Stepped-impedance Stubs Research Articles

A highly selective UWB bandpass filter using stepped impedance stubs

AbstractWe present a new ultra-wideband (UWB) band-pass filter (BPF) configuration with a stepped impedance short-circuited stub (SISS)-loaded triple-mode resonator (TMR) and stepped impedance radial stub (SIRS). The novel SISS-loaded TMR and SIRS improve the roll-off ratio at both ends. Even though this UWB BPF is based on a single resonator, the measured results show excellent in-band performance with a small insertion loss less than 0.6 dB and return loss greater than −16 dB. The proposed UWB BPF has sharp roll-off ratio of 96 and 43 dB/GHz, respectively, at the lower and upper edges of the pass-band, and a wide stop-band from 10.8 to 15.6 GHz with the rejection greater than 20 dB.

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.

Microstrip lowpass filter with flexible roll-off rates

This paper presents the design of a compact, ultra-sharp roll-off lowpass filter using stepped impedance modified T-type with stepped impedance stub (SMTS). The position of the transmission zero obtained due to the SMTS transmission line can be varied by changing the impedances and electrical lengths of the stepped impedance shunt stub (SIS) of SMTS and therefore, different roll-off rates can be obtained. The design equations used to obtain the parameters of the proposed SMTS structure are derived using the even and odd mode analysis and this enables the designers to calculate the parameters for a specific cut-off frequency (fC). Two SISs are connected, one at the input and another at the output side of SMTS to achieve good stopband characteristics. Finally, a lowpass filter with fC = 1.24 GHz and having a transition band of 0.11 GHz from 1.24 to 1.35 GHz with corresponding attenuation levels of 3–40 dB (roll-off rate is 336.36 dB/GHz) is designed, fabricated and tested. Good agreement is found between the simulated and experimental results.

Filtering Gysel power divider with arbitrary power splitting ratio

AbstractA novel filtering Gysel power divider (PD) structure based on coupled lines is presented to realize arbitrary power splitting ratio and filtering response. The proposed filtering PD consists of three parallel‐coupled lines, two short‐circuited stubs, two stepped impedance stubs and two grounded isolation resistors. Two transmission zeros (TZs) are introduced by the stepped impedance stubs, which can greatly improve the passband selectivity and out‐of‐band rejection performances. Theoretically, closed‐form equations for the proposed structure are derived based on even‐odd mode method. For verification, two filtering Gysel PDs with equal and unequal power splitting ratios ( ) are designed and experimentally demonstrated in this paper.

Compact wideband bandpass filter using quad mode resonator

This paper presents a compact wideband bandpass filter for TETRA band applications. The proposed filter design is based on a quad mode resonator designed using small rectangular loop loaded with four Stepped Impedance Stubs (SISs) and a short circuit stub. The four modes of the resonator help in generating a wide passband. The use of SISs makes the filter compact. In addition to four transmission poles, the resonator inherently generates a transmission zero above the higher end of passband. Two transmission zeros are generated by the input/output coupling which helps in increasing the selectivity and also for achieving wide stopband. This filter provides a 3 dB fractional bandwidth of 30.33% and maximum insertion loss of 1.3 dB at the center frequency 0.36 GHz with a compact size of 0.125 λg × 0.085 λg (4.1 × 2.78 cm2).

Quad notched-band UWB BPF based on quintuple-mode resonator

The design of a novel microstrip ultra-wideband (UWB) bandpass filter with quad narrow notched-band functionality is presented. The filter consists of a multi-mode resonator (MMR) constituted from two modified stepped-impedance stubs that generate six resonate modes, five of which are within the UWB passband where the sixth mode is used to extend the upper stopband of the filter. Two transmission zeroes are located at the 3-dB edge of the passband to enhance the filter's selectivity with a skirt factor of 0.955. The MMR is fed through asymmetric interdigital coupled-lines feed to produce controllable notched-band. Additional notched-bands are generated with a parasitic coupled line. The notched-bands are centered exactly to eliminate interference at 5.2 GHz (wireless local area network (WLAN)), 5.8 GHz (WLAN), 6.8 GHz (radio-frequency identification), and 8 GHz (X-band). Good agreement is obtained between simulation and measurement results. The highly compact filter has dimensions of 8.0 × 9.83 mm2.

Compact dual‐band bandpass filter based on dual‐mode modified star shaped resonator

ABSTRACTIn this article, a compact dual‐mode dual‐band bandpass filter with adjustable second passband using a star shaped resonator is proposed. It is loaded with two T‐shaped stepped impedance stubs inside the resonator and these stubs introduce a transmission zero on the upper side of the first passband. A small triangular perturbation element attached to the star loop resonator excites dual degenerate modes and is responsible for the first passband with two transmission poles. Two U‐shaped slots etched on the ground plane control second passband frequency which is derived from the first harmonic. It also helps in attaining two transmission poles in the second passband. Unlike, the conventional orthogonal feed used for dual mode filters, the proposed filter is fed by two arrow shaped feed lines oriented along the straight line and are parallel coupled to the resonator. Finally, a dual‐mode dual‐band bandpass filter is designed and fabricated for WLAN application and the dimensions of proposed filter are 16 mm × 17.32 mm. Measured results of the filter show good agreement with the Full‐Wave simulated results. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:505–511, 2017

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.

Compact paper‐substrate rat‐race coupler deploying modified stepped impedance stub and interdigitated slot resonator for wide‐band harmonic suppression

This study presents the design of a flexible compact rat-race coupler operating at 0.72 GHz on a 1 mm thick paper substrate. The ultra-wide stop-band effect caused due to the combination of the modified stepped impedance stub and the interdigitated resonator slot, offers suppression up to the 14th harmonic. The slow-wave effect caused due to the resonator slot leads to 59.6% size reduction compared with the conventional coupler at the design frequency. The signal transmission through the coupler for different substrate deformation steps has been investigated. Stable responses are reported for the same, making the prototype suitable for flexible electronics applications.

A new method for the precise multiband microwave dielectric measurement using stepped impedance stub

This article presents a new method of wideband dielectric measurement at microwave frequencies. This method can be used to determine the complex dielectric properties of solid and semisolid materials from 0.9 GHz to 4.5 GHz, including the ISM bands of 915 MHz and 2450 MHz. The new method is based on the scattering parameter measurement of a stepped impedance open circuited micro-strip stub, partly loaded with dielectric test material. Current microwave wideband spectroscopy techniques generally measure dielectric materials over a wide range of frequencies but their accuracy is limited. In contrast, narrowband techniques generally measure dielectric properties to a high accuracy but only at a single frequency. This new technique is capable of measuring dielectric properties over a wide range of frequencies to a high accuracy. The technique has been verified by the empirical characterisation of the dielectric properties of Teflon and Duroid 5880 materials. Empirical results were in good agreement with values in the manufacturer’s Data Sheets. The complex permittivity data will be useful for further microwave processing of the materials.

Design of microstrip lowpass-bandpass quintuplexer

This paper presents a novel lowpass-bandpass multiplexer consisting of one lowpass channel and four bandpass channels. Dumb-bell defected ground structures and stepped impedance resonators are employed to extend the stopband of the lowpass filter and bandpass filters, respectively. Stepped impedance stubs are used to bring a sharp selectivity in the lowpass channel design. Good isolation between channels is obtained by careful design of the input signal splitting structure, which is realized by utilizing four shunt open stubs with electric length of quarter-wavelength at the center frequency of the four bandpass channels, respectively. To verify the above concept, a lowpass-bandpass quintuplexer is designed, fabricated, and measured. The cut-off frequency of the lowpass filter is selected to be 1 GHz. The central passband frequencies are chosen to be 2.4, 3.5, 4.6, 5.8 GHz. Experimental measurements are in good agreement with simulations.

Compact ultra‐wideband bandpass filter with notch band based on the impedance matching method

ABSTRACTIn this work, a new ultra‐wideband (UWB) bandpass filter (BPF) with notch band (NB) at 5–6 GHz is presented. The design is performed using the impedance matching method based on optimization of objective function defined in the frequency range 3.1–10.6 GHz. The filter structure is composed of uniform transmission line loaded, at its center, with stepped impedance stub to generate two transmission zeros at cutoff frequencies, and uniform transmission line stub for NB purpose. The fabricated filter has a compact size of 306.17 mm2 and fulfills the UWB BPF specifications with a sharp selectivity and an efficient cancellation of two Wireless Local Area Network frequencies (5.2 and 5.8 GHz). © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2176–2178, 2016

Spoof surface plasmon-based bandpass filter with extremely wide upper stopband**Project supported by the Key Grant Project of Ministry of Education of China (Grant No. 313029), the FDCT Research Grant from Macao Science and Technology Development Fund, China (Grant No. 051/2014/A1), and the Multi-Year Research Grant from University of Macau, Macau SAR, China (Grant No. MYRG2014-00079-FST).

We investigate the guiding modes of spoof surface plasmon polaritons (SPPs) on a symmetric ultra-thin plasmonic structure. From the analysis, we deduce the operating frequency region of the single-mode propagation. Based on this property, a spoof SPPs lowpass filter is then constituted in the microwave frequency. By introducing a transmission zero at the lower frequency band using a pair of stepped-impedance stubs, a wide passband filter is further realized. The proposed filter is fed by a transducer composed of a microstrip line with a flaring ground. The simulated results show that the presented filter has an extremely wide upper stopband in addition to excellent passband filtering characteristics such as low loss, wide band, and high square ratio. A prototype passband filter is also fabricated to validate the predicted performances. The proposed spoof-SPPs filter is believed to be very promising for other surface waveguide components in microwave and terahertz bands.

Design of Microstrip Lowpass-Bandpass Triplexer With High Isolation

This letter proposes a lowpass-bandpass triplexer consisting of one lowpass channel and two bandpass channels. Stepped-impedance stubs are used in the lowpass filter (LPF) design, which bring a sharp selectivity. Defected ground structures are utilized to increase the impedance of one transmission line in the lowpass section, giving improved performance. High Isolation is achieved by careful consideration of the input signal splitting structure. To illustrate the concepts, a lowpass-bandpass triplexer is designed, fabricated and measured. The cut-off frequency of the LPF is chosen to be 1 GHz. The central passband frequencies are selected to be 2.4 and 5.8 GHz. Simulated and measured results are found to be in good agreement with each other. Isolations among the three bands are better than 40 dB.

Novel Notched UWB Filter Using Stepped Impedance Stub Loaded Microstrip Resonator and Spurlines

This paper presents a novel ultrawideband (UWB) bandpass filter using stepped impedance stub loaded microstrip resonator (SISLMR). The proposed resonator is so formed to allow its four resonant frequencies in the UWB passband, which extends from 3.1 GHz to 10.6 GHz. Moreover, two spurline sections are employed to create a sharp notched-band filter for suppressing the signals of 5 GHz WLAN devices. Experimental results of the fabricated filters are in good agreement with the HFSS simulations and validate the design.

High-Selectivity Low-Pass Filters With Ultrawide Stopband Based on Defected Ground Structures

Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband ( $>15 f_{c}$ or $20~f_{c}$ ), low passband insertion loss (<0.3 dB), compact size, and sharp skirt characteristic.

Multimode resonator based on composite right-/left-handed transmission line for UWB bandpass filter application

A new multimode resonator (MMR) using composite right-/left-handed transmission line (CRLH TL) is proposed and discussed. The CRLH TL structure is constructed by cascading interdigital coupled microstrip line sections on which short-ended stepped impedance stubs are loaded. Dispersion characteristic of the transmission line structure is obtained using the Bloch–Floquet theory. The resonator, which has multiresonances electrical behaviors, is especially suitable in ultrawideband (UWB) applications. An UWB filter is presented as an illustration. With transmission zeros introduced at upper stopband, the filter has a sharp skirt performance. In addition, rejection level at lower stopband also gets enhanced due to direct current suppression effects of the multimode resonator. The filter prototype is implemented and measured. The measured results validate the theoretical analysis and show that the filter has a sharp skirt and an out-of-band rejection level as good as 38 dB. Meanwhile, return loss is better than 16 dB. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:815–824, 2015.

Compact dual-band bandpass filter using asymmetric stepped impedance stub loaded multimode resonator

This paper presents, a dual-band bandpass filter using asymmetric stepped impedance stub loaded open loop resonator (OLR) for WLAN and WiMAX application. The outer OLR is realized to operate at lower passband of 2.45 GHz which is directly coupled to input and output ports whereas the asymmetric stepped impedance stub that loads the outer resonator contributes to 3.5 GHz passband. The introduction of asymmetric stepped impedance stub provides further control of improving the upper passband edge selectivity of second passband and in shifting the spurious modes away from second band thereby contributing to the wide upper stopband. The insertion loss is within 1.5 dB for each passband with 10 dB passband bandwidth of 250 MHz at both bands. A stopband up to 10 GHz is also obtained. A prototype is developed and the s-parameters obtained from electromagnetic simulation, equivalent transmission line model and measurement are in close agreement. The overall dimension of the filter is 25.45 × 15.89 mm2 which renders it a compact size.

Compact Quasi-Elliptic Response Wideband Bandpass Filter With Four Transmission Zeros

This letter presents a novel quasi-elliptic response bandpass filter (BPF) with 3 dB fractional bandwidth of 39.8% for 2.4 GHz WLAN application. Four resonant modes from two stepped-impedance stub loaded shorted stepped-impedance resonators (SISLSSIRs) and one dual-mode shorted stub loaded stepped-impedance resonator (SSLSIR) can constitute an asynchronously tuned coupled-resonator circuit which support a wideband performance. Four transmission zeros (TZs), i.e., one TZ due to the mixed electric and magnetic coupling, one TZ due to the harmonic effects, and another two TZs owing to the cross-couplings, are realized on both sides of the passband, resulting in its quasi-elliptic response performance. The radial stubs and high-impedance open stubs are loaded at the middle position of SISLSSIRs to improve the in-band return loss of BPF. The fabricated filter has a compact size of $0.22\lambda_{\bf g}\times 0.22\lambda_{\bf g}$ and wide upper stopband from 2.62 to 7.69 GHz. Good agreement is shown between the simulated and measured results.

Design of a compact dual‐band‐notch ultra‐wideband bandpass filter based on wave cancellation method

In this study, a compact ultra-wideband (UWB) bandpass filter (BPF) with sharp roll-off, improved out-of-band performance and dual-band-notch operation is presented and its design procedure is discussed. In the proposed structure, in order to reject the unwanted harmonic pass bands, a pair of modified cross-shaped coupled lines (CCLs) is implemented along the ports of the filter. Moreover, a pair of half-circle-shaped stubs and a stepped-impedance stub are loaded on the main resonator in order to obtain additional transmission zeros (TZs) which are controllable separately. Implementation of the CCLs and the stub loaded resonator (SLR) reduce the total size of the presented microstrip BPF. Besides, by extending and folding the upper coupled line of each CCLs and also through an open stub which is protruded inside a slot on the main resonator, dual-band-notch operation is added to the performance of the presented filter. The fabricated prototype has a small size and is capable to cover frequency band of 2.8–10.69 GHz with two band-notch functions at 4.9–5.4 and 7.83–8.25 GHz which suppresses the interference between UWB spectrum with wireless local area network (WLAN) and satellite communication frequency bands, respectively. The proposed filter has a compact size while showing good return loss and insertion loss characteristic in the frequency band of interest.