Transmission Line Stub Research Articles

Strong nonlinear effects of a transmission line stub on resonant tunneling diode oscillators

Strong nonlinear effects of a transmission line stub on resonant tunneling diode oscillators

Implementing High Q-Factor HTS Resonators to Enhance Probe Sensitivity in 13C NMR Spectroscopy

Nuclear magnetic resonance spectroscopy (NMR) probes using thin-film high temperature superconducting (HTS) resonators provide exceptional mass sensitivity in small-sample NMR experiments for natural products chemistry and metabolomics. We report improvements in sensitivity to our 1.5 mm 13C-optimized NMR probe based on HTS resonators. The probe has a sample volume of 35 microliters and operates in a 14.1 T magnet. The probe also features HTS resonators for 1H transmission and detection and the 2H lock. The probe utilizes a 13C resonator design that provides greater efficiency than our previous design. The quality factor of the new resonator in the 14.1 T background field was measured to be 4,300, which is over 3x the value of the previous design. To effectively implement the improved quality factor, we demonstrate the effect of adding a shorted transmission line stub to increase the bandwidth and reduce the rise/fall time of 13C irradiation pulses. Initial NMR measurements verify 13C NMR sensitivity is significantly improved while preserving detection bandwidth. The probe will be used for applications in metabolomics.

Ultra-Wideband Bandpass Filters Using Tapered Resonators

In this paper, ultra-wideband bandpass filters using tapered transmission line resonators are presented. The proposed filters are based on short-circuited tapered transmission line stubs. The use of tapered transmission resonators resulted in a noticeable length reduction, a wider controlled operational bandwidth, and better stopband characteristics for filter applications. Three filters are designed with different tapered ratios using exponential tapered transmission line resonators. The other three filters are also designed using equivalent linear tapered transmission line resonators. The designed filters are simulated and fabricated on a Roger RT5880 substrate with a 2.2 relative permittivity and 0.78 mm thickness. Approximately, the same performance is obtained using either exponential or linear tapered resonators. A good agreement between the simulated and measured results is reported. The realized 112.22% fractional bandwidth filter has a return loss (S11) better than 17 dB and an insertion loss (S12) better than 1 dB over the entire UWB spectrum. Notable improvements in stopband characteristics are also achieved.

Dual-broadband and single ultrawideband absorbers from the terahertz to infrared regime

This paper presents the design and analysis of broadband metamaterial absorbers with single and dual absorption bands from terahertz to infrared frequencies. The absorbers are made of a composite graphene/metallic structure. A metallic patch array is printed on a ground-plane-backed dielectric slab. A graphene patch array is stacked on top of the metallic array, whereas a dielectric spacer separates the graphene and patch spacer from each other. The tunable property of the graphene surface conductivity at terahertz frequencies together with the complex permittivity of metal at the infrared regime are used to design broadband absorbers from the terahertz to infrared regime. The design is based on the combination and excitation of the plasmon polaritons of graphene and metallic patterned arrays at terahertz and infrared frequency bands, respectively. Two broad absorption bands occur from 4.56–9.02 THz and 16.95–60.23 THz with the fractional bandwidths of 67% and 112%, respectively. Furthermore, by a proper design of the parameters, a single ultrawide absorption spectra from 6.6–58.13 THz can be achieved with a fractional bandwidth 160%. In order to validate the simulation results, a circuit model-based analysis is developed, where the patterned arrays are modeled as the surface admittances, and the dielectric spacers are modeled by transmission line stubs. The results obtained by the full-wave simulations in the high-frequency structure simulator are in good agreement with the circuit model results. The absorbers show great stability with respect to the incidence angle for both the transverse electric and transverse magnetic waves.

A Distributed Stubs Technique to Mitigate Flicker Noise Upconversion in a mm-Wave Rotary Traveling-Wave Oscillator

A rotary traveling-wave oscillator (RTWO) has an ability to generate multiple phases at millimeter-wave (mmW) frequencies while achieving low phase noise (PN). Unfortunately, due to the practically unavoidable transmission line (TL) dispersion, which causes the higher-order harmonics to travel faster than the fundamental, RTWOs suffer from flicker noise upconversion. In this article, we propose a “distributed stubs” technique to mitigate this mechanism in which tuning capacitors placed on the TL stubs away from the maintaining amplifiers will slow down the travel speed of higher-order harmonics relative to the fundamental, thus lowering the phase shifts due to the TL dispersion. We further provide a comprehensive analysis of the flicker noise upconversion mechanism due to the TL dispersion. The proposed 26.2-30-GHz RTWO is implemented in 22-nm fully depleted silicon-on-insulator (FD-SOI) CMOS with eight differential phases. At 30 GHz, it achieves PN of -107.6 and -128.9 dBc/Hz at 1- and 10-MHz offsets, respectively. This translates into figures-of-merit (FoMs) of 184.2 and 185.4 dB, respectively, for a single phase. The proposed architecture consumes 20 mW from 0.8-V supply. It achieves a flicker PN corner of 180 kHz, which is an order-of-magnitude better than currently achievable by state-of-the-art mmW RTWOs.

Optimization of high-channel count, switch matrices for multinuclear, high-field MRI.

Modern magnetic resonance imaging systems are equipped with a large number of receive connectors in order to optimally support a large field-of-view and/or high acceleration in parallel imaging using high-channel count, phased array coils. Given that the MR system is equipped with a limited number of digitizing receivers and in order to support operation of multinuclear coil arrays, these connectors need to be flexibly routed to the receiver outside the RF shielded examination room. However, for a number of practical, economic and safety reasons, it is better to only route a subset of the connectors. This is usually accomplished with the use of switch matrices. These exist in a variety of topologies and differ in routing flexibility and technological implementation. A highly flexible implementation is a crossbar topology that allows to any one input to be routed to any one output and can use single PIN diodes as active elements. However, in this configuration, long open-ended transmission lines can potentially remain connected to the signal path leading to high transmission losses. Thus, especially for high-field systems compensation mechanisms are required to remove the effects of open-ended transmission line stubs. The selection of a limited number of lumped element reactance values to compensate for the for the effect of transmission line stubs in large-scale switch matrices capable of supporting multi-nuclear operation is non-trivial and is a combinatorial problem of high order. Here, we demonstrate the use of metaheuristic approaches to optimize the circuit design of these matrices that additionally carry out the optimization of distances between the parallel transmission lines. For a matrix with 128 inputs and 64 outputs a realization is proposed that displays a worst-case insertion loss of 3.8 dB.

Design of New Dual-Band Wilkinson Power Dividers With Simple Structure and Wide Isolation

In this paper, a new scheme is proposed for a dual-band Wilkinson power divider (PD) without transmission line (TL) stubs (open- or short-circuited), or additional lumped elements (inductors and capacitors). In comparison with conventional PDs, only three additional TLs are employed. One is utilized to extend the input port, while the others are symmetrically distributed at the two branches. After applying even- and odd-mode analyses to the proposed structure, the exact closed-form design equations for a frequency ratio from 2.0 to 6.5 are derived, considering the largest realizable microstrip line impedance (150 $\Omega $ ). In addition, a new L-type TL with simple structure, compact size, and high design flexibility is proposed to replace the conventional TL to enhance its performance by introducing a transmission zero between the two passbands, resulting in good out-of-band rejection performance. Finally, two dual-band PDs centered at 1.0 and 3.5 GHz are designed and fabricated to verify the proposed design theory. One is based on the proposed structure, while the other incorporates a couple of L-type TLs to replace the conventional TLs. Good agreement with the simulated and measured results can be observed with a low in-band insertion loss and full ports matching. Moreover, the proposed PD also features a wide isolation band with a reference of 15-dB input port return loss. Moreover, the use of the L-type TL can introduce a good stopband between the two passbands, leading to an improved out-of-band rejection performance.

A Novel Uniplanar Balun With Transparent Termination Impedance

In this letter, a novel planar branch line balun with transparent port impedance is presented. The balun is designed based on a symmetric four-port network with an open-ended transmission line stub in the middle of the branch at its unbalanced port side. From the even-odd mode analysis, the equivalent network is derived to be a short circuit under even-mode excitation, and the input impedance looking into the unbalanced port satisfies impedance matching under odd-mode excitation. Unlike previous designs, the equivalent cascaded impedance transformer in the proposed structure is independent to the system reference impedance in odd-mode excitation so that the termination at the unbalanced port is transparent to balanced ports. To prove the design concept, the closed-form equations are derived, and multiple prototypes with termination impedances 35, 50, and $75 ~\Omega $ are simulated, fabricated, and characterized.

Design method of dual-band Wilkinson power divider with improved out-of-band rejection performance and high design flexibility

In this paper, a dual-band two-way equal-split Wilkinson power divider (PD) with improved out-of-band rejection and high design flexibility is proposed. The proposed structure is an originally configured impedance transformer that is composed of two impedance matching lines and a short-circuited composite right-/left handed (CRLH) transmission line (TL) stub. CRLH-TL replaces the requirement of quarter-wavelength impedance transformer and also shows the high design flexibility in proposed PDs. The characteristic impedance of composed RH-TL and LH-TL only affects the bandwidth of two pass-bands that assure high design flexibility. Whereas, π phase response in two pass-bands of short-circuited stub is attributed to the improved out-of-band rejection performance. The detailed theoretical analysis indicates the selected range of the two centre frequencies is influenced by CRLH-TL impedance matching line. The proposed dual-band PD centred at 0.90 GHz and 2.45 GHz design is theoretically calculated, simulated and fabricated. The obtained results verify that the proposed design method is having high design flexibility and good out-of-band rejection.

Novel DC-biasing circuits with arbitrary harmonics-control capability for compact high-efficiency power amplifiers

AbstractThe next generation mobile communication systems impose challenging performance, size, and cost requirements on the power amplifiers (PAs). This paper presents novel DC-biasing circuits, which are compact and yet can control the harmonics almost arbitrarily. The proposed circuit consists of a composite right-/left-handed (CRLH) transmission line (TL) stub, of which the size and harmonics-control function can be tuned by modifying the dispersion diagram of the stub line. As a proof of concept, a compact 2-GHz 7-W GaN HEMT class-F PA using the versatile CRLH-TL stubs was fabricated, demonstrating 85.8% drain efficiency and 77.3% power-added efficiency.

Time and Frequency Domain Response of HTS Resonators for Use as NMR Transmit Coils.

Replacing normal metal NMR coils with thin-film high-temperature superconductor (HTS) resonators can significantly improve the sensitivity of analytical NMR. To study the use of these resonators for excitation as well as detection, we investigated the radio frequency properties of the HTS NMR coils in both frequency and time domain at a variety of transmit power levels. Experiments were conducted on a double-sided, counter wound spiral resonator designed to detect NMR signals from 13C nuclei at 14.1 T. Power-dependent nonlinearity was observed in the transmission coefficient and quality factor. The ability of the HTS resonators to accurately generate short pulses was studied in the time domain over the range power levels. The results of this study show that some form of Q switching is needed to get good transmit performance from HTS coils for 13C. For that purpose, the effect of adding a shorted transmission line stub to improve the pulse shapes and reduce phase transients was studied.

A Zero Phase Delay Power Divider Using Zero Phase Impedance Transformer

The 3-dB power divider is one of the most common three-port device in microwave systems, which equally splits the signal at its two output ports. In previous Wilkinson power divider design, the phase delay between the input and output ports is not considered into the design requirements. However, the zero-phase shifting power divider attracts great interest in modern microwave systems. In this letter, a 3-dB power divider with zero-phase delay is designed based on a zero-phase impedance transformer. Instead of metamaterial transmission line, a transmission line stub is added to connect the isolation resistor, and a capacitor is insert between the output ports and the end of main branch to cancel out the imaginary part of even–odd mode impedances. With this new design, it releases the layout restriction that the two branches route around to connect to lumped element resistor. Closed-form design equations are derived and a prototype device is then simulated and measured. The measurement results agree well with the simulation results.

Signal Loss Compensation of RF Crossbar Switch Matrix System in Ultra-High Field MRI.

With the increased commercial availability of high channel count MR coil arrays and the associated higher number of plugs in the patient bed, it has become a common practice to include switch matrices in the receive path of MR systems. These allow the arbitrary routing of a signal from any plug to any receiver in the console. While switch matrices are standard in systems at clinical field strength and have been developed for systems operating up to 4T, they have not yet been implemented at ultra-high field (UHF). Here, we present a switch matrix suitable for operation at UHF. Crossbar switches, which are the most frequently employed forms of a switch matrix, use RF switches to connect horizontal input lines with the desired vertical output line. This leaves transmission line stubs of variable length physically connected with the selected signal path, potentially resulting in elevated signal losses. While this can be tolerated at low frequencies, and only needs partial compensation at intermediate frequencies (4T), a full compensation is required at UHF. In this study, an RF crossbar switch, which uses switchable compensation elements in both horizontal and vertical transmission lines, was implemented for a 9.4T MRI scanner. The prototype developed was evaluated for single channel and multichannel receive performance and benchmarked against a fixed wire connection.

Bianisotropic Huygens’ Metasurface for Wideband Impedance Matching Between Two Dielectric Media

There is an established equivalence between Huygens’ metasurfaces and lattice networks. This paper proposes an extension to this equivalence for bianisotropic Huygens’ metasurfaces, where bianisotropy refers to the magnetoelectric coupling between the effective electric and magnetic responses. A modified version of the lattice network is proposed that exhibits a one-to-one mapping to the bianisotropic sheet transition conditions by incorporating ideal transformers. A possible realization of bianisotropic Huygens’ unit cells is also proposed that relies on offsetting the wire with respect to the loop in the wire/loop topology. This is followed by deriving analytical expressions for the image impedances and the corresponding transfer function of bianisotropic Huygens’ metasurfaces. Inverse analytical expressions are also derived that govern the required effective electric and magnetic responses and the magnetoelectric coupling for achieving wideband electrical transparency (symmetric case) and wideband impedance transformation (bianisotropic case) with these Huygens’ metasurface unit cells. Moreover, it is shown that these expressions can be realized with transmission-line stubs. These expressions are then used to design subwavelength thin Huygens’ metasurfaces immersed in an air gap between two dielectric media. It is shown, through full-wave simulations, that wideband electrical transparency and impedance transformation are realized for a normally impinging plane wave.

Dynamic Electro-Magnetic-Thermal Modeling of MMC-Based DC–DC Converter for Real-Time Simulation of MTDC Grid

The model of a modular multilevel converter (MMC) determines the extent of critical circuit information that electromagnetic transient simulations can reveal. In this paper, two MMC models are proposed for efficient real-time hardware-in-the-loop (HIL) emulation on the field-programmable-gate-arrays (FPGA). The nonlinear switch-based model employing the insulated-gate bipolar transistor (IGBT) dynamic curve-fitting model considers factors affecting its transient performance so that device-level behavior such as power loss and junction temperature can be reproduced accurately in the electro-magnetic-thermal simulation of a power converter for its design evaluation. Meanwhile, regarding the MMC submodule as a transmission line stub achieves faster computation speed and enables the formation of a hybrid arm to save FPGA hardware resources. As the large network that the MMC presents is burdensome for real-time execution with a small time-step, circuit simplification based on partitioning and merging is conducted. Hardware implementation of a three-terminal high-voltage direct-current system containing an MMC-based dc–dc converter is carried out and the efficacy of proposed models is validated by comparing HIL emulation results with the offline simulation tool PSCAD/EMTDC.

Compact wideband bandpass filter with equiripple response in both magnitude and delay

Aiming at the reduction of the in-band delay variation, a wideband bandpass filter with equiripple response in both magnitude and group delay is presented and studied. The filter is composed of one section of end-connected coupled line and two short-circuited shunt transmission line stubs, all of them are uniform and equal in electrical length. Design formulas are given to calculate the characteristic impedances of the lines to meet the filtering specifications. By changing the coupling strength of the coupled line section, the group delay can be controlled to be equiripple in band, while the remaining equiripple response in magnitude unchanged. For verification, a filter sample is fabricated and measured. In experiment, it exhibits a delay variation of 0.11 ns and minimal insertion loss of 0.2 dB within its passband (|S11| < −14 dB) from 0.48 to 1.46 GHz, which validates the theoretical predictions.

Selectable multiband isolation of single pole double throw switch using transmission line stub resonator for WiMAX and LTE applications

This paper presents a selectable multiband isolation of Single Pole Double Throw (SPDT) switch with switchable transmission line stub resonators for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands. Two SPDT switches are presented. (Design 2) either allows selecting only one band while unselecting the other or selecting both of them. However, (Design 1) does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at center frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between all-pass and band-stop responses using discrete PIN diodes. The key advantage of the proposed SPDT with switchable transmission line stub resonators is a multiband high isolation with a minimum number of PIN diodes. Therefore, the simulated and measured results showed the followings: less than 3 dB of insertion loss, greater than 10 dB of return loss and higher than 30 dB of multiband isolation in 2.3 and 3.5 GHz bands.

Applications of Dispersion-Engineered Composite Right-/Left-Handed Transmission Line Stubs for Microwave Active Circuits

Applications of Dispersion-Engineered Composite Right-/Left-Handed Transmission Line Stubs for Microwave Active Circuits

FIXED AND SELECTABLE MULTIBAND ISOLATION OF DOUBLE POLE DOUBLE THROW SWITCH USING TRANSMISSION LINE STUB RESONATORS FOR WIMAX AND LTE

A novel selectable multiband isolation of Double Pole Double Throw (DPDT) switch with switchable transmission line stub resonators has been proposed for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands. In this paper, two DPDT switch designs are proposed; the first design is a fixed DPDT switch, and the second is a selectable DPDT switch. The second design allows selecting only one band and unselecting the other or selecting both of them. However, the first design does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at center frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between allpass and bandstop responses using discrete PIN diodes. The key advantage of the proposed DPDT with switchable transmission line stub resonators is a multiband high isolation with minimum number of PIN diodes. Therefore, the simulated and measured results showed less than 3 dB of insertion loss, greater than 10 dB of return loss and higher than 30 dB of multiband isolation in 2.3 and 3.5 GHz bands.

High-efficiency and compact metamaterial-inspired 900 MHz rectifier

ABSTRACTA novel high-efficiency, compact metamaterial-inspired rectifier is proposed for 900-MHz wireless power transmission (WPT) applications. The open-ended composite right/left-handed (CRLH) transmission line (TL) stub, which is introduced to realize metamaterials, replaces the band-pass filter (BPF) of a conventional rectifier (and is smaller than the traditional BPF). The open-ended CRLH TL stub is designed to suppress second- and third-order harmonics and to match the fundamental frequency to a 50-Ω impedance. The device is implemented using lumped elements and a microstrip line. The maximum RF-to-DC conversion efficiency of the proposed rectifier is 69.9% at an input power of 50 mW and a load of 1.8 kΩ. A design procedure that is based on minimizing the phase response of a CRLH TL is presented and validated by simulated and measured results. Because the single CRLH stub is used for harmonic suppression, miniaturization is achieved while retaining efficiency similar to that of previous rectifiers.