Short-circuited Transmission Line Research Articles

Analytical Design of Compact Multiband Bandpass Filters with Multiconductor Transmission Lines and Shunt Open Stubs

A compact topology for implementing compact multiband bandpass filters is presented in this paper. To achieve the desired frequency response, two identical short-circuited multiconductor transmission lines (MTLs) and properly connected shunt open stubs are interconnected. Using this configuration, it is possible to design multiband bandpass filters effortlessly. As both the MTLs and the stubs are distributed elements, spur-line band-stop filters are added to mitigate the first replica of the structure’s frequency response. To assess the behavior of the developed filter design procedure, a prototype consisting of a six fingers-MTL and two shunt open stubs has been designed, manufactured, and analyzed, showing excellent agreement between analytical and measured results, considering that no simulation or optimization process has been performed during the design process, just for result verification. Furthermore, it is possible to establish a design criterion that allows the fast and reliable synthesis of multiband responses by varying just a small number of geometrical parameters of the MTLs and the corresponding stubs.

Short-circuited stub-loaded spoof surface plasmon polariton transmission lines with flexibly controllable lower out-of-band rejections.

This Letter proposes an approach to develop a spoof surface plasmon polariton (SSPP) transmission line (TL) by loading short-circuited (SC) shunt stubs. Lower out-of-band rejections can be flexibly controlled without affecting the upper cutoff frequency by independently modifying the stubs. Dispersion analysis of the SSPP unit is realized by theoretical calculation and circuit simulation to predict the upper cutoff frequency of the proposed SSPP TL simultaneously. Also, parametric sweeping of the SC shunt stubs is performed based on circuit simulation to investigate their impacts on the lower and upper out-of-band rejections of the proposed SSPP TL. In addition, electric field distributions of different types of TLs are simulated and compared to study the transmission characteristics of the proposed SSPP TL. The lower cutoff frequency can be flexibly tuned in a wide range, from 1.2 to 2.1 GHz, in the simulations. The measured 3-dB fractional bandwidth is about 128.1%, covering a range from 1.19 to 5.43 GHz. The numerical and experimental results are compatible, which verifies the feasibility of the proposed approach. This approach can offer more convenience and flexibility for controlling the rejections of the SSPP by introducing up to four tuning parameters. More importantly, the proposed SSPP TL avoids using the substrate integrated waveguide (SIW) technique, which shows the potential to decrease the transverse width (0.44λg), especially at lower frequencies (e.g., 1.2 GHz), and to reduce the complexity in designing the high-efficiency transition. This work paves the way for the development of novel SSPP-based microwave devices.

Frequency Selective Impedance Transformer With High-Impedance Transforming Ratio and Extremely High/Low Termination Impedances

This article presents a novel frequency selective impedance transformer (ITs) with high transforming ratio and extremely low/high termination impedances ( 1 Ω or 2 Ω and several kΩ). The design equations are derived for both low and high termination impedances and effectively demonstrated. For transforming extremely low or high termination impedances, the characteristic impedances of open or short-circuited transmission line (TL) load can be very high or low, which cannot be fabricated with normal substrates because of the very narrow or broad width of TL. To solve the practical realization problem, the parallel-coupled lines can be adopted instated of TL. For the validation, two types of ITs are designed and measured at a center frequency ( f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ) of 3.5 GHz with impedance transforming ratios of r = 25 and r = 71.43 ( 2 Ω: 50 Ω and 35 Ω: 2500 Ω). The measurement results are consistent with simulation and theoretical predicated results. For achieving frequency selectivity, transmission zeros are generated very close to passband with stop-band suppression of higher than 40 dB.

Influence of varying particle sizes on microwave absorbing properties of U-type hexaferrites and development of broadband microwave absorber

The present study investigates the influence of particle size variation on the microwave (MW) absorbing properties of (Ba0.7Bi0.3)4Co2Fe34.8Zn1.2O60 U-type hexaferrites. The hexaferrite powders of varying particle sizes were prepared through heating at a constant optimized temperature for different holding time (4, 6, 8 and 10 h) using a novel “one-pot” chemical route. With an increase of the holding time (4 to 10 h), the average particle size is found to increase monotonically (∼65 to ∼170 nm). The hexaferrite sample prepared at a holding time of 8 h exhibits an excellent reflection loss (RL) of ‒44.2 dB (99.99% MW absorption) at 11.6 GHz frequency. In addition, a broadband MW absorber has been developed through an ingenious blending of equal amounts of all four hexaferrite powders. The mixed U-type hexaferrite displays an excellent bandwidth of ∼8.4 GHz for 90% or more MW absorption. The reflection losses (S11) are also measured experimentally through one port short-circuited transmission line method using vector network analyzer (VNA). The strong and broadband absorption results suggest that the prepared U-type samples can be utilized in the high-performance MW absorbing applications.

Optimal Bus Layout in Transmission System by Using Meta-heuristic Approaches

Transmission system expansion leads to excessive short-circuit currents that exceed the capacity of circuit breakers. To avoid over short-circuit current; transmission system operators make various alterations in the transmission system by changing the topology of the system. The feeders can be distributed to different buses in substations through disconnecting coupling circuit breaker between buses. Having been interchanged, the transmission system may face up a lot of problems even in single outage. Therefore, the optimal positions of feeders in substations are important in order to maintain system security. However, this optimization problem has non-convex properties due to AC load flow equations and it has a multi-objective structure to provide the limitation of short-circuit current and security of N-1 contingency. The constraints are the short-circuit current, voltage and transmission line limits in the single contingency. In this paper, the Genetic Algorithm and Binary Particle Swarm Optimization methods were utilized to find a near-optimal bus layout. Algorithms coding was made with Python programming language and PSS/E program was used to obtain power flow and short-circuit data. The results of applying the methods to the IEEE 14-bus test system demonstrated the effectiveness of the methods to take overloads away and restrict short-circuit current and hold voltage in its limit.

Wideband Tunable Differential Phase Shifter With Minimized In-Band Phase Deviation Error

This letter presents a tunable differential phase shifter with wideband flat phase characteristics. The proposed structure consists of a power dividing circuit and two 3-dB hybrids. To achieve the tunable flat phase characteristics over a wide bandwidth (BW), the coupled and through ports of one hybrid is terminated with short-circuited transmission lines (TLs), whereas those of another hybrid are terminated with a TL and varactor diode. For experimental validation, the proposed structure was designed and fabricated at a center frequency of 2.5 GHz. From the measurement results, the fabricated circuit provided a tunable differential phase shift range of 89° to 193° with a maximum in-band phase error of ±8.6° over a BW of 1 GHz.

Quad-mode dual-band bandpass filter based on a stub-loaded circular resonator

In this paper, a quad-mode dual-band bandpass filter (BPF) only using a stub-loaded circular resonator is presented. The odd- and even-mode resonant frequencies can be easily computed and flexibly controlled by the radius of the circle and the two sets of stubs, as all odd- and even-mode equivalent circuits are half-wavelength resonators (double-ended short-circuited uniform transmission line resonator). Introducing the resonator makes the filter be analyzed and designed easily. To further improve the isolation between the two passbands, a dual-band BPF is designed by introducing the source-load coupling technique; the simulation and test S-parameter curves show that the designed BPF has four controllable transmission zeros. The good agreement of measured data with simulation results verifies the proposed design.

Synthesis of Dual-Band Bandpass Filters With Short-Circuited Multiconductor Transmission Lines and Shunt Open Stubs

The design of dual-band bandpass filters consisting of series short-circuited wire-bonded multiconductor transmission lines and shunt open stubs is thoroughly carried out in this paper. Two different configurations are studied, and closed-form analytical design equations are derived to synthesize Chebyshev filtering functions. A novel, simplified, and time-saving synthesis procedure to design dual-band filters with narrow or moderate broad bandwidths is finally presented, attending to the required final specifications and the physical and manufacturing limitations. The usefulness and validity of the proposed analytical equations are illustrated by designing, manufacturing, and measuring three different prototypes, showing an excellent agreement between analytical and measured results.

Compact Beam-Steerable Antenna Array With Two Passive Parasitic Elements for 5G Mobile Terminals at 28 GHz

A compact beam-steerable antenna array is proposed for 28 GHz mobile terminals. The proposed array consists of one active element and two passive parasitic elements. Two switches are utilized in the design instead of phase shifters. Each parasitic element can be terminated with short-circuited transmission lines of different lengths via one switch. By controlling the two switches, different reactive impedance is loaded on two parasitic elements. The radiation pattern of the active element can be scattered into different directions by two parasitic elements. The switching loss is studied, where two switches with 2.8 dB loss cause less than 1.82 dB loss for the whole array. The small array locations on the chassis are also investigated. The designed array is smaller than 0.81 wavelength, and covers the band of 28–29 GHz with the scan angle ≥±90°. By placing two arrays on each long chassis edge, 360° beam steering can be realized. Surface currents on the chassis are efficiently excited to achieve high gain with the small array. Measurements are carried out and align well with simulations. In practical applications, several small arrays can be implemented on the metal back cover and around a cellphone to combat users’ mobility.

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.

Design and implementation of fractional‐order microwave differentiator

The new design of a fractional-order microwave differentiator is proposed. It is first of its kind and uses short-circuited stub and transmission line sections to emulate the behaviour of an ideal fractional-order differentiator. Least mean square error-based objective function is formulated to obtain the transfer function of the proposed design, using the chain scattering parameters of line elements in the Z-domain. During the optimisation process, impedance values of equal-electrical-length line elements are considered in the range 10-150 Ω, such that they are practically realisable on the microstrip format. The structure is implemented on the FR4 substrate with permittivity of 4.4 having 1.6 mm thickness. The measured result for the magnitude response of the transmission coefficient is found to be in good agreement with ideal one in the operating frequency range from 0.8 to 6.6 GHz.

Novel Matching Network and Its Application to Quad-Channel Diplexers

This letter reports a new kind of matching network for quad-channel diplexers. The matching network is comprised by some open- and short-circuited transmission lines, which can be chosen based on the design graph. The impact of loading resonators on the network is discussed. The diplexer can be easily realized by the combination of different bandpass filters without complicated tuning. To illustrate the concept, one quad-channel diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other.

A Compact Transmission-Line Self-Matched Negative Group Delay Microwave Circuit

A compact self-matched negative group delay (NGD) circuit without the need for an external matching circuit is proposed. The proposed NGD circuit is composed of two-port open-circuited coupled lines, a short-circuited transmission line and two resistors connected by two transmission lines. The coupled lines are utilized to obtain port matching. To verify the design concept, an NGD circuit with the size of $0.39\lambda _{g}\times 0.19\lambda _{g}$ is designed and fabricated. From the measurement results, NGD value of −8.75 ns at the center frequency of 1.570 GHz is obtained with NGD bandwidth of 3.82%, signal attenuation of less than 20.5 dB and return losses of more than 32 dB.

Design of Compact and High-Isolation Quadruplexer With Novel Matching Network

A novel matching network to design quadruplexer is proposed in this paper. The matching network is comprised of two parts and each part consists of a short-circuited transmission line, an open-circuited transmission line, and a series transmission line. The matching network is analyzed to obtain the design curves, which lead to various design parameters. Using this matching network, the quadruplexer can be easily realized by the connection of different bandpass filters without further tuning. Systematic design procedure for quadruplexer is fully presented in this paper. To illustrate the concept, a quadruplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other.

Compact power divider with bandpass response and improved out-of-band rejection

This paper presents a novel compact power divider (PD) with bandpass response and improved out-of-band rejection performance, which features flexible bandwidth adjustment and high passband selectivity. The proposed filtering PD consists of two coupled-line sections, two short-circuited transmission line sections (TLSs), and two cascaded stepped impedance TLSs in symmetrical arrangement. The unique loading point of isolation resistor is proposed to provide enhanced isolation performance, different from that of the conventional Wilkinson PD where the isolation resistor loaded between the output ports. Theoretical investigation adopting even–odd-mode method is presented to explain the operating mechanism. For verification, a filtering PD centered at 2.4 GHz is designed and measured. The measured results agree well with the simulated ones.

Exact Design of a New Class of Generalized Chebyshev Low-Pass Filters Using Coupled Line/Stub Sections

A method for the design of a new class of distributed low-pass filters enables exact realization of the series short-circuited transmission lines, which are normally approximated via unit elements in other filter realizations. The filters are based upon basic sections using a pair of coupled lines, which are terminated at one end in open-circuited stubs. The approach enables realization of transmission zeros at the quarter-wave frequency, hence giving improved stopband performance. A complete design theory starting from a distributed generalized Chebyshev low-pass prototype filter is presented. A design example demonstrates excellent performance in good agreement with theory.

Measurement at microwave frequencies of the magnetic properties of small quantities of powdered or diluted samples

Transmission line techniques are a convenient way to determine the electromagnetic properties of a variety of materials in the ranges of radio and microwave frequencies. Traditional methods based on the measurement of the four scattering parameters can be successfully replaced for the method presented here, in which no change in the geometry is needed, since two independent measurements are carried out, with and without an applied magnetic field. In addition, given the small size of the sample holder, the required amount of material can be drastically reduced, and allow the use of a lumped circuit model, then reducing the inherent difficulties associated with the use of distributed parameters. Even though this kind of model requires the involved wavelengths to be much larger than the size of the system, this requirement can be overcome as long as the tested materials have relative ϵ or μ lower than 100. Furthermore, the use of short-circuited transmission lines simplifies sample holding and systematizes the measurement process, which is an important target when dealing with measurements within the radio and microwave frequency ranges.

An Equivalent Circuit Model of FSS-Based Metamaterial Absorber Using Coupled Line Theory

An equivalent circuit model of an ultra-thin metamaterial absorber comprising a square-ring-shaped frequency selective surface (FSS) is presented. The model can be considered as series $RLC$ resonators connected in parallel with coupling capacitance and short-circuited transmission line. The even- and odd-mode couplings have been incorporated to accurately determine the lumped parameters as well as the absorption frequency of the absorber structure. The effects of substrate thickness and dielectric permittivity variation on the lumped parameters and full width at half-maximum (FWHM) bandwidth are investigated based on the proposed model. The absorber has been fabricated, and close matching among the calculated, simulated, and measured results has been observed.

Synthesis and design of tunable bandpass filters with constant absolute bandwidth using varactor-loaded microstrip resonator

This article presents two new types of tunable filters with constant absolute bandwidth using varactor-loaded microstrip resonators. First, the second- and third-order Butterworth tunable filters are designed based on the parallel coupled-line J inverters. Second, a fourth-order Chebyshev tunable filter is designed based on the alternative J/K inverters, in this design, two adjacent resonators are coupled with each other through a short-circuited transmission line as the K inverter. The proposed two topologies can be easily extended to high-order tunable filter. Three tunable bandpass filters with J and alternative J/K inverters, respectively, are built with a tuning range from ~1.8 to ~2.3 GHz. The measured second-order filter has a 3-dB bandwidth of 160±6 MHz and an insertion loss of 2.4-3.8 dB. The third-order filter shows a 3-dB bandwidth of 197±5 MHz and an insertion loss of 3.8-4.8 dB. The fourth-order filter shows a 3-dB bandwidth of 440±5 MHz and an insertion loss of 2.1-2.6 dB. For all the designed filters, the measured results are found in excellent agreement with the predicted and simulated results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:681-689, 2014.

Measuring the Microwave Magnetic Permeability of Small Samples Using the Short-Circuit Transmission Line Method

We present a method for estimating the bandwidth and the measurement errors of the shorted transmission line method used to obtain the permeability and the permittivity of magnetic materials. The permeability and the permittivity of a toroidal test sample are determined by measuring the reflection coefficients of a shorted coaxial transmission line and by using Newton's minimization algorithm. The permeabilities of two samples with different concentrations of cobalt nanoparticles are measured, and the validity of the shorted transmission line method is confirmed by comparing the results to a two-port transmission line approach. The sensitivity of the shorted line method to different measurement parameters is investigated in detail, and the connection between the spatial dimensions of the sample and the measurement uncertainty is studied. The bandwidth of the method is limited by the cavity resonance at the upper end of the frequency range and by the reduction of the sensitivity at the lower end. This is important because in magnetic materials research the sample sizes are generally small, which sets a limit to the lowest measurement frequency using transmission line methods. The reduction in sensitivity is demonstrated by measuring the permeability of three Teflon samples (each having different lengths), and by developing a theoretical model for the measurement errors.