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.

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

A new approach to design differential-mode (DM) bandpass filters is proposed and implemented based on the substrate integrated waveguide (SIW) technology. By properly constructing the topologies of SIW resonant cavities, the balanced section of the proposed filter achieves an attractive capacity in simultaneously realizing the desired DM transmission and expected common-mode (CM) suppression in a certain band. In design, the specified DM frequency response is achieved with an equivalent two-port circuit model. To illustrate the possibilities of the new approach, a fourth-order Ku-band prototype is designed and fabricated on a single-layer substrate. Measured results agree well with the predicted counterparts.

A New Approach to Design Differential-Mode Bandpass Filters on SIW Structure

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

This paper presents a novel high performance ultra-wideband (UWB) bandpass filter that satisfies FCC UWB specifications. The filter is based on a composite right/left handed (CRLH) structure consisting of an asymmetric unit-cell with a short circuited inductive stub that exhibits stopband rejection level greater than 25 dB at both the lower and upper band edges while maintaining an insertion-loss of less than 0.5 dB across its passband. In addition, a simple and effective technique is proposed to create and control sharp rejection notch-bands within the filter's passband in order to provide interference immunity from undesired radio signals, such as wireless local area networks (WLAN) that co-exist within the UWB spectrum. The proposed technique was verified practically to validate the design methodology. The experimental results of the prototype circuit are presented and compared with the simulation results. The dimensions of the proposed filter are 0.37λ × 0.10λ (i.e., 16.4 × 4.8 mm2). The filter's characteristics and compact size make it suitable for UWB systems.

Ultra-Wideband Bandpass Filter Based on Composite Right/Left Handed Transmission-Line Unit-Cell

A circuit for differential wideband bandpass filter (BPF) is presented. The circuit works as a bandpass and bandstop filter under differential- and common-mode excitation, respectively. Under differential-mode, two transmission zeros are generated by the short-ended parallel-coupled stubs and supply a very sharp differential passband. The circuit parameters are analyzed and given to show the circuit characteristics. Finally, the circuit is implemented using microstrip technology and a differential wideband BPF is designed, simulated and measured. Simulated and measured results are well agreed.

Differential Wideband Bandpass Filter With High-Selectivity and Common-Mode Suppression

This letter presents a new 5 GHz band-notched balanced ultra-wideband (UWB) bandpass filter (BPF), which is designed using a stepped-impedance slotline multi-mode resonator (MMR). To obtain favorable uniform differential-mode (DM) response, a microstrip-to-slotline transition is used as the signal-feeding structure and the first three resonant modes of the slotline MMR are located in the UWB passband. Common-mode (CM) signal rejection is achieved by deploying the slotline MMR in such a way that the quarter-wavelength resonances occurring near the input and output sides of the resonator are well decoupled. Also featured in this design is the blocking of unwanted WLAN signals, which is achieved by loading the input feed-lines with a stepped-impedance microstrip stub to create a notch-band centered at 5.5 GHz. The designed BPF has a measured minimum DM insertion loss of 0.83 dB in the UWB passband, in which the measured CM suppression is larger than 18.85 dB.

C-I G. Hsu

Papers

Band-Notched Balanced UWB BPF With Stepped-Impedance Slotline Multi-Mode Resonator