Miniaturized Triple-Band Bandpass Filter Based on Cylinder Dielectric Resonator with Cut Holes

A miniaturized triple-band bandpass filter (BPF) using TM mode cylinder dielectric resonators is presented in this paper. By cutting holes through the cylinder dielectric resonator,
$\mathbf{TM}_{\mathbf{010}}$
,
$\mathbf{TM}_{\mathbf{120}}$
, and
$\mathbf{TM}_{\mathbf{210}}$
modes are excited with wide range of controllation. Thus, a BPF with triple passbands can be constructed by using two coupled dielectric resonators. To demonstrate the proposed concept, a BPF with center frequency of 2.49 GHz / 3.88 GHz / 5.24 GHz and bandwidth of 140 MHz / 100 MHz / 170 MHz is designed for WiMAX application. Simulated minimum insertion loss is about 0.25 dB, and simulated return loss is better than 20 dB. Good rejection higher than 70 dB is achieved between adjacent passbands. Phase reversal between two adjacent paths results in two transmission zeros in between adjacent passbands. The final filter has a overall volume of
$\mathbf{35.7}\times \mathbf{22.7}\times \mathbf{5.4}\mathbf{mm}^{\mathbf{3}}$
.