A Balanced Substrate Integrated Waveguide 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 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.

A balanced microstrip filtering phase shifter using 2 three-end folded coupled lines and 3 transmission lines is proposed. With such structure, multiple differential-mode (DM) transmission zeros (TZs) or common-mode (CM) TZs can be obtained so that good frequency selectivity or wideband CM suppression can be achieved. The phase shift covers the DM performance. Compared with the reported design, the proposed design has wider CM suppression and better frequency selectivity. One 45° prototype is demonstrated. The measured phase shift FBW(45° ± 2.3°) is 43%, 20-dB CM suppression FBW is better than 140%, and 3-dB FBW is 39.4%.

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.

In this paper, a group of differential dual-band bandpass filters based on a single quad-mode stub-loaded twin-ring resonator (TRR) are presented, which utilize asymmetrical shunt branches for common-mode (CM) suppression. Under differential-mode (DM) operation, the stub-loaded TRR manifests quad-mode characteristic for dual-band design. The frequency ratio of the two passbands can be flexibly selected according to the form of the loaded stubs. Different from the inline topology, differential multimode structures inevitably suffer from the hardship in CM suppression, especially for dual-band designs. Despite previous work fulfilled moderate CM suppression via embedded defected ground structure units, but the CM noise in the DM lower band can just be shifted away rather than suppressed. Instead, a novel CM-suppression approach is devised attributing to the asymmetrical short-terminated branches along the bisection line of the TRR. The transmission of the CM noise near the DM passbands can be blocked effectively. Furthermore, multiple CM notches can be obtained by the cooperation of the asymmetrical branches and source–load coupling, leading to the favorable CM suppression in a wide frequency range. For verification, a prototype differential dual-band filter based on the open stub-loaded TRR has been realized with frequency ratio which is larger than two. Similarly, a differential dual-band filter using the short-circuited stub-loaded TRR is also presented as an extension for frequency ratio which is smaller than two. The simulation and experiment results of the two demonstrated filters are given, showcasing a good agreement.

Tunable balanced liquid crystal phase shifter based on spoof surface plasmon polaritons with 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.

A differential dual-band bandpass filter (BPF) based on H-shaped composite resonator (HSCR) is proposed in this paper. The proposed BPF have two independent controllable passbands performance with two steerable resonant modes and two pairs of dual feedline structure. To obtain the differential mode (DM) transmission with common mode (CM) suppression, the coupling coefficients (k) and external qualities (Qe) are designed for two DM passbands, respectively. Moreover, a pair of unequal length E-shaped elements are introduced in the symmetrical of the HSCR to improve the CM suppression. To verify the method, a Chebyshev dual-band BPF with center frequency f l = 1.95 GHz and f H = 2.35 GHz, fractional bandwidth (FBW) Δl = 5.4%, and Δη = 3.5% has been designed and simulated for SCDMA and LTE applications.

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter with all common mode suppression

In this letter, a compact dual-band dual-mode substrate integrated waveguide (SIW) balanced band-pass filter (BPF) with intrinsic common-mode (CM) suppression is designed by using a single perturbed SIW circular cavity. The vias and slot perturbations are introduced to tune the resonant modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">010</sub> , TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> (a pair of degenerate modes), and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> of a circular cavity. Thus, they can be used to form two differential-mode (DM) passbands with independently adjustable center frequencies and bandwidths. The SIW can be seen as a natural balun with intrinsic CM suppression. Furthermore, the planar differential excitation structure is designed to excite the perturbed SIW cavity. The CM noise cannot excite SIW cavity due to the characteristics of hybrid electromagnetic boundary. Finally, a compact dual-band dual-mode SIW balanced BPF at 8 and 10 GHz is designed and fabricated, and the measured results show good agreement with the simulated ones.

In this paper, we proposed a wideband common-mode suppression filter for multi differential signal pairs. The method of the proposed design is utilized by using Defected Ground Structure (DGS) of two quarter-wavelength resonators with the mutual coupling effect to achieve the wideband common-mode suppression. For observing one pair differential signal lines in the frequency domain analysis, the differential-mode insertion loss are all above −3 dB from DC to 10 GHz. For the common-mode insertion loss, a wide common-mode suppression bandwidth is 4.2 GHz by using −15 dB definition. In multi differential signal pairs, we still have a wideband common-mode suppression of advantage.

A compact high-performance differential low-pass filter (LPF) based on the double-sided parallel-strip line (DSPSL) structure is proposed simultaneously, featuring a wide upper stopband and excellent common-mode (CM) suppression. The intrinsic CM noise suppression can be realized with a compact circuit size due to the DSPSL phase inverter. For the differential-mode signal excitation, the low-pass response with small insertion loss (IL) and superior out-of-band rejection is exhibited. For practice, the fabricated and measured differential LPF prototype with the 1-dB cutoff frequency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{\text {c}}$ </tex-math></inline-formula> of 1.0 GHz demonstrates up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14f_{\text {c}}$ </tex-math></inline-formula> of a wide upper stopband rejection over 20 dB. In addition, the excellent CM suppression is better than 40 dB over the entire measured frequency range from 0 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$14f_{\text {c}}$ </tex-math></inline-formula>.

In this letter, a compact high-selectivity and common-mode (CM) suppression tunable balanced microstrip bandpass filter (BPF) with constant bandwidth is designed by adopting the magnetically coupled resonators with stepimpedance parallel coupling feedline (SIPCF) structure. The desired coupling coefficient K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> and external quality factor Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> can be obtained by the mixed coupling between the two resonators and SIPCF structure, respectively. Two differential-mode (DM) transmission zeros (TZs) near the lower and upper passband edges are created by the mixed coupling and source- load coupling, respectively. Furthermore, intrinsic high CM suppression in the DM tunable operating passband can be maintained because of the magnetically coupled resonator structure. Finally, a compact tunable balanced BPF prototype with constant fractional bandwidth of 6.5% is implemented and fabricated. The measured results agree well with the simulated ones.

A novel balanced filter realized in the form of substrate integrated waveguide (SIW) is proposed and studied in this paper. Based on the inherently horizontal and vertical symmetry of the SIW, this filter presents inherently high-performance balanced property with advantages of no identical pair requirement, being free from the limitation of symmetrical topology, easy and flexible design, high common-mode (CM) suppression, and robust CM suppression when comparing with conventional counterparts. Several prototypes are designed, fabricated, and measured to verify the expected properties.

In this paper, a novel topology of a balanced diplexer is proposed. It is composed of a dual-mode structure and two sets of resonators at distinct frequencies. The dual-mode structure has two resonances serving for two three-pole passbands, respectively, in differential mode (DM) and an intrinsic suppression for full stopband in common mode (CM). Thus, it is perfectly suited to design a filtering network in DM, and conserve suppression in CM. In order to obtain two close DM channels and good CM suppression in the meantime, two inner resonators are coupled together via a specific coupling scheme with intrinsic CM suppression to construct it. Two balanced diplexers utilizing the proposed dual-mode structures with varied configurations are proposed, designed, and fabricated, which have well verified the proposed diplexer topology and a design method.