Open-circuited Stubs Research Articles

Design and Analysis of UWB Filter with Single Notch Band

In this article, design and electrical analysis of UWB filter with a notch band is presented. Initially basic UWB filter is designed by using parallel coupled microstrip line with rectangular shaped defective ground plane. Then, to achieve band notch characteristics to eliminate satellite signal at 6.25 GHz, a quarter wavelength open circuit stub is connected with feed line of basic filter. To validate the design theory, a microstrip line UWB BPF with single notch band is designed, and fabricated. The electrical analysis of this filter is also proposed in this paper. The comparison among the results, in the simulated frequency response, measured VNA results and electrical model response shows close agreement. This filter compact in size approximately (17 mm × 8.5 mm). The filter is design by using microwave substrate GML 1000 of dielectric constant 3.2 of height 30 mil. This filter may be useful for microwave communication system.

An analysis of a DGS‐inserted stub resonator and its application to an optimum BSF

AbstractA novel defected ground structure (DGS)‐inserted stub (DIS) resonator is proposed. The proposed DIS resonator features a typical dumbbell‐shaped DGS inserted into an conventional open‐circuited stub (OCS) resonator, and it is modeled by a series LC resonator. The inserted DGS can suppress a harmonic and extend an upper passband. Therefore, the proposed DIS resonator to generate a resonance at 2.0 GHz keeps the upper passband up to 8.0 GHz or higher, while the OCS resonator with the same resonance gives rise to the harmonic at 5.78 GHz. These properties are investigated through EM simulation. Moreover, in order to verify the applicability of the proposed DIS resonator to microwave filters, two optimum bandstop filters (BSFs) with the same stopband at 2.0 GHz using the proposed DIS and OCS resonators are fabricated and measured, respectively. Compared to the optimum BSF using the OCS resonator, the optimum BSF using the proposed DIS resonator shows two notable improvements: a 50% increase in the upper passband and a 15% reduction in the size.

Gysel power divider with efficient second and third harmonic suppression using one resistor

A Gysel power divider/combiner with the second and third harmonic suppression using one resistor is proposed. Three open-circuit stubs are used to suppress the second and third harmonics. To calculate the values of the design parameters, the closed-form design equations are derived. A sample power divider is designed at 1 GHz to verify the design procedure. The measured results are nearly in agreement with the simulation results. The proposed Gysel power divider provides a high power-handling advantage over Wilkinson power divider. Moreover, it has a fractional bandwidth of 30% and harmonic suppression of 25 and 35 dB at the second and third harmonics, respectively.

Sharp Rejection and Wide Stopband Microstrip Lowpass Filters using Complementary Split Ring Resonators

Chebyshev microstrip lowpass filters with improved performance, achieved by means of circular complementary split ring resonators (CSRR), are presented. The CSRR particles exhibit a frequency rejection bandwidth in the vicinity of their resonant frequencies that can be used to meliorate both the selectivity and stopband in microstrip lowpass filters. Two configurations have been used: a stepped-impedance model and a configuration using open-circuited stubs. Microstrip filters having 5, 7 and 9 poles were designed and fabricated. Selectivity values up to 86 dB/GHz and suppression levels reaching 60 dB in the stopband were obtained. The filters have cutoff frequencies around 2 GHz and rejection band up to 10 GHz. The insertion of the designed CSRR resonators in the ground plane of the filters removes all the transmission spurious observed in the analyzed frequency band. No considerable variation in the passband group delay is observed in the CSRR-based lowpass filters. It is also made a comparison among the filters designed in this and other referenced works, considering their number of poles and size. The measured results are in good agreement with the simulated ones.Â

A 2.4/3.5/5.2/5.8‐GHz quad‐band BPF using SLRs and triangular loop resonators

A modified triangular loop resonator with an open-circuited stepped-impedance stub, which can generate two closely spaced passbands at 5.2 and 5.8 GHz, is analysed. For verification, the triangular loop resonators along with stub-loaded resonators (SLRs) are then employed to design a compact 2.4/3.5/5.2/5.8-GHz quad-band bandpass filter (BPF) for wireless local area networks as well as worldwide interoperability for microwave access applications. Each of the four centre frequencies in the proposed quad-band BPF is able to be controlled due to the design freedom.

Slow Wave Applications of Electromagnetically Induced Transparency in Microstrip Resonator

We report a novel guided-wave resonator that supports multiple bands of electromagnetically induced transparency (EIT). The platform for the spatial and spectral interference is obtained by a microstrip transmission line loaded with proximity-coupled open-circuited stubs. We show experimentally that with two microstrip open stubs, a complete destructive interference takes place leading to a single EIT band with near-unity transmission efficiency. More interestingly, the addition of a third stub results in a supplementary EIT band with a Q-factor of 147 and an effective group refractive index of 530. With the open-stub configuration, the EIT phase response can be dynamically controlled by varying the capacitance between the adjacent stubs without breaking the transmission path of the underlying electromagnetic waves. Therefore, the proposed structure is well suited for buffering and tunable phase modulation applications. Since the proposed structures are compact and fully planar, we anticipate seamless integration with low-profile high frequency electronics.

Narrowband balanced absorptive bandstop filter integrated with wideband bandpass response

A novel narrowband balanced absorptive bandstop filter (BABSF) with wideband bandpass response is proposed, which consists of four coupled-line sections with open-circuited stubs, two half-wavelength transmission lines, and two ground resistors. Excellent differential-mode response with narrowband bandstop response and wideband bandpass property is realised for high frequency selectivity. Good common-mode suppression can be achieved, rejecting the interference noise. For demonstration, a BABSF prototype operating at 2 GHz is designed with good agreement between simulated and measured results.

Dual wide‐band miniaturized negative group delay circuit using open circuit stubs

AbstractIn this letter, dual band negative group delay circuit (DBNGDC) utilizing a couple of one quarter guided wave length ( ) open circuited stubs (OCSs) is presented. The centre frequencies ( ) are fully controlled with the stub lengths. On the other hand, the target negative group delay (NGD) is obtained using couple of resistors ( ) that connect each OCS to the main microstrip line. The designed DBNGDC accomplishes 52% size diminution compared with smallest size has ever been achieved before. Moreover, 0.2 and 0.4 GHz zero‐NGD bandwidths (BW) are achieved.

A Novel Compact Wideband Power Divider with Ultra-wideband Harmonic Suppression

A compact wideband power divider based on the coupled lines and open stubs is presented in this paper. The proposed power divider has many advanced properties involving excellent input return loss, wide working band, high in-band isolation, ultra-wideband stopband, and outstanding harmonic suppression. The two sections of coupled lines are used to extend the passband while the open-circuit stubs are adopted to achieve ultra-wide stopband by introducing three transmission zeroes. Furthermore, high isolation within the operating band is realized with two resistors. The detailed design theories and procedures are provided in this paper. A power divider prototype with 10-dB bandwidth of 157.8% operating from 0.17 to 1.44 GHz and ultra-wide stopband from 2.04 to 5.07 GHz below − 30 dB is designed, fabricated, and measured for demonstration.

A Size-Reduced Tri-Band Gysel Power Divider With Ultra-Wideband Harmonics Suppression Performance

In this paper, a size-reduced tri-band Gysel power divider (PD) with ultra-wideband harmonics suppression performance, simple structure, high-power handling capability, and independently controllable bandwidth is first presented. The three passbands are introduced by two tri-band biasing networks whose impedances can also be utilized to control the bandwidths of the three passbands independently. With the introduction of slow-wave transmission lines and coupled lines with series open-circuited stubs, a reduced size and ultra-wide stopband can be obtained, respectively. Detailed closed-form design equations are derived and validated with a design of PD operating at 2.0, 2.5, and 3.0 GHz. Also, two additional circuits are designed, simulated, and fabricated. One is utilized to obtain the optional range of the three passbands, and the other is to make a comparison with the proposed PD. All the measured results agree well with the corresponding simulated ones. Proper impedance matching, isolation, and a wider 3-dB fractional bandwidth can be obtained, which is 18.5%, 20.7%, and 13.0%, respectively, at each passband. In addition, more bands can be easily extended to the proposed PD by introducing more open-circuited stubs in the tri-band biasing networks.

Compact Dual-Band Differential Bandpass Filter Using Quadruple-Mode Stepped-Impedance Square Ring Loaded Resonators

In this paper, a new quadruple-mode stepped-impedance square ring loaded resonator (SI-SRLR) is proposed, and a high-performance dual-band differential bandpass filter (BPF) is developed. Resonant characteristics of the SI-SRLR are investigated by the even-/odd-mode method and simulation techniques. Two differential-modes (DMs) of the SI-SRLR are used to form the dual differential passbands. The admittance ratio $K$ of the SI-SRLR is chosen appropriately to prevent the common-mode (CM) interference with DM operations. Moreover, an open-circuited stub is added to enhance the CM suppression, while a source-load coupling is introduced to produce multiple transmission zeros and improve significantly the frequency selectivity of DM passbands. Finally, a dual-band differential BPF is designed, fabricated, and measured. Good agreement between the simulated and measured results verifies well the proposed structure and design method.

Compact Microstrip Lowpass Filter with Low Insertion Loss for UWB Medical Applications

A microstrip lowpass filter based on transmission line elements for UWB medical applications is proposed in this paper. The filter is constructed of two symmetric shunt open‐circuited stubs and three series unit elements. The filter is designed to exhibit an elliptic function response with equal ripple in the passband and the rejection band. A prototype is successfully designed, fabricated, and measured, where a good agreement is attained. The filter shows a high filtering selectivity and an ultra‐wide stopband up to 20 GHz with an attenuation level of more than 20‐dB. The filter is compact and has a low insertion loss and an ultra‐wideband (UWB) rejection which makes it attractive for many technologies such as UWB medical applications.

Four-way Gysel power divider/combiner with back-to-back configuration for dual-band operation

In this paper, a four-way dual-band Gysel power divider (GPD)/combiner based on a back-to-back microstrip structure method is proposed and investigated. A two-layer substrate is adopted to implement this PD. In order to divide the input signal into four equivalent signals, the input and four output ports of the proposed PD are placed on the top and the four external isolation resistors are placed on the bottom layer of the substrate. Furthermore, the dual-band response is achieved by adding a short-circuit stub and an open-circuit stub to the structure. Then, the theoretical closed-form design formulas are derived based on the considered conditions and circuit transmission line theory. Finally, for verification purpose, a prototype PD is designed, fabricated, and measured which works at dual frequencies of 1 and 2 GHz simultaneously. The good agreement between simulation and measurement results, which show good impedance matching, isolation, as well as power transmission, verifies the correctness of the design theory.

Wideband Four-Way Filtering Power Divider With Isolation Performance Using Three Parallel-Coupled Lines

A wideband four-way power divider (PD) with filtering response and high isolation is presented. This divider is formed by connecting a pair of three parallel-coupled lines and two stepped-impedance open-circuited stubs to output ports of a traditional Wilkinson PD. In addition, three resistors, including two air-bridged resistors, are properly placed to achieve perfect isolations between all output ports. A prototype of the proposed PD is designed, simulated, and measured. The measured results validate the 86.4% bandwidth centered at 3.68 GHz with more than 15-dB out-of-band rejection, more than 17-dB isolations, and less than 0.3-dB amplitude imbalances, respectively.

Synthesis and Design of Miniaturized Wideband Bandpass Filters With Scaled Transmission Line for Spurious-Response Suppression

A scaled transmission line method has been proposed to realize a class of size miniaturized and spurious-response suppressed wideband bandpass filters (BPFs). The mechanism is based on a dual-band BPF with its lower passband assigned as the primary passband and far away from the upper one. Therefore, the primary passband is always at a relatively small electrical length frequency, which is a prerequisite to scale the transmission line network. Three types of line scaling/approximating are discussed as stub loaded transmission lines, short-, and open-circuited stubs. Comparing before and after scaling, these circuit components preserve an almost exact characteristic in the primary passband frequency range but introduce adjustable transmission nulls in the spurious passband. For suppressing different spurious responses, line scaling factors are varied for different circuit components to locate transmission nulls at desired places. Two circuit examples in the circuit topology as distributed and mixed circuit networks have been experimentally demonstrated, which has approved the miniaturization and spurious suppression benefits of the proposed technique.

Wideband balanced‐to‐unbalanced filtering unequal power divider with wide stopband and isolation

A novel wideband balanced-to-unbalanced filtering unequal power divider with wide stopband and isolation is proposed. The wideband filtering response with high frequency selectivity can be realised easily using the modified two-port coupled lines with short- and open-circuit stubs, thus generating two transmission zeros near the passband. The complete closed-form equations are presented. A fabricated prototype with 1 : 2 power dividing ratio is simulated and measured to validate the proposed design.

Pre-Stub Tuner for Reduction of Radio-Frequency Voltage Along Transmission Line in EAST-ICRF System

The ion cyclotron range of frequency (ICRF) heating system of the Experimental Advanced Superconducting Tokamak (EAST) is characterized by high radio-frequency (RF) power up to 12 MW and wide frequency range over 25 to 70 MHz. A high RF power transmission system composed of a liquid impedance matching device, ceramic feedthrough, decoupler, and ICRF heating antenna with four straps has been in operation for some years. In a high-power ICRF experiment, one issue that needs to be solved is the high RF voltage on the coaxial transmission line between the ICRF antenna and the impedance matching device, which is caused by low antenna loading resistance compared to the characteristic impedance of the transmission line. A stub tuner is employed to reduce the RF voltage in the EAST ICRF power transmission system. Two methods to reduce RF voltage using short-circuited and open-circuited stub tuners are introduced in detail. The optimized position and length of the stub tuner are analyzed and calculated to achieve a smaller voltage reduction ratio (VRR) on the transmission line. The test with the stub tuner to reduce the RF voltage of the transmission line is carried out, and a RF VRR of ∼0.57 is achieved. The RF voltage on the transmission line is significantly reduced, and the capability of the transmission power is obviously improved. Ohmic losses caused by the surface resistance of the conductor of the coaxial transmission line are also decreased, and the probability of breakdown within the transmission line is reduced under high RF power operation.

Design of Compact Wide Stopband Microstrip Low-pass Filter using T-shaped Resonator

In this letter, a compact microstrip low-pass filter (LPF) using T-shaped resonator with wide stopband is presented. The proposed LPF has capability to remove the eighth harmonic and a low insertion loss of 0.12 dB. The bandstop structure using stepped impendence resonator and two open-circuit stubs are used to design a wide stopband with attenuation level better than −20 dB from 3.08 up to 22 GHz. The proposed filter with −3-dB cutoff frequency of 2.68 GHz has been designed, fabricated, and measured. The operating of the LPF is investigated based on equivalent circuit model. Simulation results are verified by measurement results and excellent agreement between them is observed.

Differential‐mode bandpass filter on microstrip line with wideband common‐mode suppression

A novel differential-mode (DM) bandpass filter (BPF) on microstrip-line topology with wideband common-mode (CM) suppression is presented. The DM BPF is composed of a pair of half-wavelength (λ/2) uniform impedance resonators and two coupled-line sections as feeding scheme. By installing an open-circuited stub in the middle of the coupled-line section, spurious CM response can be tremendously suppressed over a wide band. Thus, wideband CM suppression is realised in and beyond core DM passband. Finally, a DM BPF is designed and fabricated to support the proposed design concept.

High Performance Single-Ended Wideband and Balanced Bandpass Filters Loaded With Stepped-Impedance Stubs

High-performance single-ended wideband and balanced bandpass filters loaded with stepped-impedance stubs are proposed in this paper. For the proposed wideband filter and the differential mode of the proposed balanced filter, two transmission zeros near the passband are realized by using simple stepped-impedance stubs, which enhances the passband selectivity of these new filters. The analytical and accurate design equations for transmission poles and zeros of these single-ended and balanced filters are provided based on the scattering-parameters theory. The single-ended bandpass filter, employing a T-shaped structure to produce a wide passband, is achieved with 3-dB fractional bandwidth of 79.33%, 19-dB passband return loss, and 35-dB harmonic suppression ( $1.56f_{\mathrm { {0}}}$ – $2.51f_{\mathrm { {0}}}$ , $f_{\mathrm { {0}}}$ is the center frequency of the wide passband). The 3-dB differential-mode fractional bandwidth of 33% with 22-dB passband return loss and the 30-dB harmonic suppression ( $1.29f_{\mathrm { {0}}}$ – $2.67f_{\mathrm { {0}}})$ are obtained in the proposed balanced bandpass filter. In addition, by inserting open-circuit stubs into the proposed balanced bandpass filter, over 25-dB common-mode suppression is obtained from 0 to $2.67f_{\mathrm { {0}}}$ . Good agreement is observed between the simulation and measurement results.