Coupled Line Structure Research Articles

Efficient characterization of millimeter-wave asymmetric coupled microstrip structures using the quasi-symmetric approach

To sustain the ever-increasing use of coupled-line structures in RF/microwave systems, efficient design tools should be developed. In this article, an original approach combining accuracy and speediness is proposed to shorten time-to-market design cycles when such structures are involved. By introducing the quasi-symmetric approach, CPU-time required to analyze asymmetric coupled-lines can be significantly reduced, leading to faster models without sacrificing the overall design accuracy. To achieve this aim, a rigorous formulation was developed and, for the first time, trial functions of C- and π-modes were obtained from the quasi-symmetric case and applied to the asymmetric case. The proposed approach, easily implementable in commercial simulators, was demonstrated through comparisons with published data. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A novel wideband coupled-line Gysel power divider with function of impedance matching

A new coupled-line circuit structure is proposed to design compact wideband Gysel power dividers with function of impedance matching between source and load. Based on traditional even- and odd-mode technique, closed-form equations are obtained for direct and accurate synthesis. By applying coupled lines and reducing their electrical lengths, this novel Gysel power divider has four main advantages: high power-handling capability, small size, enhanced bandwidth, and source-to-load impedance matching. The measured bandwidth ( & dB) of the fabricated Gysel power divider operating at 2 GHz is 62.6%, while the traditional one is 40.8%. Meanwhile, the size of this novel Gysel power divider is only 25.5% of the traditional one when the same substrate is used and the same operating band is considered.

Compact ultra‐wideband bandpass filter with new coupled line structure for wireless

AbstractIn this letter, a new ultra‐wideband bandpass filter using microstrip parallel coupled line structure is proposed. The filter is constructed of only two sections of three‐coupled lines, which is a quarter wavelength long at the midband frequency. In addition, one of the outer coupled lines of each section is shorted to the ground. As a result, the filter exhibits two new symmetric transmission zeros around the passband, which increase the selectivity of both edges of the passband significantly. The transmission zeros can be located at the desired frequency by adjusting the width or the length of the coupled lines or also by changing the gap between them. The desired bandwidth can be obtained where the bandwidth is reversely proportional to the gap between the coupled lines. The design is successfully realized verified by full‐wave electromagnetic simulation and the experiment. A good agreement between the expected and measured results is obtained, and it validates the efficiency of the proposed new coupled line structure and corresponding filter design technique. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1319–1321, 2012

부분방전 모니터링 시스템을 위한 광대역 RF 소자설계 연구

In this paper we present the design of Low Noise Amplifier(LNA), mixer and filter for RF front-end part of partial discharge monitoring system. The monitoring system of partial discharge in high voltage power machinery is used to prevent many kinds of industrial accidents, and is usually composed of three parts - sensor, RF front-end and digital microcontroller unit. In our study, LNA, mixer and filter are key components of the RF front-end. The LNA consists of common gate and common source-cascaded structure and uses the resistive feedback for broad band matching. A coupled line structure is utilized to implement the filter, of which size is reduced by the meander structure. The mixer is designed using dual gate structure for high isolation between RF and local oscillator signal.

Directional Coupler Compensation With Optimally Positioned Capacitances

An accurate design synthesis for the phase velocity compensation in coupled line microstrip couplers by means of parallel capacitances is presented. In contrast to previous approaches, an a priori arbitrary placement of the capacitances along the coupled line structure is considered. By optimizing these positions, the directivity-bandwidth performance is significantly improved. Cases with two and three capacitances are treated extensively. The findings are used to generalize the compensation scheme to any number of capacitances. Throughout the analysis, the parasitic even-mode capacitance is taken into account using a realistic model. Several design examples are presented. Simulation results are confirmed by measurements. They compare favorably with those reported previously.

위상특성을 이용한 공진기의 외적 양호도(Qe) 추출 방법

본 논문에서는 마이크로스트립 선로 공진기와 입출력 단자의 결합 위치에 따른 공진기의 외적 양호도를 위상 특성을 이용하여 구하는 방법을 제시한다. 마이크로파 필터 설계에서 단자 접속 구조로 많이 이용되는 접합 선로 구조와 결합 선로 구조에 대해 단자의 위치와 선로의 폭과 간격에 따른 결과를 제시한다. 이 방법으로 정확한 <TEX>$Q_e$</TEX> 값을 얻을 수 있었고, 이 결과는 결합공진기 필터 설계에 응용될 수 있다. The external quality factor (<TEX>$Q_e$</TEX>) is controlled by coupling condition between resonator and input/output ports in design of microwave filter. In this paper, we represent extracting method of external quality factor using phase response for resonator with input/output ports according to position of feed line from microstrip line resonator. The results regarding to position, coupling gap and line width for tapped line and coupled line structure are represented, and we got the exact <TEX>$Q_e$</TEX> value from the this method. This results will be applied to coupled resonator filter design.

A Compact Printed Filtering Antenna Using a Ground-Intruded Coupled Line Resonator

A compact printed filtering antenna with high band-edge gain selectivity is presented. Occupying about the same substrate area as a conventional antenna, the proposed structure not only serves as a radiator but also a second-order bandpass filter, with one filter pole provided by a Γ-shaped antenna and the other by a newly proposed coupled line resonator. High band-edge selectivity is achieved due to two additional stop-band transmission zeros provided by the coupled line resonator. To minimize the required area and reduce the spurious radiation, a coupled line structure composed of a microstrip line and a coplanar waveguide by broadside coupling is adopted and intruded into the Γ-shaped antenna area. According to the filter specifications, a design procedure for the proposed filtering antenna is depicted in detail. One example at 2.45 GHz with a second-order Chebyshev bandpass filter of 0.1 dB equal-ripple response is tackled. As compared to the conventional Γ -shaped antenna, the proposed filtering antenna not only possesses a similar antenna gain but also provides better band-edge gain selectivity and flat passband gain response. The measured results, including the S-parameters, total radiated power, and antenna gains versus frequency, have good agreement with the designed ones.

Design of Compact Quadruplexer Based on the Tri-Mode Net-Type Resonators

A compact size and high isolation microstrip quadruplexer based on the tri-mode net-type resonators is proposed in this letter. The quadruplexer is composed of four folded tri-mode net-type resonator filters with one input and four output coupled-line structures. By adjusting the structural parameters of a single tri-mode net-type resonator, its first three resonant frequencies can be controlled and, thus, it can be utilized to implement a third-order bandpass filter when these resonant frequencies are suitably assigned. The proposed third-order bandpass quadruplexer is constructed by only four tri-mode resonators, showing a small circuit size. In addition, no additional five-pole matching junction is needed for the quadruplexer design. As a result, the proposed quadruplexer occupies an extremely small area, i.e., 0.27 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> by 0.09 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (0.42 λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</i> by 0.13 λ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</i> ), while still keeping good isolation better than 40 dB for each channel.

Anomalous Negative Group Velocity in Coupled Positive-Index/Negative-Index Guides Supporting Complex Modes

Anomalous negative group velocity (NGV; group velocity antiparallel to the power flow) is reported in a guided-wave structure supporting complex modes. This structure consists of a coupled-line system comprising a positive-index microstrip line edge coupled to a negative-index line. The NGV can be observed on the positive-index line under suitable excitation and termination conditions. What is remarkable about this structure is that the anomalous NGV neither requires any material losses nor any strong reflections on the observed line. This work verifies that absorption or reflection are not necessary conditions for observing NGV, rather NGV can be observed in specific lossless coupled-line structures as well. The general conditions for obtaining NGV in coupled positive-index/negative-index guides are analytically derived and corresponding NGV observations are experimentally reported at microwave frequencies. Specifically, we report the propagation of modulated pulses exhibiting a negative group delay as well as phase shifters maintaining a constant phase over a broad bandwidth. This opens up the possibility of utilizing such coupled-line guides for applications in pulse shaping, delay control, constant phase shifters (vs. frequency) and reducing beam squinting in series-fed antenna arrays.

Mode Symmetry Analysis and Design of CMOS Synthetic Coupled Transmission Lines

This paper presents the mode symmetry analysis and design of CMOS synthetic coupled lines that are meandered for the miniaturization design. The conventional even-odd mode analysis is not appropriate to apply due to the meandering structure, which is asymmetric. The asymmetric coupled-line model is therefore adopted for analyses and the equivalent model parameters are extracted based on <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ABCD</i> -parameters converted from scattering parameters. The proposed extraction procedure is then applied on a 3-dB directional coupler as a design example. The results quantitatively show that symmetry of the coupled lines is well maintained. Symmetry of other coupled-line structures that degrade coupled-line symmetry, such as loosely coupled lines and different bend direction, are also analyzed based on this model. Finally, an equal-length bend design suitable for the CMOS synthetic coupled lines is proposed and has managed to improve symmetry on various structures.

SIR을 이용한 평행결합 선로의 소형 광대역 대역통과 필터

In this paper, the reduced size of broad bandpass filter with parallel coupled line structure is presented. This proposed filter can control bandwidth of narrow to broadband by adjusting the coupling coefficient. The conventional filter is operated with a narrow band. If a higher bandwidth is desired than the conventional narrow bandwidth, it is hard to realize due to the coupling coefficient between feeding line and resonator. In this paper, to overcome this limitation, a proposed bandpass filter is designed with reduced size due to SIR (Stepped Impedance Resonator), U-shaped open stub with hair-pin and vertical-type structure than conventional one, and it has characteristics of adjusting bandwidth freely as per quantity of coupling coefficient. The proposed bandpass filter that, experimental results of insertion and return losses are 0.42 dB and 24.5 dB with bandwidth of 60 % at the center frequency of 5.8 GHz, respectively.

Compact bandstop filter using coupled-line section

A new compact bandstop filter with a coupled-line structure is proposed. Stopband rejection depth and bandwidth can be controlled by the configuration of the coupling section, and good return loss is realised by properly adjusting the impedances of two open-circuited stubs. Design equations are obtained using a lossless transmission line model. To validate the analysis, a bandstop filter with about 72% fractional bandwidth at 5 GHz has been fabricated. The implementation area is 0.32λ g × 0.18λ g .

Enhanced Coupling Structures for Tight Couplers and Wideband Filters

Tightly coupled lines are difficult to realize on the conventional printed circuit board (PCB). This paper proposes two types of novel enhanced coupled-line structures appropriate for tightly coupled directional couplers and wideband filters. The proposed coupled-line structures both have a rectangular ground-plane aperture and two inserted signal strips in the aperture to increase the coupling strength significantly. No fine lines and narrow gaps are required so as to fit the conventional PCB fabrication process. More importantly, the proposed structures only need a single-layer substrate. To demonstrate the feasibility of the proposed structures, one 3-dB directional coupler and two four-pole Chebyshev filters with 0.05-dB equal-ripple bandwidths of 40% and 37% are designed and realized. The coupler and filters are fabricated on a PCB substrate with a dielectric constant of 3.58 and a thickness of 0.508 mm. Good agreement between measurements and simulations is observed.

Compact design of dual-band power divider with coupled-line shunt elements

A novel design of a dual-band power divider with coupled-line shunt elements is proposed. This configuration features very compact size (over 1/2 size-reduction as compared to the conventional π- or T-shaped network and quarter-wave coupled-line structure) over a reasonable frequency ratio range. First, design theory is presented, and the simulated and measured results of an implemented microstrip power divider operating at 900 and 2000 MHz are given for verification of the proposed method.

Develop compact dual‐band bandpass filters on the aluminum oxide

AbstractFor the purpose of minimizing the dual‐band bandpass filters (2.4 and 5.7 GHz), two stepped impedance resonator structures are modified and involved in a pair of distorted coupled lines to form a compact structure.And because the designed filter is printed on the high quality factor and dielectric constant aluminum oxide ceramic substrate by the screen‐printing technique, the characteristics of the filters could be improved and the size of the filters could be minimized to only 22.2 × 12 mm2. Furthermore, the modified SIR structure can be used to tune the second resonant frequency (harmonic) for the applications of dual bands, and the modified coupled line structures can be used to excite additional transmission zeros and adjust its locations, which can improve the characteristics of the filters effectively. In this article, the optimum measured insertion loss and bandwidth for 2.4 GHz are −0.98 dB and 11.1%, respectively, and for 5.7 GHz are −1.05 dB and 10.1%, respectively. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1091–1094, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25126

Suspended stripline coupled lines with grounded strips for equalization of inductive and capacitive coupling coefficients

AbstractA suspended stripline coupled‐line structure has been proposed, which allows for achieving equalization of inductive and capacitive coupling coefficients in a wide range of directional couplers' coupling C. Three different variants of the proposed structure have been considered, and the results of numerical calculations using FD technique have been presented, which show the possibility of equalization of inductive and capacitive coupling coefficients. Moreover, graphs showing structural parameters are presented in a wide range of coupling coefficient k. The results of investigations have been confirmed by the measurements of the designed 15‐dB directional coupler. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:874–877, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25085

개선된 바랙터 결합 선로를 이용한 Ku-Band 헤어핀 발진기 설계

본 논문에서는 개선된 바랙터 결합 선로를 제안하고, 이 구조를 사용한 주파수 합성기를 설계 제작하였다. 제안된 결합 선로는 기존 구조에 추가적인 <TEX>$\lambda$</TEX>/4 전송 선로를 이용하여 바랙터에서 반사되는 잡음신호를 제거하는 구조이다. 제작한 주파수 합성기는 Ku-band 대역에서 헤어핀 공진기를 사용하였으며, PLL을 사용하여 주파수를 고정하였다. 제안된 구조로 제작한 헤어핀 발진기의 경우, 38 MHz의 주파수 조정 범위와 100 kHz offset에서 -97 dBc/Hz의 위상 잡음을 나타내었다. 이러한 측정 결과는 제작한 기존 구조의 바랙터 결합 선로를 가지는 헤어핀 발진기보다 30 MHz 개선된 주파수 조정 범위와 8 dB 개선된 위상 잡음 특성을 가지는 것으로 확인되었다. In this paper, we propose a new varactor coupled line structure and design the VCO using the proposed structure. The proposed coupled line structure removes the reflected signals from the varactor diode using an added <TEX>$\lambda$</TEX>/4 transmission line. The frequency synthesizers are designed using the PLL technique at Ku-band. The synthesizer using the proposed coupled structure has 38 MHz frequency tuning range and -97 dBc/Hz phase noise characteristic at 100 KHz offset frequency. The measured results show improved tuning range as well as the improved phase noise characteristics compared to the conventional designs.

W‐band compact bandpass filters on thin‐film substrate

AbstractIn this article, the miniaturized resonator and bandpass filter for W‐band application are suggested and evaluated on thin‐film substrate.In the meanwhile, the resonator using the loading capacitor with the electrical length of 2λg/9 and the other resonator using broadside coupled line structure of λg/9 are designed and applied for the compact filter evaluation. The filter using the capacitor‐loaded resonators with the dimension of 0.2 × 0.5 mm2 shows the insertion loss of 2.1 dB at 94 GHz, and the return loss better than 10 dB at the frequencies between 91 and 98 GHz. For the filter using broadside coupled line resonators with the size of 0.33 × 0.24 mm2, the insertion loss is 2.3 dB at 92 GHz and the return loss is better than 10 dB in at the frequencies between 85 and 99 GHz. These filters show very compact dimensions retaining the filter performance commensurate with those of the filters in previous works. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 750–753, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25011

A 10:1 Unequal Wilkinson Power Divider Using Coupled Lines With Two Shorts

Abstract-A novel unequal Wilkinson power divider is presented. A coupled-line section with two shorts is proposed to realize the high characteristic impedance line, which cannot be implemented by conventional microstrip fabrication technique due to fabrication limitation. The proposed coupled-line structure is compatible with single layer integration and can be easily designed based on an even-odd mode analysis. As a design example, a 10:1 Wilkinson power divider at 2 GHz is fabricated and measured. The measured -10 dB bandwidth of S11 is about 16%, and the isolation S32 is better than -20 dB. The measured amplitude balance between output port 2 and port 3 is between -10.20 dB and -9.52 dB, and the corresponding phase difference is between 0deg and 4.6deg.

Accurate Synthesis of Four-Line Interdigitated Coupler

We present an accurate synthesis method for the design of a four-line interdigitated coupler in this paper. With the derivation of an admittance matrix of four coupled transmission lines and the use of an interconnecting condition, only half of the original coupled-line structure should be considered with its symmetric plane replaced by a perfect electric wall and/or perfect magnetic wall. Subsequently, two new mode admittances are, respectively, calculated from the propagation constants and the line impedances of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</i> - and pi-modes, which are extracted from full-wave simulation. In this way, a reference chart is generated that presents the relation between the two mode admittances and physical dimensions of the coupled lines. With any prescribed performance, the physical dimensions of a four-line interdigitated coupler can effectively be synthesized by looking up this reference chart. Two examples are given to demonstrate the accuracy and flexibility of our proposed scheme. One is a conventional 3-dB four-line Lange coupler fabricated by a miniature hybrid microwave integrated circuit process. The other is a composite microstrip coplanar waveguide coupler made by a standard printed circuit board process. For both couplers, simulated and measured results are in good agreement. The proposed method is useful for the accurate synthesis and design of four-line couplers having an interdigitated topology.