Compact Balanced Bandpass Filter Research Articles

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.

Compact balanced bandpass filter based on dual‐sided parallel‐strip line

A novel compact balanced bandpass filter with wideband common mode rejection is proposed in this article. The intrinsic out-of-phase characteristic is realized by the 180° swap structure, which is based on dual-sided parallel-strip line, wideband common mode (CM) rejection can be easily achieved with compact size and simple configuration. Modified coupled line resonator (MCLR) is applied to implement passband response, and MCLR is composed by conventional coupled line terminated with a λ/4 open stub. To validate the performance, one prototype with 20% 3 dB fractional bandwidth center at 2.2 GHz is designed and fabricated, over than 18 dB CM rejection extended to 2.94f0 can be realized, good agreement can be obtained.

Compact wide-stopband balanced bandpass filter with intrinsic common-mode suppression

A compact balanced bandpass filter (BPF) with wide-stopband and intrinsic common-mode (CM) suppression is proposed. The balanced bandpass filter is composed of a pair of shunt-connected coupled-line resonators. By short circuiting at the middle point of one side of the shunt-connected coupled-line resonator, therefore CM signal suppression is realized under differential- mode (DM) excitation. In addition, the coupled feeding position of the filter is chosen at the point which divides the branch of the single coupled-line resonator with the ratio of 1:2 and consequently wide-stopband is achieved. In addition, three transmission zeros (TZs) are generated to improve the skirt-effect. To validate the idea, the equivalent transmission line model of the proposed filter is given and the design equations are derived for theoretical analysis. Finally, the proposed balanced filter is fabricated for experiment, and the measurement and simulation are in good agreement based on which the design is verified.

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.

Compact-Balanced BPF and Filtering Crossover With Intrinsic Common-Mode Suppression Using Single-Layered SIW Cavity

In this letter, compact-balanced bandpass filter (BPF) and filtering crossover are proposed with intrinsic common-mode (CM) suppression by using a single-layered substrate-integrated waveguide (SIW) cavity. The SIW cavity with low profile is TEn0m mode resonator, which has only one nonzero electric field component. Hence, it is also a natural frequency selection device of the differential signal. Meanwhile, the CM signal cannot excite the cavity due to the characteristics of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). For the design of the balanced SIW BPF, the differential-mode (DM) equivalent half circuit is a single-ended SIW filter with height halved. Furthermore, the microstrip differential transition structure is designed to excite the SIW cavity and has little conversion between DM and CM. On this basis, a compact SIW-balanced filtering crossover is proposed using the degenerate modes TE102 and TE201. Finally, compact third-order SIW-balanced BPF and filtering crossover are designed and fabricated, and the measured results show good agreement with the simulated ones.

High selectivity and common‐mode suppression balanced bandpass filter with TM dual‐mode SIW cavity

Here, a compact balanced bandpass filter (BPF) with high selectivity and good common-mode (CM) suppression is proposed by adopting the TM dual-mode substrate integrated waveguide (SIW) cavity. The SIW cavity is connected to the input and output by the way of microstrip-slotline transition. Under differential-mode (DM) operation, two TM modes (TM 120 , TM 210 ) of the SIW cavity can be effectively excited, and simultaneously two transmission zeros (TZs) can be generated near the passband edges. Meanwhile, by designing the rotation angle and size of coupling slots reasonably, the deep stopband performance can be realised over a wide frequency range. Furthermore, the CM signal is effectively rejected because the magnetic current cannot be transferred to the coupling slot from the virtual open-ended microstrip feedline. Finally, a compact balanced BPF prototype for WLAN application has been designed and fabricated. Good agreement between simulated and measured results is obtained.

Compact single‐layer bandwidth‐enhanced balanced bandpass filter using half‐mode substrate‐integrated waveguide

A compact single-layer balanced bandpass filter using just one half-mode substrate-integrated waveguide (HMSIW) multimode resonator with slots is proposed. The pair of microstrip direct-feed lines with space about 0.5 λ g ( λ g is the guide wavelength of HMSIW at the centre frequency f 0 ) makes TEHM 103, TEHM 104 and TEHM 105 modes of the HMSIW multimode resonator operate in differential mode and TEHM 102 and TEHM 106 modes operate in common mode (CM). As a result, the features of wide bandwidth and low insertion loss (IL) can be achieved when compared with the state-of-art substrate-integrated waveguide balanced filters. Furthermore, the etched slots can be slightly tuned to make up for the performance deviations caused by the manufacturing error. A prototype is designed with a total size of 1.2 λ 0 × 0.14 λ 0 ( λ 0 is the wavelength in free space at f 0 ), the 3 dB fractional bandwidth (FBW) of 28% at the centre frequency of 6 GHz, the minimum IL of 0.86 dB, and the bandwidth of 20 dB CM suppression of 0.25 f 0 .

Transversely Compact Single-Ended and Balanced Bandpass Filters with Source–Load-Coupled Spurlines

Multi-function wireless systems demand multi-channel transmit/receive (TR) modules, particularly as multiple functions are required to operate simultaneously. In each channel, passive components, including bandpass filters, must be compact, or at least transversely compact; thus, the entire circuitry of the channel will be slender, and consequently multiple channels can be parallel-arranged conveniently. In this work, single-ended and balanced bandpass filters for multi-channel applications are presented. As a unique resonator, the U-shaped stepped impedance resonator (USIR) can achieve size miniaturization compared with its corresponding uniform impedance resonator (UIR) counterpart. Hence, with the utilization of USIRs, the proposed bandpass filters are able to acquire compact transverse sizes. Moreover, by using the source–load coupling scheme, two transmission zeros (TZs) are respectively generated at the lower and upper sides of the passbands, which is useful for improvement of the selectivity performance. In addition, spurlines are introduced at the input and output ports to produce another TZ to further enhance the stopband performance, which cannot be acquired by the UIR or stepped impedance resonator (SIR). To verify the aforementioned idea, one single-ended and one balanced bandpass filter are implemented, with experimental results in good agreement with the corresponding simulations. Meanwhile, as compared with some similar works, the proposed balanced filter achieves compact transverse size, sharp selectivity skirt, and wide stopbands up to the fourth-order harmonic with suppression over 20 dB, which illustrates its suitability for differential signal transmission application in microwave circuits and systems.

Compact microstrip balanced bandpass filter with adjustable transmission zeros

A compact microstrip balanced bandpass filter (BPF) with a pair of adjustable transmission zeros (TZs) and a common mode suppression of over 20 dB in a frequency range of >2.42f 0 by using the mixed electromagnetic coupling technology has been developed. The filter TZs in differential-mode are attributed to the mixed electromagnetic coupling, and can be adjusted by the electric/magnetic coupling individually. The filter bandwidth can also be controlled by the electromagnetic coupling. The proposed balanced BPF has been fabricated and measured, and the prediction has been demonstrated.

Compact Balanced Single-Band and Dual-Band BPFs with Controllable Bandwidth Using FoldedS-Shaped Slotline Resonators (FSSRs)

Abstract In this paper, two compact balanced bandpass filters (BPFs) using half-wavelength folded S-shaped slotline resonators (FSSRs) are designed. The proposed FSSR is realized by extending and folding a traditional S-shaped slotline resonator, which can affect the internal coupling of resonator and reduce the size of the resonator. The balanced stepped-impedance microstrip-slotline transition structures are employed to generate a wideband common-mode (CM) suppression. The proposed filters can realize a single-band differential-mode (DM) bandpass response or a dual-band one by employing one or three FSSRs, respectively. Moreover, the center frequencies of the DM passbands are independent from the CM responses, which can simplify the designs procedure significantly. In order to validate their practicability, a compact balanced dual-band BPF with controllable center frequencies and bandwidths is fabricated and good agreement between the simulated and measured results is observed.

Compact Balanced Bandpass Filter Design Using Asymmetric SIR Pairs and Spoof Surface Plasmon Polariton Feeding Structure

This letter demonstrates a design of a compact balanced bandpass filter (BPF) with stopband extension and common-mode (CM) suppression using asymmetric stepped-impedance resonator (SIR) pairs and a spoof surface plasmon polariton (SPP) feeding structure. The configuration of balanced SIR pairs is analyzed theoretically to obtain a wide stopband response and intrinsic CM suppression within differential-mode passband. Moreover, a novel SPP feeding structure is adopted as a low-pass filter and impedance matching section for enhancing filter transmission responses. Finally, a balanced BPF operating at 0.85 GHz with the SPP feeding structure is designed and fabricated to verify the design method.

Compact balanced bandpass filter design using miniaturised substrate integrated waveguide cavities

The contribution of this work is to propose a compact balanced bandpass filter design using the miniaturised full/half-mode substrate integrated waveguide cavities (SIWCs) together with the microstrip coupling slot feed. The circuit area of the proposed full-mode SIWC is only 4.64% of its conventional SIWC counterpart, and the half-mode SIWC further reduces the circuit area by half. Besides the circuit compactness, the non-coupling of the microstrip and the slot in the common-mode (CM) operation provides an excellent CM signal rejection. Prototypes of two-pole full/half-mode balanced SIWC BPFs are fabricated and measured to validate the circuit design. Agreements between measured and simulated data are observed. The CM signal rejection levels are larger than 45 dB over a wide-frequency range with the passband's differential-mode insertion losses around 1.6 and 0.8 dB for the full- and half-mode designs, respectively.

Design of a Compact Balanced Bandpass Filter based on CSRR-loaded Substrate Integrated Waveguide Structure

Abstract A compact balanced bandpass filter (BPF) based on complementary split ring resonator (CSRR) -loaded substrate integrated waveguide (SIW) structure is reported in this paper. Both TE102 and TE201 modes of the SIW cavity can be excited under differential-mode (DM) operation with the proper positions of the balanced feeds. Meanwhile, the CSRR etched on the top layer of the substrate can also be excited by the axial electric excitation. Then, three transmission poles and two transmission zeros (TZs) have been obtained which improve the selectivity of the DM passband. To verify the above design concept, an X-band prototype operating at 8 GHz has been fabricated and measured. A good agreement is observed between the simulations and the measurements.

Compact Wideband Balanced Bandpass Filters With Very Broad Common-Mode and Differential-Mode Stopbands

Compact balanced bandpass filters based on a combination of multisection mirrored stepped-impedance resonators and interdigital capacitors are presented in this paper. The considered filter topology is useful to achieve wide bandwidths for the differential mode, with broad stop bands for that mode, as well as very efficient common-mode suppression. By conveniently adjusting the transmission zeros for both operation modes, the differential- and common-mode stopbands can be extended up to significantly high frequencies. Filter size and this differential- and common-mode stopband performance are the main relevant characteristics of the proposed balanced filters. The potential of the approach is illustrated by the design of a prototype order-5 balanced bandpass filter, with central frequency $f_{0} = 1.8$ GHz, 48% fractional bandwidth (corresponding to 55.4% −3-dB bandwidth), and 0.04-dB ripple level. The filter is automatically synthesized by means of an aggressive space-mapping software tool, specifically developed, and two (pre- and post-) optimization algorithms, necessary to determine the transmission-zero frequencies. The designed filter is as small as $0.48\lambda _{g} \times 0.51\lambda _{g}$ , where $\lambda _{g}$ is the guided wavelength at the central filter frequency, and the differential-mode stopband extends up to at least 6.5 GHz with more than 22-dB rejection. The common-mode suppression is better than 28 dB from dc up to at least 6.5 GHz.

Compact balanced bandpass filter with the fractal defected structures

Compact balanced bandpass filter with the fractal defected structures

A low-cost 4.9 GHz balanced bandpass filter with good common mode isolation

This paper presents a compact and low-cost balanced bandpass filter (BPF) operating at 4.9 GHz with high selectivity using mixed coupled ‘U’ shaped resonators, parallel coupled feed line, open and centrally loaded short circuited stubs, respectively. The odd–even mode decoupling scheme and the weakly coupled resonator concepts are utilized for the analysis and validation of differential mode (DM) and common mode (CM) equivalent circuits of the proposed BPF. The passband CM response of the balanced BPF is suppressed above 30 dB by employing grounded stubs in the symmetry plane, which converts the CM response to an all stop characteristic. The second harmonics generated by the BPF is also suppressed using open stubs located near the feed lines. The proposed balanced BPF is fabricated on an FR4 substrate (εr = 4.4, h = 1.6 mm, tan δ = 0.02), which provides 10.7% measured 3 dB fractional bandwidth (FBW) and minimum 1.2 dB insertion loss in the passband (4.7–5.2 GHz). A good agreement is found between the simulated and measured results.

Compact balanced bandpass filter using isosceles right triangular patch resonator

A compact balanced bandpass filter (BPF) by using the isosceles right triangular patch resonator is presented. Stemming from the mode degeneration properties of the square patch resonator with single excitation located at its corner, the specific current distribution on this square patch resonator is investigated. Based on that, a new type of half-mode square patch resonator named as the isosceles right triangular patch resonator is derived and proposed. Afterwards, resonant properties of the new patch resonator under different excitation forms are also investigated. Subsequently, balanced BPF has been implemented by adopting appropriate coupling structure among four isosceles right triangular patch resonators. Finally, to verify the design concept, a second-order Chebyshev balanced BPF centred at 2.44 GHz with 3 dB fractional bandwidth of 6.15% is designed and fabricated. Good agreement can be observed between the simulated and the measured results.

Balanced Band-Notched UWB Filtering Circular Patch Antenna with Common-Mode Suppression

This letter presents a balanced band-notched ultra-wideband (UWB) filtering circular patch antenna fed by a microstrip line. The proposed circuit is composed of a λ/4 slotline-resonator-based balanced band-notched UWB bandpass filter (BPF) and a stub-loaded circular radiating patch. The compact balanced BPF is new in that the slotline resonator is fed judiciously at its open end so that differential-mode fields can be effectively excited in the slotline resonator. Moreover, it can achieve an all-stop-like common-mode rejection because the slotline resonator is incomplete in structure when in common-mode operation. The way the BPF is coupled to the circular radiating patch is novel in that a good impedance match can be easily obtained with the aid of two tuning open stubs. A pair of spur-lines was implemented in the microstrip feedline near the plane of symmetry to produce a notch band around 5.5 GHz. Measurement shows that the differential-mode operating band with return loss greater than 10 dB covers 2.95-10.75 GHz except for the notch band of 5.01-6.19 GHz. Very good common-mode suppression is observed with the measured common-mode reflection coefficient greater than -1.78 dB in 1-12 GHz.

Compact wideband balanced bandpass filter with high common‐mode suppression based on cascade parallel coupled lines

A novel differential bandpass filter based on the cascaded parallel coupled lines is proposed, which takes the features of wide passband, high common-mode suppression and compact size. Six transmission zeros are created and located at the frequency range of 0-2f 0 ( f 0 is centre frequency of the passband), which helps realise the wide passband performances. The balanced bandpass filter consists of the four-stage parallel coupled lines, and the even- and odd- mode characteristic impedances can be adjusted to achieve the desired bandwidth of the passband while the positions of four transmission zeros can be conveniently adjusted by changing the impedance ratio of the asymmetrical stepped impedance resonator (SIR) structures in the proposed filter. By applying the differential and common modes analysis method, the two-port bisections of the filter become a bandpass and all-stop filter topologies under differential- and common-mode excitations, respectively. For performance demonstration of the proposed differential filter, a prototype operating at the frequency band of 2.15-3.85 GHz (with fractional bandwidth of 56.7%) was designed and fabricated on a commercial printed circuit board (PCB) substrate. The insertion loss and return losses of the differential-mode filter are 15 dB in the passband and the common-mode suppression is higher than 30 dB. Good agreements between the simulated and measured results have been observed.

High CM suppression balanced broadband BPF with hybrid hairpin-interdigital structure

A compact, high selectivity and good common-mode (CM) suppression balanced broadband bandpass filter (BPF) is proposed using hybrid hairpin-interdigital structure. Under the differential-mode (DM) excitation, the filtering topology is formed by n + 1 quarter-wavelength resonators (QWRs) and n hairpin resonators (HRs) instead of QWRs with coupled-line I/O coupling structure. But, the DM circuit still maintains high selectivity and broadband characteristics of the interdigital BPF. By reasonably choosing the coupling length and the length of the HR, the balanced BPF can not only obtain the desired DM frequency response, but the CM harmonic generated by the HR can be well suppressed by the CM transmission zero created by the coupling between the HR and half-wavelength resonator (HWR). No via-hole ground for the balanced broadband BPF is required, reducing the implementation complexity. Finally, the third-, fifth-, and seventh-order balanced broadband BPF prototypes are designed and fabricated, and the simulated and measured results show a good agreement. The CM signal for seventh-order case has been suppressed below −46.5 dB in the whole DM frequency band.