Wideband Coupler Research Articles

A Lumped-Element Directional Coupler for Bandwidth Enhancement, Impedance Matching, and Harmonic Suppressions

This paper presents a lumped-element wideband directional coupler that enables arbitrary impedance matching and harmonic suppressions from 2f0. The coupler consists of four filtering networks (FNs) and an asymmetric branch-line hybrid serving as the matching network. The use of lumped-element topology helps reduce circuit size and improve harmonic suppressions. Each FN, composed of two lumped-element resonators, contributes two additional transmission poles, enabling bandwidth scaling, bandwidth enhancement, and harmonic suppressions. To demonstrate the effectiveness of the proposed design, a wideband coupler with various terminal impedances operating at 0.5 GHz is designed, simulated, and fabricated. The measured size is 0.039×0.039 λg2, the fractional bandwidth for –14.3 dB return loss is 46%, and the harmonic suppression is more than –30 dB from 0.69 to 4.5 GHz.

A Dual-Circularly Polarized Wideband Dipole Antenna With Stable Axial-Ratio and Half-Power Beamwidths

With wide impedance bandwidth (IBW), wide axial-ratio bandwidth (ARBW), stable AR beamwidth, and stable half-power beamwidth (HPBW), a dual-circularly-polarized (DCP) crossed-dipole antenna is proposed. Each dipole consisting of two patches is fed by a pair of parallel transmission line, leading to a wide IBW. To enhance the ARBW and AR beamwidth, a quadrature wideband coupler is used, and the overlapping bandwidth of IBW and ARBW is up to 100%. The quadrature coupler is integrated with two pairs of parallel transmission line, and are printed on two substrates, which are squeezed into the space between the radiators and reflector, resulting into a compact antenna structure. With a total height of 0.016 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , a prototype is fabricated and measured, showing 1.5-VSWR IBW of larger than 104% for both Left-handed CP (LHCP) and Right-handed CP (RHCP), 3-dB ARBW of up to 100% both for LHCP and RHCP, and port-to-port (polarization) isolation of lager than 30 dB in 1.70 - 2.82 GHz, so the effective bandwidth (EBW) is about 50% (1.70 - 2.82 GHz). 3-dB AR beamwidth of 76° ± 5°, stable DCP characteristics with average gain of 7.2 dBi and HPBWs of 67° ± 4° are achieved.

RF Multi-Functional Input-Reflectionless Dispersive-Delay Structure With Sharp-Rejection Filtering Using Channelization Techniques

A class of RF multi-functional input-reflectionless dispersive-delay structure (DDS) with linear-type in-band group-delay variation and sharp-rejection bandpass-filtering capability is reported. It exploits a two-branch-channelized/balanced-type circuit with similar low-order reflective DDS units inside its channels, which are connected through input/output 3-dB quadrature wideband couplers. The adopted DDS unit is based on a coupled-resonator network with a frequency-dependent cross-coupling. It introduces a pair of complex transmission zeros (TZs) to shape the intended in-band group-delay profile. Unequal transmission-line-based phase-shifting sections are also inserted at the outputs of both channels. In this manner, an input-absorptive behavior and selectivity enhancement with TZ generation are attained by means of transversal signal-interference techniques at the overall input and output nodes, respectively. Moreover, as the transfer-function phase term of the interference action in transmission is linear with frequency, the total group-delay pattern is defined by the DDS unit of the channels. As practical validation, a 1.5-GHz proof-of-concept microstrip prototype is constructed and tested.

Microstrip hybrid wideband 10 dB coupler

In this paper, the design, simulation, optimization and testing of a Microstrip Hybrid 10 dB Wideband Coupler was done. The aim of the project was to introduce a new coupler design and to achieve stable operation for as wide bandwidth as possible. For this proposed design simulated results are as follows: 3.8 GHz Bandwidth and Coupling Amplitude balance of 1 dB across it. Coupler is then produced using LPKF ProtoMat 104s machine and it is tested with Vector Network Analyzer at Istanbul Technical University.

A high-efficiency wideband coupler for nanosecond-level pulsed current injection.

Pulsed current injection (PCI), as a conducted vulnerability testing technique under nanosecond-level transient electromagnetic disturbance (TED), has gained great attention recently. Many kinds of TEDs, e.g., high-altitude electromagnetic pulse, very fast transient overvoltage, and electrical fast transients, have very fast rise time as well as pretty slow decay, whose frequency spectrum may cover a very wideband. Therefore, one of the challenges is that the existing inductive couplers cannot interact with the equipment under test (EUT) over the wideband efficiently, and consequently, they are inadequate to inject the proper disturbance at ports of EUT in PCI tests. To address this problem, a high-efficiency wideband PCI coupler is proposed in this paper. The coupling performance is analyzed theoretically based on the distributed-parameter model of an inductive coupler. By using the composited ferrites instead of the simplex Ni-Zn ferrites, the inductive coupling is enhanced. The capacitive coupling is also enhanced to improve the high-frequency performance by exploiting the distributed tubular winding. A PCI coupler with the dimension of 30 × 10 × 10cm3 is built to be validated experimentally. The 3 dB bandwidth has been improved from 421 kHz-14MHz to 77 kHz-39MHz, which indicates that the coupler can be applied efficiently over the frequency range of interest for PCI tests.

Implementation and Design of Wideband Coupler Composed of Multi-stage Branch Line

Implementation and Design of Wideband Coupler Composed of Multi-stage Branch Line

Design and implementation of LTE wide band coupler

The article is devoted to design, analysis and implementation of directional coupler for LTE wide band application. It is implemented on FR4 with substrate thickness 1.6 mm, loss tangent of 0.025 and relative permittivity 4.3. It has a coupling coefficient -20db at 2.4 GHz frequency. It is designed using CST microwave studio tool. Conventional and metamaterial ones are illustrated. The later one enhances the scattering parameter of the coupler. The isolation is improved from -27db to -36db.

Miniaturized Wideband Coupler for 60-GHz Band in 65-nm CMOS Technology

A compact and wideband coupler for the 60-GHz frequency band applications using 65-nm CMOS technology is presented. By meandering the coupled line, a miniaturized coupler can be obtained. The proposed coupler achieves a measured insertion loss between the input port and the through port ( ${S}_{21}$ ) of 6.3 dB and between the input port and the coupled port ( ${S}_{31}$ ) of 5.6 dB at 60 GHz. The measured amplitude imbalance and phase difference are 0.75 dB and 92°, respectively, at 60 GHz. Overall, the proposed coupler can achieve a measured amplitude imbalance of $156\,\,\mu \text{m}\,\,\times 157\,\,\mu \text{m}$ (0.024 mm2).

Wideband Planarized Dual-Linearly-Polarized Dipole Antenna and Its Integration for Dual-Circularly-Polarized Radiation

A planarized dual-linearly-polarized (dual-LP) antenna and an integrated dual-circularly-polarized (dual-CP) antenna are proposed in this letter. For the dual-LP antenna, two groups of dipoles are fed by two balun-included feed networks to achieve ±45° polarizations. The feed networks and the radiators are printed on two sides of a substrate, forming a fully planar structure. Taking advantage of its planar configuration, the dual-LP antenna is further integrated with a wideband coupler to realize dual-CP radiation. The coupler is bent and squeezed into the space between the radiators and the reflector, leading to a compact structure. Both the dual-LP antenna and the dual-CP antenna have very stable radiation performances across a wide operating band >66%.

Design and Simulation of a Tunable Stripline Wideband Coupler

The basic theory of coupler is introduced, and a tunable strip-line wideband coupler is designed by using radio-frequency/microwave software which is named ADS on the basis of theoretical calculations and analysis. The broadband coupler can be adjusted appropriately in different frequency regions by using a tunable band line. It has a wide bandwidth of 2G~4G, excellent return loss of (&gt;30.5) dB, stable coupling coefficient of (9.85~10.81) dB, and high isolation of (&gt;20.08) dB, the straight-through pass-band transmission coefficient of (0.41~0.62) dB. The coupler has high power tolerance and small size. It can reduce design costs by used in communication systems.

Surrogate-assisted EM-driven miniaturization of wideband microwave couplers by means of co-simulation low-fidelity models

This article proposes a methodology for rapid design optimization of miniaturized wideband couplers. More specifically, a class of circuits is considered, in which conventional transmission lines are replaced by their abbreviated counterparts referred to as slow-wave compact cells. Our focus is on explicit reduction of the structure size as well as on reducing the CPU cost of the design process. For the sake of computational feasibility, a surrogate-based optimization paradigm involving a co-simulation low-fidelity model is used. The latter is a fundamental component of the proposed technique. The low-fidelity model represents cascaded slow-wave cells replacing the low-impedance lines of the original coupler circuit. It is implemented in a circuit simulator (here, ADS) and consists of duplicated compact cell EM simulation data as well as circuit theory-based feeding line models. Our primary optimization routine is a trust-region-embedded gradient search algorithm. To further reduce the design cost, the system response Jacobian is estimated at the level of the low-fidelity model, which is sufficient due to good correlation between the low- and high-fidelity models. The coupler is explicitly optimized for size reduction, whereas electrical performance parameters are controlled using a penalty function approach. The presented methodology is demonstrated through the design of a 1-GHz wideband microstrip branch-line coupler. Numerical results are supported by experimental validation of the fabricated coupler prototype.

Two Section Wideband 90° Hybrid Coupler Using Parallel-Coupled Three-Line

Two section wideband hybrid coupler with short-circuited coupled lines in the middle branch is demonstrated. The coupled lines are designed with a parallel-coupled 3-line, which has tight coupling and symmetric transmission phase over the center frequency. Without defected ground planes and a multilayer process, the proposed two-section coupler has the widest fractional bandwidth (FBW) than other two or even three section hybrid couplers modified from branch-line couplers. The designed wideband coupler has 55% FBW at the center frequency of 1.9 GHz. The bandwidth is limited by 1-dB power imbalance and the worst return loss, isolation, and phase imbalance within the bandwidth are 20.1 dB, 20.8 dB, and 3.2°, respectively.

Miniaturized Broadband Coupler Made of Slow-Wave Half-Mode Substrate Integrated Waveguide

In this work, a size-reduced wideband coupler is presented and demonstrated, which explores the slow-wave half-mode substrate integrated waveguide (SW-HMSIW) technique on a printed circuit board process. The SW-HMSIW coupler is composed of two SW-HMSIW transmission lines loaded with a polyline network. Along the coupler, energy is coupled by the electric and magnetic field between the two parallel SW-HMSIW lines. Compared with conventional microstrip coupler, the proposed coupler presents lower loss owning to the HWSIW structure performance. In addition, the proposed SW-HMSIW coupler exhibits a smaller size against its SIW and HWSIW counterparts, thanks to slow-wave effects of the loaded polyline. Measured and simulated results are in a good agreement.

A Broadband Graphene-Based THz Coupler with Wide-Range Tunable Power-Dividing Ratios

A wide-band coupler based on the graphene with inherent DC-block function and adjustable power-dividing ratios is proposed. This coupler uses three sections of the two-line coupled lines, four sections of the three-line coupled lines, and four graphene stubs (two U-shaped stubs and two rectangular stubs). The graphene stubs allow the coupler to own dynamic surface conductivity, which could be tuned by altering the chemical potentials. The tunable power-dividing ratios could be achieved by varying the chemical potentials applied to the U-shaped graphene stubs and the rectangular graphene elements, respectively. In addition, the widths of two-line coupled lines in the proposed coupler are analyzed to affect the power-dividing ratios in detail. Finally, the power-dividing ratios of the proposed coupler have a variation range from 5.4 to 9.56 dB at 1.75 THz with a flat 90° phase shift. The minimum −10 dB impedance bandwidth is 44 % from 1.47 to 2.3 THz, thus indicating a wide-band performance.

Design of high‐performance hybrid branch‐line couplers for wideband and space‐limited applications

This study presents a new design method of high-performance broadband equal-split branch-line couplers with compact footprints. Size reduction as well as wideband operation are achieved here by using cascaded slow-wave cells in place of conventional transmission lines that are basic building blocks of a reference structure. The initial stage of the design process involves numerical optimisation of the reference coupler equivalent circuit model to enhance its performance and account for practical design limitations. The next stage concerns determination of a repetition factor of the recurrent slow-wave structure that provides sufficient bandwidth and phase characteristics to be a suitable substitute for a conventional line. The subsequent steps include cell optimisation using fine electromagnetic simulations, local response surface modelling of the single cell, and surrogate-based optimisation of the recurrent slow-wave structure composed of cascaded cell approximation models. Additionally, minor T-junction and proximity effects that deteriorate the performance of the compact coupler are compensated by means of surrogate-assisted design closure. The proposed method is demonstrated by two numerical examples. The compact couplers obtained in this study illustrate the highest bandwidth-to-size ratio when compared against state-of-the-art wideband couplers from the literature. Experimental verification of one of the examples confirms the reliability of the proposed design approach.

Wideband coupler of folded half mode substrate integrated waveguide design with combined microstrip and stripline feed

ABSTRACTThis article presents the 90° hybrid directional 3‐dB coupler design with a wideband performance. The main part of the proposed coupler is built on a folded half‐mode substrate integrated waveguide (FHMSIW) structure and the feed is composed of microstrip line and stripline. The FHMSIW is implemented by PCB technology which possesses the merits of compact size, low cost, light weight, low profile, high power handling capability, easy integration with planar transmission line, and possibly low insertion losses. In designing the circuit's feed, a quarter‐wavelength stripline is placed between the coupler's main part and each microstrip I/O port. The stripline works as an impedance transformer, which increases circuit's bandwidth (BW) and reduces the reflection. The acquired fractional bandwidth (FBW) is 47.2% with the coupler's central frequency set to 4.5 GHz. The averaged transmission and coupling losses are around 1 dB and the isolation is better than 20 dB. Experiment is conducted to validate the circuit performance. The measured data are in good agreements with the simulated ones. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1139–1141, 2016

Design of High-Directivity Wideband Microstrip Directional Coupler With Fragment-Type Structure

A novel design for a microstrip wideband directional coupler is proposed by using fragment-type structures. The use of a fragment-type structure may provide satisfactory flexibility and excellent performance. For a given design space, a fragment-type wideband coupler can be designed by first gridding the space into fragment cells and then metallizing the fragment cells selected by a multi-objective optimization searching algorithm, such as a multi-objective evolutionary algorithm based on decomposition combined with enhanced genetic operators. For demonstration, a 20-dB wideband microstrip directional coupler is designed and verified by test. A 45% bandwidth centered at 2 GHz has been measured in terms of maximum variation of 0.5 dB in the 20-dB coupling level. In the operation band, the designed coupler has directivity above 37 dB, and a maximum directivity of 48 dB at 2 GHz. In addition, some technique aspects related to multi-objective optimization searching, such as effects of design space, control of coupling level, and efficiency consideration for optimization searching, are further discussed. Fragment-type structures may also be used to design high-performance wideband directional couplers of tight coupling level.

Wideband filter-integrated coupled-line coupler with unequal power division and inherent DC-block function

This letter reports a novel single-layer planar coupled-line coupler with multiple prominent advantages. These advantages include compact size, wideband filter-integrated coupling and transmission, unequal power division, flat phase difference, and inherent DC-block function between two arbitrary ports. Eventually, a microstrip prototype with 7.1-dB power-division ratio is implemented for verification, whose fractional bandwidth of 20-dB return loss is 58.4%. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:121–123, 2016

Wideband thulium-holmium-doped fiber source with combined forward and backward amplified spontaneous emission at 1600-2300 nm spectral band.

We have experimentally demonstrated two extremely wideband amplified spontaneous emission (ASE) sources. High bandwidth is achieved by combining the backward and forward ASEs generated in thulium-holmium-doped fiber using appropriate wideband couplers. The ASE source optimized for flat spectral power density covers a spectral range from 1527 to 2171nm at a -10 dB level. The ASE source optimized for spectroscopy features an enhancement with respect to single-mode fiber (SMF) coupled halogen lamps within the spectral range from 1540nm to more than 2340nm covering the 800nm bandwidth.

A novel wide-band hybrid coupler using coupled-line power divider and improved coupled-line phase shifter

A novel hybrid coupler aiming for wide-band applications is proposed in this paper. This hybrid coupler consists of a broadband Wilkinson coupled-line power divider and an improved wide-band coupled-line phase shifter. Taking advantage of the coupled-line section, the power divider achieves both compact circuit configuration and wide-band performance. In lieu of patterned ground plane and lumped capacitors, the coupled-line phase shifter can be constructed on a single-layer printed circuit board for wide-band operation. For this proposed phase shifter, the scattering parameters (S-parameters) expressions are derived and the optimal structural design parameters for achieving zero reflection coefficients are highlighted. After carefully choosing the circuit parameters, a new wide-band hybrid is constructed by combining a power divider and the proposed phase shifter. To verify against the theoretical calculation in terms of S parameters and phase information, a hybrid operating at 3 GHz is designed, simulated, and fabricated through microstrip technology. Close agreement is obtained between simulation and measurement results.