A tunable balanced dual‐band BPF with quasi‐independently controlled center frequency and bandwidth

In this paper, a balanced dual‐band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented by employing stub loaded resonators (SLRs) and stepped impedance resonators (SIRs) into balanced microstrip‐slotline (MS) transition structures. The balanced MS transition structures can achieve a wideband common‐mode (CM) suppression which is independent of the differential‐mode (DM) response, significantly simplifying the design procedure. Six varactors are loaded into the resonators to achieve the electrical reconfiguration. The proposed balanced dual‐band BPF can realize quasi‐independently tunable center frequencies and bandwidths. A tuning center frequency from 2.48 to 2.85 GHz and a fractional bandwidth (20.16%‐7.02%) with more than 15 dB return loss and less than 2.36 dB insertion loss are achieved in the first passband. The second passband can realize a tuning center frequency from 3.6 to 3.95 GHz with more than 12 dB return loss and less than 2.38 dB insertion loss. A good agreement between the simulated and measured results is observed.     

A balanced dual‐band bandpass filter with independently tunable differential‐mode frequencies

A balanced dual‐band bandpass filter (BPF) with independently tunable differential‐mode (DM) frequencies is proposed in this letter. The proposed BPF is composed of complementary split‐ring resonators (CSRRs) etched on the ground and varactors loaded on the resonators. A balanced stepped‐impedance microstrip‐slotline transition structure is introduced to transfer the DM signals successfully and block the common‐mode (CM) signals transmission. Good DM transmission and CM suppression can be achieved. Moreover, by changing the reverse bias voltages of the varactors loaded on coupling CSRRs, two DM resonant frequencies of the proposed balanced BPF can be tuned independently. To verify the feasibility of the design method, a balanced BPF with DM frequency ranging from 0.80 GHz to 1.12 GHz and 1.55 GHz to 2.05 GHz is fabricated and measured. Good agreement between the simulation and measurement results demonstrate the validity of the design.     

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual‐band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U‐shape half‐wavelength resonator, a folded stub‐loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential‐mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common‐mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual‐band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.     

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.     

A balanced tri‐band bandpass filter with high selectivity and controllable bandwidths

In this article, a balanced tri‐band bandpass filter (BPF) with high selectivity and controllable bandwidths is proposed. Two differential‐mode (DM) passbands are formed by applying stepped impedance resonators into the design. Uniform impedance resonators are introduced to realize the third DM passband. Moreover, frequencies and bandwidths of DM passbands can be independently controlled by the lengths of resonators and the gaps between them. In addition, good DM transmission can be realized while high common‐mode suppression is achieved intrinsically without affecting the DM parts, thereby simplifying the design procedure significantly. In order to validate the practicability, a balanced tri‐band BPF operating at 2.45 GHz, 3.5 GHz, and 4.45 GHz is fabricated and designed. A good agreement between the simulated and measured results is observed.     

Dual‐band differential bandpass filter using stepped impedance resonators

In this article, a novel dual‐band differential bandpass filter using (SIRs) is designed. To demonstrate the design ideas, the differential and common mode equivalent half circuits are built and studied. Two resistors are connected between the two ends of the SIRs to consume the power in common mode. A capacitor is connected between the Ground and Center of the SIR to adjust the spurious frequencies, also strength the coupling of the two SIRs. The theoretical analysis shows the second band can be obtained by the proper impedance ratios of the resonances and the capacitor connected to the resonator. Two through ground vias (TGVs) connecting the top and bottom sides of the SIR filter, are used to realize the common mode rejection. To investigate the proposed filter in detail, a set of design equations are derived based on the circuit theory and transmission line theory. A phototype dual‐band differential filter operating at 1.5 and 2.75 GHz has been realized to validate the proposed concept and theory. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:468–473, 2015.     

Dual‐band bandpass filters with multiple transmission zeros using λ/4 stepped‐impedance resonators

Two novel dual‐band microstrip bandpass filters (BPFs) with multiple transmission zeros are proposed in this article. The dual‐band BPFs with second‐order bandpass responses are due to two λ/4 stepped‐impedance resonators (SIRs). Two passbands (center frequency ratio f _s/f₀ is 2.36) are realized based on the asymmetric SIRs. The transmission zeros near the passbands can be adjusted conveniently using the stopband transmission characteristic of the open/shorted coupled lines. Two planar microstrip dual‐band BPFs (ε _r = 2.65, h = 0.5 mm) with four and six transmission zeros are designed and fabricated. High selectivity and good in‐band performances can be achieved in the proposed filters.     

A highly efficient concurrent dual‐band GaN class‐AB power amplifier at 1.84 GHz and 3.5 GHz

This article presents the design, simulation, implementation, and experimental results of a highly efficient, concurrent dual‐band, gallium nitride (GaN), class‐AB power amplifier (PA) at two frequencies: 1.84 and 3.5 GHz. It proposes a novel dual‐band bandpass filter (DBBPF) with quad‐section stepped‐impedance resonators (SIRs) capable of rejecting the annoying frequencies of the second and third harmonics in the dual‐band. The proposed DBBPF was applied in the design of a dual‐band PA using a packaged 10 W GaN transistor. The PA prototype maintained a peak power‐added efficiency (PAE) of 75.3% at the 1.84 GHz frequency and 64.5% at the 3.5 GHz frequency. For a continuous wave output power of 40.9 dBm, the measured gain was 13 dB in the two frequency bands. Linearized modulated measurements, concurrently using 10 MHz quadrature amplitude modulation (16 QAM) signals and worldwide interoperability for microwave access (WiMAX) signals, showed an average PAE of 48.5% and 39.8% and an adjacent channel leakage ratio of ?46 and ?45 dBc with an average output power of 37.8 and 36.8 dBm at the two frequency bands, respectively. This PA is used for wireless systems. It is especially useful in standard simultaneous global system for mobile (GSM) and WiMAX wireless systems.     

Synthesis method of lumped dual–band filters with controllable bandwidths

This article presents a synthesis method for lumped dual‐band filters by directly adopting traditional Pi‐shaped and Г‐shaped capacitive networks as dual‐mode admittance inverters (J inverters). By following classic coupled‐resonator filter theory, the equivalent circuits (parallel LCs) of the dual‐mode resonators between the J inverters are derived separately at the two passbands. Each dual‐mode resonator is first approximately constructed with a series combination of the two parallel lumped circuit (LC) resonators, and then the element values are iteratively updated for better accuracy. A design example is given and good agreement is achieved between the simulated and measured results, demonstrating the feasibility of the synthesis method. The passband bandwidths are fully controllable. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:75–80, 2015.     

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.     

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.     

A dual‐band superconducting filter with a large bandwidth ratio

In this study, we propose a stepped‐impedance‐stub loaded interdigital capacitor resonator for design of a dual‐band band‐pass filter with a large bandwidth ratio. The presented resonator has strong and weak couplings in the upper passbands (UPs) and lower passbands (LPs), respectively, so as to form a large upper/lower bandwidth ratio. Adopting a dual‐branch phase‐matched feedline structure can meet the external quality factors required for the UP/LP. Therefore, these two passbands, defined by their respective center frequencies and bandwidths, can be manipulated independently. A four‐pole dual‐band example filter with a lower bandwidth of 20 MHz at 1576 MHz and an upper bandwidth of 200 MHz at 2450 MHz is successfully designed on an YBCO/MgO superconducting wafer. The filter exhibits excellent frequency responses. The upper/LPs show insertion losses below 0.07/0.22 dB and return losses above 15.3/15.3 dB. The stopband rejection is better than 57 dB until the first spurious passband up to 6150 MHz (3.9f_L).     

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.     

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.     

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.     

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 quad‐band band‐pass filters using stepped‐impedance coupled‐line resonators

In this article, compact quad‐band band‐pass filters are realized by using stepped‐impedance coupled‐line quad‐mode resonators (SICLQMRs). The compactness of the quad‐mode resonator relies in its folded structure without extra space between the parallel lines. Unlike stepped‐impedance resonators, SICLQMRs provide more design freedoms for controlling the four resonating frequencies since the even‐ and odd‐mode equivalents can be separately assigned with characteristic impedances. Internal and external couplings are also parallel couplings, resulting in very compact dimensions of the filters. Simulated and measured S parameters are compared with good agreement, demonstrating the feasibility of the design.     

A new dual‐band single‐ended‐to‐balanced filtering power divider

This article proposes a new dual‐band single‐ended‐to‐balanced (SETB) filtering power divider (FPD), which shows the excellent characteristics of wideband common‐mode (CM) suppression and good selectivity. By employing the structure of double‐sided parallel‐strip line with a mid‐inserted conductor and a T‐shaped defected ground structure etched in the mid‐inserted conductor, out‐of‐phase behavior and high CM suppression can be achieved successfully. Besides, to realize dual‐wideband filtering performance and high selectivity, two pairs of step impedance stubs (SIS) loaded quarter‐wavelength central line‐terminal‐shorted three parallel‐coupled microstrip lines structure are adopted. Meanwhile, two pairs of resistors are introduced so as to realize excellent isolation. To verify effectiveness of the design method, a prototype of dual‐band SETB FPD which operates at 3.2 and 4.9 GHz is designed, fabricated, and tested. Final results exhibit that the new dual‐band SETB FPD possess high selective dual‐band differential mode response, wideband CM suppression, and excellent isolation between the balanced output ports.     

A compact dual‐band superconducting filter with fine‐tuning coupling structure

A novel dual‐mode optimized patch capacitor loaded T‐type resonator is proposed for the design of a dual‐band filter (DBF). The resonator has its lowest even‐ and odd‐mode at the two expected passband frequencies and the first spurious mode far away from the passbands. For tuning of the two sets of coupling strengths for both passbands, open/shorted secondary coupling structures are introduced as a fine‐tuning coupling structure to increase/decrease the primary coupling strength. A four‐pole DBF with passbands centered at 2450 and 3500 MHz, respectively, is proposed and fabricated using the HTS material. The measured results of the filter indicate superior performance and good fitting with the simulation results. The return losses of both passbands and the insertion losses obtained by measurements are greater than 14 dB and less than 0.3 dB, respectively. The stopband rejection exceeds 50 dB up to 8.0 GHz.     

Microstrip dual‐band bandpass filters using parallel‐connected open‐loop ring resonators

This article proposes a microstrip dual‐band bandpass filter that uses parallel‐connected open‐loop ring resonators. Compared to many microstrip dual‐band filters, the advantages of using microstrip open‐loop ring resonators are easy calculation (half‐guided‐wavelength), easy fabrication (equal width for all 50‐Ω lines and without grounding holes), and direct connection to external feed lines (reducing insertion loss caused by gap couplings). Another advantage of the filter is an asymmetrical feed on the ring resonator that provides sharp rejections at its adjacent bands. The input and output matches of resonators to the external feed lines are derived using a simple transmission‐line theory. The results of the derivation provide a simple design rule for filter designers. Simulated and measured results are presented with good agreement. The filter has minimum insertion loss of 1.25 dB at 1.85 GHz and 1.6 dB at 2.33 GHz. The 3‐dB fractional bandwidths are 5.9% for the 1.9‐GHz bandpass filter and 4.7% for the 2.4‐GHz bandpass filter, respectively. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.