Balanced Balanced Bandpass Filter Research Articles

High common‐mode rejection balanced bandpass filter using novel coupling scheme and source‐loaded coupling technique

AbstractA balanced bandpass filter (BPF) with a novel coupling scheme and source‐loaded coupling (SLC) technique is proposed. The J‐inverter is directly connected to the source or load, and the single‐band cell (SBC) is fed by the J‐inverter. Meanwhile, the J‐inverter is also coupled to a resonator. Equivalent differential‐mode (DM) and common‐mode (CM) circuits are presented, and their ideal frequency responses under DM and CM are also provided. Furthermore, the SBC equals paralleled short‐ and open‐circuited stubs in DM and equals two paralleled open stubs in CM. To validate the design concept, a four‐pole balanced BPF working at 2.66 GHz with fractional bandwidth (FBW) of 13.8% is designed and fabricated. Three transmission zeros (TZs) are generated, and the upper stopband suppression level reaches 34 dB. Meanwhile, a high CM rejection level attains 54 dB within the DM passband.

Compact dual‐band balanced bandpass filter with controllable passbands using coplanar waveguide spiral cross resonators

AbstractIn this article, a novel coplanar waveguide (CPW) spiral cross resonators (SCRs) is introduced for creating a dual‐band balanced bandpass filter (BPF) with adjustable passbands. The resonant properties of the SCRs in both the differential mode (DM) and common mode (CM) are scrutinized. Furthermore, DM bisection offers two distinct parameters for internal coupling adjustment, enabling independent passband width control. A novel grounding wire feeding arrangement matches the external Q factor of the dual DM passbands. An additional stepped‐impedance short‐circuited conducting stub between resonators prevents excessive coupling while obtaining moderate bandwidths. Inherent CM suppression can be attained by distinguishing CM resonant frequencies distinct from the DM frequencies. To validate the design, a dual‐band balanced BPF designed and fabricated to operate at 2.42 and 5.2 GHz exhibits closely matching measured results compared to the simulated ones.

Novel quasi‐reflectionless balanced bandpass filters using absorption network for common‐mode and harmonic suppression

AbstractQuasi‐reflectionless balanced bandpass filters (BPFs) using absorption network for common‐mode (CM) rejection and stopband extension are proposed and demonstrated. First, a quasi‐reflectionless balanced BPF is constructed by using absorption network and a uniform impedance resonator (UIR), where absorption network consists of lossy stubs loaded at both the input/output port and the ends of the coupling line (CLs). Owning to the resonating of absorption network, a three‐pole balanced BPF with CM and differential‐mode (DM) reflectionless performance are realized. Meanwhile, harmonic of DM is suppressed by exploring the loading position of the resistor. Second, to improve the selectivity of the filter, two open stubs are symmetrically loaded to the center of the UIR, a five‐pole quasi‐reflectionless balanced BPF with two transmission zeros are presented. Both proposed quasi‐reflectionless balanced BPFs are fabricated and measured. The measured results are in good agreement with the simulated ones, verifying the proposed design concept.

Compact dual-band balanced bandpass filter using CRLH resonator with intrinsic common-mode suppression and multiple transmission zeros

In this paper, a newly composite right-/left-handed (CRLH) resonator is presented and applied to constitute a compact dual-band balanced bandpass filter (BPF). The proposed CRLH resonator contains two spiral coupled line segments. By imposing the differential-mode (DM) and common-mode (CM) excitation, the DM and CM equivalent circuits of the presented resonator and their lumped-element circuit models are built for investigating the resonant property. The CRLH resonator has two DM resonances and are adopted to design two DM passbands. Also, the CM resonances are all far away from DM resonances, achieved intrinsic desirable CM rejection within DM frequency range without any auxiliary elements. Attributing to the mixed electric and magnetic coupling between two coupled resonators and the introduced source-loaded coupling, multiple transmission zeros are obtained and therefore enhance the selectivity and attenuation in stopband. Finally, a well-designed dual-band balanced BPF is fabricated. Verification of the presented structure and design method’s validity is evidenced by the measured results, which are in agreement with the simulations.

A Balanced BPF with Wide Bandwidth and Steep Selectivity Based on Slotline Stub Loaded Resonators (SSLRs)

A balanced bandpass filter (BPF) with a wide differential mode (DM) bandwidth and steep DM passband selectivity and high common-mode (CM) block based on slotline stub-loaded resonators (SSLRs) is designed in this brief. The proposed SSLR, which is composed of a half-wavelength slotline resonator and a shorted slot stub loaded at the symmetrical plane, is applied to achieve a broad DM passband with a center frequency at 5.1 GHz and a 3 dB bandwidth of 92%. Meanwhile, two transmission zeros (TZs) are introduced to realize a steep DM passband selectivity. The center frequency and bandwidth of the DM passband can be adjusted by changing the dimensions of SSLRs and the gaps between them. Meanwhile, one narrow notched band with a 3 dB bandwidth of 4.9% is realized by employing one coupled quarter-wavelength short-circuited stub at the input ports. In addition, the DM stopband with a rejection level of 10 dB can be extended to 20 GHz. The designed balanced broadband filter is stimulated by a U-shaped microstrip line to slotline transition structure, which can realize wideband a CM block with a high suppression level without influencing the DM one, and this can reduce the design complexity. In order to prove the idea, a balanced broadband filter is designed and measured. The predicted results of S parameters are compared with the measured ones, and a good agreement is achieved.

Q-band balanced bandpass filter based on rectangular micro-coaxial transmission line with improved common-mode suppression

This paper presents a novel design of a wideband millimeter-wave balanced bandpass filter (BPF) for use in a high-sensitivity Q-band reception system for solar radio spectrum observation. The balanced BPF has differential-mode (DM) band-pass and common-mode (CM) band-stop characteristics, which effectively suppress noise and reduce electromagnetic interference in its operating frequency band. The filter design incorporates half-wavelength rectangular micro-coaxial transmission lines as resonators and coupling between resonators is achieved through J-inverters. The wideband CM suppression is improved by adjusting the distribution of CM transmission zeros by adding open-circuited branches on the symmetrical plane. The micro-coaxial structure is fabricated on a 4-inch silicon wafer through a three-dimensional additive manufacturing process. The compactness, low loss, and wideband performance make it ideal for this application. As a design example, a fifth-order Chebyshev balanced BPF was fabricated and measured to demonstrate the design method. The measured results indicate that the balanced BPF operates within a frequency range of 30–50 GHz, with an insertion loss of 1.63 dB and over 26 dB CM suppression in the DM passband. These results are in general agreement with simulation results. To the best of our knowledge, this is the first time that a micro-coaxial structure has been proposed for this application.

Optimization and Design of Balanced BPF Based on Mixed Electric and Magnetic Couplings

A balanced bandpass filter (BPF) with an improved frequency selectivity for differential-mode (DM) excitation and high rejection for common-mode (CM) excitation is proposed in this paper. Two half-wavelength stepped impedance resonators (SIRs) are employed based on mixed electric and magnetic couplings to realize a DM passband centered at 2.48 GHz. The center frequency and bandwidth can be easily controlled by optimizing the dimensions of SIRs and the coupling between them, respectively. Meanwhile, two transmission zeros (TZs) are generated based on the mixed electric and magnetic couplings and are independently controlled by tuning the coupling strength. Moreover, a wide DM stopband can be realized by optimizing the SIRs. The proposed balanced BPF is fed by balanced U-type microstrip–slotline transition structures, which can achieve high wideband CM rejection without influencing the DM responses, and the design complexity can be clearly reduced. Finally, a balanced BPF is fabricated, and a good agreement between the simulation and the measurement is observed, which verifies the design method.

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.

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.

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.

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.

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.

Compact Dual-Band Dual-Mode SIW Balanced BPF With Intrinsic Common-Mode Suppression

In this letter, a compact dual-band dual-mode substrate integrated waveguide (SIW) balanced band-pass filter (BPF) with intrinsic common-mode (CM) suppression is designed by using a single perturbed SIW circular cavity. The vias and slot perturbations are introduced to tune the resonant modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">010</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> (a pair of degenerate modes), and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> of a circular cavity. Thus, they can be used to form two differential-mode (DM) passbands with independently adjustable center frequencies and bandwidths. The SIW can be seen as a natural balun with intrinsic CM suppression. Furthermore, the planar differential excitation structure is designed to excite the perturbed SIW cavity. The CM noise cannot excite SIW cavity due to the characteristics of hybrid electromagnetic boundary. Finally, a compact dual-band dual-mode SIW balanced BPF at 8 and 10 GHz is designed and fabricated, and the measured results show good agreement with the simulated ones.

A compact balanced filter with quadruple-mode resonators for UWB application

A compact ultra-wideband (UWB) balanced bandpass filter (BPF) with quadruple-mode resonators on a microstrip line is proposed. The circuit of the proposed filter is analyzed, and it is shown that the differential-mode circuit performs as a UWB BPF, while the common-mode circuit performs as a UWB bandstop filter (BSF). The differential-mode circuit consists of two short-circuited stubs that are properly attached to the initial multiple-mode resonator (MMR) to form a quadruple-mode UWB BPF. Having a highly-attenuated wide upper-stopband in the frequency response of the differential-mode operation is a significant feature for this circuit. By installing two pairs of open-circuited stubs in the symmetrical line, the differential-mode frequency response remains unchanged but its common-mode frequency response is reshaped to achieve the stopband in the overall UWB. Finally, a microstrip UWB balanced BPF is designed, simulated and measured. Simulated and measured results are in good agreement with each other, showing that the proposed filter has compact size, UWB differential passband (3dB fractional bandwidth 113%) and UWB common-mode suppression (12dB attenuation across 3.3–12.4 GHz).

Filtering microwave differential signals through odd-mode spoof surface plasmon polariton propagation

Recently, spoof surface plasmon polaritons (SPPs) have been successfully applied to microwave signal propagation in ultra-thin planar circuits, due to their unique features of electromagnetic (EM) wave confinement in deep subwavelength scale and controllable dispersive properties. Both even and odd modes can be supported in symmetric spoof SPP structures. However, most device applications employ even mode propagation due to its easy stimulation. In this paper we investigate the dispersion characteristics and EM field patterns of both even and odd modes in a symmetric H-shaped spoof SPP structure. We concentrate on odd modes with an anti-symmetric electric field distribution, and their application to the propagation and filtering of differential signals. With odd modes, a balanced bandpass filter (BPF) can be constructed with a designable passband depending on the dispersion engineering of the odd modes in the spoof SPP structures. Pure odd mode propagation provides an ideal platform for differential signal transmission, with effective rejection of the common mode and an ultra-wide upper stopband in the designed filters. To validate the proposed design, two balanced BPFs operating at 2.3 GHz and 4 GHz are designed and implemented. There is good agreement between the simulated and measured results. We believe that the proposed method may encourage alternative applications of differential signal filtering with flexible frequency responses, and may play an important role in device development in wireless communication systems.

Compact balanced bandpass filters based on multilayer dual-mode substrate integrated waveguide cavities

To design size-reduced balanced bandpass filters (BPFs) with high selectivity, two new multilayer dual-mode substrate integrated waveguide (SIW) balanced BPFs are proposed. Firstly, the characteristic of dual-mode SIW cavity is analyzed in detail. Then, a balanced SIW BPF with balanced input/output (IO) ports locating on the upper dual-mode SIW cavity is proposed, and the lower dual-mode SIW cavity is coupled to the upper one using two crossed slots. Three transmission zeros (TZs) can be produced at any locations. A balanced SIW BPF with balanced IO ports locating on the upper and lower dual-mode cavities respectively is also proposed, and the two cavities are coupled by a slot. Two symmetrical TZs can be produced. Based on the proposed structures, two filters with center frequency of 10 GHz are designed, fabricated and measured. The measured results agree well with the simulated ones, which indicates the feasibility of the proposed multilayer dual-mode SIW balanced BPFs with compact size and high selectivity.

Design of Tri-Band Balanced Filter With Wideband Common-Mode Suppression and Upper Stopband Using Square Ring Loaded Resonator

In this brief, a novel multi-mode square ring loaded resonator (SRLR) is presented, and a tri-band balanced bandpass filter (BPF) with good performances is developed. The multi-mode SRLR consists of a ring resonator and six open stubs, and its resonant characteristics is obtained by the odd/even-mode method. Compared with conventional SRLR, the symmetrical SRLR has more degree of freedom in controlling the resonance modes. Thus, a wide upper DM stopband can be achieved by choosing proper electrical lengths of open stubs. Moreover, frequency dispersion technique is used to enhance common-mode (CM) suppression in the proposed balanced tri-band BPF. By loading a cross-shaped stub and open-loop stub to the center of the first and second order SRLR respectively, five CM transmission zeros (TZs) are produced. Therefore, a wideband CM suppression can be achieved with the DM response almost intact. To verify this design method, a tri-band balanced filter operating at 2.4, 3.5 and 5.2 GHz has been designed, simulated and fabricated. Measured results exhibit good agreement with the simulated ones.

Self-Packaged Balanced Bandpass Filters With Impedance Transformation Characteristic

In this article, the co-design of novel self-packaged balanced bandpass filters (BPFs) integrated with the functionality of impedance transformation is presented for the first time. The proposed design is based on a modified branch-line structure, which is composed of two different branch lines and two identical coupled-line sections. Analysis results show that the considered filters can not only achieve Chebyshev equal-ripple responses with impedance transformation properties for the differential mode (DM) but also can efficiently improve the bandwidth of the common-mode (CM) rejection with resorting to this modified branch-line structure. Furthermore, according to the specified equal-ripple fractional bandwidth (FBW), in-band return loss (RL) level, and impedance transformation ratio ${m}$ , the DM frequency response can be directly determined. Two design prototypes, the second-order balanced BPF with a 50–75- $\Omega $ ( $m= 1.5$ ) impedance transformation and the third-order one with a 50–200- $\Omega $ ( $m= 4$ ) impedance transformation, are implemented in self-packaged forms by using the multilayer liquid crystal polymer (LCP)-bonded printed circuit board (PCB) technology. Theoretical, simulated, and measured results are recorded in good agreement, well verifying the design concept.

40-GHz Millimeter-Wave Balanced Bandpass Filter Design in Standard 0.35-µm CMOS Process

In this work, a 40 GHz mm-wave balanced band-pass filter (BPF) is realized using coupled structure consisting of symmetric feed lines and stepped-impedance resonators (SIRs). For differential-mode operation, the BPF circuit exhibits band-pass characteristic; for common-mode operation it behaves as a band-stop unit. The designed balanced BPF circuit is realized by using TSMC 0.35-μm standard process. Good agreement was observed between simulated and measured results. The measured passband center frequency is at 38.8 GHz, with a minimum differential-mode insertion loss of 5.87 dB and a 3-dB bandwidth of 9.6 GHz.