Prototype Coupler Research Articles

Wideband directional coupler based on zigzag coupling and wedge structure for isolation enhancement

This paper presents the design of wideband directional coupler with enhanced isolation performance. Studies show that introducing the zigzag coupling releases the phase-velocity difference between the even- and odd-mode in the coupling region, thus improving the directivity. To further improve the performance, wedge structure is proposed, and therefore, a wideband coupled-line directional coupler is developed with enhanced isolation responses. The presented coupler characterizes simple architecture, planar layout, symmetric topology, symmetric coupling and isolation responses that are the basic difference among many reported works, wide operation bandwidth and more importantly, the wedge structure can be independently loaded and designed, and features a great advantage in this contribution. To validate this study, a prototype coupler that works from less than 7 GHz to over 13 GHz is optimally designed, fabricated and examined experimentally. The developed prototype has a size of 11.1 × 5.4 mm2 (corresponding to 0.69 × 0.34λg2 at the center operation frequency of 10 GHz) on a microwave substrate with a relative permittivity of εr = 3.5 and a thickness of h = 0.508 mm. The measurement and simulation results are in good agreement, thus confirming the design methodology.

Planar Dual-Band Branch-Line Coupler With Large Frequency Ratio

This work presents a novel planar branch-line coupler topology developed for dual-band operation using an E-shaped impedance transformer network to supplant the conventional microstrip line. Explicit closed-form design equations for dual-band operation are derived using the ABCD matrices. The studied coupler features a large dual-band frequency ratio with a compact size. A prototype coupler centered at 1 and 8 GHz is first presented and experimentally examined to demonstrate the large frequency ratio. Further, another prototype coupler centered at 2.4 and 5.2 GHz for potential WLAN applications is also developed and experimentally characterized. Measurements and simulations for both prototype couplers show good performance within the studied dual-band frequencies.

Design of Compact Hybrid Branch Line Coupler (BLC) for GSM Application

This paper presents a compact design of a hybrid branch line coupler (BLC) operating at 1.8 GHz frequency for the global system for mobile communication (GSM) applications. The miniaturization is achieved by using two short circuited stubs and one series transmission line (TL) instead of series quarter wavelength line of conventional BLC. The characteristic impedance of the shunt quarter wavelength section is optimized to improve the overall performances. Therefore, the proposed technique is 59% compact in size is compared to conventional BLC. The outputs at two ports (|S21| = |S31|) are 3.5 ± 0.3 dB with return loss (|S11|) and isolation (|S41|) is better than 20 dB. The prototype coupler is simulated using ANSYS HFSS EM simulator and fabricated on a substrate of dielectric constant (er) = 2.2, thickness (h) = 0.787 mm and loss tangent of 0.0009 and tested. The measured result is completely compiled with the simulated one.

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.

Electromagnetic simulations, manufacturing and low power measurements of a 352.21 MHz RF power coupler for the SANAEM RFQ project

Radio frequency quadrupole (RFQ) linear accelerators occupy an important place among modern accelerators since the days it was conceived and constructed because of its ability to focus, bunch and accelerate the low energy beams at high efficiency. In Turkey, recently a 352.21 MHz RFQ accelerator cavity is designed and manufactured within a proton beamline located at the Turkish Atomic Energy Authority (TAEK), Sarayköy Nuclear Research and Training Center (SANAEM). The SANAEM RFQ cavity, operating in pulsed mode needs an overall RF power of 120 kW to accelerate the proton beam up to a final beam energy of 1.3 MeV . A new prototype RF power coupler, considering multipacting effect is designed, developed and manufactured to be used to deliver the required power for the RFQ. At the beginning of this study, design and 3D EM simulations of a coaxial power coupler considered for the SANAEM RFQ accelerator is presented. The RF properties of the coupler such as external quality factor, power loss on the loop, coupling coefficient and scattering parameters are evaluated and the geometrical parameters are optimized with the CST Microwave Studio. Also, various dielectric window materials to be used in the coupler are discussed. Moreover, multipacting simulations for the coupler are carried out using the CST Particle Studio and RF power levels at which the multipacting effect occurs are obtained. Finally, the manufacturing of a prototype coupler, low power measurements and discussions are presented in the present article.

Analysis and design of a lumped-element hybrid coupler using limited quality factor of components

This paper presents the analysis and design of a hybrid lumped-element coupler in which the loss of components is considered. First, only the loss of each capacitor is considered and it is shown that return loss or isolation can be significantly improved by a controlled reduction in capacitors quality factors. Then, the corresponding expressions for these parameters by considering both the inductors and capacitors quality factors are derived. Based on these analyses, a design procedure and a design example at 3GHz are presented to achieve an integrated coupler with minimized S11 by adjusting the components quality factors while the other S-parameters are approximately preserved in comparison to ideal lossless case. So, the optimum values for components and also for their quality factors are determined, resulting in the most significant improvement in S11. Also, a design is presented to improve S41. Finally to demonstrate the feasibility of the given method, asa proof of concept a prototype coupler is fabricated and tested on a Rogers 4003 PCB at 500MHz. The measurement results show that by adjusting the capacitors quality factors through placing an appropriate series resistor with each one, S11 improves by 26dB and reaches −56 dB.

Computationally Efficient Analysis of Double PM-Rotor Radial-Flux Eddy Current Couplers

In this study, a semianalytical calculation method for obtaining 3-D solutions for the torque of radial-flux permanent magnet eddy current couplers is presented. In this way, the use of computationally expensive transient 3-D finite element solutions is avoided, which is very important when it comes to the design optimization of these machines. The proposed analytical method takes the effect of flux density harmonics into account. The 3-D end-effects are taken into account by using Russell's coefficient. The accuracy of the proposed semianalytical calculation method is evaluated against extreme variation of machine dimensions. The Russell end-effect factor is evaluated and found to be inaccurate for axially short and radially large couplers. A prototype coupler with different conductors was tested to validate the proposed semianalytical torque calculation method.

Uniform impedance ring 0°/180° couplers with arbitrary ring impedances and power division ratios

Uniform impedance ring 0°/180° couplers have been developed that possess arbitrary values for the ring impedance and the power division ratio. The power division ratio of the proposed coupler can be adjusted to an arbitrary value for any fixed ring impedance. This makes it possible to obtain a very wide range of power division ratios without any restriction to the line impedance in the design of the coupler. The proposed coupler structure has been analysed rigorously for its scattering characteristics. As a result, general solutions for the coupler are derived in a concise form in terms of the ring impedance and the power division ratio, as well as for the optimum solutions needed to minimise the overall coupler size. The relationships between the coupler size, the ring impedance and the power division ratio also have been investigated. Extensive design and circuit simulation experiments have been conducted in order to analyse the impact of the different ring impedances on the coupler performance under varying power division ratios. An optimum ring impedance value is found from this study and is used to design, fabricate and measure two prototype couplers.

Uniplanar harmonic suppressed compact rat‐race couplers

AbstractA design of a miniaturized rat‐race coupler with higher‐order harmonic suppression is presented in this article. The slow wave effect and stopband produced by a shunt open‐stub is utilized to miniaturize the occupying area and suppress higher order harmonics, respectively. Design guidelines are obtained using a transmission line model. A prototype coupler has been fabricated in microstrip line to validate the theoretical predictions. The fabricated coupler occupies 18.4% area of that of a conventional coupler. At the same time, the second to tenth harmonics are suppressed by at least 15 dB. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2812–2814, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23840

Folded Half Mode Substrate Integrated Waveguide 3 dB Coupler

In this letter, novel compact 3 dB double-slot and single-slot couplers are proposed and implemented based on folded half mode substrate integrated waveguide (FHMSIW). The size of the FHMSIW coupler is reduced by nearly 50% and 75% compared with half-mode substrate integrated waveguide coupler and substrate integrated waveguide coupler, respectively. Prototype couplers at X-band are fabricated and measured and good performance in bandwidth, insertion loss, and balance are achieved.

Miniaturized quadrature hybrid coupler using high impedance lines

AbstractIn this article, a new configuration has been proposed for miniaturization of a branch‐line 90° hybrid coupler. The present coupler is obtained by replacing the low impedance series arms of a conventional coupler by their equivalent parallel high impedance lines. This arrangement facilitates meandering, used to realize a compact geometry. The main advantage of the proposed coupler is that it has approximately the same bandwidth as that of a conventional one. A prototype coupler area is 45.3% of that of a conventional branch‐line coupler. The design is validated by full‐wave electromagnetic simulation and measurement. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1135–1137, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23320

A Symmetrical Four-Port Microstrip Coupler for Crossover Application

A symmetrical four-port microstrip coupler has been proposed for crossover application. Models have also been developed to provide insight into the performance of such a coupler, which is based on the double-ring design. Laboratory tests have confirmed that the measured isolation and return loss of the prototype coupler exceed 20 dB over a bandwidth of 20% (from 0.92 to 1.12 GHz).

Development and testing of RF double window input couplers for TESLA

More and more accelerators are built with superconducting cavities operating at cryogenic temperatures. A possible window failure might result in contamination of the cavity surface and degrade the accelerating performance. A cost effective design and fabrication method for a new coupler has been developed by AMAC. This new design is an alternative to the present TESLA cylindrical ceramic windows layout. The new design includes two planar disc windows separated by a vacuum space. An alternative design option proposes filling dry nitrogen gas in between the two ceramic windows. Furthermore the new design is optimized for RF input power, taking into consideration the possible requirements of the TESLA superstructure layout. Two prototype couplers with this design have been fabricated. The couplers are being tested on the high power test stand at DESY, Germany. This paper describes the new coupler design and discusses the first measured results.

Improving Design of Symmetrical Six-Port Microstrip Coupler

It is possible to broaden the bandwidth of the symmetrical six-port microstrip coupler by incorporating various elements into the original structure. A consolidated eigenmode-based model has also been developed to predict the performance of such a coupler (when implemented in various novel forms). Laboratory tests have confirmed that the prototype coupler thus obtained is able to meet all the design specifications over a 44% bandwidth. Introduction After Riblet [1] reported the use of a symmetrical six-port coupler as a five-way power divider, other researchers [2]-[4] have demonstrated that this new coupler can also be utilized as the core component of a six-port reflectometer capable of yielding optimum measurement performance. For the latter application, analysis [3] has shown that the coupler’s characteristics may be represented by the following scattering matrix [5]: S =   γ α β τ β α α γ α β τ β β α γ α β τ τ β α γ α β β τ β α γ α α β τ β α γ   (1) where for the ideal case [3] we need to impose the following design specifications for the four scattering coefficients defined in Eqn. 1:

Comment: 2×2 multiplexing couplers for all-fibre 1.55μm amplifiers and lasers

For the original article see ibid., vol.27, no.1, p.42-3 (1991). In the aforementioned paper by F. Gonthier et al. a fused coupler with a nonsinusoidal spectral response is described and its potential application for pumping fibre amplifiers is noted. The authors wish to point out that couplers with the same nonsinusoidal response have been described previously by Hill et al. (1990). These couplers were used in a demonstration of a novel bimodal fibre tap. Even though the application is different, the coupling ratio of the coupler has the same nonsinusoidal spectral dependence as described by Gonthier et al. The commenters point out that the potential application of these couplers in fibre amplifier pumping was also known. A prototype coupler with the nonsinusoidal spectral response was sent to Bellcore, Red Bank NJ. This coupler was used in a fibre amplifier experiment reported in May 1990 at CLEO 1990 but is is conceded that Gonthier et al. may not have been aware of the type of coupler being used in the fibre amplifier experiment.

Broadband branchline coupler for S band

The design of an S-band, broadband, microstrip 3 dB, 90 degrees branchline coupler is described and measured results for a prototype version are given. The design uses broadbanding stubs and three branches, with the central branch split into two of twice the characteristic impedance and separated by half wavelength transmission lines. This is a new technique to improve the bandwidth of which a theoretical account was given by Mayer (see ibid., vol.26, no.18, p.1477-8, 1990). Measured results for the prototype coupler show return loss greater than 17 dB and isolation greater than 16.5 dB, over a percentage bandwidth of 45%. >

First‐order eigenmode analysis of symmetrical five‐port microstrip ring coupler

AbstractExplicit formulas to predict the characteristics of a symmetrical five‐port microstrip ring coupler are obtained from a first‐order eigenmode analysis. Tests on a prototype coupler over the 2—4‐GHz bandwidth indicate that the agreement between theory and experiment is reasonably good.

Sodium tests of head-flow characteristics for prototype annular electromagnetic flow coupler.

A prototype annular electromagnetic flow coupler was tested with high temperature sodium and it worked successfully, verifying the operational principle. The pump head-flow characteristics of the coupler were first clarified from an analysis of its equivalent electric circuit. The pump head and the generator pressure drop decrease linearly with the pump flow rate under the conditions of constant generator flow rate and external magnetic flux density. The gradients of the linear changes are given by ratios of equivalent resistances in the electrical analog, and are independent of the generator flow rate, if the magnetic flux density is kept constant. Sodium tests of the prototype confirmed the above results when the Hartmann number of the test conditions is larger than 170. Both ratios of the differential pressures and the volumetric flow rate between pump and generator ducts exceed 50% while the wall loss of around 40% appears at peak efficiency due to the lack of electrical insulation and the relatively large wall thickness. The peak efficiency of the prototype coupler decreases with the sodium temperature at the rate of (2.33±0.21)x10−2 %/°C from 200 to 400°C and increases with the external magnetic flux density at 5.8±0.1 %/T from 0.36 to 0.60T.

An automatic coupling device for tractor p.t.o. drivelines

An automatic p.t.o. coupling device has been developed which may be incorporated in the telescopic part of the drive shaft. This means that the coupler can be marketed by the drive line manufactures without requiring any modifications to tractors or implements. The design involves a cone sliding on the implement drive shaft. The cone can be can be caught and locked in a second cone on the tractor shaft. The main advantage of this design is that the telescopic performance of the drive line is not affected and no mechanical wires or cables to the driver's cab are necessary. A prototype coupler has been evaluated on mounted and trailed implements. A possible future development is to incorporate an overrun clutch function in the coupler.

Edge coupling of a GaAlAs DH laser diode to a planar Ti:LiNbO_3 waveguide

The problem of edge coupling a double-heterostructure GaAlAs laser diode to a planar titanium indiffused LiNbO(3) waveguide has been studied both experimentally and theoretically. Alignment sensitivities (3-dB points) have been measured and found to be ~15 and 1 microm in the longitudinal and transverse directions, respectively. The dependence of the coupling efficiency on misalignments has been found to be in good agreement with the predictions of a simple Gaussian coupling model. In addition, a prototype coupler has been fabricated in a flip-chip configuration on a silicon substrate with ~15% coupling efficiency into the waveguide's fundamental mode.