Independently controllable dual‐band microstrip bandpass filter using quadruple‐mode stub‐loaded resonator

In this article, a quadruple‐mode stub‐loaded resonator (QM‐SLR) is introduced and its four modes are excited using a simple approach, which can provide a dual‐band behavior. By changing the length of the loaded stubs, independently tunable transmission characteristics of the proposed quadruple‐mode stub‐loaded resonator were extensively described for filter design. Moreover, microwave varactors were adopted to represent the length variation of the loaded stubs for the dual‐band tunability. The equivalent circuit modeling of the open stub with microwave varactor was given and discussed. Then, adopting the compact quadruple‐mode stub‐loaded resonator with three varactors, an independently controllable dual‐band bandpass filter (BPF) was designed, analyzed, and fabricated. Its separated bandwidths and transmission zeros can be tuned independently by changing the applying voltage of the microwave varactors. A good agreement between simulated and measured results verified the design methodology. The proposed filter possesses compact size, simple structure, and excellent dual‐band performances. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:602–608, 2016.     

Compact wideband microstrip bandpass filter with wide upper stopband based on coupled‐stub loaded resonator

A novel wideband microstrip bandpass filter (BPF) based on a coupled‐stub loaded resonator (CSLR) is presented in this article. The CSLR is constructed by attaching one short‐circuited parallel coupled microstrip line (PCML) in shunt to a high impedance microstrip line. The filter bandwidth can be conveniently controlled via reasonable adjusting of the impedance of PCML. Moreover, new defected microstrip structures (DMSs) introduced in the PCML functions as a means of adjusting the positions of transmission zeros, created by the PCML. The resonant mode and transmission zero chart are given, indicating that the higher modes could be suppressed by the transmission zeros. Finally, to validate the proposed method, two wideband BPF filters with and without DMSs centered at 3 GHz with 3 dB fractional bandwidth of 87% are designed and fabricated. The measured results show that both the return losses are better than 15.8 dB, while the BPF with DMSs has a ?19.4 dB isolation wideband from 1.57 to 4.23 . The measured results are in excellent agreement with full‐wave electromagnetic simulation results. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:122–128, 2015.     

Compact wideband bandpass filter based on double‐T‐shaped stub loaded resonator and loading technique for zero‐voltage point

In this article, a double‐T‐shaped stub centrally loaded uniform impedance resonator (UIR) is introduced and its resonant characteristics are well clarified, which provided a simple approach for triple‐mode wideband bandpass filter (BPF) design. The double‐T‐shaped stub consists of a T‐shaped stub at the center of UIR and two shunt uniform‐impedance stubs at the T‐shaped stub. Furthermore, loading technique for zero‐voltage point is employed to guide design procedure from UIR to the proposed resonator. The resonant frequencies of the first three modes for the resonator can be free to adjust by the length of the UIR and the two kinds of stub. Finally, a compact wideband BPF is designed, fabricated, and measured. The measured results are in good agreement with the full‐wave simulation results. The realized wideband filter exhibits a 3 dB fractional bandwidth of 69.1% with good in‐band filtering performance, wide stopband, and sharp out‐of‐band rejection skirt.     

Compact differential dual‐band bandpass filter using single quad‐mode metal‐loaded dielectric resonator

This letter presents a novel miniaturized differential dual‐band bandpass filter (BPF) using a single quad‐mode metal‐loaded dielectric resonator (DR). The differential dual‐band BPF is designed in a single‐cavity configuration with one quad‐mode DR and four feeding probes, featuring compact size. The rectangular DR is directly mounted on the bottom of the metal cavity and covered by a metal plate on the top surface. It allows two pairs of orthogonal modes (LSE₁₀ and LSM₁₀), which can be differentially excited and coupled by introducing proper perturbation for constructing dual‐band differential‐mode frequency response. To validate the proposed idea, a compact differential BPF with good performance using a quad‐mode DR cavity is designed, fabricated, and measured. The simulated and measured results with good agreement are presented.     

Independently controllable dual‐band filter using single quad‐mode silver‐loaded dielectric resonator

This article proposes a novel bandpass filter with two controllable passbands using a single quad‐mode silver‐loaded dielectric resonator (DR). The silver plane is inserted in the middle of the cubic DR and two degenerate pairs are used to build the two passbands. Because of the distinct E‐field distributions, the silver plane has significant effect on the degenerate pair (TE^x₁₁₂ and TE^y₁₁₂), whereas another one (TE^x₁₁₁ and TE^y₁₁₁) remains unchanged. With the aid of the silver plane, both center frequencies and bandwidths of the two bands can be controlled independently. To verify the proposed idea, a prototype dual‐band BPF is designed and fabricated. Good agreement between simulated and measured results can be observed.     

Novel slotted stepped‐impedance resonator and its application to compact and high performance bandpass filter and diplexer design

By etching slots in the low‐impedance section of the conventional stepped‐impedance resonator, a novel slotted stepped‐impedance resonator (SSIR) is proposed. As two examples, a fourth‐order bandpass filter (BPF) operating at 1 GHz with a size of 0.078 λ_g × 0.062 λ_g and a miniaturized diplexer operating at 0.9/1.57 GHz with a size of 0.054 λ₀ × 0.086 λ₀ are designed based on the proposed SSIR. The fabricated BPF exhibits a high selectivity and a wide ?30 dB rejection upper stopband from 1.13 f₀ to 6.52 f₀, while the fabricated diplexer has up to ?60 dB output isolation. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Compact dual‐band bandpass filter and diplexer using hybrid resonant structure with independently controllable dual passbands

In this article, a compact dual‐band bandpass filter (BPF) is developed using a hybrid resonant structure, which consists of a microstrip stub‐loaded dual‐mode resonator and a slotline stub‐loaded dual‐mode resonator. These two resonators, both having two controllable resonant modes and one transmission zero (TZ), are analyzed and used to construct two desired passbands of a dual‐band BPF. Multiple TZs are generated by introducing a source‐load coupling, thus improving the selectivity of the passbands. Then, the dual‐band BPF is reshaped to configure a compact diplexer. The inherent TZs of the two proposed resonators are designed to improve the frequency property and port isolation of the diplexer. Finally, a dual‐band BPF and a diplexer with the lower and upper passbands centered at 2.45 and 3.45 GHz, respectively, are designed, fabricated, and measured to verify the proposed structure and method.     

A piezoelectric transducer‐tuned microstrip‐ring resonator oscillator operating at the second resonant mode of the ring resonator

A microstrip open‐loop resonator oscillator operating at even modes is proposed. The even mode of the ring circuit can be predicted by using a simple transmission‐line model. The new oscillator has a characteristic similar to that of a push‐push oscillator. In addition, in comparison with the push‐push oscillator, the new oscillator with one active device can minimize the size and lower the cost. A voltage‐controlled piezoelectric transducer (PET) is used to vary the resonant frequencies of the ring resonator, which in turn tunes the oscillator with a good tuning range of 4.9% at around 12.1 GHz. This tuned oscillator should have many applications in wireless systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Dual‐band band pass filter using stub‐loaded open‐loop resonators with wide controllable bandwidths

Two dual‐band band pass filters (BPF) using stub‐loaded open‐loop (SLOL) resonator are presented in this article. A novel coupling tuning method by changing the relative coupling position of the resonators is proposed to control the bandwidth of each passband in a wide range. Transmission zeros are created to improve the selectivity by source‐load coupling. Because of the large ratio of two bandwidths, a novel dual‐band matching method is proposed to match the different load impedances at two passband frequencies to the same source impedance. Hence, relax the fabrication requirement of gap. The proposed dual‐band band pass filter is designed and fabricated. The measured 3 dB fractional bandwidths (FBWs) of two 2.45/5.25 GHz dual‐band BPFs are 6.5%/14.5% and 9.8%/5.5%, respectively. The results are in good agreement with the simulation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:367–374, 2014.     

High‐order dual‐band superconducting filter with independently controllable passbands and wide stopband

A stepped‐impedance‐stub loaded stepped‐impedance resonator (SISLSIR) is proposed to design a dual‐band bandpass filter. The even‐ and odd‐mode frequencies and the coupling strength of the proposed resonators can be independently designed and adjusted. A dual‐feedline structure is used to meet the required external couplings of the 2 passbands. Thus, both the center frequencies and the bandwidths of the 2 passbands can be independently controlled. A 6‐pole dual‐band filter with the passbands of 3300～3600 MHz and 4800～5000 MHz is successfully designed using the proposed method and fabricated with YBCO/MgO high‐temperature superconducting (HTS) wafer. The measured results of the filter exhibit high performance and match well with the simulations. The measured insertion losses are less than 0.2/0.3 dB, and the return losses are greater than 15/14 dB for the lower/upper passbands, respectively. The out‐of‐band rejection is greater than 68 dB up to 12 GHz.     

An unbalanced‐to‐balanced diplexer based on substrate integrated waveguide cavity

A novel unbalanced‐to‐balanced diplexer based on a dual‐mode substrate integrated waveguide (SIW) cavity is proposed and implemented. The diplexer is realized using one dual‐mode cavity and two single‐mode cavities. By properly choosing, feeding and coupling the cavity operating at the TE₁₀₂ or TE₂₀₁ mode, so as to not only provide capabilities to realize the desired unbalanced‐to‐balanced transmission within both Rx and Tx channels but also realize good differential‐mode channel‐to‐channel isolation. To the author's knowledge, we present for the first time an unbalanced‐to‐balanced type diplexer based on the application of SIW. The proposed diplexer was successfully designed, simulated, and fabricated. Good agreement can be observed between simulated and measured performances in our letter. The measured in‐band common‐mode rejection is better than 33 dB for both channels. A minimum differential‐mode isolation of about 50 dB across the Rx band and about 40 dB across the Tx band is also observed in the measurement. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:173–177, 2015.     

A tunable third‐order bandpass filter based on combining dual‐mode square‐shaped substrate integrated waveguide resonator with triangular‐shaped resonator

A frequency reconfigurable third‐order bandpass filter based on two substrate integrated waveguide (SIW) cavities is presented in this article. The purposed filter consists of a dual‐mode square‐shaped resonator and a triangular‐shaped resonator. In the square‐shaped cavity, four lumped capacitors are loaded as electrical tuning elements in the area where the electric fields of diagonal TE₂₀₁ and TE₁₀₂ modes are strongest. And an another capacitor is loaded at the suitable region of the triangular‐shaped cavity. Square‐shaped cavity introduces two transmission zeros and the triangular‐shaped cavity can suppress out‐of‐band spurious modes. The method that combines the resonators with different shapes and multiple modes into an organic whole cannot only achieve synchronous tuning but also have complementary advantages and improve out‐of‐band rejection. To verify its practicality, a SIW reconfigurable bandpass filter is simulated when the capacitance value varies from 0 to 1.4 pF and measured at 0.7, 0.8, and 0.9 pF, respectively. Measured results show that when the center frequency is tuned from 3.42 to 3.52 GHz, the proposed filter exhibits good tuning performance with insertion loss of less than 2.5 dB and return loss of better than 10 dB, which is suitable for fifth‐generation communication system.     

Compact Dual‐/Tri‐/Quad‐Band banpass filters using shorted stub loaded stepped‐impedance resonator

In this article, the shorted stub loaded stepped‐impedance resonator (SSLSIR) with the individually tunable first even resonant mode and first odd resonant mode is applied to design dual‐, tri‐, and quad‐band bandpass filters (BPFs). The SSLSIR dual‐band BPF with asymmetrical coupling is realized using the first even resonant modes and the first odd resonant modes of a set of SSLSIRs. Then, the high‐impedance feeding lines of SSLSIR dual‐band BPF is modified to produce a new passband, and thus a new tri‐band BPF is realized. The proposed quad‐band BPF consists of two sets of SSLSIRs with symmetrical coupling. Each of the designed circuits occupies a very compact size and has a good in‐band out‐of‐band performance. Good agreements are observed between the simulated and measured results. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:601–609, 2015.     

New multi‐standard dual‐wideband and quad‐wideband asymmetric step impedance resonator filters with wide stop band restriction

New multi‐standard wide band filters with compact sizes are designed for wireless communication devices. The proposed structures realize dual‐wideband and quad‐wideband characteristics by using a new skew‐symmetrical coupled pair of asymmetric stepped impedance resonators, combined with other structures. The first and second dual‐wideband filters realize fractional bandwidths (FBW) of 43.2%/31.9% at the central frequencies (CF) of 1.875/1.63 GHz, and second bandwidths of 580 MHz/1.75 GHz at CF of 5.52/4.46 GHz, respectively. The proposed quad‐band filter realizes its first/second/third/fourth pass bands at CF 2.13/5.25/7.685/9.31 GHz with FBW of 46.0%/11.4%/4.6% and 5.4%, respectively. The wide pass bands are attributed to the mutual coupling of the modified ASIR resonators and their bandwidths are controllable by tuning relative parameters while the wide stop band performance is optimized by the novel interdigital cross coupled line structure and parallel uncoupled microstrip line structure. Moreover, the quad band is generated by introducing the novel defected rectangle structure. These multi‐standard filters are simulated, fabricated and measured, and measured results agree well with both simulated results and theory predictions. The good in‐band and out‐of‐band performances, the miniaturized sizes and simple structures of the proposed filters make them very promising for applications in future multi‐standard wireless communication.     

Novel analysis of the size and orientation dependent resonance phenomenon of the microstrip line coupled complementary split‐ring resonator

The purpose of this article is to provide a comprehensive investigation on the resonance phenomenon of microstrip line coupled complementary split‐ring resonator (CSRR) with different orientation and relative size. It is shown that when the relative size of the CSRR is smaller than the host line, the CSRR with its slit oriented orthogonal to the line axis will not excite effectively and show weak resonance behavior. However, when the slit is positioned along the line axis, the cross‐polarization effect comes into play, which excites the CSRR through the mixed coupling. To ensure the correctness, several numerical simulations are carried out for different substrate height and relative permittivity. Finally, a prototype is fabricated and measured for the experimental validation.     

Compact ultra‐wideband bandpass filter with configurable stopband based on diamond‐shape resonator

An ultra‐wideband compact bandpass filter (BPF) with configurable stopband by tuning transmission zeroes is proposed in this paper. The ultra‐wideband bandpass response is based on a diamond‐shape resonator consisting of a pair of broadside coupled diamond‐shape microstrip lines, within which a diamond shape defected ground structure (DGS) is etched in the middle. Flexible transmission zeros realized by open and short stubs can be easily adjusted to improve band selectivity and harmonic suppression. Measurement result shows that the dedicated device has a 3 dB fractional bandwidth of 148% (0.94‐6.36 GHz) with 20 dB rejection stopband from 6.87 to 9.7 GHz (77.5%) which agrees good with the simulate performance. The overall size of the proposed BPF is 0.27 λ_g × 0.23 λ_g.     

Compact dual‐ and triband bandpass filter using frequency selecting coupling structure loaded stepped‐impedance resonator

This article presents two novel resonators, that is, frequency selecting coupling structure loaded stepped‐impedance resonator (FSCSLSIR) and π‐section loaded FSCSLSIR. The resonator behaviors and guidelines are given to design FSCSLSIR dual‐band bandpass filter (BPF) and π‐section loaded FSCSLSIR triband BPF. The proposed dual‐ and triband BPF have very compact sizes of 0.13 λ_gd × 0.06 λ_gd and 0.115 λ_gt × 0.074 λ_gt, respectively. Moreover, good return loss, low insertion loss, and high band‐to‐band isolation can be observed, and the proposed FSCSLSIR dual‐band BPF has an ultrawide stopband from 5.79 to 36 GHz. The experimental results are in good agreement with the simulations. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:427–435, 2015.     

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.     

Compact bandpass filter based on SIW loaded by open complementary split‐ring resonators

A compact substrate integrated waveguide (SIW) with open complementary split‐ring resonators (OCSRRs) loaded on the waveguide surface is proposed. The OCSRRs can be interpreted in terms of electric dipoles and they are good candidates to behave as electric scatterers. By loading OCSRRs on the waveguide surface, a forward‐wave pass‐band propagating below the waveguide cutoff frequency is generated. The resonance frequency of the OCSRRs is approximately half of the resonance frequency of the complementary split ring resonator (CSRR). Therefore, the electrical size of this particle is larger than the CSRRs and the OCSRRs are more appropriate for the SIW miniaturization. A bandpass response with a sharp rejection frequency band is obtained by properly manipulating the structure of the elements. By changing the orientation of the OCSRRs, two types of unit cell are proposed. Moreover, by resizing the OCSRRs, resonance frequency can be easily moved and the bandwidth can be tuned by the coupling between two OCSRRs. Compared with some other reported bandpass filters (BPFs) with SIW technique, the presented BPF has great improvements on size reduction and selectivity. To verify the methodology, two filters with center frequency of 5.5 GHz are designed and measured. The measured results are in good agreement with the simulated ones. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:674–682, 2016.     

A novel compact wideband filter using three‐mode dual‐ring resonator

A novel compact wideband filter using three‐mode dual‐ring resonator is presented in this article. The resonator is constructed by two quarter wavelength transmission lines and a cascaded half wavelength dual‐ring. Formulae based on even‐ and odd‐mode analysis are derived to analyze the locations of the transmission poles and zeros of the resonator. Due to the transmission zeros in the lower and upper stopbands, the proposed filter exhibits sharp attenuations near the passband as well as very wide stopband. The filter is successfully realized by full wave EM simulation and fabricated. The measured responses of the filter agree well with the design simulation, and show that the fabricated filter has an insertion loss of better than 1.5 dB in the passband and two rejections of greater than 20 dB in the stopbands from 0 to 10GHz.