Wideband Common-mode Suppression Research Articles

A highly selective balanced wideband bandpass filter based on nested split‐ring resonators

A balanced wideband bandpass filter (BPF) with a high frequency selectivity, controllable bandwidth, and good common-mode (CM) suppression based on nested split-ring resonators (SRRs) is proposed in this article. The proposed nested SRRs are applied to form three transmission poles (TPs) that can achieve a wide differential-mode (DM) passband centered at 3.0 GHz. Meanwhile, two transmission zeros (TZs) are generated to realize a high frequency selectivity of the DM passband. Moreover, TPs and TZs can be quasi-independently controlled by changing the physical lengths of SRRs and the gaps between them, which can greatly improve the flexibility and practicality of the design. The proposed balanced BPF is fed by balanced microstrip-slotline (BMS) transition structures. For the CM signals, the BMS transition structures can achieve a good wideband CM suppression without affecting the DM ones, thereby simplifying the design procedure. In order to validate its practicability, a balanced wideband BPF is fabricated and a good agreement between the simulated and measured results is obtained.

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.

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.

Balanced-to-Balanced and Balanced-to-Unbalanced Power Dividers With Ultra-Wideband Common-Mode Rejection and Absorption Based on Mode-Conversion Approach

In this paper, for the first time, a balanced-to-balanced (B-B) power divider (PD) and a balanced-to-unbalanced (B-UB) PD with ultra-wideband common-mode (CM) rejection and absorption characteristics are introduced based on a new design approach. The design of B-B and B-UB PD structures is using one core circuit to provide power dividing/combining and differential-mode-to-common-mode (DM-CM) converters to realize mode conversion at the balanced ports. With the use of the DM-CM converter, the boundary condition on the symmetric plane of the core circuit is then reversed. Specifically, a perfect-electric wall will be formed along the symmetric plane of the core circuit under the CM operation, with a perfect-magnetic wall under the DM operation. Based on this characteristic, the proposed B-B and B-UB PDs can then achieve wideband CM suppression and absorption with some proper designs. The measured results show that the transmission coefficients of CM operation for the proposed B-B and B-UB PDs are all less than -15 dB with a fractional bandwidth about 200%. In addition, the measured CM absorption rate is higher than 85% with a fractional bandwidth about 71.2% and 116% for the proposed B-B and B-UB PDs, respectively.

Differential Dual-Band Superconducting Bandpass Filter Using Multimode Square Ring Loaded Resonators With Controllable Bandwidths

In this paper, a fourth-order dual-band high-temperature superconducting (HTS) differential bandpass filter (BPF) with controllable midband frequencies and bandwidths is developed by using modified multimode square ring loaded resonators (SRLRs). The differential-mode (DM) bisection and common-mode (CM) bisection of the modified SRLR are analyzed by using the even- and odd-mode method twice, and the corresponding resonant properties are obtained. With a proper design of the modified SRLR, two lowest DM resonances are chosen to construct two DM passbands with high in-band CM suppression. The DM resonances can be adjusted flexibly after adding tunable patches to the square ring. Meanwhile, the internal coupling between two modified SRLRs can be controlled separately by using two geometrical parameters. Consequently, the proposed dual-band BPF can achieve independent control of both the midband frequencies and the bandwidths of its two passbands. Moreover, a wideband CM suppression is realized by a combined use of an appropriately selected feeding structure and a frequency discrepancy technique. A fourth-order dual-band differential BPF is designed with two passbands operating at 2.325 and 4.900 GHz, respectively. The filter is fabricated using HTS YBCO thin films on a MgO substrate. Good agreement between the simulated and measured frequency responses are observed, verifying well the proposed structure and design method.

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 novel balanced-to-balanced power divider based on three-line coupled structure

AbstractThis paper presents a novel balanced-to-balanced power divider (PD) based on a simple and compact three-line coupled structure for the first time. By bisecting the proposed symmetrical structure, the differential mode (DM) and the common mode (CM) equivalent circuits can be obtained for analysis. The DM equivalent circuit exhibits a three-line in-phase power dividing response, and then a resistor is added between the two outputs for achieving good isolation. Meanwhile, the CM equivalent circuit shows a three-line all-stop response so that the CM suppression in this design does not need to be considered. Accordingly, the detailed design procedure of the DM PD is given. For demonstration, a prototype centered at 1.95 GHz is designed, fabricated, and measured. The simulated and measured results with good agreement are presented, showing low DM loss and wideband CM suppression.

A Compact Balanced Phase Shifter With Wideband Common-Mode Suppression

In this paper, a balanced phase shifter using cascaded three microstirp lines and two coupled lines is proposed. The reference line is fixed without center delay line. With such configuration, wideband differential-mode (DM) phase shift can be achieved. The coupled line and half-wavelength microstrip line provide the out-of-band and in-band common-mode (CM) suppression, respectively. Compared with the state-of-the-art balanced phase shifters, the proposed balanced phase shifter has the advantages of wideband CM suppression and compact size with simple structure and fixed reference line. Theoretic analysis, parametric study and design procedure are carried out completely. To verify the theoretic prediction, two prototypes covering the frequency of 1.8 GHz are designed with the relative operating bandwidth for 45° ± 2.1° (90° ± 3.7°) phase shifter of 50% (53%), with the minimum return loss better than 14.7 dB, and the relative CM suppression bandwidth better than 150%.

A Balanced Filtering Quasi-Yagi Antenna With Low Cross-Polarization Levels and High Common-Mode Suppression

A balanced planar quasi-Yagi antenna integrated with a bandpass filtering response is presented in this paper. The proposed balanced antenna consists of a balanced stepped-impedance microstrip-slotline transition structure, a driver dipole, a parasitic strip, and a bandpass filtering unit. A good differential-mode (DM) passband selectivity is formed by inserting a microstrip stub-loaded resonator (SLR) in the feed line of the quasi-Yagi antenna. This integration enables the antenna to achieve both compact size and high frequency selectivity. By controlling the dimensions of SLR, the central frequency and fractional bandwidth (FBW) can be easy to be adjusted. Meanwhile, the microstrip-slotline transition structure can achieve a good wideband common-mode (CM) suppression without affecting the DM ones, thus simplify the design procedure. The proposed antenna with low cross-polarization level and high CM rejection is found to be comparable to the conventional quasi-Yagi antenna. Furthermore, there are two radiation nulls on both sides of the passband to improve the selectivity effectively. In order to validate its practicability, the balanced antenna is designed and fabricated. The experimental results exhibit that the designed balanced filtering antenna features good filtering response, low cross-polarization level, and high CM rejection.

A Dual-Band Balanced-to-Balanced Power Divider With High Selectivity and Wide Stopband

A dual-band balanced-to-balanced (BTB) filtering power divider (FPD) is presented, which can achieve an in-phase power division with high selectivity. The proposed FPD is composed of microstrip-to-slotline transition structures (MTSTSs), T-shaped slotline, and multiple stub-loaded resonators (SLRs). A dual-band differential-mode (DM) response with a steep filtering performance is generated by employing SLRs. By adjusting the electrical lengths of SLRs and the gaps between each resonator and microstrip lines, the fractional bandwidth (FBW) is controllable. By introducing slotline resonators loaded with surface-mounted resistors, the isolation between the two output ports is increased. Meanwhile, a wide DM stopband with a high rejection level is obtained. Moreover, good wideband common-mode (CM) suppression is achieved intrinsically, thereby simplifying the design procedure greatly. To verify the theoretical prediction, one FPD prototype is fabricated. A good agreement between the simulated and measured results is observed. To the best of authors' knowledge, the proposed dual-band BTB FPD is first ever reported.

A Reconfigurable Filter Using Defected Ground Structure for Wideband Common-Mode Suppression

A wideband common-mode (CM) suppression reconfigurable filter is proposed for high-speed all-pass differential circuits. The filter adopts three varactor-loaded compact defected ground structures (DGSs) to achieve continuous reconfigurability in its operation frequency with a large CM suppression dynamic range in the bandwidth. The varactors play an important role in widening the accessible instantaneous bandwidth and miniaturizing the structure. The three DGS cells with a total area of 15 mm × 10 mm are implemented symmetrically under the differential lines, to obtain reconfigurable CM bandstop characteristics which can be continuously adjusted from 1.8 to 8.1 GHz. A coupled LC resonator equivalent model is developed to represent and analyze the proposed filter, which explains its operation principle and assists in accelerating the reconfiguration design method. A good agreement between full-wave simulations and measured results is demonstrated, which validates the proposed design.

Multi-Band Balanced Couplers With Broadband Common-Mode Suppression

Three novel single-/multi-band balanced couplers with wide-band common-mode suppression are proposed. In these double-functionality balanced-coupler architectures, double-sided parallel-strip line 180° phase inverters are used to realize the broadband common-mode rejection. Furthermore, by loading quarter-wavelength open/short-ended coupled lines at all ports of the single-band differential-mode coupler, dual/triple-band balanced operation with high isolation for the differential-mode power-division bands can be realized into it. For practical verification, three balanced couplers with single-, dual-, and triple-band operation at 1 GHz, 0.72/1.24 GHz, and 0.66/1/1.36 GHz, respectively, are constructed in microstrip technology and tested.

A Differential UWB Quasi-Yagi Antenna with A Reconfigurable Notched Band

Abstract A compact differential ultra-wide band (UWB) planar quasi-Yagi antenna is presented in this paper. The proposed antenna consists of a balanced stepped-impedance microstrip-slotline transition structure, a driver dipole and one parasitic strip. A wide differential-mode (DM) impedance bandwidth covering from 3.8 to 9.5 GHz is realized. Meanwhile, a high and wideband common-mode (CM) suppression can be achieved by employing the balanced stepped-impedance microstrip-slotline transition structure. It is noted that the DM passband is independent from the CM response, which can significantly simplify the design procedure. In addition, a reconfigurable sharp DM notched band from 5.6 to 6.7 GHz is generated by adding one pair of quarter-wavelength varactor-loaded short-circuited stubs adjacent to the microstrip line symmetrically. In order to illustrate the effectiveness of the design, two prototypes of the antennas are designed, fabricated, and measured. A good agreement between the simulated and measured results is observed.

Differential BPFs with Multiple Transmission Zeros Based on Terminated Coupled Lines

AbstractDifferential bandpass filters (BPFs) named Filter A and Filter B based on Terminated Coupled Lines (TCLs) are proposed in this letter. The TCLs contributes to not only three poles in differential-mode (DM) for wideband filtering response but also multiple zeros in both DM and common-mode (CM) offering wide DM out-of-band rejection and good CM suppression. Fabricated filters centred at 3.5 GHz with wide DM passband and wideband CM suppression have been designed and measured. The filters improved the noise suppression capability of the communication and radiometer systems. The simulated and measured results are in good agreement.

Narrow‐band balanced filtering network using coupled lines loaded with stubs

A novel narrow-band balanced filtering network using coupled lines loaded with stubs is proposed in this letter. Two Wilkinson power dividers using coupled lines are used to realise the six-port balanced network. Wideband common mode suppression and power division isolation can be achieved due to the loaded open/shorted stubs. A narrow-band balanced filtering network for the WLAN band is designed. Good agreements can be found between the simulation and measurement results.

Balanced Filter With Wideband Common-Mode Suppression in Groove Gap Waveguide Technology

This letter is focused on the design and realization of balanced bandpass filters (BPFs) in gap waveguide technology. The procedure of filter design and resonance-mode selection to achieve the desired differential bandpass behavior with intrinsic deep and wideband common-mode suppression is explained. A third-order differential BPF is designed and fabricated for demonstration. Agreement between the computed and measured results validates the concept and the design procedure.

Compact wideband‐balanced bandpass filter with high‐selectivity and wideband CM suppression

A wideband-balanced bandpass filter is presented using two half-wavelength transmission lines, two coupled lines and one-stepped impedance stub. Compared to the reported wideband-balanced bandpass filters, the proposed one shows the advantages of small total length, high-frequency selectivity and wideband common-mode (CM) suppression. The bandwidth of CM suppression and differential-mode transmission, and the positions of transmission zeros are controllable by the parameters. One prototype was designed, fabricated and measured with the total length of 2λ g (λ g is the guided wavelength at the centre frequency f 0), 3 dB fractional bandwidth of 61% and 15 dB CM suppression bandwidth of 3.67f 0.

A Balanced Tri-band PD Based on Microstrip-slotline Transition Structure Embedded Complementary Split-ring Resonators

AbstractA balanced tri-band equal power divider (PD) is proposed based on a balanced stepped-impedance microstrip-slotline transition structure in this paper. Multi-band differential-mode (DM) responses can be realized by embedding multiple complementary split-ring resonators (CSRRs) into the slotline resonator. It is found that a high and wideband common-mode (CM) suppression can be achieved. Moreover, the center frequencies of the DM passbands are independent from the CM ones, which significantly simplifies the design procedure. In order to validate its practicalbility, a balanced PD with three DM passbands centred at 1.57, 2.5 and 3.5 GHz is fabricated and a good agreement between the simulated and measured results is observed. To our best knowledge, a balanced tri-band PD is the first ever reported.

Balanced bandpass filter with spurious mode suppression

ABSTRACTThis article presents a new and simple design approach for the balanced bandpass filter (BPF) with spurious mode suppression using half‐wavelength resonators. The second harmonic of the resonator, acting as the lowest‐frequency common‐mode (CM) noise, is suppressed by using a new differential feeding scheme. Furthermore, an electrically coupled structure, exhibiting a bandstop response at the third harmonic of the resonator [acting as the lowest‐frequency differential‐mode (DM) spurious], is introduced. As a result, both wideband CM suppression and extended DM upper stopband can be realized simultaneously due to the suppression of the second and third harmonics of the resonator. For demonstration, a second‐order balanced BPF is designed, fabricated, and measured. Good agreement between simulated and measured results can be observed. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1188–1190, 2017

Differential‐mode bandpass filter on microstrip line with wideband common‐mode suppression

A novel differential-mode (DM) bandpass filter (BPF) on microstrip-line topology with wideband common-mode (CM) suppression is presented. The DM BPF is composed of a pair of half-wavelength (λ/2) uniform impedance resonators and two coupled-line sections as feeding scheme. By installing an open-circuited stub in the middle of the coupled-line section, spurious CM response can be tremendously suppressed over a wide band. Thus, wideband CM suppression is realised in and beyond core DM passband. Finally, a DM BPF is designed and fabricated to support the proposed design concept.