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High-temperature superconducting (HTS) filters have advantages of extreme low insertion loss and high selectivity of passbands. In this paper, three types of multi-band HTS bandpass filters (BPFs) using multimode square ring loaded resonators (SRLRs) are presented. The traditional SRLR has four resonant modes and the first one is a miniaturized quad-band HTS filter using two coupled four-mode SRLRs with ultra-low insertion losses in four passbands. Next, two stubs at two sides of SRLR are folded to a hairpin ring shape for high-order circuit design, thus a eighth-order dual-band HTS BPF using the modified SRLR is designed with high selectivity passbands. To reject common mode interference, a newly modified SRLR with shunt-ed-line structure is proposed and them a four ports dual-band HTS differential filter is developed. All these BPFs shown favorable performance.

In this article, a novel band-notched ultra-wideband (UWB) bandpass fllter based on hybrid microstrip/slotline structure is proposed. A quad-mode stubs-loaded slotline resonator is fed by two orthogonal microstrip lines and ultra-wideband bandpass characteristic is excited. A stub-loaded dual- mode microstrip resonator is externally loaded to the quad-mode slotline resonator, and a notched band with sharp roll-ofi characteristic is achieved. The circuit model for the dual-mode microstrip resonator loaded slotline is given and analyzed. The proposed fllter is designed and fabricated. Simulated and measured return losses are i12dB/i18dB and i18dB/i10dB in lower and higher passband. The return loss in the notched band is greater than 15dB.

A novel method is proposed to synthesize dual-band bandpass filters (BPFs) from a prototype lowpass filter. By implementing successive frequency transformations and circuit conversions, a new filter topology is obtained which consists of only admittance inverters and series or shunt resonators, and is thereby easy to be realized by using conventional distributed elements. A microstrip dual-band BPF with central frequencies of 1.8 GHz and 2.4 GHz is designed and fabricated using microstrip lines and stubs. The simulated and measured results show a good agreement and validate thereby the proposed theory., copyright(c)2006 IEICE許諾番号：07RB0174 http://www.ieice.org/jpn/trans_online/index.html

Microstrip filter is used widely in wireless communication area, especially in WLAN. Compared to the conventional manufacturing techniques using lumped element, we can get extremely better characters in high frequency wave band using microstrip lines. ADS2008 (Agilent Advanced Design System 2008) is an excellent software platform for high frequency and high speed EDA manufacturing. In this letter, the modeling of microstrip filter which works at appointed frequency is got by transforming the lumped elements to microstrip elements. Finally, the microstrip filter simulated, optimized by ADS2008.