raw SIMS signals into B concentrations was for doped layers and not higher boron content binary alloys. The presence of B atoms in nanoclusters that did not contribute to XRD cannot be excluded, however.A definite growth rate increase (from 6 up to 21 nm min.-1) and really high substitutional B concentrations (at most: 4.8x1020 atoms cm-3) were also obtained for Ge:B, as shown in Fig. 5 and Fig. 6. The good agreement between XRD and SIMS for medium F(B2H6)/F(Ge2H6) MFR is to be underlined. The growing discrepancy for high diborane flows might be due to the same SIMS artifact as before and to the presence of B atoms in nanoclusters. x/(1-x) = m*F(B2H6)/F(Si2H6 or Ge2H6) relationships accounted for the semi-linear increase of the substitutional or atomic B concentration x with the diborane flow, with (i) msubst. = 1.85 (matom. = 7.45) in Si:B and (ii) msubst. = 0.15 (matom. = 0.68) in Ge:B. m values above 1 meant that B incorporation was easier than Si incorporation in Si:B. In contrast, B incorporation was more difficult than Ge incorporation in Ge:B alloys, as m was less than 1, then.Current growth rate increases and B concentrations are definitely higher than with mainstream chemistries. For Si:B grown at 650°C, 20 Torr with SiH4 + B2H6, we had for instance GR increases from 9 up to 23 nm min.-1, with at most 9x1019 cm-3 B ions concentrations before layers became poly-crystalline (ECS Trans. 16 (10), 485 (2008)). For Ge:B grown at 400°C, 100 Torr with SiH4 + B2H6, GR increased from 10 up to 18 nm min.-1, with at most 1020 cm-3 B ions concentrations (Thin Solid Films 557, 4 (2014)). The advantages of switching over to higher order Si and Ge precursors and adopting lower growth temperatures are obvious. Figure 1

Single-Event Transients in an IEEE 802.15.4 RF Receiver for Wireless Sensor Networks.

This paper presents a procedure to analyse the effects of radiation in an IEEE 802.15.4 RF receiver for wireless sensor networks (WSNs). Specifically, single-event transients (SETs) represent one of the greatest threats to the adequate performance of electronic communication devices in high-radiation environments. The proposed procedure consists in injecting current pulses in sensitive nodes of the receiver and analysing how they propagate through the different circuits that form the receiver. In order to perform this analysis, a Complementary Metal Oxide Semiconductor (CMOS) low-IF receiver has been designed using a 0.18 μm technology from the foundry UMC. In order to analyse the effect of single-event transients in this receiver, it has been studied how current pulses generated in the low-noise amplifier propagate down the receiver chain. The effect of the different circuits that form the receiver on this kind of pulse has been studied prior to the analysis of the complete receiver. First, the effect of SETs in low-noise amplifiers was analysed. Then, the propagation of pulses through mixers was studied. The effect of filters in the analysed current pulses has also been studied. Regarding the analysis of the designed RF receiver, an amplitude and phase shift was observed under the presence of SETs.

RF MEMS switches, switching networks and phase shifters for microwave to millimeter wave applications

This work presents design, fabrication and measurements of RF MEMS metal-contact switches, switching network and phase shifters. The complete work is broadly divided into three parts. The first part concentrates on the metal-contact switch functionalities in terms of mechanical behaviour, electrical behaviour, transient analysis, linearity, power handling, temperature, S-parameter and reliability. All these switch performances are critically evaluated for developing high-performance and reliable MEMS switch. Different single-pole-multi-throw (SPnT) switching networks are also designed and tested where n varies from two to sixteen. Next part concentrates on the design and development of narrow-band (500 MHz) MEMS digital phase shifters (2- to 5-bit) driven by an electrostatic actuation. Next and last phase of this work deals with a reconfigurable MEMS digital phase shifter using a push–pull-type beam topology. The utility of this beam design is validated and tested on a simple DMTL configuration where 11 push–pull bridges are used in a periodic placement. Finally, a modified version of the push–pull actuator is used to design a frequency reconfigurable 5-bit phase shifter over a wide band of spectrum of 10–25 GHz. The concept of the frequency reconfiguration is clearly mentioned and validated with exhaustive measurement process. In addition, a low-cost module is developed using gold-coated brass material to observe optimum device performance for end-user applications and two phase shifters are tested over large cycles including power handling, temperature stability and qualification testing such as 3-axis vibration.

Design and characterization of compact digital RF MEMS capacitors and phase shifters in CMOS 0.35 µm technology

This work reports on the design, fabrication and characterization of compact digital RF MEMS capacitors and phase shifters that are built in the back end of line (BEOL) of CMOS 0.35 µm technology. The devices are micromachined using a maskless post-processing sequence with cryogenic cooling on to control the out-of-plane warping of the metal-oxide structural layers. The implemented vertical electrostatic actuation in the developed post process allows the realization of highly compact designs of both devices, and an operating voltage of the devices is stay below 70 V. The 4-bit capacitors provide a measured tuning ratio close to 10:1 which corresponds to 0.15 pF to 1.2 pF over the frequency range 3–10 GHz. The overall footprint of the digital capacitor is 0.6 mm × 0.9 mm. The measured quality factor after de-embedding the losses due to the RF probing pads is up to 120. The measurement of the 4-bit phase shifters reveals low insertion loss <3 dB at 20 GHz along with low variation of the insertion loss <1 dB up to the same frequency. The measured phase shift is 150 at 20 GHz. The overall footprint of the 4-bit phase shifter is around 1 mm × 1 mm.

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.

Influence of the RF magnetic field on beam dynamics in SC200 cyclotron

Abstract The SC200 superconducting cyclotron is developed by the collaboration between ASIPP (Hefei, China) and JINR (Dubna, Russia). The SC200 cyclotron will deliver 200 MeV beam for proton therapy and research. The influence of the time-dependent magnetic field created by the acceleration system of SC200 should be taken into account in beam dynamics simulations and during the shimming procedure, as two conditions are present together: first — due to the spiral shape of the accelerating cavities, there is no vertical plane of symmetry through the middle of the dee; and second — second harmonic mode of acceleration in four-sector magnet structure imposes that the RF phase shift from beam entrance of the dee to its exit is not 180 degrees. Particle tracking was performed with 3D maps of electromagnetic fields obtained from computer modelling of the magnet system and the accelerating RF cavities using CST Studio Suite. We have calculated particle dynamics taking into account RF magnetic field and have estimated a value of additional mean field needed for the compensation of beam phase lag induced by RF magnetic field. And finally, we designed a shim that should form the required additional field.

Null Technique for Precision RF Phase Shift Measurements

A dual-channel intermediate frequency (IF) substitution null system is developed for precision phase shift measurements and standards in the frequency range from 1 MHz to 1 GHz. A particular programmable IF phase shifter equipped with a calibrated phase monitor is used as a phase reference standard. High-sensitivity nature of the null technique provides accurate measurements to the device under test (DUT) even with large attenuation. Excellent measurement resolutions of 0.002°, 0.006°, and 0.023° were obtained for DUT with losses of 20, 40, and 60 dB, respectively, at 1 GHz. Due to its independent and high-precision nature, this system can be used as a validation system as well as a reference standard of a broadband phase shift measurement system.

Integrated microwave photonic phase shifter with full tunable phase shifting range (> 360°) and RF power equalization.

We report a novel microwave photonic phase and amplitude control structure based on a single microring resonator with a tunable Mach Zehnder interferometer reflective loop, which enables the realization of a continuously tunable microwave photonic phase shifter with enhanced phase tuning range while simultaneously compensating for the RF power variations. The complimentary tuning of the phase and amplitude presents a simplistic approach to resolve the inherent trade-off between maintaining a full RF phase shift while eliminating large RF power variations. Detailed simulations have been carried out to analyze the performance of the new structure as a microwave photonic phase shifter, where the reflective nature of the proposed configuration shows an effective doubling of the phase range while the amplitude compensation module provides a parallel control to potentially reduce the RF amplitude variations to virtually zero. The phase range enhancement, which is first verified experimentally with a passive only chip, demonstrates the capability to achieve a continuously tunable RF phase shift of 0-510° with an RF amplitude variation of 9 dB. Meanwhile, the amplitude compensation scheme is incorporated onto an active chip with a continuously tunable RF phase shift of 0-150°, where the RF power variations is shown to be reduced by 5 dB while maintaining a constant RF phase shift.

High speed and high sensitivity fiber Bragg grating interrogator based on the RF phase-shift technique

A high speed and high sensitivity fiber Bragg grating (FBG) interrogator based on RF phase-shift measurement is presented. Using a sinusoidal modulated source and a chromatic dispersion element, Bragg-wavelength shifts are converted directly to RF phase shifts. Interrogation speeds >1 MHz with <10 pm spectral sensitivity, and sensitivity <0.1 pm at 100 Hz speed are demonstrated. An overall sensitivity vs. speed dependence of 3.4 fm/Hz, which is equivalent to 3 nanostrain/Hz, is shown. As it is based on standard telecommunication components and electronic RF processing, without moving parts or reliance on interferometry, this technique is simple, robust and inexpensive, opening new applications that require fast and sensitive sensing.

A four channel phased array transmitter using an active RF phase shifter for 5G wireless systems

This paper presents a four channel phased array transmitter at 15 GHz aimed for the upcoming 5G wireless systems. The circuit is designed and fabricated using 45 nm CMOS silicon on insulator technology. The design is programmable with exhaustive digital controls available for parameters such as bias voltage, resonance frequency, and gain. The phase shift required for the phased array is provided at RF using an IQ vector modulator (IQVM) topology, which provides both amplitude and phase control. Based on the measurement results, the IQVM provides 360° of phase shift and 15 dB of gain variation. Both phase and amplitude information are encoded in a 10 bit control word. The mean angular separation provided by the IQVM is 3° at optimum amplitude levels. Active area occupied is 2.88 square millimeter. Total DC power consumed by one transmit channel from 1 and 2.6 V supply is 268 mW. The maximum RF output power from one transmit channel is 1dBm. Measured EVM for a 256 QAM modulated signal is as low as 2.0%. All results include the impact of printed circuit board traces and pad parasitics. Based on the achieved results, the proposed architecture is well suited for the next generation of the wireless systems.

Fundamental Limits of Photonic RF Phase-Shift Amplification by RF Interferometry

The fundamental limits posed by classical noise on Photonic RF Phase amplification by RF Interferometry (PARFI) are modeled theoretically and verified experimentally. With 320-MHz modulated light and a phase-shift amplification of 3000, we demonstrate a phase-shift resolution of $1.6 \cdot {10^{ - 4}}^{\circ}$ and 200-nm distance resolution. Based on these results, we postulate that single-nanometer distance resolution can be achieved with PARFI.

Receive Spatial Modulation for LOS mmWave Communications Based on TX Beamforming

Receive spatial modulation (RSM) is a recently introduced multi-antenna transmission scheme that is capable of achieving high spectral efficiency at low hardware and processing complexity. We study RSM for application in indoor line-of-sight (LOS) millimeter-wave (mmWave) communication. Significantly different from low-gigahertz indoor channels, which are typically modeled by a Rician distribution, indoor mmWave channels are sparsely-scattered and dominated by LOS propagation. Hence, we consider the specific characteristics of the LOS mmWave channel and identify the channel conditions that minimize the symbol error probability (SEP) of RSM. We prove that the SEP of RSM in a LOS channel is minimized by imposing orthogonality conditions to the channel matrix. In addition, we propose a simple hardware architecture for the transmitter (TX), which uses only RF phase shifters for precoding. Simulation results show that RSM can successfully operate in indoor mmWave channels.