A balanced dual‐band BPF with independently controllable frequencies and bandwidths

A balanced second‐order dual‐band bandpass filter (BPF) with independently controllable center frequencies and bandwidths based on coupled stepped‐impedance resonators (SIRs) is designed in this article. To obtain a dual‐band differential‐mode (DM) response, two pairs of SIRs with different resonant frequencies are employed in the design. The bandwidths of the two DM passbands can be independently tuned by adjusting the coupling gaps and coupling lengths of the corresponding resonators. In addition, three transmission zeros are realized to enhance the selectivity of the DM passbands. The microstrip‐slotline transition structure is utilized to achieve a wideband common‐mode (CM) suppression. Moreover, the DM responses are independent of the CM ones, which significantly simplify the design procedure. Finally, a balanced dual‐band BPF is designed to validate the design method and a good agreement between the simulated and measured results is observed.     

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.     

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 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.     

Multi‐mode resonators with quad‐/penta‐/sext‐mode resonant characteristics and their applications to bandpass filters

In this article, a new class of dual‐/tri‐band and ultra‐wideband (UWB) bandpass filters (BPFs) using novel multi‐mode resonators are proposed. The classical even‐/odd‐mode method is applied to analyze the resonant characteristics of the proposed resonators, which exhibit controllable resonant modes with different dimension parameters under the same configuration. According to the analysis, three resonators with quad‐/penta‐/sext‐mode resonant characteristics are obtained by choosing the specific dimension parameters. Then, the quad‐mode resonator is used to design a dual‐wideband BPF centred at 2.39/5.14 GHz with 3‐dB fractional bandwidths (FBWs) of 36.9%/18.9%, and the penta‐mode resonator is utilized to design an UWB BPF with 3‐dB FBW of 102.2%, whereas the sext‐mode resonator is applied to design a tri‐band BPF with centre frequencies of 2.09/3.52/5.46 GHz and 3‐dB FBWs of 11.3%/20%/12.1%. All these three filters are fabricated and measured, and the measured results are in good agreement with the simulated ones.     

Design of high selectivity tri‐band bandpass filter with wide upper stopband

This article presents a dual‐plane structure high selectivity tri‐band bandpass filter (BPF) which consists of a pair of T‐shaped microstrip feed lines with capacitive source‐load coupling as well as spur lines embedded, and three resonators, i.e., a dual‐mode stub‐loaded stepped impedance resonator and two nested dual‐mode defected ground structure resonators. Using the intrinsic characteristics of the resonators and feed lines, nine transmission zeros near the passband edges and in the stopband can be generated to achieve high selectivity. An experimental tri‐band BPF located at 2.4/5.7 GHz [wireless local area networks (WLAN) application] and 3.5 GHz [worldwide interoperability for microwave access (WiMAX) application] has been simulated and fabricated. Good agreement between the simulated and measured results validates the design approach. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

A highly selective balanced wideband bandpass filter based on nested split‐ring resonators

A balanced wideband bandpass filter (BPF) with a high frequency selectivity, controllable bandwidth, and good common‐mode (CM) suppression based on nested split‐ring resonators (SRRs) is proposed in this article. The proposed nested SRRs are applied to form three transmission poles (TPs) that can achieve a wide differential‐mode (DM) passband centered at 3.0 GHz. Meanwhile, two transmission zeros (TZs) are generated to realize a high frequency selectivity of the DM passband. Moreover, TPs and TZs can be quasi‐independently controlled by changing the physical lengths of SRRs and the gaps between them, which can greatly improve the flexibility and practicality of the design. The proposed balanced BPF is fed by balanced microstrip‐slotline (BMS) transition structures. For the CM signals, the BMS transition structures can achieve a good wideband CM suppression without affecting the DM ones, thereby simplifying the design procedure. In order to validate its practicability, a balanced wideband BPF is fabricated and a good agreement between the simulated and measured results is obtained.     

Dual‐wideband differential bandpass filter with intrinsic common‐mode suppression based on hybrid transmission structure

Based on the microstrip‐line/slot‐line hybrid transmission structure, a novel method of realizing dual‐wideband differential bandpass filter (DDBPF) is proposed and demonstrated in this paper. By virtue of hybrid transmission structure, the proposed DDBPF has intrinsic common mode (CM) rejection. Moreover, the dual‐wideband transmission performance of differential mode (DM) signal can be approached by using two dual‐mode stub‐loaded stepped‐impedance resonators. The two passbands of the proposed DDBPF are respectively centered at 2.76 GHz and 4.12 GHz which fractional bandwidths are 20.7% and 11.4%. The DM harmonic suppression can extend to 43.5 GHz with rejection level of 13 dB. The CM attenuation of DDBPF can reach 60 dB within DM passband. Furthermore, the CM suppression with attenuation level of 20 dB is ranging from 0.5 GHz to 43.5 GHz. The measurement results are in good agreement with the simulation results, which validates the effectiveness of proposed design methodology.     

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.     

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.     

Inter‐digital coupled dual‐mode patch resonator with crossed‐island configuration for tri‐band filter design

The miniaturized dual‐mode tri‐band band‐pass filters (BPF) using crossed‐island patch resonator is proposed in this article. The BPF is mainly formed by a square patch resonator in which a crossed‐island configuration is embedded in the patch. The patch size reduction with 74.4% is achieved. By the perturbation and the alternative inter‐digital coupling, the tri‐band responses are obtained. The proposed filter covers the required bandwidths for WLAN band (2.26–3.11 GHz and 5.02–6.0 GHz) and X‐band (7.58–8.41 GHz) applications. Five transmission zeros are placed between three pass‐bands and resulted in a good isolation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:457–463, 2014.     

A balanced UWB power divider based on parallel coupling slotlines with improved isolation

A balanced‐to‐balanced ultra‐wide band (UWB) equal power divider (PD) based on parallel coupling slotlines is presented in this article. An ultra‐wide differential‐mode (DM) impedance bandwidth covering from 2.8 to 9.4 GHz can be achieved. It is noted that the DM performance is independent of the common‐mode (CM) response, which reduces the design complexity greatly. Meanwhile, CM response with a larger bandwidth and a higher suppression is obtained intrinsically. More importantly, two methods are designed and adopted to improve the DM isolation between the two output ports. To validate the correctness of the design method, a prototype circuit is fabricated and measured. The contrast of the simulated and measured results shows a good agreement.     

Balanced power dividers with improved bandwidth using folded lines

Two novel wideband balanced‐to‐unbalanced power dividers based on transmission lines and coupled lines are proposed in this article. Multifunction can be realized without cascading single devices with common mode suppression. The desired power divider configurations can be obtained using the even/odd‐mode characteristic impedance of the coupled lines and characteristic impedance of the transmission lines. A resistor in the middle of two single‐ended ports is used to realize isolation between output ports. Two prototypes of wideband balanced‐to‐unbalanced power dividers operating at 2.3 GHz with differential‐mode bandwidths of 79.6 and 134.1% are designed and fabricated. The theoretical and measured results are in good agreement and show good in‐band performances.     

A BTB UWB power divider with arbitrary power‐dividing ratio based on three‐slotline structure

In this article, a balanced‐to‐balanced (BTB) ultra‐wide band (UWB) power divider (PD) is proposed, which can realize arbitrary power‐dividing ratio (PDR) with improved transmission bandwidth flatness. The proposed PD is primarily based on microstrip/slotline (MS) transition structures and parallel‐coupled three‐slotline structure. U‐type microstrip feed lines integrated with stepped‐impedance slotline resonators are adopted at the input and output ports, which make the differential‐mode (DM) responses independent of the common‐mode (CM) ones. Meanwhile, superior DM transmission and CM suppression are achieved intrinsically, thereby simplifying the design procedure significantly. By changing the distances between the coupled three slotlines, the PDR between the output ports is controllable. In order to verify the feasibility of the proposed design method, several prototype circuits of the proposed PDs with different PDRs are simulated and a prototype circuit with the 2:1 PDR is fabricated and measured. A good agreement between the simulation and measurement results is observed.     

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.     

Dual‐band filtering power divider with widely separated passbands

This article presents a dual‐band microstrip filtering power divider with widely separated passbands. The design topology is mainly constructed by two pairs of dual‐mode resonators, an open‐ended input line and two T‐shaped output lines. Owing to the field symmetry at the two sides of the input line, two identical signals are coupled to the resonators and finally transmitted at two output ports. Since each pair of the employed dual‐mode resonators can be independently designed, widely separated dual‐passbands response is specified and derived in this work with the even‐mode/odd‐mode analysis. Moreover, good isolation with wide isolated frequency band is realized by introducing resistors between each pair of resonators. To validate the design concept, a prototype centering at 2.39 and 3.83 GHz is implemented following the given design procedure. Measured results of the fabricated circuit agree well with the simulated ones, exhibit high frequency selectivity, good port‐to‐port isolation, and port matching.     

Novel planar balanced bandpass filter with wideband common‐mode suppression and in‐band common‐mode noise absorption

This paper presents a novel planar balanced bandpass filter (BPF) with wideband common mode (CM) noise suppression and in‐band CM noise absorption using coupled lines (CLs) with short‐circuited stubs to realize high selectivity and wideband differential mode (DM) filtering performance. Two one‐quarter wavelength stubs loaded with grounded resistors are introduced to realize wideband CM noise suppression. Thus, CM noise can be suppressed under a certain level at all frequencies. Four resistors are used to achieve CM noise absorption by dissipating the CM noise into heat, which can avoid the noise being reflected to the communication system and realize a wide absorption bandwidth with 90% absorption efficiency. For demonstration, an absorptive balanced BPF operating at 3.5 GHz with wide 3‐dB fractional bandwidth (FBW) of 79.43% is fabricated and experimentally validated. It is worth noted that the absorptive balanced BPF can realize broadband CM noise suppression from 0 to 8 GHz, and the CM noise is well absorbed more than 10 dB from 2.41 to 4.63 GHz. Besides, wideband CM noise absorption with 90% efficiency from 2.51 to 4.60 GHz is realized, which indicates potential applications in improving the performance of the balanced radio frequency (RF) circuits. Good agreements between the simulated and measured results are observed.     

Dual‐mode resonator with modified dual‐square‐Loop for WLAN and WiMAX quad‐band filter design

We propose the improved configurations with dual‐mode dual‐square‐loop resonators (DMDSLR) for quad‐band bandpass filter (BPF) design. The modified DMDSLR filter employs two sets of the loops. The square loop is designed to operate at the first and third resonated frequencies (2.4/5.22 GHz) and the G‐shaped loop is employed at the second and fourth resonated frequencies (3.59/6.6 GHz). The resonant frequency equations of DMDSLR are introduced for simply designing quad‐band BPF. Resonant frequencies can be controlled by tuning the perimeter ratio of the square loops. A systematic design procedure with the design map is applied for accuracy design. To obtain lower insertion loss, higher out‐of‐band rejection level and wider bandwidth of quad‐band, the miniaturized DMDSLR with meander‐line technique is proposed. The proposed filters are successfully simulated and measured showing frequency responses and current distributions. It can be applied to WLAN and WiMAX quad‐band systems. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:332–340, 2014.     

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 UWB bandpass filter with dual‐notch bands using asymmetric tri‐section stepped impedance resonator

In this study, a novel high selective UWB band pass filter (BPF) with dual notch band is presented. UWB BPF is realized using stub‐loaded multiple‐mode resonator (MMR). The MMR is constructed by loading a quintuple mode open stub at the centre in an asymmetric tri‐section stepped impedance resonator (ATSSIR). Five modes, including two odd modes and three even modes, placed within UWB band. Two transmission zeros generated by the fractal stub improve the passband selectivity greatly. Two half wavelength long fractal Hilbert resonators are embedded near I/O line to achieve notch bands at 5.1 and 5.9 GHz. Aperture‐backed interdigital coupled‐lines are implemented to improve the coupling. The proposed prototype is fabricated and tested. The measured insertion loss is observed to be within 1.5 dB over the passband. By virtue of two transmission zeros (TZs), on either side of the passband, at 5.1 and 5.9 GHz, respectively, the passband selectivity is achieved with measured roll‐off factor at around 34 dB/octave. The out‐of‐band rejection of the filter is greater than 22 dB up to 18 GHz. The simulated results are in good agreement with the measured responses.