Realization of attenuation poles, spurious resonance suppression and size reduction by microstrip SIR loaded with dielectric rods

Characteristics of a class of stepped-impedance resonators (SIRs) which is loaded with two dielectric rods, are investigated by a Finite-Difference Time-Domain (FDTD) method. Dielectric rods to be inserted between a strip conductor and the ground plane have higher relative permittivity than that of the substrate. When a tapped half-wavelength (λ/2) microstrip resonator is loaded with two dielectric rods, the electric length of a loaded λ/2 resonator becomes longer than λ/2, which makes its fundamental resonant frequency (f_r′) to be generated on the region lower than that of an unloaded λ/2 resonator (f_r) and its first spurious response (f_sp1) is generated on the region higher than 2f _r′. Therefore, to shift f_r′ back to f _r, the resonator's length is to be reduced, and this, in turns, suppress the spurious responses. Then, the resonant characteristics of an SIR employing the proposed method has also been investigated, and it is found that this is capable of suppressing the spurious responses in wideband together with an attenuation pole in the stopband, and of further reducing the resonator's length. Therefore, wide exploitation of the presented method can be expected in the filter design based on the LTCC technique.