Researches On Microstrip Multi-mode Ultra-wideband Bandpass Filters With High Selectivity

With high-speed development of communication business and systems, ultra-wideband(UWB) technology is becoming more and more attractive because of its wide bandwidth, hightransmission data rate, simple structure, high security, low cost, etc. Planar UWB bandpassfilter is a key component in the UWB system, since it is important for signal transmission.This dissertation gives a detail study about multiple design methods on planar microstripUWB bandpass filters, and several UWB BPFs are designed with good performance andcompact size. The main contributions of the dissertation can be summarized as follows:1. In this thesis, coplanar waveguide (CPW) resonators are used as triple-mode andquadruple-mode resonators and applied in UWB BPFs design. Based on themicrostrip-slotline transition structure, a novel transition with via-hole loaded structure isproposed, with the benefit of miniaturization. By adding stubs and band-stop resonators,transmission zeros could be introduced and thus notch-bands are generated, in order to avoidsignal interference between UWB systems and other communication systems.2. Novel T-shaped resonator is presented and applied in UWB BPF design in this thesis.Two transmission zeros are produced at the upper-and lower-edge of the passband, resultingin good skirt selectivity. Besides, a new way of introducing notch-band is presented by addinga slot on the T-shaped resonator.3. Based on the conventional dual-stub loaded resonator, a novel dual-stub loadedresonator with two short-circuit-stubs and two open-circuit-stubs loaded is proposed. Thedistribution of resonant modes are calculated and analyzed, and then applied in UWB BPFdesign. With two short-circuit stub and two open-circuit stub loaded at the same time,transmission zeros appear at upper stopband of the passband, and thus the harmonic modes.4. Ring resonators are studied and discussed in this thesis. Based on the conventionalring resonators, multiple stubs are loaded to suppress spurious harmonics. By using theproposed stub-loaded ring resonator (SLRR), a novel design of quadruple-mode UWB BPF isbuilt. By adding various kinds of bandstop units within the SLRR, one or more transmission zeros are introduced to generate notch-bands. This method is simple, easily-controlled, andgood for miniaturization.5. Based on the conventional bandstop structure, open-circuit and short-circuit stubs areadded to design single-and dual-passband wideband bandpass filters. Transmission poles andzeros are easily controlled by tuning the electrical length and impedance of transmission lines.At last, two designs with single and dual passband are simulated, fabricated and tested usingplanar microstrip structure. The measured results are agreed with the simulated ones, whichdemonstrating the validity of the design procedure.