Hybrid Coupler Research Articles

Head‐only21MHzradiofrequency exposure system design and implementation

In this work a 21 MHz radiofrequency (RF) exposure system was designed, constructed and evaluated as a testing platform for MRI device safety. The exposure system consisted of a birdcage coil powered in quadrature by a power system consisting of a hybrid coupler, a power splitter, a phase shifter and two baluns. The birdcage coil was designed as a low-pass 16 rung coil. Both the coil and the power system were fabricated as printed circuit boards with a copper thickness of 205.7 μm and a G10 substrate thickness of 581.7 μm. The birdcage was assembled by wrapping the copper clad G10 inside of an acrylic tube. A shield for the coil was created as a cylindrical ground plane with a diameter of 39.7 cm. The birdcage and the power system were simulated in ADS and EMPro, Keysight Technologies Inc. both as lumped elements and using full wave 3D simulations. Simulation results were compared to measurements of the produced components to validate each component and entire system. In addition, a 3D magnetic field probe was developed to measure and compare the fields to analytical and numerical calculations.

High-performance dual circularly-polarized antenna arrays using 3D printing for 5G millimetre-wave communications

In this paper, we propose a 3D-printed millimeter-wave (mmW) antenna array with high performance for 5G applications. In order to enhance the gain by reducing the feed loss, high-order mode cavity backed cross-dipole antennas were deliberated. By adopting the 3D printing, a layer-driven air-filled waveguide feeder with a tailor-made hybrid coupler were designed so a high efficiency at low fabrication cost was realized. A 2 × 2 dual circularly polarized (CP) antenna subarray was firstly designed to suit for the 5G mmW new radio (NR) of 24.75 to 27.5 GHz with polarization diversity. A 4 × 4 dual CP array was finally accomplished using the subarrays as the basic building blocks. The full-corporate waveguide technology was employed to reduce the antenna weight and transmission loss but enhance the isolation for dual CP operation. Measured results validated the proposed design and showed that a wide operating bandwidth of 13% (24.4–27.8 GHz) with peak gain of 21 dBic and an isolation of better than 15 dB were achieved. Moreover, a high radiation efficiency (95%) and a medium aperture efficiency (53%) were attained by the dual CP array. The advantages of low cost, low loss, and flexible fabrication make the 3D-printed antenna array be outstanding.

5G beamforming techniques for the coverage of intended directions in modern wireless communication: in-depth review

AbstractThe growing need of the compact and portable antennas with high speed and low latency wireless communication is the present and future demand of the voice over Internet protocol, on-demand bandwidth, and multimedia applications. Fifth-generation (5G) covers certain low-frequency bands under 6 GHz spectrum, and most of the high-frequency bands under 60 GHz. 5G is the part of the millimeter wave spectrum (30–300 GHz) and is introduced to overcome the problem of spectrum shortage due to exponential enhancement of wireless applications in industry, medical, airborne, radar, satellite, and research fields. The International Telecommunication Union's objective of wireless communications promises to provide higher data rates up to 10 Gbps for 5G mobile users and connectivity to the artificial intelligence devices, along with high spectral efficiencies and enhanced coverage. The users for the 5G require around 5 and 50 Gbps of data rates for low and high mobility, respectively. Beamforming in 5G is the modern powerful technique for the coverage of the intended user/direction using the narrow beam width radiation patterns. A brief survey on 5G beamforming techniques, i.e. analog, digital, hybrid, switched, and adaptive etc. and its types, working algorithms, design of compact antennas, gain, and size/type of the substrates is carried out in this paper. The study of the hybrid coupler, branchline coupler, Wilkinson power divider, and Butler matrix in beamforming is required for 5G smart antennas. Different beam widths like ±15, ±35, ±45, and ±55° etc. are produced for the intended directions using a variety of beamforming techniques. From lower to higher frequency band beamforming applications with Roger's Duroid 4003/4350/5880, tectonic, and aluminum oxide dielectric substrates are discussed here. Various beamforming techniques with their merits, demerits, and applications are included in the paper for the knowledge extension of the beamforming antenna designers and research community.

Complete analysis and design for a Q/V band (46‐52 GHz ) wideband analog predistorter

This article shows the complete analysis and design for a Q/V (46-52 GHz) band wideband analog predistorter (APD). First, the reflection coefficient for hybrid coupler's through port with complex impedance is corrected. Second, the acceptable error region is introduced to analyze the influence of different nonlinear loads. Levenberg-Marquardt algorithm is then used to solve the circuit parameters of the hybrid T matching network. Finally, a Q/V band (46-52 GHz) wideband APD is fabricated and measured. The measurement results are in good agreement with the analysis results. Furthermore, the linearized traveling-wave tube amplifiers (TWTA) gain compression is less than 0.5 dB, and the phase change of TWTA after linearization is less than 4°. The C/IM3 shows more than 10 dB improvement.

Improved measurement techniques for high-power transistor modeling.

Measurement for modeling of the high-power transistors is difficult due to its high-power and low-impedance characteristics. In this paper, novel methods and devices were designed and applied to achieve precise measurements of the high-power transistors. Fixtures capable of withstanding high voltage and current were designed to replace traditional radio frequency (RF) probes for higher power capacity. To reduce the impact of capacitive and inductive components of traditional bias tees on the rising/falling edge, two wideband 90° hybrid couplers that were connected back-to-back were designed for pulsed measurements. The measurement system of stable S-parameters with the Vector Network Analyzer (VNA) was reported, which could protect the devices and laboratory equipment from damage of self-oscillation. Application of several innovative approaches enabled accurate I-V characteristic and S-parameters measurements of high-power transistors in DC or pulsed mode. Experimental results of a 30 W gallium nitride high-electron-mobility transistor verified the validity.

An Integrated 65-nm CMOS SOI Ka-Band Asymmetrical Single-Pole Double-Throw Switch Based on Hybrid Couplers

This letter presents the design of an asymmetrical Ka-band single-pole double-throw (SPDT) switch, based on two integrated hybrid couplers. The principle of operation of this switch and its two asymmetrical receiving (Rx) and transmitting (Tx) states are detailed. The circuit theory is supported by the implementation of a demonstrator using an advanced integrated technology: 65-nm substrate on insulator (SOI) CMOS from STMicroelectronics. To the author's best knowledge, it is the first implementation of such topology using an integrated CMOS technology. The demonstrator is designed considering a system-level tradeoff between the two states, in order to implement 28-GHz duplexers for 5G front-end modules (FEMs). The Rx state exhibits 1.9 dB of insertion loss, 24 dB of isolation and a 1 dB input compression point of 17.5 dBm, whereas the Tx state has 2.9 dB and 35 dB of insertion loss and isolation, respectively. Besides, the gain compression in the Tx state is lower than 0.3 dB, considering an input power of 18 dBm.

Optical single sideband modulation with tunable optical carrier-to-sideband ratio using DP-BPSK modulator

In this paper, a novel approach to achieving optical single sideband modulation with tunable carrier-to-sideband ratio (OCSR) is proposed and demonstrated. The key of the scheme is a DP-BPSK (Dual Polarization BPSK) modulator. The DP-BPSK modulator is integrated and consists of two parallel dual-drive Mach-Zehnder modulator, an optical power splitter, a 90° polarization rotator, and a polarization beam combiner. The upper modulator of the DP-BPSK modulator is set to single sideband modulation and the lower modulator of DP-BPSK modulator is not modulated by radio frequency, then we can achieve a single sideband modulation signal with tunable OCSR by adjusting the angle of PC2. The scheme uses only one light source, one signal generator, one 90° hybrid coupler, one DP-BPSK modulator, two polarization controllers, one DC power supply and one linear polarizer. Compared with optical filter, optical grating, multiple modulators or other devices used in the previous schemes, the proposed structure is much simpler. The proposed approach is first theoretically analyzed and then verified by experiment. The single sideband modulation signals are obtained with a wide OCSR range of −20 dB to 38 dB in the experiment, and the performance of the scheme in the transmission link is also verified by simulation.

Parasitic spirals for enhancing bandwidth of a simultaneous transmit and receive patch antenna

Two pairs of spiral-shape parasitic elements are proposed to improve the bandwidth of a microstrip patch antenna for simultaneous transmit and receive in 2.4–2.5 GHz ISM band. The antenna has two low-cost FR4 substrate layers and a ground plane between the layers. The top layer consists of the patch and parasitic spirals, and a modified 180° rat-race hybrid coupler is printed on the bottom layer. Adding the parasitic spirals enhance the antenna bandwidth by 15–25 MHz in both transmit and receive modes based on simulation and measured results. The hybrid coupler is used to maintain the high isolation between transmit and receive operations of the antenna. The antenna offers low-cross polarization for both modes at boresight (near 20 dB on the x–z plane and larger than 40 dB on the y–z plane). The design also has high self-interference cancellation, a spherical directional radiation pattern, good impedance matching, and reasonable gain values.

A Simple Scheme for Photonic Generation of Microwave Waveforms Using a Dual-drive Mach–Zehnder Modulator

In this paper, a novel photonic scheme for the generation of square and triangular waveforms is proposed and experimentally demonstrated by using a dual-drive Mach–Zehnder modulator (DDMZM) without any optical signal processing. By properly setting the modulation index of the DDMZM, the square and triangular microwave waveforms could be easily achieved in conjunction with a 90° hybrid coupler. Furthermore, the modulation index of the DDMZM could be tuned for a low radio frequency (RF) signal power requirement by tuning the phase difference of the RF signals applied to the two arms of the DDMZM. The proposed scheme for the photonic generation of microwave waveforms is theoretically analyzed and experimentally demonstrated. The periodical triangular and square waveforms with repetition rates of 5 GHz, 8 GHz, and 10 GHz are successfully obtained. The root-mean-square errors between the generated and theoretical triangular and square waveforms with a repetition of 5 GHz are 0.042 and 0.053, respectively.

Uniplanar Beam-Forming Network Employing Eight-Port Hybrid Couplers and Crossovers for 2-D Multibeam Array Antennas

A multibeam beam-forming network (BFN) for generating 2-D multibeam array antenna (MAA) is proposed using single-layer substrate integrated waveguide (SIW) technology. Firstly, a new topology for building $16\times 16$ BFNs is proposed, which successfully transforms the traditional topology from a 3-D configuration to a 2-D (or uniplanar) one. Two major challenges are tackled during this transformation, namely, the planarization of basic components and the reduction of excessive intersections between multiple paths. To this end, a novel design of eight-port hybrid couplers, as critical components of this BFN, is developed to transform a 3-D to a 2-D structure. Furthermore, a new design of eight-port crossover, which can address four path intersections simultaneously, is proposed to reduce the total number of path intersections from 16 to only 4. The proposed topology for $16\,\times \,16$ BFNs allows all the basic components, including eight-port hybrid couplers, eight-port crossovers, and phase shifters, to be placed within a single-layer configuration. Fed by the proposed uniplanar $16\times 16$ BFN, a 2-D MAA with 16 ( $4\,\times \,4$ ) beams, which is capable of switching the beams in both elevation and azimuth directions, is realized. Compared with the previous 2-D Butler matrix (BM) designs using multilayer technology, it is for the first time that a uniplanar design of $16\times16$ BFN is proposed and realized, which significantly simplifies the design and fabrication complexity.

Novel Magnitude and Phase Reconfigurable 1 × 4 RF Power Distribution Network

This article presents a new circuit topology for a highly reconfigurable 1×4 radio frequency network that, for a given input, is able to modify magnitude and phase relations among its output signals with great flexibility while preserving matching at all ports. The circuit, based on a four-way power divider, four hybrid couplers, and eight variable phase shifters, is first theoretically analyzed. It is shown that magnitude and phase relations among signals at the output ports can be modified just by changing the state of the variable phase shifters, while the sum of the squared magnitude of the transmission coefficients of the network is always equal to one. For the specific purpose of the experimental validation of the developed theory, a particular version of the network, working at 3.6 GHz, is then designed and tested. All configurations are affected by the same insertion loss, depending on the adopted phase-shifting technology. The obtained results show the potential of the conceived circuit and testify its unprecedented degree of reconfigurability.

A Compact Wideband Millimeter-Wave Quadrature Hybrid Coupler Using Artificial Transmission Lines on a Glass Substrate

In this letter, a compact branch-line-based quadrature hybrid coupler using a line miniaturization technique for a 28-GHz application is presented. Coplanar waveguide-based artificial transmission lines are used in the miniaturization, and T-equivalent circuit models are exploited to elaborate on the optimization method. A multistage T-model is utilized to eliminate the need for lumped elements, improve bandwidth performance, and simplify the fabrication process. To validate the proposed approach, the designed quadrature hybrid coupler was fabricated on a glass substrate. The measured insertion loss and phase difference at 28 GHz were 3.86 dB, 3.94 dB, and 90.4°, respectively. The output amplitude imbalance was within a 1-dB range from 25.3 to 31.0 GHz, and the total device area, excluding the measurement pad, was $1.15\times0.98$ mm2.

Design and Analysis of a New Hybrid Wireless Power Transfer System With a Space-Saving Coupler Structure

This article is to present the design, analysis, and verification of a new hybrid wireless power transfer (HWPT) system, which has a space-saving coupler structure. The key of the design is to simplify the two coupling capacitor plates into one single frame-shaped plate at each side. Then, the coupling coil for inductive power transfer (IPT) is embedded into the metal frame to form a compact hybrid coupler. Meanwhile, the coupling polarity between the coils is specified to realize the superposition of the inductive and capacitive coupling. As a result, the proposed HWPT system can offer a good comprise of efficiency promotion and a space-saving coupler structure simultaneously. To illustrate the system working principles, the equivalent circuit model is first derived. Then, a detailed analysis is conducted in terms of the reflected impedance. Consequently, the mechanism of the efficiency promotion can be clearly explained. Finally, a prototype is constructed with several experiments, which validate the effectiveness of the proposed HWPT system. Results show that an efficiency increase of 14% over the pure IPT is obtained at 35-cm distance. Moreover, the effects of varying the resonant frequency are also carried out to instruct the practical system design.

Absorptive K-Band Bandpass Filter Using a Balanced Recursive Structure

This article presents a new K-band absorptive bandpass filter (ABPF) based on a microwave balanced recursive architecture. The proposed structure was configured using two passive microwave hybrid couplers, two conventional bandpass filters (BPFs), and a recursive path control module consisting of a phase shifter and an optionally variable gain amplifier. Using the proposed structure, stable return characteristics that were insensitive to the output load variation in the passband, a reduction in standing wave due to absorption in the stopband, and potentially high reliability could be achieved. Furthermore, since the same BPFs were reused, the electrical filtering order within the given physical BPF stages could be increased effectively. The proposed architecture was verified by comparing it with the performance of the conventional two-stage cascaded BPF. The measured results showed a 3 dB passband at 280 MHz with the center frequency at 19.9 GHz and improved roll-off characteristics. Furthermore, the stopband showed the reflectionless characteristic with the return loss being better than 7 dB.

Multichannel Transmitting System Based on High-Temperature Superconducting Phase Shifter

Multichannel very high frequency (VHF) high-power transmission system, based on a 90 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> , high-temperature superconductor YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> (YBCO) hybrid coupler is presented. The small dimension coupler performs as a phase shifter utilized for matching several different channels into a single junction. The planar coupler was implemented in a microstrip geometry by patterning a thin layer of YBCO on a sapphire substrate. Superconductivity is essential for obtaining low losses and high-power capabilities. The system was tested for power transmission of up to 52.9 dBm over a period of several hours. No deterioration with time was recorded. Maximum losses of 0.8 dB per channel were measured. The proposed system shows high-precision tuning capabilities, a critical feature for multichannel systems.

Multibeam Phased-Arrays Using Dual-Vector Distributed Beamforming: Architecture Overview and 28 GHz Transceiver Prototypes

This article presents a dual-vector distributed beamformer architecture that employs a series-feed network and is capable of supporting up to four simultaneous beams. The multibeam array uses scalar functions within each front end to create Cartesian-weighted signals needed for phase shifting. A dual-vector series-feed network combines/distributes these signals for the receiver/transmitter whereas a global quadrature interpolator is used to create two conjugate beams. By using an interpolator on either end of the series feed, a total of four beams can be obtained. Among these four beams, a first beam can be controlled independently, a second beam is formed as an image of the first, a third beam is offset from the first based on the amount of phase shift within the series-feed structure, and a fourth beam is an image of the offset beam. In this work, the theory of operation of the series-feed DVDB is presented and then two different four-element 28 GHz DVDB transceiver array prototypes in 120 nm SiGe BiCMOS technology are described. One uses a hybrid coupler for global interpolation at radio frequency (RF) and the other uses quadrature mixers for global interpolation at baseband. Measurement results for the array employing passive interpolation at RF show excellent phase-shifting performance, including < 1 dB root-mean-squared (RMS) gain error, < 2 degree RMS phase error, 24% 3 dB bandwidth, with 16–18.6 dBm saturated output power in transmit mode and 4.9–7.3 dB noise figure in receive mode. Measurement results for the array employing mixer-based interpolation likewise show excellent phase-shifting performance with similar RMS gain and phase errors and slightly degraded overall RF performance. Comparing the two, we conclude that the DVDB with passive interpolation at RF is better suited for partitioned systems where beamformers and transceivers are realized on separate chips to support larger, scalable arrays. In contrast, the DVDB with mixer-based interpolation is better suited for integrated systems where beamformers and frequency translation functions must be integrated together.

Compact and low-loss 90-deg optical hybrid based on silicon-on-insulator 2 × 2 multimode interference couplers

We design an ultracompact, broadband, and low-loss 90-deg optical hybrid coupler using a silicon-on-insulator (SOI) material platform for coherent receivers in optical communication systems. The proposed hybrid coupler uses a cascaded topology that includes five 2 × 2 multimode interference (MMI) couplers in three different fundamental kinds. The working principle of the suggested 90-deg optical hybrid is based on theoretical analysis on the MMI effect and the transfer matrix relations. The optimization of geometrical parameters and the optical characteristics are employing through the numerical simulation method. The investigated 90-deg optical hybrid coupler can be integrated on a microscale footprint as much as 6 μm × 172 μm. Furthermore, our hybrid coupler expresses lots of advantages of optical performances, with an insertion loss lower than 2.6 dB, a common-mode rejection ratio better than −25 dB, and phase error smaller than 5 deg in 90-nm wavelength-bandwidth in the third telecom window. In addition, the designed device, based on the SOI platform, is endowed with large geometrical tolerances possessing width, height, and multimode tolerances corresponding to ±20, ±10, and ±10 nm in the 1-dB variation limit of transmission, respectively. Such advantages of good performances thus make the proposed hybrid device playing the role of a promising potential candidate for widely varying applications of silicon photonics, such as coherent optical receivers, optical interconnects, and high-bitrate optical phase modulators.

Low-Cost Broadband Electronic Coupler for Estimation of Radiated Emission of Integrated Circuits in TEM Cell

Transverse electromagnetic (TEM) cell is a well-known method for the qualification of radiated electromagnetic emission from integrated circuits (ICs). Combined with a 180° hybrid coupler, it provides a simple method for quantifying radiated emission (RE). However, typical transformer or coupled line based hybrid couplers have limited bandwidth which cannot cover the full frequency range required by IC emission tests (150 kHz to 1 GHz). This article presents the design and the validation of a low-cost broadband electronic version of a 180° hybrid coupler dedicated to the estimation of radiation emission from TEM cell measurements. The proposed prototype is able to cover a large frequency range (from dc to 1 GHz) with a sufficient sensitivity and dynamic range for RE tests in TEM cell. The cost of the presented coupler is very reasonable as it is entirely based on commercial operational amplifiers.

Thermally Actuated SOI RF MEMS-Based Fully Integrated Passive Reflective-Type Analog Phase Shifter for mmWave Applications

This article presents a monolithically integrated reflective-type phase shifter (RTPS) utilizing silicon-on-insulator (SOI) radio frequency (RF) microelectromechanical systems (MEMS). The analog phase shifter employs a hybrid coupler and two identical reflective loads optimized to achieve a large phase shift range. The hybrid coupler is designed using two CPW-based couplers connected in a folded tandem configuration to achieve a compact size design. Various reflective load topologies are studied for optimum phase shift range and phase linearity over the bandwidth of interest. Measurement results demonstrate a continuous 120° tunable range from 26 to 30 GHz. The mmWave phase shifter exhibits a low insertion loss of 5.35 dB ± 0.6 dB at 28 GHz. The fabricated phase shifter has an overall device footprint of 4.0 mm × 2.6 mm. All the components of the phase shifter module are co-fabricated in the 20 μm device layer of a SOI wafer, which provides the flexibility of monolithic integration with other RF modules in phased array antenna systems. Contactless thermally actuated MEMS varactors are used in the reflective loads which do not suffer from the conventional contact-based reliability issues.

Phase shift switching of a miniaturized ultra‐wideband hybrid coupler for 5G technology

AbstractThe main purpose of this letter is to develop a miniaturized ultra‐wideband hybrid coupler with an adjustable phase shift (90°‐180° and vice versa) that operates around the resonant frequency of 3.8 GHz with a fractional bandwidth of 26% required for 5G applications. The design approach is based on a microstrip waveguide technique with localized lumped elements to control the phase shift between the input and output ports. The performance of the coupler can be seen from its important characteristics: adaptation, coupling, isolation, and phase shift. All these mentioned parameters are approved by simulation and validated by measurement. The measurement results show good agreement with the simulation, which confirms the success of the theoretical part and the importance of our proposed structure.