Balanced Bandpass Filter Research Articles

Multilayer packaging dual‐band balanced bandpass filter based on dual‐mode substrate integrated waveguide cavities with split‐type topology

A new design method of the dual-band balanced bandpass filter (BPF) using multilayer packaging dual-mode substrate integrated waveguide (SIW) cavities is proposed. Split-type coupling topology based on dual-mode resonators is developed for the design. Firstly, a single-band balanced filter with perturbed metal vias is designed. The TE201 mode and the TE202 mode perturbed by the metal vias can form a passband. Secondly, an additional metal vias perturbed SIW cavity with the same dual-mode is placed in the lower layer for the bandstop function. A dual-band balanced BPF with split-type coupling topology is successfully realised. Compared with the traditional cascaded single-mode form, the proposed dual-mode split-type design has more compact size and can be more easily extended to multi-passbands. To verify the proposed method, a dual-band balanced filter operating at 13.3 and 14.2 GHz is designed, fabricated and measured. The designed dual-band balanced filter has good filtering performance including differential mode passband transmission and common mode rejection. Measured results show good agreements with simulated ones.

Attenuation‐tunable balanced bandpass filter based on graphene nanoplates

In this letter, a unique type of balanced bandpass filter (BPF) with high selectivity and tunable attenuation is proposed through the comprehensive design of a microstrip balanced BPF and graphene nanoplates. In order to achieve the passband response in differential-mode (DM) excitation and produce a wide and deep stopband in common-mode (CM) excitation, the balanced couple of lines are used in balanced BPF. The graphene nanoplates are loaded on the open ends of λ/4 stepped-impedance resonators to dissipate the electromagnetic field. By raising the bias voltage applied to the graphene nanoplates, the values of the graphene's surface impedance can be adjusted from high to low. The insertion loss of the balanced BPF can be indirectly tuned while maintaining the return loss at a comparatively low level. A prototype of the proposed gain tunable balanced BPF is fabricated and measured. The measured results show that a tuning range of insertion loss from 1.75 to 10.7 dB can be obtained for the DM circuit over the operating bandwidth centered at 1.84 GHz, without interrupting the signal rejection of the CM circuit.

Balanced Dual-Band HTS BPF With Controllable Frequency Ratio and Transmission Zeros Using Mixed Cross-Coupling

In this brief, a fourth-order balanced dual-band high temperature superconducting (HTS) bandpass filter (BPF) is presented based on modified stub-loaded resonators (SLRs). Firstly, the differential mode (DM) and common mode (CM) resonant characteristics of the modified SLRs are analyzed. Under DM operation, two types of mixed cross-coupling topologies are constructed by placing the spiral modified SLRs and their DM equivalent structures in an appropriate way. Then, a dual-band response with controllable center frequencies, bandwidths, and transmission zeros (TZs) is achieved. Under CM operation, an effective CM suppression circuit is proposed for improving the in-band CM suppression level. Finally, for verification, a fourth-order balanced dual-band HTS BPF with center frequencies of 3.494/4.797 GHz and insertion loss of 0.26/0.21 dB is designed and fabricated on MgO substrate with double-sided YBCO thin films. The measured results agree well with the simulated ones, and the BPF shows the attractive features of low insertion loss and good out-of-band rejection.

A balanced tri-band BPF with high selectivity based on ASSLR

Abstract In this paper, a balanced second-order tri-band bandpass filter (BPF) with high selectivity is proposed. Three differential-mode (DM) passbands are formed by applying one pair of asymmetric short stub-loaded resonators (ASSLRs) and uniform impedance resonators (UIRs) into the design. Meanwhile, the frequencies and bandwidths of the DM passbands can be quasi-independently controlled by the lengths of resonators and the gaps between them. In addition, broadband common-mode (CM) suppression is achieved intrinsically without affecting the DM parts based on the U-type balanced stepped-impedance microstrip-slotline transition (BSIMST) structures, thereby simplifying the design procedure significantly. In order to validate the practicability, a balanced tri-band BPF operating at 1.8, 3.5 and 4.45 GHz is fabricated and designed. A good agreement between the simulated and measured results is observed.

A Balanced Tri-Band Substrate Integrated Waveguide Bandpass Filter With High Selectivity

This paper proposed a balanced tri-band bandpass filter (BPF) with high selectivity based on substrate integrated waveguide (SIW) technology. The tri-band filtering response and multiple transmission zeros (TZs) are attained by elaborately merging cascaded quadruplet (CQ) topology and split topology. The proposed balanced tri-band bandpass filter is designed, which integrates high selectivity differential-mode (DM) transmission and good common-mode suppression by cleverly placing TE102-mode SIW cavity on the symmetric plane. To verify the proposed concept, a prototype of balanced tri-band BPF operating at 9.33, 9.67, and 10.02 GHz has been implemented. Measured results show eight TZs at out of DM passbands and more than 35 dB CM suppression within the DM passbands, which agree well with the simulated results.

Balanced quasi-elliptic-type dual-passband filters using planar transversal coupled-line sections and their digital modeling

AbstractA class of balanced dual-band bandpass filters (BPFs) with planar transversal-signal-interference coupled-line sections is reported. In their building balanced dual-band BPF stage under differential-mode excitation, a second-order quasi-elliptic-type dual-band bandpass filtering transfer function is obtained. Specifically, from the transversal interaction among their two open-ended and virtually-short-ended half-wavelength coupled-line paths, sharp-rejection differential-mode dual passbands with several out-of-band transmission zeros at both sides are realized. To attain high common-mode suppression levels within the differential-mode passbands, two open-ended line segments are connected at the symmetry plane of the devised balanced dual-band BPF stage. Moreover, higher-order schemes based on in-series-cascaded multi-stage designs to further increase differential-mode selectivity and in-band common-mode rejection are illustrated. The operational principles and parametric-analysis design rules of the engineered transversal-coupled-line-based balanced dual-band BPF approach are detailed. Additionally, for a rigorous interpretation of their zero/pole characteristics, a digital-modeling framework is applied to them to connect RF balanced filters with their discrete-time versions. For practical-validation purposes, a microstrip prototype of two-stage/fourth-order balanced dual-band BPF is built and tested. It exhibits measured differential-mode dual passbands with center frequencies of 1.464 GHz and 2.294 GHz, 3-dB fractional bandwidths of 8.74% and 9.68%, and in-band common-mode rejection levels above 23.16 dB and 31.36 dB, respectively.

Supercompact Balanced Wideband Bandpass Filter Using Capacitor-Loaded Three-Line Coupled Structure

A supercompact balanced wideband bandpass filter (BPF) based on capacitor-loaded one-eighth wavelength three-line coupled structure is proposed. Multiple differential-mode (DM) transmission poles, DM transmission zeros, and common-mode (CM) transmission zeros can be obtained and controlled by loading multiple capacitors on the three-line coupled structure, which makes the filter achieve wideband DM filtering response and CM suppression. Compared with the state-of-the-art balanced wideband BPFs, the proposed design has the advantages of compact size and simple structure. A prototype centered at 0.66 GHz with the 3-dB fractional bandwidth of 43.8% is demonstrated, which exhibits the supercompact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.003~\lambda ^{2}_{g}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{g}$ </tex-math></inline-formula> is the guided wavelength at the center frequency) and the minimum insertion loss of 0.43 dB.

Design of dual‐band balanced bandpass filter based on a single substrate integrated waveguide cavity

This paper proposes a dual-band balanced bandpass filter (BPF) based on a single interfered substrate integrated waveguide (SIW) cavity. The TE201, TE202, TE401, and TE402-modes are controlled by the metallic vias and divided into two groups. The first passband is made up of the affected TE201 and TE202-modes, while the second passband is made up of the disturbed TE401 and TE402-modes. In this balanced BPF design, it realizes the requested differential-mode (DM) transmission and common-mode (CM) suppression. Particularly, the bandwidths (BWs) of the two DM passbands can be efficiently controlled by only adjusting the locations of these metallic vias. A prototype dual-band balanced BPF operating at 16.71 and 22.23 GHz with BWs controllable is fabricated and measured for verification. Good accordance between simulation and measurement can be observed.

Balanced Dual-Band BPF and FPD Using Quad-Mode RLR With Improved Selectivity

In this brief, a balanced dual-band bandpass filter (BPF) using quad-mode ring loaded resonator (RLR) is presented. The resonance characteristics of the proposed quad-mode RLR are analyzed and the design graphs of the electrical lengths and the four resonant modes are given. Based on the above analysis, four resonant modes are applied to achieve two differential-mode (DM) passbands. U-shaped microstrip lines and stepped impedance microstrip/slotline (MS) transition structures are employed to achieve good common-mode (CM) rejection without affecting DM ones. In addition, an additional transmission pole is realized in the lower passband due to the stepped impedance slotlines. Meanwhile, six transmission zeros (TZs) are generated due to the horizontal transmission interference of the resonator and new coupling path, which improves the selectivities of the passbands. Furthermore, based on the proposed filter, a balanced dual-band filtering power divider (FPD) is designed for miniaturization. By loading isolation resistors on the slotline, the output ports isolation is improved. To verify the theoretical design, two proposed designs have been manufactured and measured. The measured and simulated results are presented with a good agreement.

High-Order Balanced Dual-Band HTS BPF With Flexible Frequency Ratio and Sharp Rejection Skirts

In this article, a new class of high-order balanced dual-band high-temperature superconducting (HTS) bandpass filter (BPF) based on modified multimode stub-loaded resonators (SLRs) is presented. First, a detailed theoretical analysis of the multimode SLRs is provided to obtain insight into their frequency response characteristics under the differential-mode (DM) and common-mode (CM) operations. Specifically, the SLRs under the DM operation are designed to generate their second and third resonant modes in the two specified passbands, and they are sequentially cascaded by alternate <inline-formula> <tex-math notation="LaTeX">$J$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> inverters for sharp rejection skirts. Following that, the working mechanism of the CM rejection of the resonator is investigated for achieving good CM suppression performance for this filter. Finally, for experimental validation, an eighth-order prototype filter is designed and fabricated on the MgO substrate with double-sided YBa2Cu3Oy (YBCO) thin films. Good agreement between measured and simulated results is obtained, and the filter is at the same time with low insertion loss, flexible frequency ratio, sharp rejection skirts, and good CM suppression level.

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

Abstract By introducing an open stub loaded resonator (OSLR) and a uniform impedance resonator (UIR) into balanced stepped-impedance microstrip-slotline transition structures, a balanced dual-band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented in this paper. The balanced microstrip-slotline transition structures can achieve a wideband common-mode (CM) suppression. Meanwhile, the differential-mode (DM) passbands are independent from the CM responses, which greatly simplifies the design procedure. In addition, four varactors are loaded into OSLR and UIR to achieve the electrical reconfiguration. The proposed balanced dual-band BPF can realize quasi-independently tunable center frequencies and bandwidths. In order to verify the feasibility of the proposed design method, a prototype circuit of the proposed reconfigurable balanced dual-band BPF is simulated, fabricated and measured. A good agreement between the simulation and measurement results is observed.

Tunable balanced bandpass filter with wide frequency‐tuning range and high selectivity

AbstractA tunable balanced bandpass filter (BPF) with a wide frequency‐tuning range (FTR) and high selectivity is presented. The designed BPF is implemented by utilizing varactor‐tuned square ring resonators (SRRs) with parallel‐coupled feedlines. A wide FTR with an almost constant absolute bandwidth (CABW) can be realized by varactors Cv2 connected between SRRs. Four transmission zeros (TZs) can be obtained by the mixed electric and magnetic coupling, source‐load (S‐L) frequency‐variant coupling, and four shunt quarter‐wavelength open and short stubs. Meanwhile, two TZs on both sides of the passband keep the relative position unchanged to achieve high selectivity. The other two are generated to improve the out‐band rejection. In addition, by employing additional stubs and capacitances on the symmetry plane, the common‐mode (CM) suppression can be enhanced. For verification, a tunable balanced BPF with 0.62‐1.27 GHz and four TZs was designed, manufactured, and tested. And experimental results agree well with the simulated ones.

High-Performance Common- and Differential-Mode Reflectionless Balanced Band-Pass Filter Using Coupled Ring Resonator

In this brief, for the first time, we propose common-mode (CM) and differential-mode (DM) reflectionless balanced bandpass filters (BPFs) using half-wavelength ring resonator. By loading absorptive stubs at input/output ports and the ends of the coupled-lines (CLs), the BPFs can realize input-/two-port wideband CM and DM reflectionless performance from dc, as well as wide filtering band and all-stop CM suppression. As for the input-reflectionless type, two extra transmission zeros (TZs) can be obtained by loading <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda /2$ </tex-math></inline-formula> stubs between the CLs. Besides, the impedances of the CLs can determine the CM suppression level, and the absorption performance can be independently adjusted. The operational foundations and explicit equations are discussed and derived. Good agreements between the simulated and measured results verify the design theory.

Compact Multilayered Balanced-to-Balanced Dual- and Tri-Band Diplexers Based on Magnetically Coupled Open-Loop Resonators

Two new compact balanced-to-balanced diplexers composed of two multiband balanced bandpass filters in a multilayer configuration are proposed in this letter to perform dual- and tri-band responses. The balanced bandpass filters are based on the use of magnetically coupled open-loop resonators. The magnetic coupling results in a strong inherent common-mode rejection, greater than 40 dB within all the dual-band diplexer passbands and greater than 30 dB for the tri-band diplexer passbands. All passbands in both diplexers are close to each other and well separated thanks to the presence of several transmission zeroes between them. Operating frequencies have been selected to be within the L band, used for many applications such as mobile services or satellite navigation. Specifically, the dual-band diplexer passbands are located at 1.08/1.58 GHz and 1.3/1.8 GHz with fractional bandwidths of 7/5.2 % and 7.4/5.5 %, while the tri-band diplexer passbands are located at 1.7/2.2/2.79 GHz and 1.97/2.37/2.95 GHz with fractional bandwidths of 4.1/4.6/3.5 % and 5.6/4.6/3.7 %. Measurements of two different prototypes are provided to validate the obtained simulation results, illustrating in this manner the usefulness of the proposed design methodology.

Compact Balanced Bandpass Filter Based on Equilateral Triangular Patch Resonator

In this brief, a new balanced bandpass filter based on equilateral triangular patch resonator (ETPR) is presented. By introducing rectangular slot in the middle of the ETPR, TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode can be controlled for miniaturization of design and separated away from disturbed mode near the passband for decent performance. Furtherly, based on the developed coupling topology, six adjacent slotted ETPRs are elaborately arranged to construct a fourth-order balanced BPF with a good differential-mode (DM) passband, sharp frequency selectivity, as well as high common-mode suppression (CM). To validate the design concept and method, a balanced BPF operating at 5.7 GHz with a 3-dB fractional bandwidth of 12% is designed and fabricated. Good agreement between simulated and measured results validates the proposed design concept.

A Dual-Wideband Balanced Bandpass Filter Based on Branch-Line Structure With Controllable Common-Mode Suppression

In this paper, a novel dual-wideband balanced bandpass filter (BPF) based on branch-line structure is proposed. For analysis, the equivalent circuits of differential-mode (DM) and common-mode (CM) of the filter are built based on the even- and odd-mode method. With a proper synthesis design of DM bisection, dual passbands with a multi-order filtering response can be obtained. Additionally, three open-circuited stubs are centrally loaded on the CM bisection and six controllable transmission zeros are therefore generated. Thus, two stopbands are formed and then a favorable CM suppression within DM passbands is obtained. For demonstration, a third-order dual-wideband balanced BPF is designed with two passbands operating at 2.54 and 4.62 GHz. Good agreement between the simulated results and measured results is obtained, which verifies the validity of the proposed design method.

Compact balanced tri‐band bandpass filter based on stub loaded resonator with high selectivity

A compact balanced microstrip tri-band bandpass filter (BPF) using short and open stubs loaded resonators (SOSLRs) is achieved in this article. Three differential-mode (DM) passbands can be adjusted by properly controlling the dimensions of the loaded short and open stubs, and the first and third DM center frequencies can be implemented independently. By introducing interdigital coupling microstrip lines, five transmission zeros (TZ) are implemented to achieve a higher selectivity. The positions of TZs can be controlled by adjusting the coupling gaps between SOSLRs and interdigital coupling microstrip lines. In addition, balanced microstrip line to slotline transformation structures is introduced as the feed structure, which can be used to block the common-mode (CM) transmission inherently. Therefore, the DM performances are independent from the CM responses, which can simplify the design procedure significantly. For demonstration, a balanced tri-band BPF centered at 1.57, 2.45, and 3.5 GHz was fabricated and measured. Comparison with other reported balanced BPFs indicates that the proposed design exhibits the advantages of high selectivity and good CM suppression responses.

A Reconfigurable Balanced Dual-Band Bandpass Filter With Constant Absolute Bandwidth and High Selectivity

A reconfigurable balanced dual-band bandpass filter (BPF) with constant differential-mode (DM) absolute bandwidth (ABW) and high selectivity is designed in this article. The proposed BPF is composed of a set of asymmetric short stub-loaded resonators (A-SSLRs) and balanced microstrip-to-slotline transition structures (MSTSs). Four varactor diodes are employed to achieve the reconfigurable characteristics with small insertion losses. By changing the coupling distances and selecting the positions of the loaded varactor diodes on A-SSLRs, the DM coupling coefficients <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K_{i}$ </tex-math></inline-formula> and quality factors <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{i}$ </tex-math></inline-formula> of the proposed BPF can be easily controlled to keep a constant DM ABW. In the overall tuning range, a superior common-mode (CM) suppression is achieved intrinsically, and the DM responses are independent of the CM ones. Furthermore, five DM transmission zeros (TZs) are generated by the mixed-coupling and source–load coupling, which can improve the selectivity obviously. Compared with the published reconfigurable balanced BPFs, the proposed one has the advantages of constant DM ABW, smaller insertion losses, and more independent control on the two DM passbands. In order to validate the design strategies, a prototype circuit is designed, fabricated, and measured. The simulated and measured results are presented with a good agreement to verify the theory and design.

Balanced wideband bandpass filter design based on asymmetric split ring resonators (ASRRs) with wide stopband and multi-transmission zeros

In this paper, a balanced wideband bandpass filter (BPF) using the asymmetric split ring resonators (ASRRs) is proposed. The analysis of resonant characteristics and high freedom of design of the multi-physical parameters ASRRs are performed and utilized to design the balanced wideband BPF. Based on the subwavelength size of ASRR, the miniaturization of BPF is realized. To obtain a wide stopband and enable the suppression of spurious resonance in differential mode, the efficient generation of the desired multiple transmission zeros (TZs) is implemented with the employment of the quarter/half-wavelength uniform impedance resonators. By maintaining the performance of filtering function, the different generation mechanisms of TZs based on the multi-path transmission of signal and terminated short-circuited coupled lines are theoretically explored and discussed. The designated balanced BPF is centered at 3.5 GHz with a fractional bandwidth of 32.8%, an extended stopband bandwidth and a miniaturized circuit size of 0.10λ g × 0.28λ g. Two prototypes are fabricated and measured to validate the design methods and the significant filtering performance of wideband BPFs constructed by ASRRs. The simulated and measured results are in good agreement to verify the design.

Design of a Multilayer Dual-Band Balanced Bandpass Filter on a Circular Patch Resonator

This letter presents a novel multilayer dual-band balanced bandpass filter (BPF) design by using two perturbed circular patch resonators. The TM11 mode and TM21 mode of the resonator with odd-symmetric field distributions are explored to realize the desired differential-mode (DM) transmission and common-mode (CM) suppression. Two circular patches are properly coupled in the back-to-back form to realize a dual-passband balanced response by virtue of coupling apertures etched on the ground. In addition to the internal coupling, the above apertures are also further utilized for the undesired degenerate mode harmonic suppression. Besides, slot perturbations on the patch are introduced to perturb the TM21 resonant mode to independently adjust the center frequency of the higher passband, while the lower passband remains almost unchanged. Thus, two passbands can be flexibly controlled by simultaneously tuning the above slots and size of the patch. For validation, a dual-band balanced BPF prototype is implemented. The results indicate 18 and 26% wide fractional bandwidths centered at 5.5 and 7.5 GHz with return loss higher than 20 dB under DM operation and CM suppression higher than 40 dB over an ultra-wide frequency band.