Balanced Bandpass Filter Research Articles

Novel microwave balanced bandpass filter with high common mode rejection ratio and wide rejection band under common mode operation

ABSTRACTIn this work, a new balanced band pass filter and its design procedure are proposed. The filter is based on a novel resonator, named LTLC resonator, which consists of two inductors (L), two Transmission Lines (TLs) and one capacitor (Cs). The resonators are designed by using its equivalent circuits and its design equations which are presented in this work. The filter exhibits central frequency at f0d = 0.988 GHz, Fractional Band Width (FBW) of 10.1%, Common Mode Rejection Ratio (CMRR) better than 51 dB at the center frequency, Common Mode (CM) rejection better than −40 dB from 0.5 GHz to 3.3f0d and better than −30 dB from 0.5 GHz to 4f0d. This paper includes analysis, design methodology and experiments.

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 .

A Balanced Dual-Band BPF Based on C-CSRR with Improved Passband Selectivity

Abstract A balanced dual-band bandpass filter (BPF) is proposed by embedding two nested coupled complementary split-ring resonators (C-CSRRs) into a H-type balanced stepped-impedance slotline resonator in this paper. C-CSRR is composed of a complementary split-ring resonator (CSRR) with a pair of coupling slotlines in the open end, which can generate a bandpass response. In order to improve the passband selectivity further, source-load-coupled structure is employed. Moreover, it can be found that the proposed BPF has a wideband common-mode (CM) suppression, which is independent from the differential-mode (DM) passbands. Therefore, the design procedure can be significantly simplified. In order to validate its practicalbility, one balanced dual-band BPF is fabricated. The predicted results on S parameters are compared with the measured ones and a good agreement is found.

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.

Design of Balanced Filtering Components Based on Isosceles Right-Angled Triangular Patch

In this paper, a balanced bandpass filter (BPF), a balanced-to-balanced filtering power divider (FPD), and a balun filter are implemented using the isosceles right triangular patch element. Two isosceles right triangular patch elements are coupled through an open stub for a triple-mode passband response under differential-mode operation and wide common-mode suppression simultaneously. To further improve the selectivity, an open stub is loaded on each feed-line. Based on these elements, a balanced BPF with excellent performance can be implemented. As an extension, a balanced-to-balanced FPD and a balun BPF are implemented based on the structure of the filter. For validation of the proposed configurations, all the balanced BPF, FPD, and balun BPF have been fabricated and measured. All measured results are found to be in a reasonable agreement with the simulation results.

A New Concept of Partial Electric/Magnetic Walls for Application in Design of Balanced Bandpass Filters

In this paper, a concept of partial electric/magnetic walls is proposed and applied to design a class of balanced bandpass filters on (modified) doublet topology with differential-mode (DM) transmission zeros (TZs). It is first demonstrated that the partial electric/magnetic walls are equivalently attained along certain parts of these balanced filters. Using this concept, a dual-mode ring balanced bandpass filter on modified doublet topology with two DM TZs is designed, fabricated, and measured. Furthermore, another balanced bandpass filter on doublet topology with three DM TZs and wide upper stopband is designed and implemented, so as to exhibit the attractive application of the proposed concept. Good agreements between the expected response, simulated results, and measure results are observed.

Novel Absorptive Balanced Bandpass Filters Using Resistive Loaded Transmission Lines

This paper reports on design of novel balanced bandpass filters (BPFs) using quarter-wavelength stub resonators. For the design purposes, differential-mode (DM) and common-mode (CM) half-equivalent circuits are established and analyzed carefully. In this paper, CM noise is introduced into the filter and dissipated on the resistors on periodic bands. First, a balanced BPF topology based on conventional quarter-wavelength stub filter is presented. By symmetrically introducing series matching resistors to the ground at the center of the stub, CM noise can be rejected either reflectively or reflectionlessly without affecting DM performance. The harmonic property of stubs provides periodic CM suppressing response as long as the resistor has no serious parasitic reactance. By doing so, CM noise can be suppressed under a certain level at all frequencies. However, the harmonic property also leads to some spurious passbands. This defect can be avoided by an improved filter topology with two additional capacitors. To reserve the CM feature, the corresponding DM and CM half equivalent circuits are developed as well. The proposed layouts are fabricated on a two-layer printed circuit board. The resulting experimental circuits exhibit the expected electrical performance, forming balanced BPFs with CM noise suppression level over 12 dB at all frequencies, and show an agreement with the simulated results.

Compact Tunable Balanced Bandpass Filter With Constant Bandwidth Based on Magnetically Coupled Resonators

In this letter, a compact high-selectivity and common-mode (CM) suppression tunable balanced microstrip bandpass filter (BPF) with constant bandwidth is designed by adopting the magnetically coupled resonators with step-impedance parallel coupling feedline (SIPCF) structure. The desired coupling coefficient $K_{12}$ and external quality factor $Q_{e}$ can be obtained by the mixed coupling between the two resonators and SIPCF structure, respectively. Two differential-mode (DM) transmission zeros (TZs) near the lower and upper passband edges are created by the mixed coupling and source–load coupling, respectively. Furthermore, intrinsic high CM suppression in the DM tunable operating passband can be maintained because of the magnetically coupled resonator structure. Finally, a compact tunable balanced BPF prototype with constant fractional bandwidth of 6.5% is implemented and fabricated. The measured results agree well with the simulated ones.

Balanced bandpass filter using TE01δ-mode dielectric resonator

ABSTRACTIn this paper, a surface-mounted dielectric resonator-based balanced bandpass filter is proposed. By utilizing the TE01δ mode as a dominant mode of the cylindrical dielectric resonator, it can be excited in differential mode to achieve good common-mode suppression in differential filter passband. To validate the design idea, a second-order balanced narrowband bandpass filter with center frequency at 5.53 GHz has been designed, fabricated, and measured. The design parameters of the proposed filter are: insertion loss 0.2, 3 dB Bandwidth (BW) 67.1 MHz, and return loss 23 dB, and common-mode separation is more than 30 dB. There is good agreement between the simulated and measured results.

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.

Design of a Sixth-Order Switchable Superconducting Balanced Filter Using Asymmetric Coupled SIRs

A stopband-extended sixth-order balanced bandpass filter with switchable passband function and stopband response is proposed in this paper. Based on the use of asymmetric coupled stepped-impedance resonators, the upper differential-mode stopband can be extended, and high common-mode suppression can be performed within passband. By means of high-order structure and cross coupling, which introduce transmission zeros closely around the passband, high selectivity is attained. The configuration utilizing switchable cross coupling is eventually employed in the balanced filter to perform either Elliptic function with steep passband edge or Chebyshev function with flat and deep stopband. The circuit is fabricated in high-temperature superconducting technique on an MgO substrate with YBCO thin films, which can result in relatively low insertion losses. Experiment at the temperature of 77 K was carried out to validate the design concept. The results attain good agreement with the predicted ones in simulation.

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.

UWB Balanced BPF Using a Low-Cost LCP Bonded Multilayer PCB Technology

This paper presents a new miniaturized ultra-wideband (UWB) multilayer balanced bandpass filter (BPF) using the liquid-crystal polymer technology. The design is based on the use of two baluns and uses the transversal signal-interference concept for the realization of differential-mode (DM) passband and common-mode (CM) stopband. The broadside coupled stripline structure is adopted in this paper to realize UWB performances and pure TEM mode. The fabricated prototype is self-packaged, light in weight, and cost effective with a small footprint. The demonstrated balanced BPF achieves the excellent DM and CM responses within the entire bandwidth, centered at 6.85 GHz. The simulation and measurement results show good agreement.

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.

A Balanced Quad-Band BPF With Independently Controllable Frequencies and High Selectivity

A balanced microstrip quad-band bandpass filter (BPF) with independently controllable frequencies, controllable fractional bandwidths (FBWs) and high selectivity is designed in this paper. The proposed BPF is achieved by employing two pairs of folded asymmetric stub-loaded resonators (FASLRs) and balanced microstrip/slotline transition structures (MSTSs). The center frequencies of the four differential-mode (DM) passbands can be controlled independently by changing the electrical lengths of each FASLR. A novel interdigital coupled line is firstly proposed to enhance source-load coupling further, which contributes to a higher selectivity. Meanwhile, the DM passbands are independent of the CM responses, which significantly simplifies the design procedure. In addition, eight transmission zeros (TZs) are generated to improve the selectivity of the four passbands obviously. The measured results of the fabricated balanced BPF centered at 2.48/3.45/5.17/5.78 GHz agree well with the simulated ones, which validates the proposed design method well.

High Selective Balanced Bandpass Filters Using End-Connected Conductor-Backed Coplanar Waveguide

In this paper, an end-connected conductor-backed coplanar waveguide (CBCPW) balanced bandpass filter and a size reduction one with adjustable multiple transmission zeros have been developed by using the separated electric and magnetic coupling, and quarter-wavelength short-circuited stubs. The differential mode (DM) and the common mode (CM) equivalent transmission line circuits have been modeled and verified, and the DM/CM parts can be designed individually. The proposed CBCPW balanced bandpass filters have been fabricated and measured, and their advantages of multiple transmission zeros, high out-of-band suppression, and high common mode suppression characteristics have been demonstrated.

A New Design Approach for Balanced Bandpass Filters on Right-Angled Isosceles Triangular Patch Resonator

A new approach to design a balanced bandpass filter (BPF) is presented in this letter. By virtue of resonant properties of a right-angled isosceles triangular patch resonator (RAITPR), a modified RAITPR with one electric wall and two magnetic walls is constructed. This resonator, namely, half-mode RAITPR, can support half-TM10-mode of the RAITPR. By adopting proper coupling topology between three adjacent RAITPRs and two half-mode RAITPRs, a third-order balanced BPF is proposed to achieve good differential-mode filtering selectivity and high common-mode suppression. To verify this design concept, a balanced BPF operating at 2.0 GHz with a 3-dB fractional bandwidth of 12.9% is in final designed and fabricated. Good agreement is achieved between the simulated and measured results over a wide bandwidth from 0 to 4.0 GHz.

Balanced Quad-Band Bandpass Filter With Controllable Frequencies and Bandwidths

A balanced microstrip quad-band bandpass filter (BPF) employing balanced microstrip/slotline (MS) transition structures and two pairs of folded asymmetric short stub-loaded resonators (ASSLRs) is presented in this paper. The center frequencies of the four differential-mode (DM) passbands can be controlled by changing the electrical length ratio of each ASSLR. Meanwhile, the fractional bandwidths (FBWs) can be adjusted by controlling the coupling gaps between the resonators and interdigital coupled line. High selectivity of the four DM passbands is achieved by introducing eight transmission zeros (TZs). Moreover, the DM passbands are independent from the common-mode (CM) responses, which significantly simplifies the design procedure. In order to validate the design strategies, a balanced quad-band BPF centered at 2.54/ 3.46/ 4.5/ 5.2 GHz was fabricated and a good agreement between the simulated and measured results is observed.

An X‐band push‐push oscillator with parallel feedback configuration designed by microstrip balanced bandpass filter

In this article, a push-push oscillator with parallel feedback configuration designed by the microstrip balanced bandpass filter (BPF) is proposed. The push-push oscillator consists of two sub-oscillators with a balanced BPF. The balanced BPF with the open-circuited stubs exhibits the desired differential-mode frequency response and achieves high common-mode suppression simultaneously. Based on the technique of the balanced BPF, the out-of-phase fundamental signals and odd harmonic signals are canceled out while the even harmonic signals are well combined. The prototype of the push-push oscillator is designed and fabricated. Measured results show that the proposed push-push oscillator works at 9.96 GHz of the second harmonic frequency. The actual output power is −8.57 dBm. The rejection of the fundamental signal and third harmonic signal are better than 27 and 42 dBc, respectively. The phase noise of the proposed push-push oscillator is −128.3 dBc/Hz at 1 MHz frequency offset.

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.