High-impedance Transmission Line Research Articles

Design of High-Performance Lowpass Filter Using Inter-Coupled Compact Microstrip Resonator Cells

This paper presents a high-performance lowpass filter (LPF) using periodical inter-coupled compact microstrip resonator cells (CMRCs) in series. The CMRC consists of high impedance transmission line and symmetrical T-shaped structure at both sides with ended transmission line arms. By using a bridge structure to introduce controllable inter-coupling between the adjacent tapered CMRC units, the proposed CMRC structure exhibits quasi-elliptic lowpass response with improved stopband performance. Final design of an exemplary LPF using proposed design structure and methodology verify the feasibility of the structure and its high performance including compact structure, low insertion loss, sharp transition and expanded stopband.

Low Actuation Wideband RF MEMS Shunt Capacitive Switch

A wide bandwidth low actuation voltage RF MEMS capacitive shunt switch is designed and simulated. The proposed switch is designed for a low actuation voltage of 12 volts applicable to wireless systems. High frequency characteristics of the RF MEMS switches can be specified by coupling capacitors in up-state position Cu. This capacitor is in trade-off with actuation voltage. In the proposed switch, the capacitor is compensated by incorporating two short high impedance transmission lines as a T matching circuit. Simulating the switch demonstrates great improvement in RF characteristics of the switch particularly in reflection coefficient in up-state position.

A Miniaturized 3 dB Branch-Line Hybrid Coupler With Harmonics Suppression

This letter presents a miniaturized 3 dB branch-line hybrid coupler with second harmonic suppression using high-impedance transmission lines and interdigitated shunt capacitors. By using the interdigitated capacitors shunt with the transmission lines, further minimization of the 3 dB branch-line hybrid coupler can be achieved compared with previously reported techniques. The design of the interdigitated shunt capacitors requires concurrent optimization of the capacitance to the ground and the edge-coupling interdigitated capacitance between the ports. For validation, a miniaturized 3 dB branch-line hybrid coupler at 836.5 MHz was designed and implemented. The proposed 3 dB branch-line hybrid coupler achieved a compact size of 27.75 mm × 25.7 mm, or equivalently 0.077λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> ×0.072λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> is the free-space wavelength. Moreover, the coupler can suppress second harmonic components by 20 dB while maintaining similar measured performance compared to the conventional branch-line hybrid coupler.

Velocity-Matching Enhancement in Cascaded Integration of EAMs and SOAs Using Bypass High Impedance Transmission Lines

Velocity-matching effect in cascaded integration (CI) of electroabsorption modulators (EAMs) and semiconductor optical amplifiers (SOAs) utilizing bypass high impedance transmission lines (HITLs) is analyzed and demonstrated in this work. By experimentally and theoretically comparing different types of CI structures, the retarded phase in slower microwave waveguide of EAMs can be compensated from the fast waveguide of HITL to match the optical wave in EAM and SOA waveguides, improving high-speed electrooptical (EO) conversion. It thereby suggests high-frequency EO response of CI structure can be beneficial from not only the impedance-matching, but also further phase-matching condition. A 1.3-mm-long SOA-integrated EAM with phase retardation of less than 0.2 radii at 40 GHz and impedance matching has been demonstrated, leading to a -3-dB EO bandwidth of 46 GHz. It suggests that a controllable phase delay through HITL can be used for releasing the design burden of the long-integrated optoelectronic devices for high-speed high-efficient performance.

Wide stopband compact microstrip lowpass filter using circular ring resonator and split ring resonators

In this contribution, a microstrip low-pass filter with a wide stop-band using split ring resonators and a circular ring resonator is introduced. The passband ripple of proposed filter was measured 0.6 dB and minimum insertion loss of passband is about 0.75 dB at 0.5 GHz frequency. Moreover, the 1.0 dB cut off frequency of proposed filter is 1.45 GHz in measurement. Designing this type of low-pass filter requires a high impedance transmission-line. However, the microstrip line width cannot be taken less than 0.2 mm in practical implementation. This causes to a small mismatch in passband. Furthermore, these results show wide stop-band up to 9.0 GHz with more than 30 dB rejection. The dimensions of proposed compact filter are about 12.5×30 mm2 (excluding extra substrate width). The proposed filter is a microstrip filter and can compete with defected ground structure (DGS) or defected microstrip structures lowpass filters in miniaturizing and wide stopband. However, the DGS or DGS filters have some problems in manufacturing applications such as radiation fields from defected structures and requiring a specific box. In addition, a distributed equivalent circuit model based on geometrical filer parameters is introduced, and good agreement can be seen between EM simulation and distributed equivalent circuit model up to 6.0 GHz frequency. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26203

The mesa merging oxidation method for creating low-loss dielectrics and transmission lines on low-resistivity silicon

A mesa merging oxidation method has been developed to create large low-loss SiO2 dielectrics on low-resistivity silicon. In the mesa merging method, thermal oxidation converts an array of silicon mesas into a solid block of SiO2. The SiO2 dielectrics are combined with further micromachining steps to create high aspect ratio coplanar waveguide (hicoplanar) transmission lines. The large SiO2 dielectrics enable high-impedance and low-loss hicoplanar transmission lines to be created with this method. Hicoplanar transmission lines with high impedance of 80 Ω and loss less than 1 dB cm−1 up to 67 GHz have been successfully fabricated.

To compact branch‐line couplers using parallel high‐impedance transmission lines

AbstractIn this article, a new way is proposed to compact the transmission lines of microstrip devices such as branch‐line couplers (BLCs).In this way, two unequal‐length high‐impedance (thin) transmission lines paralleling with each other are used instead of a single transmission line. The shorter and greater lines can be implemented in a right and meander forms, respectively. The usefulness of the proposed way was verified by designing, simulation, and fabrication of a compacted BLC at frequency 2 GHz. An area compactness of about 64.2% is achieved. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1996–1999, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25369

Dual-Band Impedance Transformer Using Two-Section Shunt Stubs

This study presents a modified shunt-stub dual-band impedance transformer. The load impedances can be complex and unequal at two uncorrelated frequencies. The proposed transformer has two parts; each part is composed of a two-section transmission line. Similar to the single-stub matching network at a single frequency, a two-section transmission line is connected to the load and transforms the load impedances to normalized unit conductance at the two designated frequencies simultaneously. The resulting susceptances are then canceled out simultaneously by a two-section shunt stub at the two frequencies. The required nonlinear simultaneous equations are derived and solved to obtain the physical parameters of transmission lines. Rearranging the simultaneous equations to construct an objective function with only one unknown variable makes it easier to solve the equations. This approach avoids high-impedance transmission lines by choosing the characteristic impedance of each transmission line first. Return losses for various load impedances are simulated to validate the proposed structures. Good agreements between numerical and measured results validate the proposed structure.

Capacitive RF MEMS Switches Fabricated in Standard 0.35-$\mu{\hbox{m}}$ CMOS Technology

The objective of this paper is to investigate the integration of capacitive type RF microelectromechanical systems (MEMS) switches in a standard CMOS technology. A maskless monolithic integration process dedicated to electrostatically actuated capacitive type RF MEMS switches is developed and optimized. The fabricated switches consist of composite metal-dielectric warped membranes. The warped-plate structure is used to increase the capacitance ratio of the switch. The switches are fabricated using the interconnect metal and dielectric layers available in a standard 0.35-μm CMOS process. Measurement results for the first switch show an insertion loss less than 0.98 dB, a return loss below 13 dB up to 20 GHz in the up-state, and a down-state isolation of 12.4-17.9 dB from 10 to 20 GHz. The capacitance ratio is enhanced up to 91:1 using the warped-plate structure. A second cascaded switch consisting of two shunt capacitive switches and a slow-wave high-impedance transmission line section is designed and fabricated for high-isolation applications. The measured insertion loss for this switch is less than 1.41 dB up to 20 GHz, the return loss is below 19 dB, and the isolation is 19-40 dB across the frequency band from 10 to 20 GHz. The proposed RF MEMS switches can be used in millimeter-wave CMOS RF front-ends where multiband functionality and reconfigurability is required.

Compact and Wideband DC Bias Line Based on Defected Ground Structure

In this paper, a technique using a novel cross-shaped defected ground structure (DGS) to broaden the operating bandwidth and reduce the size of a conventional DC bias line is proposed. The conventional DC bias line is composed of a λ/4 high impedance transmission line and a proper fan-shaped capacitor. Due to the slowwave characteristics introduced by the DGS, the original length of the λ/4 high impedance transmission line can be shortened while maintain the same electrical length. The experimental result shows that the proposed DC bias line has a much wider operating bandwidth than that of the conventional one by 153% and 83.3% of the initial λ/4 length.

Analysis and Design of a Chip Filter With Low Insertion Loss and Two Adjustable Transmission Zeros Using 0.18-$\mu{\hbox{m}}$ CMOS Technology

This paper presents the structure of a high-selectivity bandpass filter that is fabricated on low-resistivity silicon substrate with a commercial CMOS technology. The filter is constructed using crossed coplanar waveguide (CPW) lines and metal-insulator-metal capacitors to ensure that it has the desired passband characteristics. An adjustable capacitor between the input and output ports is employed to form a capacitive cross-coupled path, yielding two transmission zeros in the lower and upper stopbands, respectively. Additionally, the coupling mechanism can be modified by turning on or off the gate of an nMOS transistor to adjust the positions of the transmission zeros by applying an externally controlled voltage. To obtain a low passband loss and to minimize the chip size, high-impedance CPW transmission lines are adopted. Our analysis indicates that the CPW line possesses more advantages than the preferred stacked-ground CPW line for constructing the proposed filter. A very compact X -band experimental prototype with a size of 0.88 × 0.54 mm2 was designed and fabricated. The measurements reveal an insertion loss of less than 3.2 dB in the passband, which is from 10.6 to 12.7 GHz, and rejection levels greater than 35 dB at the designed frequencies of transmission zeros. Moreover, the lower and upper transmission zeros can be shifted from 5 to 6.5 GHz and from 18 to 21.4 GHz, respectively, by changing the controlled voltage.

Equivalent Transmission-Line Sections for Very High Impedances and Their Application to Branch-Line Hybrids with Very Weak Coupling Power

As operating frequency is raised and as more integration with active and passive elements is required, it becomes difficult to fabricate more than 120 <TEX>${\Omega}$</TEX> characteristic impedance of a mierostrip line. To solve this problem, an equivalent high impedance transmission-line section is suggested, which consists mainly of a pair of coupled-line sections with two shorts. However, it becomes a transmission-line section only when its electrical length is fixed and its coupling power is more than half. To have transmission-line characteristics(perfect matching), independently of coupling power and electrical length, two identical open stubs are added and conventional design equations of evenand odd-mode impedances are modified, based on the fact that the modified design equations have the linear combinations of conventional ones. The high impedance transmission-line section is a passive component and therefore should be perfectly matched, at least at a design center frequency. For this, two different solutions are derived for the added open stub and two types of high impedance transmission-line sections with 160 <TEX>${\Omega}$</TEX> characteristic impedance are simulated as the electrical lengths of the coupled-line sections are varied. The simulation results show that the determination of the available bandwidth location depends on which solution is chosen. As an application, branch-line hybrids with very weak coupling power are investigated, depending on where an isolated port is located, and two types of branch-line hybrids are derived for each case. To verify the derived branch-line hybrids, a microstrip branch-line hybrid with -15 dB coupling power, composed of two 90<TEX>$^{\circ}$</TEX> and two 270<TEX>$^{\circ}$</TEX> transmission-line sections, is fabricated on a substrate of <TEX>${\varepsilon}_r$</TEX>= 3.4 and h=0.76 mm and measured. In this case, 276.7 <TEX>${\Omega}$</TEX> characteristic impedance is fabricated using the suggested high impedance transmission-line sections. The measured coupling power is -14.5 dB, isolation and matching is almost perfect at a design center frequency of 2 GHz, showing good agreement with the prediction.

Novel monolithic integration scheme for high-speed electroabsorption modulators and semiconductor optical amplifiers using cascaded structure

A new monolithic integration scheme, namely cascaded-integration (CI), for improving high-speed optical modulation is proposed and demonstrated. High-speed electroabsorption modulators (EAMs) and semiconductor optical amplifiers (SOAs) are taken as the integrated elements of CI. This structure is based on an optical waveguide defined by cascading segmented EAMs with segmented SOAs, while high-impedance transmission lines (HITLs) are used for periodically interconnecting EAMs, forming a distributive optical re-amplification and re-modulation. Therefore, not only the optical modulation can be beneficial from SOA gain, but also high electrical reflection due to EAM low characteristic impedance can be greatly reduced. Two integration schemes, CI and conventional single-section (SS), with same total EAM- and SOA- lengths are fabricated and compared to examine the concept. Same modulation-depth against with EAM bias (up to 5V) as well as SOA injection current (up to 60mA) is found in both structures. In comparison with SS, a < 1dB extra optical-propagation loss in CI is measured due to multi-sections of electrical-isolation regions between EAMs and SOAs, suggesting no significant deterioration in CI on DC optical modulation efficiency. Lower than -12dB of electrical reflection from D.C. to 30GHz is observed in CI, better than -5dB reflection in SS for frequency of above 5GHz. Superior high-speed electrical properties in CI structure can thus lead to higher speed of electrical-to-optical (EO) response, where -3dB bandwidths are >30GHz and 13GHz for CI and SS respectively. Simulation results on electrical and EO response are quite consistent with measurement, confirming that CI can lower the driving power at high-speed regime, while the optical loss is still kept the same level. Taking such distributive advantage (CI) with optical gain, not only higher-speed modulation with high output optical power can be attained, but also the trade-off issue due to impedance mismatch can be released to reduce the driving power of modulator. Such kind of monolithic integration scheme also has potential for the applications of other high-speed optoelectronics devices.

Use of High-Impedance Surfaces in Electromagnetic Compatibility Applications

This paper presents the results of an investigation into numerical simulation tools for high-impedance surfaces (HIS), with the primary aim of assisting in the design and optimization of these structures in electromagnetic compatibility (EMC) applications. The mathematically simple stub technique was used for capacitors and inductances to model lumped L and C in transmission line configurations. The basic principles of the transmission line modeling (TLM) method, such as the equivalences between the field quantities and circuit parameters, are briefly discussed and are applied on a uniform and a high-impedance transmission lines.

Application of the Sensitivity Analysis to the Optimal Design of the Microstrip Low-Pass Filter With Defected Ground Structure

This paper shows applied sensitivity analysis for easier design and practical application of a planar half-wavelength low-pass filter (LPF) using defected ground structure (DGS). Typically, it is difficult to deploy planar half-wavelength low-pass filters when high power durability is required because of the very narrow line-widths of high impedance transmission line. Here, we propose a new configuration for the high impedance microstrip line using DGS structure to allow broader line width and high power handling capability. The sensitivity of the scattering parameters was calculated using the self-adjoint sensitivity formula in order to determine the proposed filter's dimension. The paper also highlights the validity of the proposed LPF optimization with its measured performance.

A Design Methodology for Miniaturized 3-dB Branch-Line Hybrid Couplers Using Distributed Capacitors Printed in the Inner Area

This paper proposes a methodology to design and optimize the footprint of miniaturized 3-dB branch-line hybrid couplers, which consists of high-impedance transmission lines and distributed capacitors. To minimize the physical size of the coupler, the distributed capacitors are placed within the empty space of the hybrid. The proposed design methodology calls for the joint optimization of the length of the reduced high-impedance transmission lines and the area of the distributed capacitors. A prototype at S-band was designed and built to validate the approach. It showed a size reduction by 62% compared with the conventional 3-dB branch-line hybrid coupler while providing similar performance and bandwidth.

Understanding Power-System Stability

This paper discusses power-system instability and the importance of fast fault-clearing performance to aid in reliable production of power. An explanation regarding small-signal stability, high-impedance transmission lines, line loading, and high-gain fast-acting excitation systems is provided. Transient stability is discussed, including synchronizing and damping torques. The power-angle curve is used to illustrate how fault-clearing time and high initial response excitation systems can affect transient stability. The term ldquopower-system stabilityrdquo has become increasingly popular in generation and transmission. The sudden requirement for power-system stabilizers (PSSs) has created confusion about their applicability, purpose, and benefit to the system. This paper discusses the fundamentals of the PSS and its effectiveness. In today's paper industry, PSSs are being applied on larger machines in the northwest United States and Canada.

Wideband radar absorbing material combining high-impedance transmission line and circuit analogue screen

A novel design for thin and wideband absorbers is presented. The proposed absorber is a two-dimensional periodic array of unit cells, which are a combination of the high-impedance transmission line and the circuit analogue screen. The combined absorber exhibits a multiple-resonant characteristic and provides a very wide absorbing bandwidth. Measured results show that this new absorber has a bandwidth of 108% for 10 dB radar cross-section reduction with a thickness of only 7.1 and 23.7% of the free-space wavelengths at the lowest and highest operating frequencies.

Microwave Group Delay Time Adjuster Using Parallel Resonator

This letter describes the design of a group delay time adjuster (GDTA) using a parallel resonator. The GDTA consists of a variable capacitor and a variable equivalent inductor. These components are controlled by two bias voltages separately. The variable equivalent inductor is realized using a high impedance transmission line terminated with the variable capacitor. Group delay time can be adjusted by varying the capacitance and the inductance while keeping the fixed resonance frequency. When the proposed GDTA is fabricated on the Korean RFID frequency band (908.5-914MHz), we could obtain about 3ns group delay time variation with excellent flatness

New approach for modelling distributed MEMS transmission lines

The paper presents a new and more accurate model for the distributed MEMS transmission line (DMTL) structures. In this new model, the MEMS bridges that are used as the loading elements of the DMTL structures are represented as low-impedance transmission lines, rather than a lumped CLR circuit. The model also includes LC networks at the transition points from the MEMS bridges to the unloaded parts of the DMTL, which are simply high-impedance transmission lines. These LC networks are employed to model the effects of the impedance discontinuities. The accuracy of the model is verified with simulations and measurements in the range 1-20 GHz on various DMTL structures that are fabricated with an RF MEMS process based on electroforming on a glass substrate. The measurement results of the fabricated devices are in good agreement with the model with an error less than 5%. It is shown that this new model provides better agreement than the conventional method for the DMTL structures with a bridge width larger than 50 /spl mu/m.