Wideband Common-mode Suppression Research Articles

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.

A Novel Wideband Common-Mode Noise Suppression Filter That Combines Mushroom and Defected Corrugated Reference Plane Structures

A novel wideband common-mode (CM) suppression filter is proposed for high-speed transmission. The filter is embedded in 3 10 mm × 10 mm layers of a printed circuit board (PCB) that combines a mushroom structure and a defected corrugated reference plane structure (MDCRP). Using the novel MDCRP structure generates more resonance frequencies in the CM current return path. This generates a wider CM noise suppression performance. We used a simulation method to obtain the best geometric parameters for the MDCRP structure. The experimental results proved that the full-wave simulation results were consistent with the actual measurement results. This novel filter shows good signal integrity according to actual measurements, and the insertion loss can be kept to less than −2.306 dB from DC to 21 GHz in differential mode (DM). The CM noise can be suppressed by over −10 dB from 5.09 GHz to 20.62 GHz. The fractional bandwidth is 120.8%, and the CM noise improves by 64.5%. An eye diagram proves that the filter can support a 20 Gb/s transmission rate with complete differential signal transmission capability. The MDCRP structure filter can support HDMI 2.0, PCI Express 4.0, USB 3.2, and SATA Express. Therefore, the filter meets current computer and server system products’ design needs.

A Balanced Substrate Integrated Waveguide Phase Shifter with Wideband Common-Mode Suppression

In this paper, a slotted substrate integrated waveguide (SIW) is used to create a balanced phase shifter with wideband common-mode (CM) suppression. Differential-mode (DM) impedance matching and CM suppression are achieved by utilizing the fact that TE20 mode and TE10 (TE30) mode can only transmit DM signals and CM signals, respectively, and by increasing the bandwidth for CM suppression via slots. Furthermore, a wideband phase shift with low phase deviation can be obtained due to the phase slop counteract between the slot and the delay line. Compared with the state-of-the-art, the proposed one has the advantages of wideband CM suppression, wide phase shift range, and a simple and easy-to-make structure. Five prototypes covering the frequency of 3.5 GHz are designed with the relative operating bandwidth for 45° ± 2° (90° ± 4.5°, 135° ± 6°, and 180° ± 8°) phase shifter of 20% (20%, 20%, and 20%), with the minimum insertion loss of 0.41 dB (0.5 dB, 0.58 dB, and 0.59 dB), with the minimum return loss greater than 15 dB, and with the relative bandwidth for 15-dB CM suppression of 59% (59%, 58%, and 57%).

A Compact Dual-Band Differential Negative Group Delay Circuit With Wideband Common Mode Suppression

A compact dual-band differential negative group delay (DNGD) circuit with wideband common mode suppression is proposed. Two small 180° phase shift swap structures of double-sided parallel striplines (DSPS) are adopted to realize intrinsic wideband common-mode suppression. The dual-band DNGD characteristic is achieved by the DSPS coupled asymmetrically with two different-length open-circuited resonators. The DNGD times and center frequencies of the lower and upper bands can be tuned independently. To verify the proposed DNGD circuit topology, a prototype is designed, fabricated, and measured. From the measured results, DNGD times are −1.60 ns and −1.43 ns at the center frequencies of 1.227 GHz and 1.575 GHz, respectively. The differential insertion loss is lower than 3.55 dB, the differential return loss is larger than 13.3 dB and the common-mode suppression is over 30.8 dB in both DNGD bands.

Design of Balanced Wideband BPF Based on Tri-Mode Slotline Resonators

In this brief, a tri-mode slotline resonator (TMSR) is designed. The proposed resonator has similar performances to those of the conventional microstrip multimode resonator (MMR), while it is located at the bottom ground layer. Meanwhile, the method of characteristic mode analysis (CMA) is innovatively applied to the design process of TMSR, and specific formula results can be obtained. By properly adjusting the dimensions of the proposed TMSR, three resonant modes can be controlled easily, so that a broad differential-mode (DM) transmission response can be realized and the DM stopband can be up to 17.5 GHz (<inline-formula> <tex-math notation="LaTeX">$3.04f_{0}$ </tex-math></inline-formula>). By employing balanced microstrip/slotline transition structures, a high and wideband common-mode (CM) suppression can also be achieved, which is independent of the DM responses. Hence, only the DM performances need to be focused, which simplifies the design procedure significantly. In order to suppress the special electromagnetic interference, a notched band structure is added without increasing the size of the filter. Moreover, three-slotline couple structures and enhanced coupled structures are discussed to further optimize the filter performances. To validate the design concept, one prototype is implemented following the given design procedure. Good agreement between the measurement and simulation results can be observed.

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.

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.

A broadband and low cross‐polarization balanced dual‐polarized cross quasi‐yagi antenna

A broadband balanced fed dual-polarized cross quasi-Yagi antenna with a compact size, low cross-polarization, and good common-mode (CM) suppressions is provided. The proposed antenna consists mainly of two balanced quasi-Yagi antennas, which are vertical to each other. Balanced microstrip-slotline feeding line structures are utilized to excite the two quasi-Yagi antennas to achieve ±45° linear polarizations. A good end-fire radiation in a broad bandwidth is achieved by introducing the directors above the dipoles of the cross quasi-Yagi antenna. Meanwhile, a good wideband common-mode (CM) suppression and low cross-polarization levels are realized by the balanced microstrip-slotline feeding line structure. Besides, superior DM transmission and CM suppression are achieved intrinsically, thereby simplifying the design procedure significantly. Finally, the balanced dual-polarized antenna is fabricated to validate the feasibility of this design method. The measured dates show that the designed antenna characterizes broadband, high port isolation and CM suppression, low cross-polarization levels and stable gain radiation.

A Miniaturized Balanced-to-Unbalanced In-Phase Filtering Power Divider With Wide Upper Stopband and Wideband Common-Mode Suppression

A miniaturized balanced-to-unbalanced in-phase filtering power divider with wide upper stopband and wideband common-mode suppression is proposed. The in-phase feature is realized by the coupled/non-coupled lines. The stub with shunt-capacitor is used to realize the functions of filtering and miniaturization. The closed-form design equations are provided and discussed. To verify the design equations, one prototype with a center frequency of 1.0 GHz is designed and fabricated. The measured differential return loss is greater than 15 dB in the range of 0.82-1.22 GHz (39.2%). The upper stopband rejection is better than 20 dB from 1.41 to 3.57 GHz. Common-mode suppression is greater than 20 dB from 0 to 3.7 GHz. The measured results are in good agreement with electromagnetic simulations.

High Performance Balanced Bandpass Filters With Wideband Common Mode Suppression

Two compact and high selectivity balanced bandpass filters with excellent common mode rejection are designed in this brief. Compared with the half-wavelength microstrip transmission line, 180° phase shift is realized by two small swap structures, which are composed by double-sided parallel-strip line (DSPSL), and this way can easily realize a wideband common mode rejection with compact circuit size. Two out-of-band transmission zeros are introduced by the dual-mode ring resonator in the first proposed structure; thus, high selectivity can be achieved. In the second filter, shorted/open coupled microstrip lines are added between the dual-mode ring resonator and 180° swap structure, two additional transmission zeros can be achieved. Finally, two prototypes center at 2.2 GHz are fabricated, and the measured 3-dB bandwidths for the differential mode are 23.6% and 11.8%, respectively.

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

In this paper, a balanced dual-band bandpass filter (BPF) with high selectivity and low insertion loss performance is presented by employing stub loaded resonators (SLRs) and stepped impedance resonators (SIRs) into balanced microstrip-slotline (MS) transition structures. The balanced MS transition structures can achieve a wideband common-mode (CM) suppression which is independent of the differential-mode (DM) response, significantly simplifying the design procedure. Six varactors are loaded into the resonators to achieve the electrical reconfiguration. The proposed balanced dual-band BPF can realize quasi-independently tunable center frequencies and bandwidths. A tuning center frequency from 2.48 to 2.85 GHz and a fractional bandwidth (20.16%-7.02%) with more than 15 dB return loss and less than 2.36 dB insertion loss are achieved in the first passband. The second passband can realize a tuning center frequency from 3.6 to 3.95 GHz with more than 12 dB return loss and less than 2.38 dB insertion loss. A good agreement between the simulated and measured results is observed.

Compensating Mode Conversion Due to Bend Discontinuities Through Intentional Trace Asymmetry

In this letter, a comparative analysis is carried out between the mechanism of mode conversion in differential microstrip lines due to bend discontinuities on one side and trace asymmetry on the other side. With the help of equivalent modal circuits, a theoretical basis is provided for the idea to compensate the undesired common mode (CM), due to the presence of the bend, by intentionally designing asymmetric traces. As an application example, the proposed CM-reduction strategy is used in conjunction with another recently-presented wideband CM suppression filter for differential microstrip lines. It is shown that the proposed solution enhances the overall CM-reduction performance of the filter by some decibels, while preserving its transmission properties.

A new dual‐band single‐ended‐to‐balanced filtering power divider

This article proposes a new dual-band single-ended-to-balanced (SETB) filtering power divider (FPD), which shows the excellent characteristics of wideband common-mode (CM) suppression and good selectivity. By employing the structure of double-sided parallel-strip line with a mid-inserted conductor and a T-shaped defected ground structure etched in the mid-inserted conductor, out-of-phase behavior and high CM suppression can be achieved successfully. Besides, to realize dual-wideband filtering performance and high selectivity, two pairs of step impedance stubs (SIS) loaded quarter-wavelength central line-terminal-shorted three parallel-coupled microstrip lines structure are adopted. Meanwhile, two pairs of resistors are introduced so as to realize excellent isolation. To verify effectiveness of the design method, a prototype of dual-band SETB FPD which operates at 3.2 and 4.9 GHz is designed, fabricated, and tested. Final results exhibit that the new dual-band SETB FPD possess high selective dual-band differential mode response, wideband CM suppression, and excellent isolation between the balanced output ports.

An Approach to $N$ -Stage Balanced-to-Single- Ended Out-of-Phase Power Divider With Enhanced Operating Bandwidth

In this paper, an approach to n-stage (n= 3, 4, 5...) balanced-to-single-ended out-of-phase power divider is proposed, which enhances the bandwidths for port matching, isolation and common-mode suppression firstly. Compared with the traditional single-ended multistage power divider, this approach has special circuits (common-mode and isolation circuits) for improving common-mode suppression and isolation, respectively. For common-mode suppression, the 180° microstrip line between the balanced port and the common-mode circuit composed by one parallel open stub are adopted to achieve wideband common-mode suppression. For isolation, the isolation circuits formed by cascade stage structure and parallel resistors are both adopted to improve the isolation bandwidth. The basic analysis at the center frequency is given, and for verifying the theoretical prediction, two prototypes of the 3-and 4-stage power dividers are fabricated and measured, which show 46.7% and 63% 20-dB operating bandwidths, and 0.25 dB and 0.3 dB minimum insertion loss, respectively. These two prototypes present that the 20-dB operating bandwidths are 16.7% and 33% wider than the single-stage balanced-to-single-ended power divider.

Balanced Rat-Race Couplers With Wideband Common-Mode Suppression

In this article, various types of six-port balanced rat-race couplers with wideband common-mode suppression characteristics are presented. In these couplers, the input and output ports can functionalize either as single-ended or differential terminals to realize different operational modes. The power-splitting ratio for these balanced couplers can be flexibly adjusted by means of the values of the characteristic-impedance parameters of their constituent transmission-line segments. Furthermore, the employment of double-sided-parallel-strip-line-(DSPSL)-based 180° phase inverters instead of half-wavelength transmission-line-based ones allows for the considerable enlargement of their operation bandwidth in more-compact circuits with lower in-band insertion-loss levels. For experimental-validation purposes, two microstrip prototypes at $f_{0}=0.9$ GHz with equal and unequal power division are fabricated and characterized. They exhibit common-mode rejection levels higher than 15 dB from 0 to 1.8 GHz (i.e., 0– $2f_{0}$ ) and differential-to-common- mode-conversion suppression levels above 15 dB within the spectral range 0–1.49 GHz (i.e., 0– $1.65f_{0}$ ).

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.

A balanced dual‐band bandpass filter with a wide stopband and controllable differential‐mode frequencies and fractional bandwidths

In this article, a balanced microstrip dual-band bandpass filter (BPF) is designed. The proposed filter is achieved by employing a microstrip U-shape half-wavelength resonator, a folded stub-loaded resonator and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths of the two differential-mode (DM) passbands can be controlled independently by changing the physical lengths of the two resonators and the gaps between each resonator, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common-mode (CM) suppression. Meanwhile, the DM passbands are independent from the CM responses, which significantly simplify the design procedure. In addition, a wide DM stopband is also realized. In order to validate the design strategies, a balanced dual-band BPF centered at 2.57 and 3.41 GHz was fabricated and a good agreement between the simulated and measured results is observed.

Differential Transmission Lines Loaded With Magnetic LC Resonators and Application in Common Mode Suppression

This paper presents the analysis of magnetic LC (MLC) resonators loaded with differential microstrip transmission lines. The analysis is based on an equivalent circuit model describing the electromagnetic behavior of the MLC resonators. It is shown that a pair of microstrip lines loaded with MLC resonators exhibit a dual-mode bandstop response in the common mode of operation, while being transparent to the differential signals. This characteristic can be used in the design of differential transmission lines with wideband common mode suppression. Circuit models together with Bloch theorem are applied for the systematic design, where the dispersion analysis helps to estimate the maximum achievable common-mode rejection bandwidth. A systematic design procedure is developed for designing differential transmission lines using this method. The theoretical analysis is validated by designing and measuring a balanced transmission line using three cascaded MLC-based cells. The measurements exhibit more than 40-dB common-mode signal suppression for a fractional bandwidth of 32% around 1.3 GHz, whereas the fraction bandwidth for 20-dB suppression level is 57.5%. The fabricated prototype has a compact size of $0.09\lambda _{g}\times 0.37\lambda _{g}$ , where $\lambda _{g}$ is the guided wavelength at 1.3 GHz. A detailed comparison between the designed MLC-based differential transmission line and the state-of-the-art designs shows a superior performance of the MLC-based transmission lines in terms of size, fabrication simplicity, and the common-mode rejection level.

Design of compact single‐ended‐to‐balanced filtering power divider with wideband common‐mode suppression

A new design of single-ended-to-balanced (SETB) filtering power divider (FPD) with wideband common-mode (CM) suppression is presented. To effectively realise high suppression of CM noise, a hybrid structure constructed by both the double-side parallel-strip line (DSPSL) and a half-mode defected ground structure (HMDGS) serving as the mid-inserted conductor plane are adopted. Besides, due to the effect of HMDGS, the rejection of second harmonics for the differential-mode (DM) transmission is also improved. Meanwhile, by employing two pairs of dual-mode resonators symmetrically coupled with a stepped-impedance input feed line and adding a DSPSL stub, wideband-filtering performance with high selectivity is achieved. For validation, a prototype of the proposed SETB-FPD centred at 5.9 GHz with a 3-dB fractional bandwidth (FBW) of 27% is designed, fabricated and measured. Results indicate that the proposed SETB FPD exhibits good performances of high selectivity, wide upper stop band, good isolation between two balanced output ports and 30-dB suppression of CM noise over the DM pass band.

A Balanced Dual-Band BPF with High CM Suppression and Improved Selectivity

Abstract In this paper, a balanced dual-band bandpass filter (BPF) is designed based on microstrip folded stepped impedance split ring resonators (SISRRs) and balanced microstrip/slotline transition structures. The center frequencies and the fractional bandwidths (FBWs) of the two differential-mode (DM) passbands can be tuned by changing the physical lengths of two SISRRs and the gaps between the two resonators, respectively. The balanced microstrip/slotline transition structures can achieve a wideband common-mode (CM) suppression. Moreover, the DM passbands are independent from the CM responses, which significantly simplifies the design procedure. In addition, due to 0-degree feed structure and cross coupling structure, more transmission zeros can be realized, which can improve the passbands selectivity greatly. In order to validate the design strategies, a balanced dual-band BPF centered at 2.47 GHz and 5.21 GHz was fabricated and a good agreement between the simulated and measured results is observed.