However, they have the major drawback in that their outputs can be noisy due to the high switching transients. They are valued for their small size, low cost, and efficiency. These days switching power supplies are nearly ubiquitous and used throughout every electronic device. The overall size is only 24.7 × 12 mm 2.Designing Second Stage Output Filters for Switching Power Supplies 3 shows the photograph of the fabricated UWB BPF with the triple sharply notched bands. The structural parameters for the UWB filter circuit are (as illustrated in Fig. The UWB BPF has been designed on a substrate RT/Duroid 5880 with a dielectric constant of 3.38, a thickness of 0.813 mm and a loss tangent of 0.0027. Therefore, the three notched bands can be independently achieved at the desired frequencies. It can be found that by, respectively, varying each UDMS dimension, the frequency location of the corresponding notched band can be widely adjusted, whereas the other two frequency locations of the notched bands remain almost unchanged. The frequency characteristics of the UDMSs with various dimensions are simulated by HFSS 11.0 to validate the resonant properties, as shown in Fig. (1)where ( W + L) is the total length for each UDMS, ɛ eff is the effective dielectric constant and c is the light speed in free space. The parallel UDMSs embedded into the middle section of the EMMR can be modelled as three shunt series resonant branches. The interdigital coupled lines can be deemed as two single transmission lines at two sides and a J-inverter susceptance in the middle. The equivalent circuit network of the proposed filter is shown in Fig. It comprises interdigital coupled lines and EMMR embedded three parallel UDMSs. 1 shows the layout and the equivalent circuit network of the designed UWB BPF. Finally, both the simulation and the measurement results are provided to verify the design method. Then, three parallel U-shaped defected microstrip structures (UDMSs) are etched into the EMMR to obtain triple sharply notched bands with a high degree of adjusting freedom. The E-shaped MMR (EMMR) is utilised to realise an initial UWB BPF with a pair of transmission zeros appearing in the lower and the upper stopbands to improve the skirt selectivity. In this Letter, a novel compact UWB BPF with triple sharply notched bands and good selectivity is proposed and designed. Layout and equivalent circuit network of proposed UWB BPF with triple sharply notched bands In , a coupled triple-mode stub loaded resonator is employed to obtain three notched bands however, the proposed UWB BPF has a relatively low selectivity and the rejection level in the notch bands is not ideal. In , a novel asymmetric coupling strip is used to generate dual notched bands, but the out-of-band harmonic suppression of the proposed UWB BPF needs to be improved. In , a pair of asymmetric loading stubs is introduced to block the undesired radio signals, but only one notched band is achieved. 8.0 GHz bands) signals can interfere with UWB networks thus, compact UWB BPFs with multiple notched bands are emergently required to reject these interfering signals . 5.2 and 5.8 GHz bands) and the satellite communication (i.e. However, the existing wireless networks such as WLAN (i.e. For example, the multiple-mode resonator (MMR) , the cascaded lowpass/highpass filters and the multilayer coupled structure have been widely employed to achieve UWB characteristics. There are many techniques presented to design the UWB BPFs . UWB bandpass filters (BPFs), as one of the essential components of UWB systems, have gained much attention in recent years. In February 2002, the US Federal Communications Commission allocated the 3.1–10.6 GHz band as the unlicensed spectrum for ultra-wideband (UWB) systems.
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