Short-circuited Stubs Research Articles

Compact, High Power Capacity, and Low Insertion Loss Millimeter-Wave On-Chip Limiting Filter With GaAs PIN Technology

In this paper, a collaborative design of compact, high-power capacity, and low insertion loss millimeter-wave limiting filter using gallium arsenide (GaAs) PIN technology is presented. Parallel topology is employed to distribute the PIN diodes of the first stage of limiting circuit for high power handling capacity. In order to reduce the circuit size, the filtering function structure is incorporated into the limiter. Four transmission zeros (TZs) are introduced to improve the out-of-band suppression performances of the limiting filter. By utilizing the inductive short-circuited stub, a parallel resonator is introduced to exhibit the passband characteristic. Semi-lumped and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -type topologies are employed to reduce the size of the conventional quarter-wavelength transmission line and introduce several TZs within the stopband. An on-chip limiting filter sample is fabricated by the GaAs PIN process and occupies an area of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.1\times 0.9$ </tex-math></inline-formula> mm2. It is measured with the insertion loss of 1.67 dB at the center frequency of 35 GHz, the stopband suppression of better than 20 dB, and the tolerable input power of greater than 40 dBm. Compared with the traditional designs, good features of high-power capacity, low insertion loss, and miniaturization are obtained with the presented on-chip limiting filter.

Novel Nth/2Nth Order Two-Band Bandpass Filters for Sub-6 GHz 5G Applications

In this paper, a new design method is proposed for multi-mode two-band bandpass filters based on combining a square loop resonator that has a capacitive perturbation element and short-circuited stubs. This concept is a new multi-mode two-band filter design having Nth and 2Nth order for the first and second passbands that appear in f0 and 3f0 center frequencies, respectively. It has been shown that the number of transmission modes in each passband can easily be increased by periodically cascading one unit filter cell including one square loop resonator and two short-circuited stubs. This also provides a reconfigurable filter property, namely the obtaining of two different filtering characteristics in the second passband by means of the reverse and straight placing of the cascaded unit filter cells in the horizontal axis. Two 2nd/4th order two-band bandpass filter prototypes are fabricated and tested to validate the proposed design method. The total surface areas of these fabricated prototypes are 26.0 mm × 9.0 mm and 24.4 mm × 16.8 mm, and the measured insertion losses in the first/second passband are about 0.63 dB/0.96 dB and 0.59 dB/0.83 dB. It is observed that the filter prototypes have the advantages of low insertion loss, compact size, and flexible filtering characteristics. The designed filters are suitable for operation in the 5G spectrum, which includes a range of radio frequencies sub-6 GHz.

Integrated Design of Multimode and Multifrequency Miniaturized Handset Antenna at VHF/UHF Bands

This paper presents an integrated design of a multimode and multifrequency miniaturized handset antenna working at the lower band (0.24–0.7 GHz) with linear polarization and higher band (1.98–2.01 GHz and 2.17–2.20 GHz) with circular polarization simultaneously. At the higher band, the quadrifilar helix antenna (QHA) is utilized with each arm developed into two arms of different lengths and linearly tapered widths to realize double resonance and increase the bandwidth. Moreover, a helical stub behaving as a director is introduced to improve the antenna gain. At the lower band, the outer conductor of the QHA feedline and four QHA arms are designed to constitute a monopole antenna through proper feeding and introducing four quarter-wavelength short-circuit stubs. With this radiator-sharing technique, the QHA not only works at the higher band with a circular polarization pattern but can act as a monopole antenna working at the lower band with a linear polarization pattern simultaneously. As a result, the size of the antenna can be reduced remarkably. Finally, the proposed antenna is fabricated with a total length of 228 mm and a diameter of 15 mm. At the lower band, the measured S11 is below −8 dB, and the gain is larger than 0.5 dBi. At the higher band, the measured S11 and AR are better than −13 dB and 3 dB, respectively, and the gain within the zenith angle range of 0°−35° is greater than 2.5 dBi, which demonstrates better performance.

Tunable differential phase shifter with low in-band phase deviation error over wide phase shift range

In the brief, a tunable differential phase shifter (D-PS) which features the characteristics of low in-band phase deviation error, wide phase shift range (PSR), and compact structure is presented. The main and reference lines of the D-PS are constructed by reflection-type phase shifters (RTPSs). In the main line, the reflection load is composed of two varactors and a short-circuited stub in parallel connection. While the reflection load in the reference line is consisted of an inductor paralleled with a short-circuited stub. Design equations of the proposed D-PS is derived, and the influences of the reflection loads on the performances of the D-PS are investigated. For validation, a prototype operating at 2 GHz is designed. Measurement results show that the 10-dB impedance matching bandwidth is 20.7 %. During the tuning, a PSR of 243° is obtained and the bandwidth for phase difference error <10° is 12.1 %.

A Tunable Bandpass Filter with Arbitrarily Terminated Port Impedance Using Dual-Mode Resonator

This paper presents a design for a compact arbitrarily terminated port impedance tunable bandpass filter (BPF) with transmission zeros (TZs) that employs a dual-mode resonator. The proposed dual-mode resonator comprises two varactors along with series transmission lines and a shunt short-circuited stub. The resonant frequency separation of the dual-mode resonator can be adjusted by changing the length or characteristic impedance of the short-circuited stub. To achieve arbitrarily terminated port impedances, the coupling between the source/load and the dual-resonator is modified from the originally designed 50-to-50 Ω termination filter. Frequency selective characteristics are achieved by generating two TZs at the lower and upper frequencies of the passband. The location of the TZs can be changed by controlling the source-load coupling. To experimentally validate the proposed tunable BPF, three prototypes (50-to-50 Ω BPF, 25-to- 50 Ω BPF, and 20 + &lt;i&gt;j&lt;/i&gt;10-to-50 Ω BPFs) are designed and fabricated. The measurement results revealed that the center frequency can be tuned from 2.10 GHz to 3.02 GHz (920 MHz tunability), where the insertion loss varies from 1.50 to 2.5 dB.

A compact tri-band bandpass filter using asymmetrical stub-loaded resonator

ABSTRACT This paper proposes a novel compact tri-band bandpass filter based on two coupled asymmetrical stub-loaded resonators (ASLR). The proposed filter can achieve three resonant frequencies by tuning uniform impedance line, short-circuit stub, and open-circuit stub, respectively. In addition, the asymmetrical stub can be loaded at any position of the main branch, which will facilitate the circuit design for no impedance of special ratio is needed, and the design bound can be alleviated. Meanwhile, thanks to its simple structure, the whole filter occupies an area of 0.021 λg 2 based on RO4350B substrate, much smaller than other similar tri-band filters. Measurement results show that the filter achieves fractional bandwidths (FBW) of 7.5%, 6.4% and 4.2%, respectively for three bands. The proposed filter is small and can achieve a high-frequency selectivity at 2.45 GHz, 3.5 GHz and 5.25 GHz, corresponding to Bluetooth, World Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN), respectively. The proposed filter will find a wide application in wireless communications thanks to its attractive advantages.

Design Theory of Equal Split Dual- Band Power Divider without Reactive Elements

In this paper, a design approach for getting dual-band working in a Wilkinson-based power divider (WPD) without adding any reactive elements or open- or short-circuited stubs is presented. The transfer matrix approach is used to get the analytical solutions of the required design equations. Admittance representation with respect to the input and output ports is done to perform even-odd mode analysis. In this impedance of each section is kept constant but the electrical length varies. Different combinations of electrical lengths are taken such that the overall length remains constant. The electrical lengths are selected based on dual-band analysis and depend on the tuning ratio. The conditions for attaining the impedance matching are applied to the obtained design equations and hence found out the values of the matching resistors to be placed between the transmission line sections. The proposed power divider centered at 2.5GHz and 7GHz is theoretically calculated simulated and fabricated. Finally, design procedures and experiments show good agreement with theoretical simulation.

Enhanced-Stopband Dual-Polarized Filtenna Without Extra Circuit for Tile Array Applications

In this communication, a dual polarized (DP) stacked patch filtenna (filtering antenna) with a wide stopband is developed for tile array applications. The bandpass filtering property is realized by improving the feeding network and patch without adding extra bandpass circuit or size. An elaborate feeding structure with complementary pair of a short-circuited stub and an open-circuited stub (CSSOS) is developed, which generates two transmission nulls effectively enhancing the selectivity and suppressing the harmonic. Moreover, CSSOS has a small size and broadens the impedance bandwidth apparently by introducing an in-band resonance. By properly etching four U-shaped slots on the driven patch, a radiation null in the upper stopband is also generated. The nulls generated by the two approaches can be adjusted independently in wide ranges. For further harmonic suppression, bandstop striplines (BSSs) with ultralow insertion loss are developed. Measured results show that the filtenna performs a wide operating band (3.10–3.95 GHz) and a wide stopband up to 8 GHz with a rejection level higher than 16 dB. Besides, a 32-element tile phased array employing the filtennas is also fabricated and measured. A compact configuration, high selectivity, and good beam steering capacity are exhibited.

Miniaturized ultra-wideband filter with independently controlled notch bands for 5.1/6/8 GHz wireless applications.

A novel three-mode step impedance resonator (TSIR) is developed to design a miniaturized multi-pole microstrip planar ultra-wideband (UWB) filter with independently controlled notched bands at different frequencies is presented in this work. The basic UWB filter consists of four L-shaped λ/4 short-circuited stubs operating in the range of i.e. 2.7 to 12.1 GHz with fractional bandwidth (FBW) 127%, and the TSIR is constructed using two T-shaped λ/2 open ended step impedance resonator (SIR) and one λ/4 short-circuited uniform impedance resonator (UIR) is coupled to the basic UWB design in order to achieve the stopbands performance at 5.1 GHz, 6 GHz, and 8 GHz, to supress the unwanted bands of WLAN, Wi-Fi 6E, and X-band satellite communication system, respectively. Commercial full-wave electromagnetic (EM) software HFSS-13 was used to design an ultra-compact structure having size 0.07 λg×0.02 λg on Rogers RT/Duroid 5880 substrate to justify good agreement between simulated and measured S-parameters.

Miniature Dual-Band Absorptive Bandstop Filters With Improved Passband Performance

In this paper, a miniature dual-band absorptive bandstop filter (ABSF) design with improved lower passband performance is proposed. Specifically, a stepped-impedance short-circuited stub is introduced to a bridged-T coil-based dual-band ABSF design, such that the insertion loss around the desired passband center frequency can be largely reduced while the absorptive stopband performance remains intact. This also helps equalize the lower passband insertion loss response and achieve a flatter passband, which is especially advantageous when cascading multiple ABSFs for improving the stopband rejection or increasing the number of stopbands. Closed-form design formulas are established to facilitate the synthesis of proposed dual-band ABSF. As an example, a 4.8/9.6-GHz dual-band ABSF in GaAs is realized with a measured insertion loss within 0.85± 0.12 dB from dc to 2.6 GHz. The circuit size is only 1.6 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 1.84 mm, and the corresponding electrical size is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.013\lambda _{0} \times 0.015\lambda _{0}$ </tex-math></inline-formula> at the designated passband center frequency of 2.4 GHz. Application of the proposed dual-band ABSF for the passband performance improvement of cascaded ABSF designs is also demonstrated, and good performance is obtained.

A compact high‐sensitivity tangential E‐probe with resonator and coupled balun

A compact high-sensitivity probe for sensing up tangential E-field is proposed and measured in this paper. The probe consists of an electric dipole with patches used to induce the tangential E-field, a resonator made up of open circuit stubs (capacitor) and short circuit stubs (inductor), for achieving a specific resonance, and a compact coupled balun for transforming the differential-mode voltage into the single-output voltage and impedance matching. The probe is fabricated on five-layer dielectric lamina. Compared with the referenced broadband probe, the measured |S12| of the probe is enhanced by 18.81 dB. The proposed probe in this paper is validated with simulation and measurement.

Design of wideband 4 × 4 Nolen matrix using m ultistub loaded phase shifters

In this article, a wideband microstrip 4 × 4 Nolen matrix using novel phase shifters is proposed. Because of the unequal electrical paths connecting one input to every output, Nolen matrices in standard form usually introduce significant phase dispersion and amplitude instability, limiting the effective bandwidth. A novel phase shifter consisting of multiple open- and short-circuited stubs is designed, whose rate of change of phase with frequency can be conveniently adjusted. This phase shifter can be used to balance the rate of change of phase with frequency of the unequal electrical paths to reduce the phase dispersion and amplitude instability, thus realizing wide bandwidth of the output phase differences and output amplitudes. To verify the proposed concept, a wideband 4 × 4 Nolen matrix operating at 6 GHz is designed and fabricated, showing a bandwidth up to 33% within ±15° phase imbalance and 21.5% within ±1 dB amplitude imbalance.

Wideband three-way power divider with bandpass filtering response using unequal-width three-coupled line

In the paper, a wideband three-way power divider (PD) with bandpass filtering response is proposed. It consists of short-circuited-stub (SCSs) loaded unequal PD, unequal-width three-coupled lines (TCLs) and isolation resistors. By using the TCLs, as well as inserting the SCSs to the connections of the PD and the TCLs, wideband bandpass filtering response with high frequency selectivity is realized. Double even-odd mode decomposition technique is adopted for analyzing the PD with asymmetric structure, and design procedures are provided for guidance. For demonstration, a prototype operating at 1.5 GHz is designed and fabricated. Measurement results coincide well with the simulated results which show that the fractional bandwidth (FBW) of more than 80% is achieved with less than 0.8 dB insertion loss and larger than 15 dB isolation. In the bandwidth, the return losses are better than 14 dB and 18 dB for the input and output ports, respectively.

A Simple Method to Design a UWB Filter with a Notched Band Using Short-Circuit Step Impedance Stubs

This article presents a simple method to design an ultra-wideband (UWB) bandpass filter (BPF) with a notched band. The structure of the filter is simple and is composed of a single half-wavelength resonator loaded with three sets of short-circuit step impedance stubs. An equivalent circuit model is presented to analyze the resonance characteristics. Compared with the traditional quarter-wavelength uniform impedance stub, the novelty of the short-circuit step impedance stub introduces two design parameters: the impedance ratio (K) and the electrical length ratio (α). Therefore, by adjusting these design parameters, the frequencies of the first two notched bands can be tuned widely, so a wide frequency band with a notched band can easily be achieved. With a K of 0.36 and an α of 0.6, the designed filter achieved an ultra-wideband bandpass response with a notched band. The UWB response had a passband range of 2.5 GHz–10.5 GHz and a notched band around 5.1 GHz with an attenuation of about 45 dB. The insertion loss in the entire passband was less than 1.26 dB, and the return loss was larger than 10 dB on average. The maximum group delay variation in the two passbands was less than 0.3 nS. The measurement results showed good agreement with the simulation results.

Liquid Metal-Embedded Layered-PDMS Antenna for Flexible and Conformal Applications

This article proposes a dual-band slot IFA antenna using a combined technique of liquid metal (LM) filling and polydimethylsiloxane substrate. The antenna working at 2.4 and 5.8 GHz consists of three liquid metal layers—radiation patch, short circuit stub, and ground plane and can be bent to different radiuses for flexible, conformal, and wearable applications. The vacuum filling method enables realization of a monolithic-integrated substrate. The applicability of this antenna for a wearable wristband is validated through simulation.

A Wideband Functionality-Reconfigurable RF Building-Block With Four Operating Modes

In this brief, a wideband functionality-reconfigurable RF building-block with in-phase/out-of-phase powering dividing (PD) and single-/dual-band Single-Pole-Double-Throw (SPDT) filtering switching modes is proposed utilizing a novel Switched Central-Loaded Parallel Coupled-Line (SCLPCL) structure. By independently forward-or reverse-biasing the four PIN diodes in the SCLPCL structure, three reconfigurable sub-block statuses (Status I, II and III) can be obtained, which further leads to four operating modes of the whole building block. With the aid of the stepped-impedance compensation network and the Central Loaded Short-Circuited Stubs (CLSCS), the 180∘ phase-shift difference at two achieved pass-through statuses (Status I and II) can be balanced, together with an enhanced out-of-phase bandwidth. In addition, the compensation network can also be used to ease the trade-off between wide out-of-phase bandwidth at the passthrough statuses and high isolation at the isolated circuit status (Status III). The SCLPCL is further modified and optimized to achieve the three-port functionality-reconfigurable RF buildingblock. The implemented prototype demonstrates a wide bandwidth in all modes. Moreover, less PIN diodes are applied to obtain more operating modes, verifying the simplicity of the proposed method to design functionality-reconfigurable RF circuits.

A Wideband Bandpass Power Divider With Out-of-Band Multi-Transmission Zeros and Controllable Equal-Ripple Levels

In this article, a novel wideband bandpass power divider (PD) with out-of-band multi-transmission zeros (TZs) is presented. It consists of <inline-formula> <tex-math notation="LaTeX">$2M$ </tex-math></inline-formula> shunted short-circuited stubs (SCSs), (<inline-formula> <tex-math notation="LaTeX">$M + N$ </tex-math></inline-formula>) cascaded coupled line sections, and (<inline-formula> <tex-math notation="LaTeX">$M + N - K_{N}$ </tex-math></inline-formula>) isolation resistors. There are two types of topologies, and the number of TZs is solely determined by <inline-formula> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula>. Through even- and odd-mode analyses, general simultaneous equations for characteristic impedances, coupling strengths, and isolation resistors are derived with the proposed algorithm. By suitably selecting all the design parameters, all the <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula>-parameters (<inline-formula> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$S_{21} = S_{31}$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$S_{22} = S_{33}$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$S_{32}$ </tex-math></inline-formula>) of the proposed topology could provide an equal-ripple response with controllable ripple level in the passband. For a given fractional bandwidth (FBW), TZs and out-of-band rejection level can be designed independently. For further optimization, several isolation resistors can be omitted with the unchanged performances. For verification, two experimental circuits are fabricated and measured. Good agreement between the measured and simulated results is attained so as to successfully validate the correctness of the proposed design approach.

Design of a Compact Novel Stub Loaded Pentaband Bandpass Filter for Next Generation Wireless RF Front Ends

This paper presents a compact novel pentaband bandpass filter using a dual path stub loaded step impedance resonator (SLSIR). The proposed topology consists of a dual path λ/4 and 2λ/3 long uniform impedance resonator centered separated by 2λ/3 open and λ/12 short circuit stubs respectively. The superposition of signals from the two transmission routes results in a fifth-order pentaband bandpass response with six finite frequency transmission zeroes and out-of-band rejection of 11dB from 12 GHz up to 20 GHz. The filter produces five frequency bands at 1.06 GHz, 3.24 GHz, 5.36 GHz, 8.55 GHz and 10.78 GHz with fractional bandwidth (FBW) of 25.59%, 22.22%, 19.48%, 16.03% and 17.17% respectively. The proposed design is fabricated on a high-frequency substrate with a physical size of (0.23λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> × 0.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> ). The new pentaband bandpass filter has a simple and compact design with good electrical performance. A fair match can be found between the simulated and experimental results.

Design of a new anti-metal RFID temperature tag antenna based on short-circuit stub structure

With the increasing maturity of the power Internet of things (pIoT), radio frequency identification technology (RFID), is more applied to the fault monitoring of power equipment, of which the temperature monitoring of power equipment is one of the focuses of fault monitoring. When the traditional RFID temperature measurement tag is applied to high-voltage electrical equipment, it often produces metallic interference to the RFID temperature measurement tag antenna because it is attached to the surface of metal conductor, such as large synchronous machine and high-voltage transmission line, which greatly shortens the identification range of the traditional RFID temperature measurement tag on the metal surface and even cannot work normally. To solve the problems above, a new anti-metal RFID temperature tag antenna is designed in this paper. The internal antenna of the RFID temperature measurement tag adopts the anti-metal design based on the short-circuit stub structure, so that the temperature measurement tag can achieve the purpose of good anti-metal performance. Finally, through the simulation of HFSS, this paper verifies that the designed RFID temperature measurement tag can not only resist metal effect, but also be well applied to complex metal environment.

A low‐profile microwave device integrating dual‐polarized filtering antenna and lowpass filter

This paper presents a low profile, multifunctional microwave device, which behaves either as a dual-polarized filtering antenna or as a lowpass filter. For the dual-polarized filtering antenna, two introduced quarter-wavelength open-circuit stubs can generate a radiation null at the lower frequency stopband to obtain good frequency selectivity. Moreover, to improve the out-of-band radiation suppression level at high frequencies, the C-shaped short-circuit stubs and U-shaped metal strips are loaded at feeding structures. In the case of the filter, the feeding network and part of the patchwork together to form a lowpass filter. The overall height of the designed microwave device is only 0.05 wavelengths at 2.6 GHz. The results show that the average gain is 8.09 ± 0.54 dBi in the antenna frequency band with out-of-band gain suppression level of 25.1 dB. Moreover, when the device act as a lowpass filter, the insertion loss between the two ports is less than 0.7 dB at the lower working band.