Compact Dielectric Resonator Filter for Mobile Communications

Using very low-loss ceramic resonators with dielectric constant of 100, design of a very compact single mode fourth-order 75 MHz Chebyshev filter operating at 1.8 GHz, is presented. This miniaturized filter, which out-performs the counterparts in its class, is about 11 cm long, 3.5 cm wide and 3.5 cm thick and has maximum insertion-loss of 0.25 dB. The filter utilizes direct-coupled resonators excited in TE_01δ mode. The first higher order mode of the resonators is HEM₁₂ with a resonance frequency which is about 350 MHz above that of the fundamental mode, leading to an excellent out-of-band response for the filter.