Balanced Substrate Integrated Waveguide Filter

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.

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, 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%).

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.

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 balanced tri-band bandpass filter (BPF) is proposed based on octo-section stepped-impedance ring resonator (SIRR). The relation and design graphs between the differential-mode (DM) and common-mode (CM) characteristics with different physical parameters are analyzed. It reveals that the proposed SIRR has more degrees of freedom in controlling DM and CM characteristics for tri-band design with excellent out-of-band performances and high CM suppression. Moreover, the SIRR is loaded by open stubs with different lengths to further improve the CM suppression. Finally, a balanced tri-band BPF prototype is fabricated and measured. Good agreement between simulated and experimental results verifies this design method.

Hybrid-coupler-based quasi-reflectionless balanced bandpass filter with all 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 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.

In this work, a fourth-order balanced dual-band superconducting bandpass filter (BPF) is developed by using the newly symmetric-stub-Ioaded resonator (SSLR). The proposed SSLR has the advantage of two controllable differential-mode (DM) and more flexible control of the internal coupling. The DM bisection and common-mode (CM) bisection of the proposed SSLR are analyzed by applying the even- and odd-mode method and the corresponding resonant properties are investigated. With a proper design of SSLR, two controllable DM resonances that far away from CM resonance are obtained, which used to form the dual differential passbands. Finally, a balanced dual-band high-temperature superconducting (HTS) BPF operating at 1.9 GHz and 4.9 GHz for wireless communication application is successfully designed, and it demonstrates high selectivity for DM passbands and deep in-band CM suppression.

Tunable balanced liquid crystal phase shifter based on spoof surface plasmon polaritons with common-mode suppression

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>.

This communication presents a novel design of a differentially fed wideband circularly polarized (CP) slot antenna. The CP antenna consists of two opposite-fed C-shaped radiating patches and a stub-loaded corner-truncated rectangular slot. With the slot designed to be antisymmetric with respect to the bisection plane and oppositely fed by two microstrip lines, good differential-mode (DM) performance was obtained. On the other hand, the radiations contributed by the corresponding parts of the antisymmetric CP antenna will be destructive when in common-mode (CM) operation. This results in high CM suppression without a preceding CM-rejection bandpass filter. Also, low DM axial ratios (ARs) were achieved by tuning the truncated corner length, the protruded stub length, and the coupling length and gap of the C-shaped radiating patches. The measurement shows that the designed CP antenna has a wide 10 dB DM impedance band of 5–6.49 GHz and a 3 dB DM AR band of 4.94–6.03 GHz, corresponding to a CP fractional bandwidth of 18.7%. Also, in 4.5–6.5 GHz, the proposed antenna can effectively reject CM input signals because the measured CM return loss is smaller than 2.91 dB, and can convert only very little DM input power into CM reflected power since the DM-to-CM conversion is less than −50 dB.

In this paper, the RF design of differential quasielliptic-type dual-and tri-band bandpass filters (BPFs) is reported. They are based on series-cascaded multi-resonant cells that result in: i) quasi-elliptic-type passbands in the differential-mode of operation that are shaped by 3N poles and 3N-1 transmission zeros (TZs)-N is the number of bands-and ii) high common mode (CM) suppression through multi-TZ generation-5N-1 in total-and resistively-loaded poles. Coupling-routing diagrams that facilitate the RF design of these type of filters with standard coupled-resonator synthesis are presented. For proof-of-concept demonstration purposes, a dual-band microstrip prototype was manufactured and measured with the following RF performance characteristics: passbands centered at 2.53 and 3.49 GHz, fractional bandwidths of 13 and 12%, and minimum in-band insertion loss levels of 1.27 and 1.43 dB, respectively. Moreover, the CM is suppressed by >52 and >38 dB at the center of the bands.

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.