Hybrid Coupler Research Articles

A quadrature‐hybrid‐integrated reconfigurable feeding network for wideband quad‐polarization‐agile antenna design

In this article, a reconfigurable antenna with quad-polarization radiations is proposed based on a switchable feeding network. A wideband quad-mode feeding network is first designed by integrating a simple impedance converter with a modified hybrid coupler. By switching the p-i-n diodes, four-transmission status with specific amplitudes and phase differences at feeding output ports can be obtained over a wide frequency range, hence enhancing the radiating bandwidth of two linear and two circular polarizations. Finally, a prototype of the proposed quad-polarization-agile reconfigurable antenna is designed and fabricated. The measured results show a wide overlapped bandwidth of 782 to 1010 MHz (25.4%) for all four polarizations with a competitive size and gain performance.

Vertical Integration of Passive Microwave Components Using Functional Via Structures in LTCC Multilayer Substrates

A recently developed concept for designing passive microwave components using functional vertical interconnect accesses (vias) for vertical integration in printed circuit boards (PCBs) is extended and transferred to the low temperature cofired ceramic (LTCC) technology. Given the changed material properties and new technology constraints, it is shown how and to what extent the controlled vertical interconnect accesses (via) structures can behave as quasi-transmission lines, thus allowing for another degree of freedom in component design. To demonstrate the validity and utility of functional vias, several novel microwave components are proposed and subsequently analyzed including vertically integrated 2- and 3-way Wilkinson power dividers, as well as vertically integrated 90° and 180° hybrid couplers. Prototypes for the 2-way and 3-way power dividers were manufactured on an LTCC multilayer substrate. Both measurement and full-wave simulation results are in excellent agreement and thus provide a proof of the concept.

Planar Feeding Circuit Integrated With a Compact Dielectric Resonator for Polarization Diversity

A compact two-port feeding circuit that supports a dielectric resonator (DR) element is presented for applications requiring polarization diversity. The L-band structure consists of a cylindrical DR that can generate right-handed circular polarization (RHCP), left-handed circular polarization (LHCP), and linearly polarized radiation. The DR dimensions have been optimized considering a relative dielectric constant of ε <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 27, and the entire structure (the circuit and DR) has dimensions of 9 cm ×9 cm ×2 cm (or about 0.3 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.3 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.07 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> at the lower operational frequency range). Radiation by the DR originates from four orthogonal HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11δ</sub> modes that are excited by four radial slots etched out of the ground plane (all underneath the DR) printed on top of an FR-4 substrate. Each of these four slots is unconventionally driven by two 50- Ω microstrip lines, and all four radial slots conform to the shape of the top cylindrical DR element. Polarization diversity is achieved with this DR and circuit system (DRCS) arrangement, mainly by the design of its fully integrated and planar circuit, which routes power to the eight microstrip lines for DR excitation. This FR-4 printed circuit board (PCB) feeding system consists of two meandered Wilkinson power dividers, two 180° delay lines, and four surface mount 90° hybrid couplers. The complete DRCS is compact in size, is broadband (more than 40%), and offers the advantage of requiring only two external ports, one for LHCP the other for RHCP, while an external phase shifter and a combiner are needed for linearly polarized radiation.

A magnetic‐free in‐band full‐duplex RF front‐end with antenna balancing structure

In this article, a design of magnetic-free in-band full-duplex (IBFD) RF front-end with antenna balancing structure is presented. The proposed magnetic-free IBFD RF front-end consists of 3 dB hybrid couplers, a Wilkinson power divider, two transmitter (Tx) antennas, and two receiver (Rx) antennas. The proposed IBFD RF front-end can be implemented and integrated at high frequencies because all the components used in the circuit are non-magnetic devices. Proposed IBFD RF front-end eliminated the 3-dB Tx insertion-loss of the Balun and transformer in conventional IBFD RF front-ends using antenna balancing structure. Moreover, there is no noise figure degradation at Rx because it realized only a passive circuit. The mathematical analysis of the cancellation characteristics between two different signals with magnitude and phase difference variations according to the normalized frequencies is presented. Accordingly, the broadband out-of-phase balancing power splitter and the antenna balancing structure are adopted to achieve broadband SIC. In order to verify the electrical performances of the proposed magnetic-free IBFD RF front-end, it was implemented at the 2.5 GHz WiMax frequency band. When the fabricated IBFD RF front-end was operated with antenna balancing structure, the measurement results show that the 60 dB SIC bandwidth and maximum SIC were 113 MHz (2.446 - 2.559 GHz) and 75.6 dB, respectively.

Photonic Generation of Multi-Band Linearly Frequency-Modulated Signal Based on a Dual-Parallel MZM

A photonics-based approach for multi-band linearly frequency-modulated (LFM) signal generation is proposed and demonstrated by using a dual-parallel Mach-Zehnder modulator (DP-MZM) injected by a dual-band LFM signal with opposite chirp rates. The dual-band LFM signal is applied to the DP-MZM that is biased as a frequency quadrupler via a 90° hybrid coupler. The 1st-order and the 2nd-order optical sidebands of the dual-band LFM signal, as well as two single-tone optical sidebands, are generated at the output of the DP-MZM due to the nonlinearity of the modulator and the non-ideal bias condition. After the optical signal from the DP-MZM is detected in a photodetector, multi-band LFM signals with multiplied bandwidth are generated. The generation of the two single-tone optical sidebands from the dual-band LFM signal greatly increases the number of the generated LFM signals. An experiment is conducted to verify the approach. Eight LFM signals up to 27 GHz in different frequency bands are simultaneously generated. The performance of the multi-band LFM signal including frequency recovery and pulse compression capability is also verified.

Wide-Range Rectifier for Wireless Power Transfer Based on Power Compensation

In this letter, a rectifier based on the reflected power compensation network (RPCN) is designed, which enables the rectifier to maintain high efficiency over a wide range of incident power and load impedance. The proposed rectifier mainly includes a hybrid coupler, phase shift units, matching networks, Dickson circuits, and resistive loads. By integrating the hybrid coupler with the phase shifter, the rectifier can reduce the impact of the non-linear effect of the diode caused by the input power and load impedance change. Through theoretical analysis and processing validation, this rectifier can achieve a power conversion efficiency (PCE) over 60% from −2 to 15 dBm; meanwhile, it can maintain a relatively high PCE over 50% when load range varies from 8 to 97 $\text{k}\Omega $ under the incident power Pin = 7.5 dBm. The rectifier structure fully meets the power supply requirements when applied to the wireless sensor nodes.

Modelling and Impact of 3D Print Inaccuracies on the Performance of Circular Waveguide Hybrid Coupler

Circular waveguide hybrid coupler operating over a frequency range of ISM 57-64 GHz, additively printed and metal plated using electroless technique is introduced. Effects of orientation of print and thickness of intricate structures on the performance of circular waveguide hybrid coupler are presented. The structure is printed using commercially available stereolithographic (SLA) printer. Circulatory system operated by a peristaltic pump is used for selective silver deposition of the hybrid coupler.

1 × 2 Switchable Dual-Mode Optical 90° Hybrid Device Based on Thermo-Optic Phase Shifters and 2 × 2 MMI Couplers on SOI Platform

This paper designs a 1 × 2 switchable dual-mode optical 90° hybrid device on the silicon-on-insulator (SOI) platform for the mode division multiplexing hybridized coherent transmission systems in optical communication. Our proposed hybrid uses various 2 × 2 multimode interference (MMI) couplers, symmetric Y-junctions, and thermo-optic phase shifters. The suggested hybrid device working principle is proved on theoretical analysis about the multimode interference and the transfer matrix relation. The optimization of geometrical parameters and metallic micro-heaters is executed through the numerical simulation method. The proposed hybrid coupler expresses lots of optical performance advantages, with an insertion loss lower than 2.5 dB, a common-mode rejection ratio (CMRR) better than −24 dB, and phase error smaller than 4° in the 50-nm wavelength bandwidth of the third telecom window for both two TE modes. Besides, the device is proven large geometrical tolerances in terms of width and height tolerances larger than ±50 nm and ±6 nm in the 1.5-dB variation limit of transmission, respectively. In addition, the proposed device attains relatively low power consumption under 75 mW and an ultrafast switching time below 10 μs. Such advantages of good performances make the device a promising potential for broadband and intra-chip MDM-hybridized coherent optical communication systems and photonic integrated circuits.

A Coupler With Wide Power Division Ratio Tuning Range and Flexible Coupling Direction

We propose a new tunable coupler with flexible coupling direction and a wide power division ratio (PDR) tuning range. The structure consists of two 90° hybrid couplers with two reconfigurable synthesized transmission lines (RSTLs) inserted in between. The RSTL is designed to operate either in the passband as an analog phase shifter or in the transition region and stopband as a mismatched circuit with tunable reflection/transmission coefficients. By properly controlling the electrical responses of RSTLs, the PDR tuning range can be greatly extended in both forward- and backward-wave coupling operations. The proposed coupler was designed and tested at 2.4 GHz. Our design, among one of few couplers exhibiting switchable coupling paths, yields the widest measured PDR tuning range in both operations while still keeping comparable performance with previous works.

Doppler frequency shift measurement and direction discrimination based on a bidirectional phase modulator and a Sagnac loop

A photonic approach to implement Doppler frequency shift (DFS) measurement and direction discrimination is proposed and demonstrated. In the proposed approach, a bidirectional PM and a Sagnac loop are used to obtain the orthogonally polarized optical signals. Combined with a wavelength division multiplexer (WDM), the upper and lower sidebands of the orthogonally polarized signals are separated. After two balanced photodetectors (BPDs), I/Q balanced detection is realized. Subsequently, the value and direction of DFS are estimated at the output ports of the electrical low-frequency 90° hybrid coupler (90° HC) simultaneously. In the proposed approach, using BPD can suppress some spurious signals and improve resolution. The use of double-sideband improves spectrum utilization. Meanwhile, the polarization drift of polarization controller (PC) and the phase offset of 90° HC have little influence on the discrimination of the DFS direction. That is to say, the proposed system for DFS measurement is stable.

Phase shifters with multiple independently controllable bands utilising frequency‐selective variable gain networks

A dual-band vector-sum phase shifter with independent phase control of the 2.4 and 5 GHz Wi-Fi bands is presented. The network uses band-limited variable gain amplification, with a broadband hybrid coupler at the input and an in-phase recombiner at the output. The circuit is prototyped on RF printed circuit board and exhibits performance characteristics comparable to the state-of-the-art single band vector-sum phase shifters. The prototype achieved an average gain of 2.16 dB over the 2.4 GHz band, with less than 0.26 dB and 1.32° root-mean-square (RMS) gain and phase error across all 2.4 and 5 GHz band tuning states. In the 5 GHz band, an average gain of 0.17 dB is achieved, with less than 0.21 dB and 3.88° RMS gain and phase error. The network's ability to generate band-independent vector modulation over a 12 dB/90° tuning range is demonstrated as well, achieving less than 0.12 dB and 0.27° RMS gain and phase error in the 2.4 GHz band, and less than 0.27 dB and 2.94° gain and phase error in the 5 GHz band.

Dual-Polarized High-Isolation Antenna Design and Beam Steering Array Enabling Full-Duplex Communications for Operation Over a Wide Frequency Range

A new dual-polarized antenna and array are presented for In-Band Full-Duplex (IBFD) applications, offering high inter-port isolation. The single-element antenna system consists of four H-shape slots, stacked patches for wide bandwidth, and two external hybrid couplers. The multilayer antenna is well matched from about 2.1 to 2.4 GHz and provides high isolation in this frequency range in excess of 60 dB. Two different prototypes are simulated and measured to highlight the design process. In addition, a new and compact hybrid coupler with excellent phase and magnitude stability is also presented for improved antenna radiation and IBFD performances. When compared to other similar types of hybrid coupler and antenna systems, the proposed configurations are simple to manufacture, provide a higher isolation bandwidth (10%), and higher gain of 7.3 dBi with cross-polarization levels of 30 dB or lower. The single-element design was also extended to a 2×2 array and studied for different beam steering and feeding scenarios. The operating bandwidths and isolation values offered by these S-band antenna and array systems can support new data link possibilities for beam steering and future low-cost IBFD wireless networks by simple antenna fabrication.

Novel Dual-Band Beam-Scanning/Switching Network Based on a Hybrid Coupler With Synchronously Tuned Phase Differences

This paper proposes a novel feeding network that enables the antenna array to perform dualband continuous beam scanning and beam switching between forward and backward directions. Specifically, the switchable beam is controlled by the network input and the beam in each direction is continuously steerable at either frequency. To support a wide range of beam-scanning angles, a novel dual-band coupler with synchronously tuned differential phases is applied to the feeding network, together with a pair of phase shifters. The operating principles and design equations of the dual-band beam-scanning/switching network, coupler, and phase shifters will be given in detail. As a proof-of-concept, a 0.9-GHz/1.8-GHz beamscanning/switching network was prototyped alongside a 1W4 linear array. Experimental results show that the array can scan and switch its main beam from -24° to -42° in the backward direction and from 24° to 34° in the forward direction at 0.9 GHz, while the beam scanning is from -12° to -24° and from 12° to 22° at 1.8 GHz.

On the Ungerboeck and Forney Observation Models for Spatial Combining And Their Application to 5G Millimeter-Wave Bands

Equivalent discrete-time models for a variety of spatial combining techniques operating in a frequency-selective multipath fading channel are derived. The equivalent discrete-time models are used to perform computer simulations of the post-equalizer bit error rate over a frequency-selective multipath channel whose derivation preserved polarization state information. Two sets of computer simulations were performed. In the first set, the performance of co-located cross-polarized antenna elements was investigated. The results showed that maximum likelihood combining maximizes polarization diversity, but that maximum ratio combining and selection combining were very competitive in the case where the cross-polarized antennas produce one strong channel and a relatively weak channel. Elliptical combining, using a 90° hybrid coupler, produced the worst results. The second set of simulations used a combination of spatial and cross-polarized antenna elements, for a total of eight antenna elements. The simulation results showed that maximum likelihood combining was best, followed by maximum ratio combining, equal gain combining, and selection combining. Again, elliptical combining was the worst, leading to the conclusion that other combining techniques are preferred in frequency-selective fading environments.

A Systematic Design of a Compact Wideband Hybrid Directional Coupler Based on Printed RGW Technology

Printed ridge gap waveguide (PRGW) is considered among the state of art guiding technologies due to its low signal distortion and low loss at Millimeter Wave (mmWave) spectrum, which motivates the research community to use this guiding structure as a host technology for various passive microwave and mmWave components. One of the most important passive components used in antenna beam-switching networks is the quadrature hybrid directional coupler providing signal power division with 90° phase shift. A featured design of a broadband and compact PRGW hybrid coupler is propose in this paper. A novel design methodology, based on mode analysis, is introduced to design the objective coupler. The proposed design is suitable for mmWave applications with small electrical dimensions ( $1.2\,\,\lambda _{o} \times 1.2\,\,\lambda _{o}$ ), low loss, and wide bandwidth. The proposed hybrid coupler is fabricated on Roger/RT 6002 substrate material of thickness 0.762 mm. The measured results highlight that the coupler can provide a good return loss with a bandwidth of 26.5% at 30 GHz and isolation beyond 15 dB. The measured phase difference between the coupler output ports is equal $90^\circ \pm ~5^\circ $ through the interested operating bandwidth. A clear agreement between the simulated and the measured results over the assigned operating bandwidth has been illustrated.

Highly Efficient Front End Direct Conversion Receiver for 28-GHz Wireless Access Point

The manuscript presents the design and characterization of a wideband front-end receiver, based on hollow waveguide technology, for the wireless access point (WAP) applications. The Ka-band receiver is comprised of a low-loss beam-switching antenna network (BSAN) with two-dimensional (2D) scanning property. For demodulation, the receiver uses an efficient six-port network (SPN) that is composed of four 90° hybrid couplers and a 90° phase shifter. To suppress the phase imbalance on the entire band of interest, 27 GHz to 33 GHz, a frequency-independent phase shifter with a minimum phase error is suggested. The SPN receiver is integrated with antenna-in-package in waveguide technology to decrease the insertion losses and noise levels at the first stages. To determine the SPN phase errors, a theoretical and experimental analysis of real-time wireless data transmission utilizing phase-shift keying (PSK) and quadrature amplitude modulated (QAM) signal is conducted. Besides, channel capacity along with beamformer influence on channel performance improvement are determined.

Triangular Phase Shift Detector for Drone Precise Vertical Landing RF Systems

This article presents a circuit for the precise vertical landing of drones based on a three phase-shifts detection of a single frequency transmitted from the landing point. The circuit can be considered as a new navigation sensor that assists in guidance corrections for landing at a specific point. The circuit has three inputs to which the signal transmitted from an oscillator located at the landing point arrives with different delays. The input signals are combined in pairs in each of the three analog phase detectors, after having passed through 3 dB at 90° hybrid couplers that guarantee a theoretical nonambiguous phase shift range of ±90°. Each output has a voltage that is proportional to the phase shift between each of the input signals, which in turn depends on the position relative to the landing point. A simple landing algorithm based on phase shift values is proposed, which could be integrated into the same flight control platform, thus avoiding the need to add additional processing components. To demonstrate the feasibility of the proposed design, a triangular phase shift detector prototype has been implemented using commercial devices. Calibration and measurements at 2.46 GHz show a dynamic range of 30 dB and a nonambiguous detection range of ±80° in the worst cases. Those specs let us track the drone during the landing maneuver in an inverted cone formed by a surface with a ±4.19 m radius at 10 m high and the landing point.

Modeling and Characteristics of a 3 dB Hybrid Coupler for 5G Applications

Modeling and Characteristics of a 3 dB Hybrid Coupler for 5G Applications

Elliptically Bended Hybrid Ring Coupler

In this paper, a size reduced elliptically bended hybrid ring coupler is proposed with better directivity, isolation factor, coupling factor, better impedance matching and undesired signal suppression for wideband applications. The proposed elliptically bended compact hybrid coupler is desired to operate at 1.8 GHz providing wide bandwidth, better return loss, and isolation with less insertion loss where a novel gradual impedance bending technique is implemented to suppress unwanted signals.

Accuracy-Enhanced Angle-of-Arrival Finding System Using Switched Six-Port Network

In this letter, a switched six-port (SP) receiver is proposed for an accurate angle-of-arrival (AoA) finding system. The proposed switched six-port network consists of four antennas, two hybrid couplers, two dual-pole-dual-throw switches, and four power detectors. The proposed switched six-port receiver periodically selects two different antennas from four antennas, providing four different antenna spacings for a more accurate AoA detection. As a result, a smaller and more accurate AoA finding system has been achieved than a conventional dual six-port receiver that uses two different antenna spacings from four antennas. For validation, the proposed method was simulated, implemented, and measured. In the measurement, the averaged root-mean-square error of the estimated angle over the range of $-\text{90}^\circ$ to $\text{90}^\circ$ was $\text{3.16}^\circ$ with 20 sample numbers and a signal-to-noise ratio (SNR) of 15 dB.