Transmission Line Stub Research Articles

Novel dual-band hybrid coupler using improved simplified CRLH transmission line stubs

In this article, a novel dual-band hybrid coupler is designed by adopting improved simplified composite right-/left-handed (ISCRLH) transmission line (TL) stubs.An ISCRLH TL stub is composed of two ISCRLH TL unit cells with input and output uniform TL sections at the terminals, which can produce specified impedance and phase shift at two (arbitrary) different frequencies. The conditions for synthesizing the dual-band ISCRLH TL stub are discussed in detail, and then such a stub is applied to implement a novel dual-band hybrid coupler in microstrip configuration, and excellent agreement between the simulated and measured results is achieved, which reveal good performance and dual-band operation. The novel device is small, fully planar, and easily designed and fabricated. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:2473–2476, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25491

A New Design Method for Unequal Dual-Band Modified Wilkinson Power Divider

A new design method for a dual-band (or dual-frequency) modified Wilkinson power divider with an unequal power dividing ratio is proposed in this article. First, a dual-band transformer with a flexible transmission line stub, which can be fabricated by a shorted-circuit stub or an open-circuit stub, for two arbitrary real impedances is analyzed, and the rigorous design method is obtained. It is necessary to apply the asymmetric structure in all unequal power dividers in order to obtain unequal power dividing; thus, an asymmetric structure, which consists of two equivalent asymmetric dual-band transformers with a parallel transmission line stub in the input matching part, is developed for an unequal dual-band power divider. A resistor is then used in this proposed power divider, as the effective isolation structure to obtain ideal isolation between two output ports while two-section transmission line transformers are applied to match impedances at two output ports. In the synthesis procedure, two groups of closed-form design equations of this unequal dual-band power divider without reactive lumped-elements are given. Furthermore, simulations of two sample examples have verified the new structure and the design method for this power divider in theory. Finally, a practical microstrip power divider, which operates at both 0.95 GHz and 2.28 GHz with 3 dB power dividing ratio, is designed, fabricated and tested. There are good agreements between the simulated and measured results.

A Universal Equivalent Circuit Model for Ceramic Capacitors

A physics-based equivalent circuit model of the ceramic capacitor is proposed, which can reproduce frequency characteristics of its impedance including the often observed yet hitherto physically unexplained kinks appearing above the primary series resonance frequency. The model can also account for parasitic effects of external inductances. In order to efficiently analyze and gain engineering insight into ceramic capacitors with a large number of metallic laminae, a two-dimensional method of moments is developed that treats the laminar structure as a uniform, effective medium. It turns out that the primary resonance and the kinks can be well understood and modeled by a lossy transmission line stub with a drastic wavelength reduction. The capacitor model is completed by adding components describing the skin effect and external inductances. The modeled impedance stays within a 4% margin of error up to 5 GHz. The proposed model could greatly improve the accuracy of power distribution network simulation.

A Novel Dual-Frequency Wilkinson Power Divider with Unequal Power Division

An unequal dual-frequency Wilkinson power divider with a novel structure and analytical design method is presented in this article. A new asymmetric structure consisting of a parallel open-circuited transmission line stub and eight sections of transmission lines is proposed, and this structure can satisfy rigorous unequal power division and impedance matching theoretically. Considering that the transmission line stub has the equivalent characteristics of reactive lumped elements (such as inductors and capacitors), a single resistor R is only used in the isolation structure to obtain ideal isolation between two output ports of this proposed unequal dual-frequency power divider. For verification, simulated results of two examples are shown first, and it can be observed that ideal matching at three ports, perfect isolation between two output ports, and accurate unequal power division can be simultaneously achievable at desired two frequencies. Finally, comparison results of simulation and measurement of a practical microstrip example verify this proposed power divider experimentally.

Synthesis Design of Ultra-Wideband Bandpass Filters With Composite Series and Shunt Stubs

This paper presents a direct synthesis procedure for efficient design of a class of ultra-wideband bandpass filters with composite series and shunt transmission-line stubs. The proposed single-stage bandpass prototype is formed by cascading two sets of series open-ended and shunt short-ended stubs through a multisection nonuniform transmission line. All the stubs are set with an identical electrical length, i.e., thetasc , at lower cutoff frequency fc and the middle connecting line is composed of stepped-impedance transmission line with i sections, and each section has an electrical length thetasc. The proposed filter topology aims to construct an ultra-wide bandpass filter with Chebyshev equal-ripple responses and (i + 3) in-band transmission poles. Based on the derivation of the transfer function, a synthesis approach is established and systematically described to design this type of filters according to the specifications such as lower/upper cutoff frequencies. Next, a multistage bandpass filter prototype is proposed and the synthesis design procedure is also presented. The implementation is achieved by using hybrid microstrip line and slotline sections. Compared with traditional stub filters, the proposed filters achieve higher order transmission zeros and thus provide higher selectivity. As design examples, two single-stage and one three-stage bandpass filters are designed and fabricated to confirm the theoretical predictions.

A New Symmetric Modified Wilkinson Power Divider Using L-Type Dual-Band Impedance Matching Structure

Based on L-type dual-band impedance matching structure, this paper presents a new symmetric modified Wilkinson power divider for dual-band applications. In the matching structure, two transmission line stubs can be used to implement impedance matching and space isolation for two transmission ways, simultaneously. In the isolation structure, a single resistor is applied, and the design values are adjusted according to the center frequency ratio. In this proposed power divider, the ideal matching of all ports, equal power splitting and isolation between the output ports can be achieved. Theoretically, the nonlinear design equations for normalized parameters are directly derived based on the conventional even- and odd-mode analysis. In microstrip experiments, simulated and measured results of two fabricated power dividers with different frequency ratios are given. It can be clearly seen that there are good agreements between the theoretical and experimental results.

DUAL-BAND MODIFIED WILKINSON POWER DIVIDER WITHOUT TRANSMISSION LINE STUBS AND REACTIVE COMPONENTS

In this paper, a novel modifled Wilkinson power divider without transmission line stubs (such as short-circuit stubs and open- circuit stubs) and reactive components (such as isolation inductor L and capacitor C) is developed for dual-band applications. This symmetric power divider consists of six sections of transmission lines and an isolation resistor, and the corresponding nonlinear design equations are derived by using the even- and odd-mode analysis. Moreover, by solving the flnal nonlinear design equations, accurate numerical design data along with difierent frequency ratios are obtained, and the efiective normalized parameters are given simultaneously in the flgure and table formats for speciflc applications. To theoretically verify the design parameters, an ideal equal power divider operating at both 900MHz and 5.85GHz is simulated. Finally, the proposed structure and design method are validated by simulated and experimental results of a typical microstrip planar power divider operating at both 1GHz and 3.5GHz.

An impedance matching design approach for a dual‐band coplanar‐waveguide‐fed slot antenna

AbstractIn this study, it is shown how dual‐band performance can be achieved from a single coplanar‐waveguide‐fed slot by using an impedance matching design approach. The coplanar‐waveguide‐fed slot is connected to a high‐impedance coplanar‐waveguide transmission line stub terminated with a capacitor. The two elements (slot and terminated stub) forming the antenna can be designed such that the series slot impedance added to the input impedance of the terminated stub result in two distinct resonances at the desired center frequencies for a dual‐band application. A dual‐band 2.4/5.2 GHz antenna is designed, and simulations are validated by the measured reflection coefficient and radiation pattern results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2031–2034, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23565

A Dual-Band Wilkinson Power Divider

A new scheme is proposed for the dual-band operation of the Wilkinson power divider/combiner. The dual band operation is achieved by attaching two central transmission line stubs to the conventional Wilkinson divider. It has simple structure and is suitable for distributed circuit implementation.

TEM transmission line coil with double nuclear capability

MR imaging and spectroscopy requires RF fields of high homogeneity. Quadrature volume coils meeting this requirement include the birdcage coil and the TEM resonator. We describe here a quadrature volume coil designed around a modified coaxial transmission line in which multiple inner conductors are arrayed on a circular perimeter and surrounded by a common shield. Current antinodes are established at appropriate points on the inner conductors by series transmission line stubs, either open circuit or short circuit, which terminate the line. Quadrature phasing is generated by a novel circuit constructed from a pair of high-performance current baluns and a commercial quadrature hybrid. The coil is a "pure" TEM coil as it is simply a resonant transmission line. There is no mode structure to consider. The construction of a prototype quadrature four-element coil is described and preliminary test results from this coil in a 4.7T horizontal bore magnet are reported. A related double nuclear coil design for (3)He and (1)H in which two linear transmission line coils are arrayed on a circular perimeter and simultaneously tuned and matched to their respective frequencies is also described. Preliminary tests from this coil in a 1.5T clinical scanner are reported.

Miniature planar notch antenna of J shape

A miniature monopole slot antenna implemented by suitably meandering the notch into a J shape and seriesly coupling to an open transmission line stub is reported. Overall occupation area of the proposed antenna, ~7.94times7.41 mm 2 , is achieved. 10 dB impedance bandwidth of about 8% is obtained, which is twice that of a simple half-wavelength slot antenna tested. Guidelines for the design of the proposed antenna are provided

Efficient material-gain models for the transmission-line laser model

Transmission-line laser models (TLLMs) are time-domain models suitable for the simulation of complex phenomena in semiconductor lasers. TLLMs include time-domain filters based on transmission-line stubs to model the spectral dependence of the material gain. In this paper, numerical simulations are presented which show that the accuracy of these gain models is dependent on the model's iteration timestep. Analytical formulae are derived that relate the accuracy of the filters to the timestep, filter centre frequency, and filter bandwindth. A new wideband stub filter which allows the material gain to be modelled using a larger timestep is presented. This is equivalent to a digital infinite-impulse-response filter, which is more computationally efficient than finite-impulse-response filters, and is unconditionally stable. The new gain model can improve the computational speed for simulating for multimode Fabry-Perot lasers by a factor of 10–100.

A hybrid‐ring directional coupler with modified ring impedances and two compensation stubs

AbstractNew explicit formulas for calculating the scattering parameters of a modified hybrid‐ring directional coupler are presented. It is also shown how port junction discontinuities of real couplers of this type, employed as equiphase antenna dividers, can be effectively compensated by using a pair of short open‐circuited transmission line stubs. The efficacy of the proposed approach is illustrated both by theoretical and by experimental results. © 1995 John Wiley & Sons. Inc.

Instability in self-pulsation in laser diodes and its effect on all-optical synchronization

The effect of short- and long-term frequency instability in self- pulsation on all-optical synchronization using a twin-section laser diode is experimentally investigated. Short-term frequency instability broadens the unlocked full width at half maximum (FWHM) of the fundamental of the ii spectrum of the self-pulsating laser diode. We show experimentally that the value of the unlocked FWHM, and thus the level of short-term instability, has a direct effect on the optical power required to maintain synchronization. A novel means of reducing the FWHM is presented, based on a reflective transmission line stub connected to the absorber of the twin-section self-pulsating laser diode in use. A reduction of up to 5 dB in the average optical power required for effective synchronization is observed. Long-term frequency instability can prevent synchronization from taking place because of the limited lock-in frequency range of a self-pulsating laser diode. It is shown that for the devices used here, the dominant cause of long-term instability is temperature. A new method of sensing the temperature in a twin-section laser, called absorber current temperature sensing, which reduces the measured unsycnchronized frequency drift by more than 5:1, is demonstrated. The results have important implications for the design of new all-optical synchronization subsystems, based on self-pulsating laser diodes.

TLM stub-link conversion technique

A novel conversion technique is presented which can transform a transmission-line stub into a link or vice versa. This technique allows multistage circuits with different operating frequencies to be decoupled and simulated concurrently with different time steps in each decoupled circuit. The technique is applied to a two-stage circuit and the simulations confirm the validity of the method.

The simulation of high-speed, high-density digital interconnects in single chip packages and multichip modules

The development of a comprehensive electromagnetic (EM) modeling tool, the Networking Algorithm, is discussed. This tool is capable of simulating on a digital computer the complexities inherent in real-world interconnects and packages, including simultaneous treatment of the effects of mixed types of transmission line interconnects (i.e. mixtures of stripline, microstrip, and coplanar lines), stubs and branches, reflections, and crosstalk between multiple nets. The type of modeling tool which has been developed is described, the mathematics of the Networking Algorithm is discussed, and a number of examples taken from a high-frequency digital package design are given to show how such a computer-based EM modeling tool set can assist in the design of high-performance packages. >

Model for multimode picosecond dynamic laser chirp based on transmission line laser model

Laser chirp contributes significantly to the linewidth of near single-mode injection modulated semiconductor laser devices, and is a consequence of the carrier dependence of the active layer's refractive index. A model is developed that can accurately predict the multimode chirped spectra of Fabry-Perot devices based on the transmission line laser model (TLLM), with the addition of a transmission line stub and attenuator to the end facets. This time-domain model is easily interfaced to both drive circuit and fibre impulse response models. A 1550 nm InGaAsP device model under picosecond modulation is tested against experimental and analytical results of other workers.

Simulation of Fluid Network Dynamics by Transmission Line Modelling

The classical solution to the acoustic wave equation reveals decoupled left- and right-going waves carrying pressure and flow. Using a variant of these waves representing power, it is shown that such decoupled waves permit fluid transmission lines in circuits to be modelled simply as pure time delays. It is also demonstrated that lumped inertance and capacitance may be modelled as transmission line stubs. Thus all dynamic elements in a circuit are represented as pure time delays and the only computations required are of wave scattering at junctions. Linear resistance is most easily admitted, especially if it is concentrated at the junctions. Computations on simple circuits are presented and shown to compare favourably with classical ‘lumped’ analyses. The significance of various approximations made is discussed. The method may be applied to fluid circuits of arbitrary size and complexity, and to circuits of other wave-propagating elements.

Optoelectronic switching in a stub transmission line

We have demonstrated optoelectronic switching in a pulse-forming microstrip line, which utilizes the energy in a laser pulse for triggering. Electrical pulses 1 ns in width and of 1–2 V in amplitude were produced using a 10-ns dye laser pulse of 1-kW amplitude. The possibilities of further pulse shortening appear very promising.

The trap-loaded cylindrical antenna

The trap-loaded cylindrical antenna is a cylindrical antenna having one or more traps located in its arms. The traps are either parallel inductor-capacitor circuits or short-circuited transmission line stubs that are designed to be antiresonant (having essentially an infinite input impedance) at some particular frequency. The location and the antiresonant frequency of the traps are selected to enhance the radiation pattern or input impedance of the antenna. This study is confined to the properties of trap-loaded cylindrical antennas that contain only one trap in each arm. The effect of the length of the outer section, length of the inner section, diameter of the cylinder and characteristic impedance or inductance-capacitance ratio of the trap on the input impedance, radiation pattern, and current distribution were studied both experimentally and with the aid of two numerical solutions of an integral equation for the current distribution. The conclusions drawn from this study are that the design procedure for the multiband trap antenna described by Greenberg [1], adjusting the antiresonant frequency of the trap to control the upper resonant frequency, is indeed valid. Graphs suitable for designing trap antennas using this procedure are available in this paper. Furthermore, it is shown that the characteristic impedance or inductance-capacitance ratio of the trap can also be adjusted to vary the lower resonant frequency of the antenna. Design graphs using this procedure are also available in this paper. This study also showed that a relatively wide range of upper to lower antenna resonant frequency ratios can be obtained while still maintaining radiation patterns and input impedances close to those of a half-wave dipole at both frequencies. Graphs are available showing the tradeoff in pattern shape and input impedance that must be made to obtain resonant frequency ratios other than 2 to 1. It was discovered that the trap antenna, sometimes called a Franklin array, must be operated somewhat below the nominal design frequency or have the spacing between traps shortened somewhat, for it to have a radiation pattern similar to a collinear array of half-wave dipoles. Furthermore, the thicker the antenna, the more pronounced this effect is. While the nominal design was discovered to give an input impedance nearly resistive and near 70\Omega (for a dipole), any of the aforementioned modifications resulted in a nonresonant highly capacitive input impedance.