Common-mode Transmission Zeros Research Articles

A tunable balanced phase shifter with wide operating bandwidth

Abstract A wideband tunable balanced phase shifter is achieved by utilizing varactor-loaded coupled lines (VLCLs)-embedded multistage branch-line structure. The tunable phase shift with low in-band phase deviation is attributed to the regulation in phase shift of the VLCLs and the horizontal microstrip lines in series. The wideband differential-mode (DM) impedance matching and common-mode (CM) suppression are due to multiple DM transmission poles and CM transmission zeros, which are brought about by the cascade of VLCLs and a microstrip line with short-circuited stubs in the DM-equivalent circuit and open-circuited stubs in the CM-equivalent circuit, respectively. Compared with the state-of-the-art tunable balanced phase shifters, the proposed design not only has the advantages of wide operating bandwidth (BW) with low in-band phase deviation but also has low insertion loss and easily fabricated structure. Theoretical analysis and design procedure were conducted, resulting in a prototype covering the frequency of 1.8 GHz. This prototype offers a tunable phase shift capability ranging from 0° to 90°. The prototype exhibits an operating BW of 45%, with a maximum phase deviation of ±6°. It also achieves a 10 dB DM return loss and CM suppression, while maintaining a maximum insertion loss of 2.5 dB.

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 Voltage-Controlled Tunable Differential Dual-Band Bandpass Filter With Compact Size and Wide Tuning Range

A compact differential tunable dual-band bandpass filter is achieved by using cascaded capacitor-loaded coupled microstrip lines and voltage-controlled varactors. Six differential-mode (DM) transmission zeros (TZs), four DM transmission poles (TPs), and four common-mode (CM) TZs can be obtained by controlling values and positions of capacitors and the even-odd mode impedances of coupled microstrip lines. What's more, the first three DM TZs, two TPs and three CM TZs will change with the capacitance of varactors. Thus, the proposed filter possesses a tunable lower passband and a fixed upper passband. Compared with the state-of-the-art differential tunable DBBFs, the proposed design has the advantages of wide tuning range, compact size, low number of control voltages, and simple structure. Theoretic analysis, parametric study and design procedure are carried out completely. A prototype with the size of 58.2 × 10.1 mm (1.13 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> × 0.20 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> is the microstrip guided wavelength at the center frequency of the upper passband) is designed for demonstration, which exhibits the center frequency of the lower passband can be tuned from 1.55 to 2.42 GHz. Meanwhile, the center frequency and 3-dB bandwidth of the upper passband keep constant at 3.79 GHz and 8.5%, respectively.

Quad-Mode LTCC Surface Mounted Packaging Common-Mode Filter Based on the Asymmetric Short-Stub Loaded Resonator

A novel quad-mode common-mode filter (CMF) with ultra-wideband and high common-mode (CM) rejection-level is proposed based on the asymmetric short-stub loaded resonator (ASSLR). By utilizing the ASSLR, four resonant modes can be introduced for the initial CMF design under the even-mode operation, and correspondingly generate four CM transmission zeros. However, the initial CMF design achieves a weak CM noise suppression performance. Then, the CMF using the modified ASSLR is proposed for CM stopband enhancement. Finally, a surface mounted packaging CMF prototype is fabricated with the physical size of 6mm×4.5mm×0.6mm by using low-temperature co-fired ceramic (LTCC) technology. The measured results agree well with the simulated ones. The proposed quad-mode CMF exhibits excellent performances including high differential-mode cutoff frequency (10GHz), and an ultra-wide -15dB CM stopband with a fractional bandwidth of 104.5%.

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 Synthesized Method for Common-Mode Noise Suppression Filters With Specified Common-Mode and Differential Mode Response

In this paper, a synthesized method for broadband lumped-element-based common-mode noise suppression filter (CMNSF) is proposed. Such CMNSF can achieve theoretically lossless performance and controllable dispersive group delay response for differential signals. Besides, the proposed CMNSF can achieve two common-mode transmission zeros, and both frequencies can be arbitrarily assigned to strengthen the suppression ability at certain bands. To validate the synthesized method, a CMNSF with fourth-order equiripple group delay response is demonstrated and validated in an integrated passive device process. The filter can suppress the common-mode noise more than 10 dB from 1.92 to 5.02 GHz or more than 20 dB from 2.20 to 4.20 GHz. At the same time, differential insertion loss is kept less than 3 dB up to 15 GHz and the group delay is kept in a ±5% error up to 12 GHz, which is widest one compared to the published works. In addition, the occupied area with probing pads is 1047 μm × 954 μm, which is compatible to previous works. Therefore, the proposed method is suitable for implementing a lumped-element-based CMNSF with ultraflattened group delay for differential signals based on nonferrite material.

Automated design of balanced wideband bandpass filters based on mirrored stepped impedance resonators (SIRs) and interdigital capacitors

This paper presents small balanced bandpass filters exhibiting wide differential-mode pass bands and high common-mode suppression. The filters are implemented in microstrip technology and their topology consists of multisection mirrored stepped impedance resonators (SIRs) alternating with mirrored interdigital capacitors. The mirrored SIRs provide the required common-mode transmission zeros to achieve effective rejection of that mode in the region of interest, i.e. the differential-mode pass band. An automated design method for such filters, based on aggressive space mapping, is reported. The method uses the equivalent circuit model of both the mirrored SIRs and the interdigital capacitors, and filter synthesis is based on a quasi-Newton iterative algorithm where parameter extraction is the key aspect. The automated design approach is illustrated through an order-3 filter, where it is demonstrated that the filter topology is generated from the specifications. As compared with previous balanced filters based on mirrored SIRs coupled through admittance inverters, the proposed filters of this work are smaller and the design method is simplified, since bandwidth compensation due to the narrowband functionality of the inverters is avoided.

A Wideband Differential BPF With Multiple Differential- and Common-Mode Transmission Zeros Using Cross-Shaped Resonator

Wideband differential bandpass filter (BPF) with multiple differential-mode (DM) and common-mode (CM) transmission zeros (TZs) is presented in this letter. This filter is designed based on Cross-Shaped Resonator (CSR) alone that is intrinsically attributed by three DM transmission poles (TPs), four DM TZs and one CM TZ. Adding loaded coupled structures, two extra DM and CM TZs are generated respectively. A prototype differential BPF centered at 3.5 GHz with 40% fractional bandwidth (FBW) is designed and experimentally characterized. The experimental results are in good agreement with theoretical and simulated results. Allocating three CM TZs in the DM passband, the suppression is better than 40 dB in average, and the maximum rejection is as high as 80 dB, while the DM passband is sharpened by two extra DM TZs.

Synthesis Model and Design of a Common-Mode Bandstop Filter (CM-BSF) With an All-Pass Characteristic for High-Speed Differential Signals

A new common-mode bandstop filter (CM-BSF) with an all-pass performance (from dc to 9 GHz) for differential signals is proposed by using a C-shaped patterned ground structure (PGS) with meandered signal lines on a two-layer printed circuit board (PCB). This technique can successfully generate two close transmission zeros in common-mode within the frequencies of concern. A corresponding equivalent circuit model is established to predict the filter behaviors, and a formula for common-mode transmission zeros is derived based on the circuit model. Next, a design method is developed and a synthesis procedure is proposed. According to the procedure, a wideband CM-BSF is synthesized and fabricated on a two-layer PCB. In addition, the simulation and experiment results are demonstrated to verify the technique and show excellent performance of the proposed CM-BSF. It is shown that common-mode noise can be suppressed over 10 dB from 1.9 to 8.9 GHz with 130% fractional bandwidth (FBW) while the insertion loss of differential-mode can be kept less than 3 dB from dc to 9 GHz. The electrical size is only 0.21 λ g ×0.21 λ g , where λ g is the wavelength of the stopband central frequency. To sum up, the proposed CM-BSF has merits of low cost (two layer), a simple geometric structure, a compact size, and a large common-mode FBW. Most importantly, the filter can keep good signal integrity of the digital differential signals due to its all-pass characteristic.

High CM suppression balanced BPF with two CM transmission zeros

ABSTRACTA new compact, low insertion loss, and wide stopband balanced bandpass filter (BPF) with two common‐mode (CM) transmission zeros within the differential‐mode (DM) passband is designed in this article. The DM filtering topology is formed by two quarter‐wavelength resonators and a short stub loaded source‐load coupling structure which can generate new transmission zeros to improve the selectivity and suppress the harmonic to widen the stopband. The center‐loaded step‐impedance open stub can be applied to misalign two CM fundamental resonant frequencies, meanwhile adjust one CM transmission zero to the DM passband. To enhance the CM suppression within the DM passband, another CM transmission zero is created by the folded stub loaded in the 50‐Ω input feedline which creates the first DM transmission zero located at 2 ( is the center frequency of DM passband) and has little effect on the DM in‐band and lower‐stopband performance. Finally, a high CM suppression balanced BPF prototype for WLAN application is designed and fabricated. The simulated and measured results show a good agreement. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:135–141, 2014