Balanced Filter Research Articles

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 balanced UWB BPF based on quint‐mode slotline resonator

In this paper, a quint-mode slotline resonator (QMSR) is analyzed and designed. The proposed resonator has similar performances to those of the conventional microstrip multimode resonator, while it is located at the bottom ground layer. To the best of our knowledge, this is the first time that QMSR is proposed. By properly adjusting the dimensions of the proposed QMSR, quasi-independent control of the five resonant frequencies is realized, thereby an ultrawideband (UWB) differential-mode (DM) transmission passband can be obtained. By employing balanced microstrip/slotline transition structure, a high and wideband common-mode (CM) suppression can also be realized, which is independent of the DM responses. Thereby, only the DM performances need to be considered, which simplify the design procedure greatly. In addition, one notched band is achieved to suppress the special electromagnetic interference. To validate the design concept, one prototype circuit of the proposed balanced UWB bandpass filter is implemented following the given design procedure. Good agreement between the measurement and simulation results can be observed.

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.

A Dual-Band Tunable Balanced Filter With Independently Tuning Bands

A dual-band tunable balanced filter based on one hybrid microstrip-cavity structure is proposed in this paper. The cavity acts as one multimode resonator, and the differential feeding networks are printed on the PCBs. According to the electromagnetic (EM) field theory, TE101 and TE011 modes are generated under differential-mode (DM) excitation, and highly suppressed under common-mode (CM) excitation. The dielectric posts in the cavity can independently shift the resonant frequencies of the two modes. Moreover, the inter-resonator coupling of each band is independently controlled by the cross-shaped coupling slot. Therefore, good filtering differential response can be realized with in a wide band. For demonstration, a dual-band tunable balanced filter is designed and measured. The measured results indicate that the center frequencies of the two bands are tuned from 7.51 GHz to 8.22 GHz and 9.34 GHz to 10.56 GHz, respectively. Over the tuning range, the insertion losses vary from 0.5 dB to 1.5 dB and the CM suppressions in both passbands are under 50 dB and 42 dB. In this way, the proposed hybrid microstrip-cavity structure is feasible to design a reconfigurable balanced filter with wide tuning range and high CM suppression.

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.

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.

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.

Balanced Dielectric Resonator Filters With Multiple Reconfigurable Passbands

Balanced dielectric resonator (DR) filters with multiple reconfigurable passbands are proposed in this article. Based on the field distributions of two pairs of orthogonal degenerate modes, quad-mode differential-mode (DM) operations are achieved by the specific probe feeding structure. More importantly, the four modes are flexibly controlled by different inserted screws and the detailed principle is illustrated for reconfiguration. For demonstration, a dual-band balanced filter with independently frequency-tunable passbands and a quad-band one with selectable number of passbands are fabricated and measured. Good agreement between the simulated and measured results is observed. The exhibited low DM loss, high common-mode (CM) rejection, and independent tuning abilities verify the proposed method in miniaturized reconfigurable filter designs.

Compact quartz-enhanced photoacoustic sensor for ppb-level ambient NO2 detection by use of a high-power laser diode and a grooved tuning fork

A compact quartz-enhanced photoacoustic sensor for ppb-level ambient NO2 detection is demonstrated, in which a high-power blue laser diode module with a small divergence angle was employed to take advantages of the directly proportional relationship between sensitivity and power, hence improving the detection sensitivity. In order to extend the stability time, a custom grooved quartz tuning fork with 800-μm prong spacing is employed to avoid complex signal balance and/or optical spatial filter components. The sensor performance is optimized and assessed in terms of optical coupling, power, gas flow rate, pressure, signal linearity and stability. A minimum detectable concentration (1σ) of 7.3 ppb with an averaging time of 1 s is achieved, which can be further improved to be 0.31 ppb with an averaging time of 590 s. Continuous measurements covering a five-day period are performed to demonstrate the stability and robustness of the reported NO2 sensor system.

Production of water-based mud for drilling operation application

A successful drilling operation is heavily dependent on the effectiveness of the drilling fluid's design in use. This study attempts to evaluate the rheological and filtration properties of water-based drilling mud (WBDM) upon the addition of Stearyl Acrylate-Behenyl Acrylate (SABA) copolymer, silicon dioxide (SiO2), and nickel (III) oxide (Ni2O3) nanoparticles. This SABA copolymer-nanofluid was prepared by dissolving the nanofluid in a SABA polymer solution and homogenizing it using ultrasonication. The properties were studied using mud balance, viscometer, and low-pressure low-temperature (LPLT) filter press. The rheological and filtration properties of SABA copolymer were found to imply that it could improve drilling fluid performance. However, the addition of nanoparticles gave a better performance of rheological and filtration properties on WBDM. SABA copolymer with 5000 ppm concentration shows the best performance due to showing the highest viscosity compared to basic drilling fluid. Also, the addition of 800 ppm of Ni2O3 concentration into 5000 ppm of SABA shows the lowest fluid losses. The experimental results indicate that SABA copolymer shows a great potential application and the addition of nanoparticles shows that nanotechnology has a lot of potentials to improve WBM performance

Balanced multiple‐layer dual‐mode substrate integrated waveguide filters with controllable finite‐transmission zeros

This paper proposes three balanced multiple-layer dual-mode substrate integrated waveguide (SIW) bandpass filters. The first balanced filter has two substrate layers, and two pairs of balanced feeding ports are located on the upper substrate layer. The lower and upper dual-mode SIW cavities are coupled by two crossed slots in the middle metal layer. The second balanced filter has two substrate layers, and two pairs of balanced feeding ports locate parallelly on the upper and lower substrate layers, respectively. The third balanced filter has three substrate layers, and two pairs of balanced feeding ports locate vertically on the upper and lower substrate layers, respectively. The proposed three balanced filters can produce three, two and one finite-transmission zeros (FTZs), respectively. Characteristics of the proposed multiple-layer SIW filters with controllable FTZs' locations are analysed in detail. For the demonstration, some design examples with the centre frequency of 7.5 GHz and bandwidth of 240 MHz are presented, and three design examples are fabricated to verify the performance of the proposed balanced filters. The measured results agree well with 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.

Differential-to-differential and single-ended-to-differential bandpass filters for 5G applications

This paper presents the design and implementation of bandpass filters for millimeter-wave (mm-Wave) applications. The filter structures are based on transmission line hybrid T-resonators and consist of differential input, differential output (DIDO) and differential/single-ended input, single-ended/differential output (DISO/SIDO) configurations. A prototype from each configuration is designed and fabricated using a microstrip substrate. In addition to good agreement with the simulation results, the measurement results of the fabricated prototypes exhibit higher selectivity, common-mode (CM) suppression and upper stopband attenuation compared to the state-of-the-art balanced filters, rendering the proposed concept suitable for the fifth generation (5G) telecommunication applications. Besides, this work presents the first reported balanced microstrip bandpass filter based on printed circuit board (PCB) at mm-Wave frequencies.

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.

Compact dual-band balanced bandpass filter based on circular SIW cavity

Abstract A compact dual-band balanced bandpass filter with high frequency selectivity and adjustable passband based on the perturbed circular substrate integrated waveguide cavity is firstly proposed in this paper. Two pairs of metallic vias are located at 45°direction of cavities to separate a pair of degenerate modes (TM110 modes) to achieve the differential-mode (DM) dual-band response. Moreover, the perturbation vias can also be used to control the center frequency of the second DM passband while the first one still stays unaffected. The introduction of source-load coupling makes the filter exhibit excellent selectivity. And four controllable transmission zeros appear near two DM passbands. Finally, good common-mode suppression has been got owing to the proposed balanced structure. The measured results are in accordance with the simulated ones well.