Coupled-line Directional Couplers Research Articles

인공전송선로를 이용한 결합선로 방향성 결합기

본 논문에서는 인공전송선로 중 LUC(Low-pass filter Unit Cell) 구조를 이용한 결합선로 방향성 결합기를 제안한다. 일반적인 결합선로 결합기는 <TEX>${\lambda}/4$</TEX> 길이의 전송 선로를 사용하므로 소형화에 한계가 있다. 반면에 제안한 결합기는 <TEX>$90^{\circ}$</TEX>보다 아주 작은 두 결합선로 사이에 위상 지연선로를 삽입하여 전체적으로 <TEX>$90^{\circ}$</TEX>보다 작게 결합기를 구현했고, 일반적인 전송선로의 특성을 특정 주파수 내에서 만족하는 인공전송선로를 이용하여 결합기에 위상 지연선로를 구성함으로써 물리적 크기를 감소시켰다. 중심주파수 700 MHz에서 -10 dB의 결합량 특성을 갖는 방향성 결합기를 설계 및 제작, 측정하였다. 측정된 결과는 기존 결합기와 비슷한 성능을 보였다. 반면, 제작한 결합기의 결합선로는 기존 결합기의 약 45% 크기를 가지고 있다. In this paper, a coupled line directional coupler using an LUC(Low-pass filter Unit Cell) of artificial transmission line is presented. The conventional coupled line coupler is limited in length by the <TEX>${\lambda}/4$</TEX> transmission line while the proposed coupling structure is implemented smaller than <TEX>$90^{\circ}$</TEX> by inserting the phase delay line between two coupled line, reduced in physical size by configuring a phase delay line with an LUC having the characteristics of a typical transmission line in a particular frequency. A coupler having -10 dB coupling factor at the center frequency of 700 MHz is designed, fabricated. The measured result agrees well with that of conventional one. The length of the fabricated coupled line coupler has about 45 % in length compared to the conventional one.

Application of RH and LH sections for reduction of coupling coefficients in two-section asymmetric directional couplers

A method allowing for reduction of coupling coefficients required for realization of two-section asymmetrical coupled-line directional couplers has been proposed. It has been shown that by connecting uncoupled left-handed and right-handed transmission lines between two coupled-line sections one can obtain greater design flexibility of the resulting circuit, simultaneously with the coupling reduction in coupled-line sections. Moreover, the proposed circuit features the properties of two-section asymmetric directional couplers offering wide operational bandwidth. The theoretical analysis has been verified by measurements of a 3 dB directional coupler operating at the center frequency f0 = 1.5 GHz having coupling imbalance δC = ±0.4 dB and bandwidth 0.75–2.3 GHz.

Two‐section asymmetric coupled‐line impedance transforming directional couplers

Two-section impedance transforming directional couplers have been proposed. It has been shown that such asymmetric coupled-line directional couplers can provide equal power split between the coupled and transmission ports as well as impedance transformation in the same broad frequency range, as classic two-section coupled-line couplers. The theoretical analysis has been presented and appropriate formulas allowing for calculation the required per-unit-length parameters of broadband two-section impedance transforming couplers have been derived. Moreover, it has been shown that the impedance transformation ratio of the presented coupler can be increased by the appropriate modification of the two-section coupled-line directional coupler in a way that the directly fed and coupled-line transformation ratios are different. The proposed modification allows for the design of broadband impedance transforming directional couplers with increased transformation ratio over the limit fixed by the coupling coefficient of the tightly coupled section and having at the same time acceptable impedance match and isolation between the respective ports. The presented theory has been confirmed by the measurements of a two-section 3 dB impedance transforming directional coupler having bandwidth fu /fl = 3:1 and impedance transformation ratio R = 2.

Multisection Couplers With Coupled-Line Sections Having Unequal Lengths

A new type of broadband multisection coupled-line directional couplers is proposed. The investigated directional couplers are composed of coupled-line sections having unequal electrical lengths and a transmission-line section. The presented couplers feature similar bandwidth to the standard multisection directional couplers with significantly reduced maximum coupling coefficient, and the overall size smaller than in the case of tandem couplers. Moreover, it is shown that in the presented couplers an ideal 90 ° differential phase characteristic can be achieved when such couplers are solely composed of coupled-line sections having appropriate electrical lengths. Additionally, it is shown that the proposed couplers' bandwidth can be increased by increasing the number of quarter-wave-long coupled-line sections. Theoretical analysis has been validated by three designs of broadband directional couplers operating at a frequency f 0 =1.8 GHz. Measurements of the manufactured directional couplers have been shown to experimentally confirm their properties.

Reduced-Length Two-Section Directional Couplers Designed as Coupled-Line Sections Connected With the Use of Uncoupled Lines

Broadband coupled-line directional couplers having the properties of two-section coupled-line directional couplers are proposed. The presented couplers are composed of two-coupled line sections having the same coupling coefficient which are connected with the use of two sections of uncoupled transmission lines. It is shown that in such a structure it is possible to achieve an equal-ripple coupling characteristic similar to the coupling response of classic-two section coupled-line couplers. It is also shown that, in comparison to the classic counterparts, in the proposed couplers the required coupling between the coupled-lines is slightly weaker and the overall electrical length is reduced. The theoretical analysis and measurement results of a 3 dB directional coupler operating at a center frequency of 1.8 GHz are presented.

Phase Property of Central-Symmetric Four-Ports Applied to Quadrature Directional Coupler Design in Asymmetric Coupled-Line Technology

Properties of ideally matched lossless four-port networks having central symmetry have been investigated. It has been shown that such networks feature ideal quadrature differential phase characteristics. It is shown that this unique property can be utilized for phase improvement of asymmetric coupled-line directional couplers. The presented theoretical investigation has been proven by measurements of two different directional couplers with a central symmetry designed in technology of multilayer asymmetric coupled lines.

A Broadband 3 dB Tandem Coupler Utilizing Right/Left Handed Transmission Line Sections

A new type of broadband 3 dB tandem coupler has been proposed featuring frequency characteristics of the resulting coupling similar to those of a classic 3 dB two-section asymmetric coupled-line directional coupler. The coupler is composed of two loosely coupled-line sections having electrical lengths close to quarter-wavelength connected by right-handed and left-handed transmission line sections. Theoretical analysis and design equations have been presented with an exemplary realization. Measurements of the manufactured tandem coupler operating at f0 = 1 GHz having wide operational bandwidth have been shown to validate the presented analysis.

Broadband magic-Ts with the use of coupled-line directional couplers and left-handed transmission line sections

The problem of broadband magic-T realization with the use of coupled-line directional couplers and left-handed LH transmission-line sections has been comprehensively investigated. Broadband amplitude characteristics of the proposed networks are ensured with the use of coupled-line couplers, whereas the required phase characteristics have been achieved by the appropriate selection of right- and left-handed transmission line sections. To analyze the properties of the proposed networks, a model of an ideal left-handed transmission line has been utilized. The presented concept has been verified by two designs of broadband magic-Ts operating in 2.5-3.5 GHz and 0.8-2.3 GHz, respectively. The obtained results proved that the proposed magic-T networks allows one to obtain broadband amplitude and phase responses together with its compact structure. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:513-521, 2014.

2.4-GHz Power Amplifier with Power Detector Using Metamaterial-Based Transformer-Type On-Chip Directional Coupler

This letter presents a power amplifier (PA) with an on-chip power detector for 2.4-GHz wireless local area network application. The power detector consists of a clamp circuit, a diode detector, and a coupled line directional coupler. A series inductor for an output matching network in the PA is combined with a through line of the coupler, which reduces the coupling level. Therefore, the coupler employs a metamaterial-based transformer configuration to increase coupling. The amount of coupling is increased by 2.5 dB in the 1:1 symmetric transformer structure and by 4.5 dB from two metamaterial units along the coupled line.

2.4-GHz Power Amplifier with Power Detector Using Metamaterial-Based Transformer-Type On-Chip Directional Coupler

This letter presents a power amplifier (PA) with an on-chip power detector for 2.4-GHz wireless local area network application. The power detector consists of a clamp circuit, a diode detector, and a coupled line directional coupler. A series inductor for an output matching network in the PA is combined with a through line of the coupler, which reduces the coupling level. Therefore, the coupler employs a metamaterial-based transformer configuration to increase coupling. The amount of coupling is increased by 2.5 dB in the 1:1 symmetric transformer structure and by 4.5 dB from two metamaterial units along the coupled line.

Compact UWB directional coupler with one notch-band

An ultra-wideband (UWB) parallel coupled-line directional coupler (DC) with one notch-band based on folded stepped impedance resonator (SIR) is investigated in this paper. The proposed UWB DC is comprised of one conventional microstrip directional coupler, two folded shunt quarter-wavelength short-circuited stubs and one SIR with metalized via hole to ground. The SIR is studied and employed to generate one desired notched band. The predicted results are compared with measured data and good agreement is reported.

High-Directivity MEMS-Tunable Directional Couplers for 10–18-GHz Broadband Applications

This paper reports on two novel concepts of area-efficient ultra-wideband microelectromechanical systems (MEMS) reconfigurable coupled line directional couplers, whose coupling is tuned by mechanically changing the geometry of 3-D micromachined coupled transmission lines, utilizing integrated MEMS electrostatic actuators. Concept 1 is based on symmetrically changing the geometry of the ground coupling of each signal line, while Concept 2 is simultaneously varying both the ground coupling and the coupling between the two signal lines. This enables uniform and well predictable performance over a very large frequency range, in particular a constant coupling ratio while maintaining an excellent impedance match, along with high isolation and a very high directivity. For an implemented micromachined prototype 3-6-dB coupler based on Concept 1, the measured isolation is better than 16 dB, and the return loss and directivity are better than 10 dB over the entire bandwidth from 10 to 18 GHz. Concept 2 presents an even more significant improvement. For an implemented 10-20-dB prototype based on Concept 2, the measured isolation is better than 40 dB and the return loss is better than 15 dB over the entire bandwidth from 10 to 18 GHz for both states. The directivities for both states are better than 22 and 40 dB, respectively, over the whole frequency range. The measured data fits the simulation very well, except for higher through-port losses of the prototype devices. All devices have been implemented in a silicon-on-insulator RF MEMS fabrication process. Measured actuation voltages of the different actuators are lower than 35 V. Reliability tests were conducted up to 500 million cycles without device degradation.

Theoretical limits on miniaturization of directional couplers designed as a connection of tightly coupled and uncoupled lines

The problem of miniaturization of coupled-line directional couplers designed as a connection of tightly-coupled and uncoupled sections has been comprehensively investigated for the first time.It has been proven that in such couplers the stronger coupling is available in the structure, the greater miniaturization is achieved. A novel approach allowing for theoretical analysis of such couplers has been proposed. Moreover, a special case has been considered, in which couplers are designed with the use of a single section of uncoupled lines placed in the middle of a tightly-coupled section. The proposed approach has been utilized for derivation of theoretical limits describing the maximum achievable minimization of the overall electrical length of couplers designed as a connection of coupled and uncoupled lines. The theoretical analyses have been confirmed by the measurements of two different directional couplers designed with the use of the proposed approach. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:223–230, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27233

A Distributed Circuit Model for Side-Coupled Nanoplasmonic Structures With Metal–Insulator–Metal Arrangement

A transmission line model is developed for coupled plasmonic metal-insulator-metal (MIM) waveguides. In the proposed model coupling between electric fields of two plasmonic waveguides is modeled by distributed mutual capacitor while distributed mutual inductor accounts for magnetic field coupling. These mutual elements are determined using propagation constants of supermodes of coupled waveguides. The model is applied to analyze coupled line directional coupler and side-coupled rectangular resonators. The effectiveness of the model is assessed using fully numerical finite-difference time-domain (FDTD) technique. The results have excellent agreement with the numerical methods.

Approach to the Design of Asymmetric Coupled-Line Directional Couplers With the Maximum Achievable Impedance-Transformation Ratio

A novel approach to the design of asymmetric coupled-line impedance-transforming directional couplers with the maximum achievable impedance-transformation ratio is proposed. It is shown that the couplers in which one conductor is completely shielded from the other can be represented by two uncoupled transmission lines, which significantly simplifies the design procedure. Furthermore, the proposed approach of the directional couplers' analysis has been utilized for the derivation of a general condition describing the maximum impedance transformation ratio that can be achieved for directional couplers designed in inhomogeneous media. It has been also shown that impedance-transforming directional couplers, in which the capacitive coupling coefficient differs from the inductive coupling coefficient feature limited isolation, and that such couplers can be represented by two uncoupled lines having different electrical lengths. Subsequently, it has been shown that this isolation can be improved when the electrical lengths of the two uncoupled lines are equal, which corresponds to the equalization of capacitive and inductive coupling coefficients. The theoretical analyses have been confirmed by the measurements of two different 3-dB impedance-transforming directional couplers designed with the use of the proposed simplified approach.

Erratum for ‘Microstrip coupled-line directional coupler with enhanced coupling based on EBG concept’

Erratum for ‘Microstrip coupled-line directional coupler with enhanced coupling based on EBG concept’

Broadband Planar Fully Integrated 8$\, \times \,$8 Butler Matrix Using Coupled-Line Directional Couplers

An innovative approach that allows for realization of broadband planar fully integrated 8 × 8 Butler matrices is presented. Coupled-line directional couplers have been utilized, which enable broad operational band. A novel arrangement of the network has been proposed that allows the creation of an entirely planar design having two metallization layers and no interconnections between these layers. Four selected crossovers have been realized as a tandem connection of two 3-dB/90° coupled-line directional couplers, which, together with reference lines having appropriate electrical lengths, perform simultaneously crossovers of signal lines, and all needed broadband constant value phase shifters. Moreover, two of the needed 3-dB/90° directional couplers have been designed as tandem connections of two 8.34-dB directional couplers, acting as 3-dB/90° directional couplers having crossed outputs. With such a modification, a fully planar design with no inter-layer connections is possible. The proposed network arrangement has been experimentally tested with the design of an 8 × 8 Butler matrix operating at the center frequency of 3 GHz. The obtained measurement results fully confirm the validity of the proposed approach.

Asymmetric Coupled-Line Directional Couplers as Impedance Transformers in Balanced and $n$-Way Power Amplifiers

Asymmetric 3-dB coupled-line directional couplers for application in balanced circuits have been considered, and it has been theoretically shown that such couplers allow for simultaneous (equal) power division and impedance transformation. A limitation on achievable impedance ratio has been derived. The theoretical analysis has been experimentally verified by the measurements of a number of passive circuits and an exemplary application of the proposed circuits in a four-way power amplifier has been shown.

Generalized Methods for the Design of Quasi-Ideal Symmetric and Asymmetric Coupled-Line Sections and Directional Couplers

Generalized methods for the design of quasi-ideal symmetric and asymmetric coupled-line sections have been proposed. Two cases of coupled-line sections, in which the inductive coupling coefficient is either greater or smaller than the capacitive coupling coefficient, have been separately considered. To compensate for the coupling coefficients' inequality, a combination of lumped capacitors and short coupled-line sections has been introduced into the coupled-line section. The proposed methods allow for designing quasi-ideal coupled-line sections in nearly arbitrarily chosen dielectric media and for arbitrarily chosen coupling. The theoretical analyses have been verified by the design and measurement of three compensated coupled-line directional couplers illustrating application of the proposed methods in different dielectric structures.

Microstrip coupled-line directional coupler with enhanced coupling based on EBG concept

A novel microstrip coupled-line directional coupler with enhanced coupling factor is proposed. It is based on the introduction of an electromagnetic bandgap (EBG) structure on the coupled lines to strongly enhance the designed backward coupling. Accurate analytical expressions are obtained for the main design parameters of the coupler. A 3 dB EBG coupler has been designed, simulated and measured, demonstrating 6.4 dB improvement in the coupling level when compared to a classical coupled-line directional coupler.