Quadrature Coupler Research Articles

Theory and Design of Dual-Band Microstrip Networks Using Embedded Metamaterial-Based Electromagnetic Bandgap Structures

This article examines implementations of the recently introduced metamaterial-based electromagnetic bandgap (MTM-EBG) structure, which may be embedded directly into the transmission-line (TL) segments of microstrip (MS) networks and whose dispersion properties may be accurately determined using multiconductor TL (MTL) theory. Two methods of imparting dual-band behavior to MS-based networks are introduced: utilizing stopband and passband regions of the EBG for frequency-selective signal routing, and using the phasing properties of the EBG to provide equal phase shifts at two separate frequencies. Two topological variants of the MTM-EBG are introduced and shown to provide different bandgap sizes, suiting each proposed application. A dual-band Wilkinson power divider, a dual-band quadrature hybrid coupler, and a dual-band impedance transformer are designed with embedded MTM-EBGs, which due to their ability to be realized in an entirely uniplanar form without vias and using a single dielectric layer, allow these devices to be entirely printable as well. The performance characteristics of all three devices are simulated and demonstrate excellent agreement with measurements. The design methodology is general and based on a rigorous MTL circuit model, making this approach amenable to a variety of MS networks, beyond what is presented.

Miniaturised quadrature hybrid coupler using composite planar transmission lines

In this Letter, a novel miniaturisation technique for a 3-dB quadrature hybrid coupler is described. The revolutionary structure is composed of folded microstrip lines and folded coplanar waveguides that are printed on the top- and bottom-surfaces of a dielectric substrate, respectively. The two different planar lines are connected by copper vias to form the double-path composite microstrip-coplanar waveguide (CMCPW) line. To demonstrate the effectiveness of the technique, a simple yet miniaturised hybrid coupler is devised by introducing folded S-shaped CMCPW-lines, wherein their lengths are gradually changed to address the design goals. The simulated and measured results of the proposed coupler validate its good performance metrics in the amplitude responses of power splitting, return- and insertion-loss. Moreover, its isolation and quadrature phase between outputs have been examined. A very small footprint size of 0.0667 λ 0 × 0.0667 λ 0 at 0.5 GHz has been realised.

A Flexible Quadrature Coupler With Reconfigurable Frequency and Coupling Ratio in Switchable Coupling Direction

A highly reconfigurable and switchable quadrature coupler with simultaneous control in terms of operating frequency, coupling ratio, and coupling direction is presented. To start with, a prototype coupler based on an ideal admittance-inverter model is investigated, and a method to obtain the admittance-inverter values for an arbitrary coupling ratio is described. Next, a tunable-admittance-inverter network implemented with lumped inductors and varactors, which features reconfigurable operating frequency, and tunable-admittance-inverter value is discussed. The conceived reconfigurable coupler is then realized by replacing the ideal admittance inverters with the proposed tunable-admittance-inverter circuit to provide it with operating-frequency and coupling-ratio controllability. Furthermore, when exchanging the admittance-inverter values in the coupler, the coupling direction is switched from forward to backward. The proposed technique is further developed into a general design procedure for reconfigurable-coupler implementations with an arbitrary admittance-inverter-based network. Wilkinson power dividers with equal and unequal power-division ratios are also shown as examples. For experimental/demonstration purposes, a reconfigurable coupler prototype is fabricated and characterized. It demonstrates a tunable operating frequency from 1 to 1.5 GHz, a controllable power-division ratio between output ports from 1 to 0.7, and switchable operational direction between forward and backward.

A Millimeter-Wave Miniature Branch-Line Coupler in 22-nm CMOS Technology

A 60-GHz innovative quadrature branch-line coupler is proposed in this letter. The device was implemented in a 22-nm CMOS process, from global foundries. The proposed design merges two miniaturization techniques. On the one hand, slow-wave microstrip (SW-MS) lines based on bed of nails are demonstrated in CMOS technology for the first time. On the other hand, the two quarter-wavelength MS line sections required for the branch-line coupler implementation are realized using the SW-MS transmission line configurations with different form factors. As a result, the achieved miniaturization versus electrical performance is very good as compared to the state-of-the-art. Design insights addressing the coupler dimensions and losses are discussed. The experimental assessment shows an adequate frequency response with amplitude and phase imbalance of 0.8 dB and 1.8° at 60 GHz, respectively. The measured insertion loss is 2.35 dB at 60 GHz and the return loss is better than 15 dB at any port (from 54 to 66 GHz). The isolation is better than 15 dB (from 51 to 68 GHz). The overall size of the coupler is 0.3 mm $\times $ 0.22 mm, which is equivalent to $0.06 \cdot \lambda _{0} \times 0.044 \cdot {\lambda }_{0}$ , at 60 GHz.

Wideband mm-Wave CMOS Slow Wave Coupler

In this letter, we have presented a design of on-chip millimeter-wave 3-dB quadrature coupler that utilizes the coupled slow wave coplanar waveguide. The designed CMOS coupler covers the whole $E$ - and $W$ -band and occupies a silicon area of only 0.0115 mm2, which is significantly smaller compared to the conventional microstrip-line-based Lange couplers. Measurement of the quadrature coupler shows a −3.5 dB through and a −4.4-dB coupling at 90 GHz. A less than ±1-dB amplitude and a ±4° phase errors from 55 to 110 GHz are recorded.

Wideband Dual-Polarized Multiple Beam-Forming Antenna Arrays

Wideband multibeam antenna arrays based on three-beam Butler matrices are presented in this paper. The proposed beam-forming arrays are particularly suited to increasing the capacity of 4G long-term evolution (LTE) base stations. Although dual-polarized arrays are widely used in LTE base stations, analog beam-forming arrays have not been realized before, due to the huge challenge of achieving wide operating bandwidth and stable array patterns. To tackle these problems, for the first time, we present a novel wideband multiple beam-forming antenna array based on Butler matrices. The described beam-forming networks produce three beams but the methods are applicable to larger networks. The essential part of the beam-forming array is a wideband three-beam Butler matrix, which comprises quadrature couplers and fixed wideband phase shifters. Wideband quadrature and phase shifters are developed using striplines, which provide the required power levels and phase differences at the outputs. To achieve the correct beamwidth and to obtain the required level of crossover between adjacent beams, beam-forming networks consisting of augmented three-beam Butler matrices using power dividers are presented to expand the number of output ports from three to five or six. Dual-polarized, three-beam antenna arrays with five and six elements covering LTE band are developed. Prototypes comprising beam-forming networks and arrays are tested according to LTE base station specification. The test results show close agreement with the simulation ones and compliance with LTE requirements. The designs presented are applicable to a wide range of wideband multibeam arrays.

High-Performance Tunable Narrowband SIW Cavity-Based Quadrature Hybrid Coupler

This letter presents, for the first time, a tunable narrowband substrate integrated waveguide (SIW) cavity-based quadrature hybrid coupler. Four high-quality factor ( $Q$ ) SIW evanescent-mode cavity resonators are employed in the design and tuned using piezoelectric actuators. This allows the proposed coupler to have wide spurious-free range (SFR), low-power consumption, and high-power handling capability compared to other tunable planar couplers. The coupler can be tuned starting from 1.32 to 2.22 GHz with a measured insertion loss range from 1.29 to 0.7 dB. Over the full range, the measured 3-dB fractional bandwidth ranges from 5% to 18% while the measured ±5° phase error ( $\angle S_{21} -\angle S_{31}$ ) absolute bandwidth ranges from 40 to 82 MHz with an amplitude imbalance range between 1 and 0.3 dB. The measured reflection and isolation are better than 12 and 17 dB, respectively. Moreover, the coupler has a measured SFR of 5.1– $3f_{o}$ (lowest–highest frequency).

A Dual Band Branch Line Coupler With Wide Frequency Ratio

A dual-band quadrature branch line coupler (BLC) with wide frequency ratio has been proposed in this paper. A dual-band quarter wave ( $\lambda $ /4) transmission line structure with wide frequency ratio operation has also been presented here with closed-form design equations. An analysis for the BLC’s circuit parameters variations versus frequency ratio in the view of the implementation has been carried out as well. In order to the experimental verification, a dual-band BLC has been designed, implemented, and analyzed then tested for long term evolution (LTE) 0.7GHz and public safety band (PSB) 4.9GHz. The novelty of the proposed design is the wide frequency ratio of its dual-band operation, which can reach up to 11.8.

Design of a GaN-on-Si Single-Balanced Resistive Mixer for <italic>Ka</italic>-band Satcom

Design and performance of a gallium nitride (GaN)-on-Si mixer for the Ka -band satellite telecom applications are presented in this letter. GaN-on-Si offers the advantage of high-volume production even for millimeter-wave applications. A single-balanced architecture is selected as an optimum tradeoff between circuit complexity and rejection of local oscillator (LO) harmonics. An alternative circuit topology is adopted where the in-phase combiner and hybrid quadrature couplers, used to obtain the desired signal phasing at mixer output, are also employed as circuit elements to inject external bias voltages so to optimize the mixer’s conversions loss (CL). The mixer features 11-dB CL, 11- and 22-dBm P1dB and IIP3 respectively, in the 26–31-GHz bandwidth when driven by a 10-dBm LO level. Monolithic microwave integrated circuit area is less than 6 mm2.

Miniaturized quadrature hybrid couplers based on novel U‐shaped transmission lines

AbstractIn this paper, a miniaturized microstrip quadrature hybrid coupler (QHC) using U‐shaped transmission lines (USTLs) is presented. The proposed approach replaces all arms of the conventional QHC with its equivalent USTL to achieve compactness. The proposed coupler structure is designed to operate in the 1.5 GHz (1427‐1518 [MHz]) band which is one of the 5G bands of interest. At such low RF/microwave bands below 3‐4 GHz, the size of the conventional coupler is considerably very large which raises a concern for the next generation networks. The proposed coupler is designed, simulated and fabricated using Rogers 5880 with thickness of 0.79 mm, dielectric constant (εr) of 2.2 and loss tangent of 0.0021. The proposed QHC size is 70% smaller in circuit area (30% relative area) than the conventional equivalent. Simulation and measured results are presented and good matching between the results is observed, confirming the outstanding coupler performance properties. The proposed miniaturized QHC structure will play a vital role for next generation 4G and 5G wireless communication systems operating below 6 GHz.

A new dual band 4 × 4 butler matrix with dual band 3 dB quadrature branch line coupler and dual band 45° phase shifter

A new dual band 4 × 4 butler matrix (BM) without crossover has been proposed, implemented and analyzed in this paper. A new dual band 45° phase shifter has also been proposed. The dual band BM, dual band 3 dB quadrature branch line coupler (BLC) and dual band 45° phase shifter have been designed using Keysight Technologies’ Advanced Design System (ADS) software and implemented on the RO 5870, having a thickness of 0.787 mm for 1.0 GHz and 2.5 GHz operating frequencies. Before the implementation of the proposed BM, the dual band 3 dB quadrature BLC and dual band 45° phase shifter have been designed, implemented and analyzed. The proposed dual band 4 × 4 BM has been developed by placing four dual band 3 dB quadrature BLCs and two dual band 45° phase shifters at their appropriate positions. Circuit parameters variation of the proposed BLC, phase shifter and BM with frequency ratios have been studied in this paper. The measured and simulated results of the dual band BM validated the design methodology. A performance analysis comparing the proposed BM with the existing butler matrices has also been carried out.

57–67-GHz Highly Compact Bidirectional 3-Bit Phase Shifter in 28-nm CMOS

This letter describes a highly compact, low-loss, high-bandwidth, bidirectional, passive 3-bit phase shifter (PS) implementation for 5G and WiGig applications at 57–67 GHz, fabricated in Taiwan Semiconductor Manufacturing Company 28-nm CMOS technology. First, a highly compact, differential quadrature hybrid coupler is used for the I/Q generation. Consuming only 0.006 mm2, it achieves 4.5-dB insertion loss (IL) with less than 1-dB amplitude imbalance, and 6° I/Q phase imbalance, for the entire frequency band. The hybrid coupler is followed by a novel compact transistors switching matrix to create the 3-bit, bidirectional, 360° PS, which provides impedance matching for all states. It consumes the smallest ever reported PS chip area of only 0.007 mm2 with state-of-the-art results of the maximum rms phase and gain errors of 6.3° and 0.94 dB, respectively. The measured IL was 10.8 dB between 57 and 67 GHz.

Fundamental/Subharmonic Photonic Microwave I/Q Up-Converter for Single Sideband and Vector Signal Generation

Microwave I/Q up-converter is widely used in modern electronic systems to achieve single-sideband (SSB) up-conversion and vector modulation. However, due to the frequency-dependent mixer and quadrature coupler, conventional electronic I/Q up-converters suffer limited operating bandwidth. In this paper, a photonic microwave I/Q up-converter is proposed using a polarization-division multiplexing modulator. The I/Q up-conversion channels are built in all-optical methods without any frequency-dependent devices, so a wide operating bandwidth is obtained. Balanced detection is also realized to reduce the noise figure. In the experiment, SSB signals with wide operating bandwidth (14–40 GHz), high sideband and carrier suppression (>20 dB), and large spurious-free dynamic range (110.4 Hz2/3) are generated. 16 and 64 quadrature amplitude modulation vector signals with data rates of 400 and 600 Mb/s at 40-GHz carrier frequency are also demonstrated. Furthermore, subharmonic I/Q up-conversion with similar performance is also realized using the same structure, which can well reduce the frequency requirement of the local oscillator signal and the drive circuits.

Comparison of 5-GHz Quadrature Couplers Using GaAs and Silicon-Based IPD Technologies

The 5-GHz quadrature couplers implemented in GaAs and silicon-based integrated passive device (IPD) technologies are presented. Although GaAs technology is superior to silicon-based technology in terms of substrate resistivity and back-side vias, the quadrature coupler using a silicon IPD process achieved better insertion loss due to thick metal traces and comparable substrate resistivity. While the coupler using the GaAs process employed 4- $\mu \text{m}$ -thick metal traces, the coupler using silicon IPD technology employed 10.8- $\mu \text{m}$ -thick traces realized with via connections between a top metal of 5.3- $\mu \text{m}$ thickness and a bottom metal of 5.5- $\mu \text{m}$ thickness. The couplers using the silicon and GaAs IPD process technologies showed 0.15 and 0.27 dB of insertion loss, respectively. Also, the silicon IPD design uses a slightly different topology which splits a coupled inductor into two coupled inductors with shunt capacitors to achieve a broader distributed bandwidth.

Design of a Class of Filtering Couplers With Reconfigurable Frequency

This paper reports on, for the first time, the design of filtering couplers with reconfigurable frequency. The reconfigurable filtering transmission lines (RFTLs) with 90° or −90° phase shift are first designed, and then the reconfigurable filtering couplers are constructed by substituting the basic unit of quarter-wavelength ( $\lambda/4$ ) transmission line in the conventional couplers with the proposed RFTL. The tunable capacitor loaded half-wavelength ( $\lambda/2$ ) resonators are used to tune the center frequency of RFTL. By properly controlling the electric or magnetic coupling between the resonators, the phase shift of 90° or −90° of the RFTLs can be realized, respectively, while maintaining a near constant bandwidth. The external coupling along with a pair of transmission zeros is achieved by asymmetric tap feeding of the RFTLs. For verification, a class of frequency-reconfigurable filtering couplers is designed and fabricated. First, a reconfigurable filtering rat-race coupler is designed and fabricated. The measured center frequency is tuned from 700 to 1840 MHz while maintaining a 3-dB fractional bandwidth of 13% ± 0.5%/13.7% ± 0.6%, insertion loss of 8.1–6.9/8.3–5.9 dB, return loss of better than 13 dB, and isolation of better than 21 dB. Second, a reconfigurable filtering quadrature coupler is designed and fabricated. The measured center frequency is tuned from 947 to 1775 MHz while maintaining a 1-dB bandwidth of 75 ± 5/65 ± 10 MHz, insertion loss of 8.3–6.9/8.3–7.1 dB, return loss of better than 14 dB, and isolation of better than 14 dB.

Design of a Compact Wideband Butler Matrix Using Vertically Installed Planar Structure

In this paper, a novel $4 \times 4$ Butler matrix with wide bandwidth and compact size is presented. The existing coupled-line-based quadrature coupler cannot be used to construct a Butler matrix due to the location of output ports. To solve this problem, a swap is introduced in a vertically installed planar structure to implement the quadrature coupler and a crossover required by a Butler matrix. For demonstration, the proposed coupler and crossover and the corresponding Butler matrix operating at 1.8 GHz are designed, fabricated, and measured. The implemented Butler matrix exhibits a wide bandwidth of 56.4% defined by 10-dB return loss and 1-dB insertion loss variation, by occupying a circuit size of $0.25\lambda _{g}\times 0.74\lambda _{g}$ . Simulated and experimental results are in good agreement.

Microfluidically Reconfigurable Reflection Phase Shifter

A microfluidic-based reconfiguration approach is presented for realizing a reflection phase shifter. The phase shifter consists of quadrature hybrid coupler with reflective microstrip line terminations. A selectively metallized plate (SMP) that can be repositioned inside a microfluidic channel is brought in close proximity ( $\mu \text{m}$ ) of the reflective microstrip line terminations to vary their electrical lengths through capacitive RF short mechanism. The concept is demonstrated through a 9.5 GHz $X$ -band phase-shifter design. Specifically, the design exhibits a footprint of $24\times15$ mm2, operates with <0.95 dB insertion loss, and attains the 360° phase shift with a total of 9.5 mm SMP motion resulting in 1.95 s total actuation time with the selected external micropumps. These phase shifters may be suitable for applications that prioritize low-loss and high power handling capability over reconfiguration speed.

A Planar Balanced Quadrature Coupler With Tunable Power-Dividing Ratio

This paper reports on, for the first time, planar balanced quadrature couplers with wide tunable power-dividing tuning ratio using two tuning capacitors. The differential-mode operation, common-mode rejection, and cross-mode conversion suppression are obtained for all power-dividing ratios. Closed-form design equations are derived. For verification, a 2-GHz tunable balanced quadrature coupler is designed and measured. The measured power-dividing ratio is in the range of −11.3–10.2 dB with better than 15-dB return loss and isolation. Furthermore, the insertion loss and phase difference resulting from the varactors and transmission lines are compensated using an active capacitance circuit with negative resistance. The worst case of phase imbalance is improved from 25° to 2°. The insertion loss is improved by ∼1.2 dB and nearly close to the theory value.

Two Methods for Miniaturization of Stub Quadrature Couplers

Two circuit-topological methods for reducing the overall dimensions of stub quadrature coupler (SQCs) are considered. The essence of the presented methods lies in replacing quarter-wave stubs with low-pass filters and artificial transmission lines (ATLs). It is shown that, using these methods, it is possible to reduce dimensions of two-stub and five-stub coupler by 71.9%. The design and experimental characteristics are presented; it is found out that the band of operating frequencies of compact SQCs is 1.4 times less than the bandwidth of conventional coupler and the imbalance of the power division coefficient increases.

A W-Band Balanced Power Amplifier Using Broadside Coupled Strip-Line Coupler in SiGe BiCMOS 0.13-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu\text{m}$ &lt;/tex-math&gt; &lt;/inline-formula&gt; Technology

Load-variation insensitivity, for impedance matching between power amplifiers (PAs) and transmitting antennas, contributes to challenging the design of millimeter-wave wireless systems. In this paper, a $W$ -band two-way balanced PA based on a compact quadrature coupler with a broadside coupled strip-line (BCSL) as the core is presented to enhance the load-variation insensitivity and stability. The proposed coupler is truly broadband with low amplitude and phase imbalance. The proposed $W$ -band balanced PA achieves higher power-added efficiency (PAE) and unsaturated output power ${P} _{\mathrm{ sat}}$ over wide frequency bandwidth. The $W$ -band balanced PA is implemented in a 0.13- $\mu \text{m}$ SiGe BiCMOS process and achieves a measured ${P} _{\mathrm{ sat}}$ of 16.3 dBm and a peak PAE of 14.1% at 100 GHz (with 1.6-V power supply). The measured ${P} _{\mathrm{ sat}}$ with 1-dB bandwidth is from 91 to 102 GHz. The measured results present the feasibility of the compact quadrature coupler. The total chip surface area (with pads) is 0.64 mm2, where the size of the proposed quadrature coupler area is only 0.04 mm2.