Wideband Common-mode Suppression Research Articles

Tunable Balanced Bandpass Filter with High Common-mode Suppression Based on SLSRs

AbstractA tunable balanced bandpass filter (BPF) with a good common-mode (CM) suppression based on slotline resonators is proposed in this letter. Two novel stub-loaded slotline resonators (SLSRs) terminated with varactors are designed to obtain tunable differential-mode (DM) responses. It is found that a high and wideband CM suppression can be achieved by employing balanced stepped-impedance microstrip-slotline transition structures. Moreover, the DM passbands are independent from the CM ones, which can significantly simplify the design procedure. To validate the design theory, a compact tunable balanced BPF with an operating frequency band ranging from 3.09 GHz to 3.6 GHz is designed and fabricated. The measured results are found to agree well with the simulated ones.

Wideband balanced networks with wideband common mode suppression and arbitrary power-dividing ratio

ABSTRACTTwo novel wideband balanced networks with wideband common mode suppression and arbitrary power-dividing ratio are proposed in this paper. The differential/common mode equivalent circuits of the balanced networks can be easily reduced based on the matrix transformation. Microstrip-slotline 180° phase inverters loaded with four isolation resistors are used to realize high isolation for the power division output ports. Two planar wideband equal and unequal power division balanced networks with bandwidths of 33% of (1:1, equal) and 39% (1:2.22, unequal) for the differential mode and over 120% common mode suppression (0.96–3.6 GHz, |Scc21, 31| < –10 dB) are designed and fabricated.

Compact wideband differential filter using quarter-wavelength coupled lines

A compact wideband differential bandpass filter with wideband common-mode suppression using quarter-wavelength coupled lines is proposed. Third-order wide passband for the differential mode can be easily realized by the half wavelength ring resonator. A planar wideband differential filter with 3-dB fractional bandwidth of 60% is designed and fabricated. The theoretical and measured results agree well and show good in band filtering performances and high selectivity.

A Balanced-to-Balanced Network With Unequal Power Division and Wideband Common Mode Suppression

A novel wideband balanced-to-balanced network with unequal power division is proposed in this letter. Two open stubs and half-wavelength transmission lines are used to realize wideband common mode suppression, two ideal double-sided parallel-strip line (DSPSL) 180 $^{\circ}$ phase inverters with isolation resistors are used to realize high isolation for the power dividing output ports. A planar wideband balanced network with bandwidth of 38.6% (power division ratio: $1:2^{2}$ ) for the differential mode and over 113.6% common mode suppression (1.06–3.56 GHz, $| S_{{cc}21,31}| ) is designed and fabricated.

Design of compact balanced ultra‐wideband bandpass filter with half mode dumbbell DGS

A new compact balanced ultra-wideband (UWB) bandpass filter using half mode dumbbell defected ground structure (DGS) is presented. To realise the UWB response, the `T' shape multiple-mode resonator with short-ended stub is employed. To achieve wideband common mode (CM) suppression and compact design simultaneously, the concept of half-mode DGS is introduced in the two stacked microstrip layers. Afterwards, a balanced UWB filter is designed and measured for verifying the feasibility of the presented design method. The measured results match well with the expected results which indicate the proposed filter exhibits better than -30 dB CM suppression within the DM passband covering from 3.1 to 10.6 GHz.

Compact Balanced Dual- and Tri-Band BPFs Based on Coupled Complementary Split-Ring Resonators (C-CSRR)

Two multi-band balanced bandpass filters (BPFs) are proposed by embedding multi-band coupled complementary split- ring resonators (C-CSRRs) into a balanced stepped-impedance microstrip-slotline transition structure. The proposed C-CSRR is made from two or three nested CSRRs with a pair of coupling slotlines in the open end of each ring, which can result in dual-band or tri-band bandpass responses, respectively. It is found that a high and wideband common-mode (CM) suppression can be achieved for the proposed filters. Moreover, the center frequencies of the differential-mode (DM) passbands are independent from the CM responses, which significantly simplify the design procedure. In order to validate its practicability, two balanced BPFs with two and three DM passbands are fabricated and good agreement between simulated and measured results is observed.

A Compact Meander Line-Resonator Hybrid Structure for Wideband Common-Mode Suppression

In this paper, a novel compact and wideband common-mode suppression structure is proposed, which is composed of a meander line and several quarter wavelength resonators. A simple and accurate transmission line model is employed to describe the stopband behavior of the proposed structure. The resonance frequencies and harmonics of quarter wavelength resonators are employed to form stopbands of the common mode. Those stopbands together with the stopband of the meander line are connected in series, which are useful to expand the common-mode suppression bandwidth. Meanwhile, compensation strips are proposed to reduce the insertion loss of the differential mode. A reduction of 15 dB of common-mode propagation above 0.8 GHz is obtained by using the proposed hybrid structure. The measurement results of printed circuit boards, which are designed and fabricated on the simulation model, show good correlation with the simulation results.

Balanced filters with wideband common mode suppression using dual-mode ring resonators

Two novel balanced filters with wideband common mode suppression using dual-mode ring resonators are proposed in this paper. Two and four transmission zeros close to the passband are realized to improve the selectivity for the differential mode. In addition, over 20-dB common mode suppression can be realized from 0 GHz to $5f_{0}$ ( $f_{0}$ is the center frequency of the passband), due to the all-stop transmission characteristic of the open/shorted coupled lines. To verify the presented concepts, two prototypes ( $\varepsilon_{r}=2.65$ , $h=1.0 {\rm mm}$ ) with 3-dB fractional bandwidths of 22.9% and 21.9% for the differential mode are designed and fabricated. The theoretical and measured results agree well and show good in-band filtering performance and high selectivity.

COMPACT DIFFERENTIAL BANDPASS FILTERS BASED ON COUPLED-LINE RESONATORS WITH IMPROVED PERFORMANCE AND MINIATURIZED SIZE

Two compact differential bandpass filters (BPFs) based on coupled-line resonators and loaded capacitors are proposed in this work. By properly designing the coupled resonator and the loaded capacitance of original filter model, differential-mode (DM) passband responses and common- mode (CM) rejection can be obtained. For validation, two differential BPFs named Filter I and Filter II are discussed and experimentally characterized. One more DM transmission zero generated by out- of-phase cross-coupling is employed to control the DM bandwidth and sharpen the selectivity in Filter I while lumped capacitors are loaded in Filter II to replace capacitive coupled resonators for miniaturized size. Both filters are centered at 4.5 GHz with about 9% DM fractional bandwidth (FBW), less than 1.5 dB insertion loss, more than 15 dB return loss, and wideband CM suppression with more than 18 dB rejection. Furthermore, the size of Filter II is substantially smaller than Filter I and previously reported differential BPFs.

HIGH SELECTIVITY BALANCED BANDPASS FILTER WITH TUNABLE BANDWIDTH USING STUB-LOADED RESONATOR

A new balanced bandpass filter (BPF) with tunable bandwidth using tri-mode stub- loaded resonators is proposed. To tune the differential-mode bandwidth, the two even-mode resonance frequencies and two transmission zeros (TZs) are tuned while the odd-mode resonance frequency keeps unchanged. To realize high selectivity for differential mode, another two TZs are created by the source-load coupling and coupling sections. Furthermore, wideband common-mode (CM) suppression is achieved. The fabricated filter has 3-dB fractional bandwidth ranging from 20.0% to 26.0% centered at 1.71 GHz and wideband suppression (17 dB from 2 to 4.4 GHz) for the differential mode, as well as common-mode suppression better than 20 dB from 0 to 4.5 GHz.

Wideband balanced out‐of‐phase network based on double‐sided parallel‐strip line

A new wideband out-of-phase balanced power dividing/combining network is proposed in this study. Large bandwidth for the differential mode with broadband common mode suppression can be easily realised. Out-of-phase power division can be also achieved for Ports 2, 3 (Port 2′, 3′) by the double-sided parallel-strip line 180° swap. A planar wideband balanced out-of-phase network with bandwidth of 33% for the differential mode with wideband common mode suppression is designed and fabricated for demonstration. Good agreement is observed between simulated and measured performances, indicating the validity of the proposed design strategies.

Wideband In-Phase and Out-of-Phase Balanced Power Dividing and Combining Networks

Two new wideband in-phase and out-of-phase balanced power dividing/combining networks are proposed in this paper. Based on matrix transformation, the differential-mode and common-mode equivalent circuits of the two wideband in-phase and out-of-phase networks can be easily deduced. A patterned ground-plane technique is used to realize the strong coupling of the shorted coupled lines for the differential mode. Two planar wideband in-phase and out-of-phase balanced networks with bandwidths of 55.3% and 64.4% for the differential mode with wideband common-mode suppression are designed and fabricated. The theoretical and measured results agree well with each other and show good in-band performances.

COMPACT WIDEBAND DIFFERENTIAL BANDPASS FILTER USING A MARCHAND BALUN

A novel compact wideband differential bandpass filter with wideband common mode suppression using a Marchand balun is presented in this paper. Open/shorted coupled lines and stubs are used to improve the selectivity for the differential mode and common mode suppression. The demonstrated filter with a compact size of 50 mm × 30 mm exhibits a fractional bandwidth of 53% centered at 3.0 GHz and 13 dB common-mode suppression from 0 to 9 GHz. The theoretical and measured results agree well with each other and show good in-band performances.

A novel simple wideband common-mode suppression filter

A novel simple wideband common-mode suppression filter

Compact Low-Loss Wideband Differential Bandpass Filter With High Common-Mode Suppression

Compact low-loss wideband differential bandpass filters are presented in this letter. The proposed filters are constructed by a pair of multilayer differential microstrip-slotline transitions (MDMSTs) and microstrip line resonators. Wideband common-mode suppression and low insertion loss can be easily achieved by employing the MDMSTs. Wideband differential-mode passband and sharp notched band can be obtained by combining the microstrip resonators at the middle and the two sides with the pair of MDMSTs, respectively. The demonstrated filters with a compact size of 24 mm × 12 mm (0.56λg × 0.28 λg) exhibits a fractional bandwidth of 115% centered at 4.25 GHz (f0) with minimum insertion loss of 0.43 and 20 dB common-mode suppression from 1 to 10 GHz (2.35 f0).

Compact Wideband Differential Bandpass Filters Using Half-Wavelength Ring Resonator

A new compact wideband differential bandpass filters with wideband common mode suppression using half-wavelength ring resonator is presented in this letter. Five-order passband for the wideband differential mode with two transmission zeros close to the passband is realized with four open stubs. A planar wideband differential filter (3 dB fractional bandwidth 79%) with wideband common mode suppression is designed and fabricated. The theoretical and measured results agree well and show good in-band filtering performances and high selectivity.

A Wideband Common-Mode Suppression Filter for Bend Discontinuities in Differential Signaling Using Tightly Coupled Microstrips

A new type of bend is proposed that reduces differential-to-common mode conversion occuring at the bend discontinuity in coupled microstrip lines for high-speed digital circuits. Simultaneously, great care has been taken to minimize the differential reflection coefficient and insertion loss, leading to an overall improved signal integrity. This is achieved by tapering the microstrip lines to tightly or very tightly coupled ones in the area of the bend. Full-wave simulations in the DC to 6 GHz frequency range show that over 9 dB and 14 dB suppression of conversion noise is achieved for tightly coupled and very tightly coupled bends, respectively. Also for these new structures, with a total length of 100 mm, the insertion loss remains below 0.6 dB. Measurements on prototype bends show very good agreement with full-wave simulations. Also time domain measurements demonstrate the significant reduction in conversion noise while keeping return loss low. Moreover, for design purposes, a dedicated circuit model which closely matches the full-wave characteristics of the proposed bends is presented.

A Novel Wideband Common-Mode Suppression Filter for Gigahertz Differential Signals Using Coupled Patterned Ground Structure

A wideband and compact filter design for common-mode noise suppression in high-speed differential signals is proposed based on two U-shaped and one H-shaped coupled patterned ground structure. An equivalent model of three coupled LC resonators to predict the common-mode suppression characteristics is also developed with good agreement to the full-wave simulation and measurement result. A test sample is designed and fabricated on a standard printed circuit board (PCB). It is found the common-mode noise can be reduced by the filter over 15 dB from 3.6 to 9.1 GHz and over 75% of amplitude in the time domain. More important, the differential signal integrity, in terms of insertion loss and group delay in the frequency domain and eye diagrams in the time domain, is not degraded within the wide bandwidth. The fractional bandwidth of the stopband can reach 87% and the filter size is about 0.44 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> times 0.44 lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> . The radiation caused by the common-mode current on the attached I/O cables is also efficiently suppressed by 10 dB on average within the designed stopband. To our best knowledge, it is the first low-cost common-mode filter designed for the gigahertz high-speed signals with the largest fractional bandwidth and most compact size on a PCB.