Odd-mode Characteristic Impedances Research Articles

Design Synthesis of a Microstripline Coupler

Several authors have developed various methods for the study of characteristics of single & coupled microstriplines. This paper deals with the analytical studies of the design synthesis of microstripline couplers and their variation with geometry and frequency using Alumina substrates for the design synthesis of the microstripline coupler which is the aim of the present work. All the parallel line couplers, whether mode of propagation is true TEM or not, have the even and odd-mode property which always results in even- mode characteristic impedance (Zoe) and odd-mode characteristic impedance (Zoo).

Compact phase shifter using arbitrary length of two coupled transmission lines

This article presents a compact structure of two coupled transmission lines with two reactive loads for the tunable phase shifter using a printed-circuit board. The proposed circuit offers size reduction and wide phase shift range. The conventional reflection-type phase shifter approach has large total electrical length and high insertion loss. To overcome such technical issues, arbitrary-length two coupled transmission lines were introduced in this work. After optimising the length and the even-mode characteristic impedance of the coupled transmission lines, tuning the odd-mode characteristic impedance can decide the variation of two adjustable reactive loads. Based on the proposed structure, further discussion of the wideband tuning operation and measurement of the phase shift range with −20 dB return loss are addressed in this article. The fabricated circuit is measured at 700 to 2400 MHz. The even- and odd-mode characteristic impedance of two coupled transmission lines are 100-Ω and 70-Ω having about 2.16 dB maximum insertion loss, while maintaining 181-degree phase shift range and 40-degree total electrical length of transmission lines at 700 MHz, respectively, providing about 78% to 89% size reduction compared with the previous research. Our data indicates that insertion loss, multi-band operation, and miniaturisation are superior to any published data.

E-Band RF MEMS Differential Reflection-Type Phase Shifter

A systematic approach in the design methodology, leading to the optimization of a differential reflection-type phase shifter (RTPS), is presented. The key parameters of the quadrature coupler and the reflective loads are analyzed for optimum RTPS performance, showing that: 1) equality between the coupling and through transmission coefficients provides the best return and insertion loss; 2) a minimized coupler reflection coefficient with negative phase optimizes the return loss and the phase performance; and 3) a wide tunable reflective load with minimized resistance assures lower insertion loss and larger phase range. The even–odd mode analysis leads to the coupler miniaturization. The differential microstrip line dimensions are determined by the minimum feature size of our fabrication process. By choosing the separation between the coupled lines, the even- and odd-mode characteristic impedances satisfy the derived design equations for equalized quadrature outputs and provide the matching capacitance. By exploiting the virtual ground of the differential structure, a novel RF MEMS reconfigurable short circuit is introduced for the reflective loads aiming at 180° phase shift range and low insertion loss. Over the 70–86-GHz range, the measurements show good agreement with the simulations. The measured RTPS achieves a 195.6° phase shift range with a phase error less than 8.6° and insertion loss error less than 0.7 dB. For all phase states, the reflection coefficients are below −18 dB, and at 74 GHz, the insertion loss is 4.4 ± 0.5 dB.

Forward‐wave directional coupler based on slow‐wave coupled microstrip lines

This study presents the design of a forward-wave directional coupler based on slow-wave coupled microstrip lines realised in a multilayered printed circuit board technology. Thanks to the concept of slow-wave, a high difference between the even- and odd-mode phase velocities can be inherently achieved. Hence, by choosing adequate even- and odd-mode characteristic impedances close to 50 Ω, reduced-length forward couplers can be designed. As a proof of concept, a 0 dB forward coupler operating at 4.5 GHz is proposed. It exhibits a very high coupling of 0.56 dB at the centre frequency and a very large bandwidth of 43%, corresponding to 10 dB of isolation. A length miniaturisation of 84% is obtained as compared to the standard microstrip, leading to a total surface area of 0.132 λ g 2 , the smallest one reported so far.

Modeling a Planar Coupled Microstrip Lines using various Wavelets and Method of Moments

In this paper, we apply a several wavelets basis functions to the method of moments to modeling the parallel-coupled microstrip lines. The first set of equations is for the shielded microstrip line solved with moment’s method and wavelets. The Green’s function is obtained from the theory of images. The second set are for the parallel-coupled microstrip lines operating in the TEM mode or when the analysis can be based on quasi-static approximation, the properties of coupled lines can be determined from the self- and mutual inductances and capacitances for the lines. To demonstrate the effectiveness and accuracy of the proposed technique, numerical results of even- and odd-mode characteristic impedances, coupling coefficient, percentage sparsity achieved in the impedance matrix, the CPU Time to reverse impedance matrix, and error relative for Daubechies, Coiflets, Biorthogonal and Symlets wavelets are presented. Numerical results are in good agreement with those in previous publications.

Development of broadband forward-wave directional couplers loaded by periodic patterned ground structure

In this paper two wideband Forward-Wave Directional Couplers (FWDCs) with 0 dB and 3 dB coupling level are proposed. Using periodic patterned ground structure in a microstrip coupled lines by a new unit cell; even- and odd-mode characteristic impedances of the couplers are equal over a wide frequency range. Moreover, it provides a constant phase difference between even and odd-modes. The proposed cell is modeled using the equivalent circuit model and a design procedure is introduced for designing FWDCs for an arbitrary value of coupling level. The introduced couplers are numerically investigated and a prototype of both couplers is made. It is shown that for 0 dB coupling level, the measured coupling is 0.85 dB with 1 dB flatness over fractional bandwidth of 96% bandwidth. In case of 3 dB coupling, the measured coupling level is 3.5 dB at 7.42 GHz with 1 dB flatness over fractional bandwidth of 67.1%.

Compact Single-/Dual-Band Planar Crossovers Based on Strong Coupled Lines

Three compact planar crossovers based on strong coupled lines loaded with open stubs are proposed in this paper. Two conventional coupled lines loaded with different electrical wavelength open stubs are used to realize the single/dual passband. The center frequencies of the three planar crossovers can be adjusted over a wide frequency band by changing the even-/odd-mode characteristic impedance of the coupled lines and the characteristic impedance of the open stubs. Three compact planar crossovers located at 1.78, 1.88, and 1.02/2.98 GHz are designed and fabricated for verification. The theoretical and measured results are in good agreement and show good in-band performances.

Novel Dual-Band Coupled-Line Quadrature Couplers with Unequal Power Division

ABSTRACTA dual-band coupled-line 90° unequal coupler is proposed in this paper. It is simply composed of three pairs of coupled lines and four port extensions. Analytical design methodology and detailed design guidance are given, which significantly simplifies the design procedure. Due to the utilization of coupled lines, the proposed coupler possesses tight circuit configuration, and since the degree of freedom is increased for the even- and odd-mode characteristic impedances, the coupled lines enable the dual-band operation. Meanwhile, the coupler can operate with unequal power division. Furthermore, the employment of port extensions eliminates the additional insertion loss caused by additional port lines. Eventually, two prototypes of the proposed coupler are designed and fabricated. The good agreement between the expected and measured results confirms the design methodology in this work to be correct and effective.

High selectivity wideband filtering crossovers using stub-loaded ring resonators

Two high selectivity wideband filtering crossovers using stub-loaded ring resonators are proposed in this paper. Cascaded coupled lines and open stubs are used to generate two/four transmission zeros each near the crossover passbands. In addition, patterned grounded conductor in the ground plane can enlarge the coupling coefficient for the coupled lines with increasing the even-mode characteristic impedance, and the isolated conductor placed inside the slot can decrease the odd-mode characteristic impedance. Two filtering crossovers operated at 2.2 GHz with bandwidths of 27.5% from 1.945 to 2.55 GHz are designed and fabricated. They show good return loss more than 20 dB and nice insertion loss less than 1.7 dB in passband.

Modeling of Inline Transitions Between Different Waveguides as Impedance Inverters for the Use in Novel Filter Designs

In this paper, a novel approach for field coupled inline transitions between different waveguides is proposed. The immittance inverting characteristics of these transitions are simultaneously utilized for filter design. Based on scattering parameters, an exact relation is derived between the desired inverter constants and the even and odd mode characteristic impedances. The well-known approximation introduced by Cohn is improved. Further it will be shown that the introduced inline transitions can be effectively modeled with a contra-directional symmetrical coupler. The description of the field coupled waveguide transitions as inverters allows a “straight on design method” for general field coupled structures and accelerates the optimization process. The integration of the inline transitions into the filter design is applied for two different types of transitions, namely, the transition between a parallel-plate waveguide and a rectangular waveguide (RWG) and the transition between a microstrip line and a RWG, using a ridged waveguide section for the coupling. For both configurations a third-order bandpass filter was realized by using three coupled waveguide resonators. Two of the coupling structures were made up of inline transitions. To verify the approach and quantify losses, a filter was fabricated and its scattering parameters measured. With this new approach low-loss waveguide filters can be integrated into a planar RF circuit while minimizing space. No delicate manufacturing processes are required.

Design of compact multiband bandpass filter with suppression of second harmonic spurious by coupling gap reduction

In this paper, we describe a method to implement compact multiband bandpass filters with suppression of second harmonic frequency. This filter design approach is based on decreasing the coupling gap between adjacent resonators of a parallel-coupled-line bandpass filter in order to achieve both the desired multiband frequency response and the spurious suppression. We present the theoretical analysis of the proposed structure that consists of modeling the frequency dependence of the even- and odd-mode characteristic impedances as well as due to the different phase velocities of the parallel-coupled microstrip lines. As an example, a compact tri-band parallel-coupled-line bandpass filter with suppression of second harmonic frequency was implemented operating at 1.9/3.2/4.6 GHz to cover PCS1900, WiMAX, and C-band applications. A three-pole Chebyshev parallel-coupled microstrip bandpass filter was designed at a center frequency of 3.2 GHz and used as the basis to validate the gapping effect on the filter response which also achieves a narrower bandwidth for the second harmonic. Finally, the filter performance with minimized coupling gap is compared to a filter enhanced by the insertion of apertures in the ground plane. Generally speaking, good agreement was accomplished between simulated, calculated, and measured results.

ANALYTICAL INVESTIGATION OF PERIODIC COPLANAR WAVEGUIDES

This paper presents an analytical formula to evaluate evenand odd-mode characteristics of infinitely parallel coplanar waveguides (CPW) with the same dimensions in each CPW, given name as periodic coplanar waveguides (PCPW). The analysis yields a closed-form expression based on the quasi-TEM assumption and conformal mapping transformation. Calculated results show that both the evenand odd-mode characteristic impedances are in good agreements with the results generated by numerical solvers and available experimental data. The results are important especially for highly demand on miniaturization of circuit design to place multiple CPWs in parallel.

EM Parameters of Slotted Elliptical Tube-Lines

This article presents the electromagnetic parameters (EM) of slotted elliptical tube-lines (SETL) using the method of moments (MoM) in two dimensions. This technique is adapted to study the complex configuration of the line's system, which does not have a simple analytical solution. The modeling of the SETL structure consists in analyzing the even- and odd-mode characteristic impedances (Z0e, Z0o), the coupling coefficient (k), and the primary inductive and capacitive matrices ((L) and (C)). The EM parameters of the SETL shown into this article are essential for the design of couplers, resonators, and probes among other microwave and wireless components. To demonstrate the SETL in applications, the line's system was used as a directional coupler and as an MRI probe. The coupler was designed with 10-dB coupling and excellent performance in terms of high directivity and good isolation whereas the MRI probe was designed to operate at 340 MHz (proton imaging at 8 T) and has -66.7 dB minimum reflection and unloaded quality factor (Qo) more than 500 at 328 MHz.

Ultra-Wideband Bandpass Filter with Sharp Attenuation Slope Using Inter-Digital Finger Resonator and Parallel-Coupled Lines

This paper presents an ultra-wideband (UWB) bandpass filter (BPF) with sharp attenuation slope characteristics. The circuit structure consists of an inter-digital finger resonator, parallel-coupled lines and phase matching line. The design of the bandwidth was described by using the even and odd mode characteristic impedances in the resonator structure. The parallel-coupled lines were also designed in the same manner. The parameters of the resonator and two parallel-coupled lines in combination as the BPF were then optimized by the simulation with HFSS. The designed BPF was experimentally fabricated and its measured performances showed the bandwidth from 3.6 to 10GHz with the 20dB outband rejection. For the U.S. UWB band design, the matching line was inserted between the two parallel-coupled lines. The matching at both band edges was then qualitatively analyzed on the smithchart. The HFSS simulation results of the structure realized the bandwidth from 3.1 to 10.6GHz with sharp attenuation slope characteristics for SWR < 2.0. The measurement results agree well with the simulation results.

A novel model for a planar wideband Marchand balun

A new lumped element model for conventional Marchand baluns is presented. Analyzed by the even- and odd-mode method, the equivalent equations are derived for λ/4 coupled lines. Based on the proposed 5th-order lumped equivalent circuit for λ/4 coupled lines, the self-inductance, mutual inductive coupling and the capacitance can be calculated according to the even- and odd-mode characteristic impedance, therefore, the model parameters of the balun can be easily gained from the derived equations. To verify the model, a GaAs monolithic wideband Marchand balun was implemented and tested. The EM simulation and experimental results show a good agreement with the model simulation. This model is available in a wide frequency range and makes the design procedure of the Marchand balun faster and easier.

Dispersive Delay Line With Effective Transmission-Type Operation in Coupled-Line Technology

This letter reports on a new design method for dispersive delay lines in coupled-line technology. Based on the reflective chirped delay line concept, a continuous modulation of the even- and odd-mode characteristic impedances in symmetrical coupled-lines is shown to produce a new structure that presents a flat magnitude response and a linear group-delay variation along the operation frequency band. The use of coupled-lines avoids the need for a circulator giving rise to more practical devices, where the processed signal is redirected to the coupled port instead of being reflected back to the input port, thus providing a valuable effective transmission-type operation. The technique of designing a device is validated for ultra-wideband signal processing applications.

An Analytical Approach for a Novel Coupled-Line Dual-Band Wilkinson Power Divider

A novel generalized coupled-line circuit structure for a dual-band Wilkinson power divider is proposed. The proposed power divider is composed of two coupled lines with different even- and odd-mode characteristic impedances and two lumped resistors. Using rigorous even- and odd-mode analysis, the analytical design equations for this proposed power divider are obtained and the ideal closed-form scattering parameters are constructed. Since the traditional transmission line is a special case of coupled line (coupled coefficient is zero), it is found that traditional noncoupled-line dual-band (including single band) Wilkinson power dividers and previous dual-band coupled-line power dividers are special cases of this generalized power divider. As a typical example, which could only be designed by using this given design equations, a compact microstrip 3-dB power divider operating at both 1.1 and 2.2 GHz is designed, fabricated, and measured. There is good agreement between calculated and measured results.

CROSSTALK AND DISCONTINUITIES REDUCTION ON MULTI-MODULE MEMORY BUS BY PARTICLE SWARM OPTIMIZATION

Due to high-density routing under the CPU and DIMM areas, the original design of even and odd mode characteristic impedances changes. The occurrence of multi-drop problem between the CPU and memory chip causes over- and under-driven that reduce the eye opening. Furthermore, the difierent phase velocities of even- and odd-modes cause timing jitter at the receiver end. This paper proposes two steps to solve the complex issue of signal integrity for the multi-module memory bus. First, particle swarm optimization (PSO) is used to tune the characteristic impedance of the transmission line and on-die termination (ODT) values to improve transmission line impedance changes to obtain maximum power delivery. The fltness function of the algorithm is deflned by selecting the minimum re∞ection coe-cient at the driver side and maximum the transmission coe-cient at the receiver side to reduce the over- and under-driven Second, the timing jitter can be reduced by placing a capacitor to compensate for the velocity difierence caused by difierent propagation modes. Finally, signal integrity enhancements for the DDR3 are verifled by measuring S parameters in the frequency domain and postprocessed eye diagrams in the time domain.

A NOVEL HIGH-POWER AMPLIFIER USING A GENERALIZED COUPLED-LINE TRANSFORMER WITH INHERENT DC-BLOCK FUNCTION

The purpose of this paper is to propose a novel generalized single-band transformer for two arbitrary complex load and source impedances and a novel high-power amplifler using this new transformer. By adding two reactive parts at across terminals, the coupled line with ∞exible electrical length has practical even- and odd-mode characteristic impedances. Thus, the total circuit layout can be realized on common printed circuit board without any restriction. The synthesis theory of this proposed transformer is complete and analytical. Furthermore, unlike conventional quarter- wavelength transformers, this structure exhibits four main features such as efiective matching for extremely low-resistive load impedance, efiective matching for extremely high-resistive load impedance, tunable characteristic for equivalent electrical length and inherent DC-block function. For theoretical veriflcation, several impedance transformers, which include some flxed operating-frequency cases and a tunable case, for smaller than 7Ohm or larger than 1500Ohm, are presented. As a typical experimental example, this analyzed transformer with inherent DC-block function has been applied in a 4-Watt power amplifler as output matching structure.

A Simple Microstrip Bandpass Filter with Analytical Design Theory and Sharp Skirt Selectivity

A simple coupled-line circuit configuration is proposed to design microstrip bandpass filter with sharp skirt selectivity in this paper. This novel circuit consists of two-section coupled lines with a common connected point. An equivalent odd-mode and even-mode analysis is applied to analyze transmission and reflection property, and the effective analytical scattering parameters' expressions are achieved. Design curves for this novel bandpass filter are given while six typical numerical examples are presented. The presented simulation results show that the reflection zeros in pass band and transmission zeros in stop band can be tuned by changing the even- and odd-mode characteristic impedances of these coupled lines. Finally, two microstrip bandpass filters with different transmission and reflection zeros are fabricated, measured and compared. The experimental results show excellent bandpass filtering property with sharpened rejection skirts and low insertion loss.