Dual-Mode Filter with High Design Flexibility Using Short-Loaded Resonator

─ This work presents a series of independent bandpass filters (BPFs) based on dual-mode resonators (DMRs) with short stub-loaded. BPFs conform to the 802.11n protocol and include three passbands with center frequencies and bandwidths of 2.46 GHz, 3.55 GHz and 5.22 GHz, 130 MHz, 130 MHz and 470 MHz. Insertion loss and reflection loss are 1.5 dB, 1.6 dB and 1.3 dB, 18 dB, 20 dB, 30 dB. The filters are useful in the WLAN/WIMAX applications with compact size. According to the current distributions along the resonator, the feed-lines with high design flexibility arms were introduced in order to supply the needed external coupling for the dual-/tri passbands simultaneously, and achieve good impedance matching in each passband. Finally, by the version 15 of High Frequency Structure Simulator (HFSS), three BPFs with single, dual and triple passbands were designed on the Rogers 5880 substrate with the relative dielectric constant ɛr = 2.2, substrate loss tanδ = 0.002, and the thickness h = 0.508 mm. The BPFs are measured by Agilent 85058E Vector Network Analyzer (VNA). The measured results have good agreement with the simulated ones. Index Terms ─ Bandpass filter, dual-mode resonator, odd and even-mode theory, tri-band filter.