Compact Tri-Band Bandpass Filter Using Quintuple-Mode Stub-Loaded Resonator

A miniaturized tri-band bandpass filter using a quintuple-mode stub-loaded resonator and a folded half-wavelength resonator is presented. The characteristics of the quintuple-mode resonator are investigated by using even- and odd-mode analysis, generating tri-band response. By adding a half-wavelength resonator, the bandwidth of the second passband can be controlled easily. Three passbands of the filter are designed at 1.8, 2.4, and 3.5 GHz for global system for mobile communication, wireless local area networks, and worldwide interoperability for microwave access applications. The center frequencies of the three passbands can be independently controlled, and their bandwidths can be tuned properly by controlling the dimension parameters of the filter. In addition, six transmission zeroes are produced to improve the selectivity of this filter. Measured results have good agreement with simulations.