Shunt Stubs Research Articles

Design and analysis of a planar UWB bandpass filter with stopband characteristics using MMR technique

AbstractIn this paper, a ultra-wideband (UWB) bandpass filter with stopband characteristics is presented using a multi-mode resonator (MMR) technique. An MMR is formed by loading three dumbbell-shaped (Mickey and circular) shunt stubs placed in the center and two symmetrical locations from ports, respectively. Three circular and arrowhead defected ground structures on the ground plane are introduced to achieve UWB bandwidth with a better roll-off rate. The proposed filter exhibits stopband characteristics from 10.8 to 20 GHz with a 0.4 dB return loss. The group delay and roll-off rate of the designed filter are <0.30 ns in the passband and 16 dB/GHz at lower and higher cut-off frequencies, respectively. The dimension of the filter is 0.74λg × 0.67λg mm2 and was fabricated on a cost-effective substrate. All simulated results are verified through the experimental results.

Filtering phase shifter with wide bandwidth and multiple transmission zeros

A wideband filtering phase shifter is proposed using a cascaded single line and coupled line as a shunt stub of the centre-coupled line. Such kind of a shunt stub provides the possibility to achieve wideband impedance matching, wideband phase shift, and multiple controllable transmission zeros (TZs) at the same time. The coupling between the shunt stubs of the practical layout can generate extra TZs and enhance the frequency selectivity. Compared with the state-of-the-art designs, the proposed one has wider bandwidth, more TZs and medium size, and the former cannot juggle bandwidth and size. Two prototypes at 1.76 GHz are designed with the relative operating bandwidth for 45°±3° (90°±4.2°) phase shift of 75% (76%), five TZs and the minimum return loss of 14.7 dB.

Balanced Dual-Band Superconducting Filter Using Stepped-Impedance Resonators With High Band-to-Band Isolation and Wide Stopband

A balanced dual-band and wide-stopband high-temperature superconducting (HTS) bandpass filter (BPF) with deep stopband rejection is designed using modified stepped impedance resonators (SIRs) in this brief. The center frequencies of the two differential-mode (DM) passbands can be controlled by adjusting two electrical length ratios of the proposed SIR, while keeping the third spurious frequency far away for wide-stopband design. An inherent common-mode (CM) suppression can also be obtained due to the discriminating CM resonant frequencies different from the DM ones. Multiple transmission zeros (TZs) are achieved to realize high passband selectivity and enhanced DM stopband by multipath coupling and shunt stubs loaded on the I/O ports. The proposed balanced dual-band filter operating at 1.78/4.0 GHz is eventually fabricated using HTS YBCO thin films on a MgO substrate, which can significantly lower the insertion losses. The circuit was measured at the temperature of 77 K, which shows maximum insertion losses of 0.42/0.37 dB and a DM stopband of 5.0f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sup> with 40-dB attenuation, respectively.

Broadside Scanning Fixed Frequency LWA With Simultaneous Electronic Control of Beam Angle and Beamwidth

In this article, a periodic leaky wave antenna (LWA) is presented for fixed frequency beam scanning in microstrip line technology. Both the beam angle and the beamwidth can be controlled electronically. The unit cell of the antenna is loaded with shunt stubs, which are either short or open-circuited, using p-i-n diodes as a switch. The switching of the stub alters the impedance loading of the antenna, leading to a change in the propagation constant and thus the main beam angle. The input impedance of the stubs is chosen for symmetrical beam scanning through the broadside direction. A total of 50 distinct main beam positions with an angular separation of approximately 1° are selected from the different switching states using an iterative process. The second set of p-i-n diodes are inserted between the consecutive unit cells to control the leakage and, hence, the beamwidth. The antenna is fabricated and measured at 2.45 GHz. The measured main beam angle scans from −26° in the backward direction to +24° in the forward direction, through broadside, with an overall measured gain variation of 1.2 dB. Also, the beamwidth can be continuously tuned up to a maximum of 204%, keeping the gain variation within 1.2 dB.

A T‐junction power divider with tunable operating frequency and dividing ratio

AbstractThis letter presents a T‐junction power divider (PD) with both tunable operating frequency and dividing ratio, simultaneously. The proposed design consists of two adjustable 90° phase shifters and a pair of shunt stubs loaded with two varactor diodes. The operating frequency can be tuned by controlling the varactor diodes loaded onto the 90° phase shifters. In addition, the tunable shunt stubs comprised of a short circuited and an open circuited stubs loaded with varactor diodes are employed to realize impedance matching and different dividing ratios at accurate operating frequencies. For verification, a prototype of the proposed PD with dimensions of 25.9 mm × 50 mm is designed, fabricated, and measured. The measured results show that the operating frequency can be tuned from 1 to 1.55 GHz, while the power dividing ratio can be tuned from 2:1 to 20:1. Good agreement between the simulation and measurement results is observed.

A Novel Microstrip Line Balun With Transparent Port Impedance and Flexible Open Arm Structure

In this letter, a novel microstrip line balun with transparent port impedance and unconnected flexible output arms is presented. The proposed balun is designed from a symmetric four-port device with an open end at its isolation port. To achieve balun function, a shunt stub is attached between the unbalanced port and the virtual open-ended port to generate a transmission zero under the even-mode circuit. Its odd-mode circuit is treated as an impedance transformer, where the transformer is independent of the terminal impedance. In addition, the proposed balun has flexible open arm branches and does not require a closed loop structure, which provides design flexibility to integrate with other devices compared to conventional closed-loop branch line baluns. The theoretical design equations are derived first to prove the design concept. Then, two prototypes are designed with 35 $\Omega $ system impedance and loaded with 50 and 75 $\Omega $ port impedance, and the measured results match well with the simulation, which further validates the proposed design theory.

Geometrically progressive stub loading scheme for miniaturization of transmission line‐based components

This paper presents a novel slow wave structure (SWS) using geometrically progressive loaded shunt stubs for miniaturization of microstrip lines. It is observed that, compared to the conventional periodically stub loaded SWS, the proposed technique renders further miniaturization of around 20%, theoretically. Apart from that, this technique also helps in suppression of higher pass bands inherently present in SWSs. A detailed analysis of this technique has been carried out with corresponding design scheme. For proof of concept, this miniaturization scheme is applied to a rat-race coupler designed at 2 GHz, where 75% reduction in overall footprint is observed. The simulated and measured results are found to be in good agreement with the proposed theory.

Branch Line Couplers With Small Size and Harmonic Suppression Based on Non-Periodic Step Impedance Shunt Stub (SISS) Loaded Lines

This paper presents branch line couplers with compact size and harmonic suppression based on non-periodic reactively loaded artificial lines. The reactive loading elements of the lines are step impedance shunt stubs (SISSs). Such elements provide transmission zeros, which are useful to efficiently suppressing the harmonic content of the device. Moreover, by virtue of reactive loading, the reported artificial lines exhibit a slow wave effect of interest for device miniaturization. The combination of size, harmonic suppression efficiency, and design simplicity (with a clear design methodology) is of interest within the framework of artificial transmission lines and their application to the optimization of microwave passive components.

Platform tolerant dual‐band UHF‐RFID tag antenna with enhanced read range using artificial magnetic conductor structures

In this work, a platform tolerant novel dual band tag antenna is proposed for UHF-RFID bands used in Europe (855-867 MHz) and Japan (950-955 MHz). Asymmetrical shunt stub feed network is employed to effectively match its impedance to the microchip (Alien Higgs-4). The antenna miniaturization is achieved by embedding inverted L-shaped slit on left side of the patch. Also, asymmetrical stepped rectangular slot is embedded to further achieve the optimized dual band response at the desired resonant frequencies (f1 = 866 MHz and f2 = 953 MHz). To further enhance its radiation performance on conductive objects like metallic surfaces, the proposed tag is integrated with artificial magnetic conductor (AMC) structure. Also, antenna parameters such as main lobe gain, directivity, front-to-back ratio parameters are examined for the integrated tag in free space and on metallic sheet. The proposed integrated tag exhibits directional radiation pattern making it insensitive to underlying object and thus platform tolerant. Further, the proposed integrated tag exhibits steady gain response inside the resonating bands on different sized metallic sheets. The proposed integrated tag is compact (2635 mm3) covering European band with a read range of 7.3 m and Japanese band with a read range of 10.8 m.

Highly-Accurate Fractional-Order Microwave Differentiators for Band-Specific UWB Applications

Highly accurate designs of band-specific fractional-order microwave differentiators are proposed to operate in lower and upper frequency bands of UWB range. Firstly, fractional-order digital differentiators are obtained by minimizing the magnitude error function of a single-zero multi-pole transfer function. Absolute relative error (ARE) analysis clearly demonstrates that the proposed lower and upper band fractional-order digital differentiator designs are having highly accurate magnitude response and outperform the existing fractional-order differentiators with maximum ARE values of − 44.14 dB and − 48.79 dB respectively. To operate in microwave range, these designs are realized using Z-domain chain scattering parameters of equal-electrical length line elements. Microstrip configurations obtained for lower and upper band fractional-order microwave differentiators consist of a short-circuited shunt stub and three serial transmission line sections. Implementation of designs is done on Rogers RO3003 substrate having thickness 0.75 mm. Measured results for transmission coefficient of lower and upper frequency band designs are found to be in good agreement with simulated ones over the frequency range 1.2 to 6.2 GHz and 6 to 10.9 GHz respectively.

IL analysis for 8‐way power combining network in 77–110 GHz 40 nm‐complementary metal–oxide–semiconductor PA design

In this study, the authors will investigate the insertion loss (IL) of the broadband 8-way power combiner used in their millimetre-wave power amplifier (PA) design. By treating this combiner as impedance transformer under resistor-capacitor (RC)-loading condition, both the characteristic impedance and electrical length of the constituting metal lines can be obtained, where the much shorter line length suggests wider bandwidth and lower IL. However, proper loss analysis must take into account the multi-reflection of voltage wave along these mismatched transmission lines, i.e. the use of the power attenuation expression is just not accurate enough. With their derived equations, it shows that the IL of their proposed 8-way combiner can be as low as 0.92 dB at 94 GHz, which is much smaller than the 1.5 dB for the conventional quarter-wavelength combiner. Mathematics for the IL of the drain-bias shunt stub and the output DC-blocking capacitor has also been derived. As a demonstration, a 77–110 GHz 40 nm-complementary metal–oxide–semiconductor PA made of cascode transistors is then designed that has more than 18 dB gain, and its OP1 dB is around 13 dBm across the whole frequency range.

Miniaturized Chipless RFID Tags Based on Periodically Loaded Microstrip Structure

A compact chipless radio frequency identification (RFID) tag-based on slow-wave technology is introduced in this paper. The tag consists of a resonant circuit based on open stub resonators periodically loaded by shunt stubs allowing a coding capacity of 9 bits and operating in a frequency range from 2 to 4GHz. The receiving and transmitting antennas of the tag are particularly designed to minimize the tag size as much as possible. The proposed tag presents a robust bit pattern with a compact and fully printable structure using FR4 substrate for a low-cost tag.

Reconfigurable RF Dispersive Delay Circuits by Stepped Impedance Shunt Stubs

A design of RF dispersive delay circuits with both convex and concave delay profiles using stepped impedance stubs are presented in this brief. A transmission line model is used to analyze the structure and to obtain design equations. Three prototypes with different delay profiles are fabricated to validate the proposed technique. Next, a reconfigurable delay line with switchable delay profiles is presented. However, because of its parasitic, PIN diodes used for switching change the delay profile. A procedure is described to compensate the loading effect of PIN diodes. A prototype is fabricated. In all the cases, good agreement is obtained among the predicted and measured results. A comparison with recent works shows that present unit provides highest peak group delay with minimum insertion loss. The dispersive delay lines operate as a linear device at least up to 23 dBm of input power.

A New Design of Ultrawideband Single-Layer 90° Phase Shifter in the View of Group Delay

This letter proposes a novel design method of the single-layer ultrawideband (UWB) 90° phase shifter, which consists of a multimode resonator with shunt stubs and longitudinally cascaded coupled lines. The physical insight and working mechanism of its ultrawide operation bandwidth are extensively illustrated in the view of group delay for the main and reference lines. Meanwhile, the return loss and phase deviation can be appropriately adjusted in the design process. The measured results exhibit its bandwidth is 122% of 10 dB, and insertion loss of <1.04 dB. The comparison shows the proposed design not only achieves wide bandwidth but also attain small phase deviation, simple geometry, and compact size. The predicted results have been well validated in the experiment.

Reactively-loaded non-periodic slow-wave artificial transmission lines for stop band bandwidth enhancement: application to power splitters

AbstractThis paper presents slow-wave transmission lines based on non-periodic reactive loading. Specifically, the loading elements are stepped impedance shunt stubs (SISS). By sacrificing periodicity using SISS tuned to different frequencies, multiple transmission zeros above the pass band arise, and the rejection level and bandwidth of the stop band is improved as compared with those of periodic structures. Through a proper design, it is possible to achieve compact lines, simultaneously providing the required electrical length and characteristic impedance at the design frequency (dictated by specifications), and efficiently filtering the response at higher frequencies. These lines are applied to the design of a compact power splitter with filtering capability in this work. The length of the splitter, based on a 35.35 Ω impedance inverter, is reduced by a factor of roughly two. Moreover, harmonic suppression better than 20 dB up to the fourth harmonic is achieved.

Compact bandpass filter using CMRC‐based dual‐behavior resonator

This article presents a novel bandpass filter (BPF) using two proximity-coupled dual-behavior resonators (DBRs). The employed DBR is implemented by a single shunt stub with the compact microstrip resonator cell at its open end instead of the traditional dual stubs in cross-shape. Due to the adoptions of the proposed DBR and proximity-coupling scheme, both the transverse and longitudinal dimensions of the proposed BPF are reduced significantly. To verify the proposed idea, a demonstration microstrip BPF is designed and fabricated, and good agreement between the simulated and measured results can be observed, showing low loss and high selectivity due to four transmission zeroes in the stopband.

Effective Design of Microstrip-Line Chipless RFID Tags Based on Filter Theory

This paper presents an effective design method of chipless RFID tags. With $n$ -bit first- and second-order chipless tags’ equivalent circuits proposed based on filter theory, the relationship between bits and frequency bands of tags is characterized by formulas. Combining with microstrip-line theory, the first-order chipless tag with single quarter-wave open-circuited (O.C.) shunt stub units, and second-order chipless tag with parallel pairs of quarter-wave O.C. shunt stubs are designed, respectively. The pros and cons for each type of the chipless tag are discussed. Two types of 5-bit chipless tag examples are given with good consistent simulated and measured results. In addition, for the second-order chipless tag, we propose a miniaturization scheme, enhancing the antidamage ability simultaneously. Damage test shows that the second-order chipless tag has the good antidamage ability, especially for the miniaturized tag. Finally, the bit extension by the formulaic method is discussed, emphasizing a promising practicability.

The optimal design and analysis of wideband second-order microwave integrator

AbstractThe implementation of stable, accurate, and wideband second-order microwave integrators (SOMIs) is presented in this paper. These designs of SOMIs are obtained by using different combinations of transmission line sections and shunt stubs in cascading. Particle swarm optimization (PSO), cuckoo search algorithm (CSA), and gravitational search algorithm (GSA) are applied to obtain the optimal values of the characteristic impedances of these line elements to approximate the magnitude response of ideal second-order integrator (SOI). The performance measure criteria for the proposed SOMIs are carried out based on magnitude response, absolute magnitude error, phase response, convergence rate, pole-zero plot, and improvement graph. The simulation results and statistical analysis demonstrate that GSA surpasses the PSO and CSA to approximate the ideal SOI in all state-of-the-art, that is eligible for wide-band microwave integrator. The designed SOMI is compact in size and suitable to cover microwave applications. The magnitude errors for the proposed SOMIs GSA based are as low as 4.9954 and 3.6573, respectively. The structure of the designed SOMI is implemented in the form of microstrip line on RT/Duroid substrate with dielectric constant 2.2 and having height 0.762 mm. The simulated and measured magnitude result agrees well with the ideal one in the frequency range of 3–15 GHz.

Enhancing the Per-Unit-Length Data Density in Near-Field Chipless-RFID Systems With Sequential Bit Reading

In this letter, a novel near-field chipless-Radio Frequency Identification (RFID) system with sequential bit reading is reported. The main novelty concerns the tags, implemented by means of straight half-wavelength resonators separated by a small distance and forming a linear chain in the direction orthogonal to their axis. By this means, the number of resonant elements (or bits) per unit length of the tag is significantly increased, as compared to the previous implementations, with the result of very competitive tags in terms of data density. The active part of the reader is a microstrip line loaded with a shunt stub. Through a proper design, it is possible to achieve a significant excursion of the transmission coefficient when the stub is either loaded or unloaded with a functional resonant element of the tag. Consequently, by tag motion over the reader (stub), it is possible to infer the Identification (ID) code by simply injecting a harmonic signal to the input port of the stub-loaded line (the ID code is contained in the amplitude modulated, signal at the output port). This system has been validated by considering 100 b tags exhibiting a surface data density of 4.9 b/cm2. However, the relevant parameter is the data density per unit length, as high as 16.7 b/cm, i.e., much larger than previous values reported in the literature in similar chipless-RFID systems.

Compact left-handed dual-band filters based on shundted stub resonators

In this paper, super-compact microstrip dual-band resonator is presented, designed using the superposition of two simple left-handed (LH) resonators with single shunt stub. The proposed resonator exhibits spurious response in wide frequency range and therefore allows construction of dual-band filters using the superposition principle. The equivalent circuit model of the proposed resonator is crated and the influence of different geometrical parameters to the performances of the resonator are analyzed in details. As an examples, two dual-band filters that operate simultaneously at the WiMAX frequency bands are designed.