Compact Dielectric Loaded Combline Filter with Low Insertion-loss

A new compact combline filter structure with very low insertion-loss, is proposed. This structure, which offers 75% saving in space as compared with its air-filled counterpart, uses combline (coaxial) resonators loaded with high dielectric constant ceramic cylindrical rings. Based on the new structure, a fourth-order elliptic filter suitable for mobile communications, is explained. In an aluminium manifold, this filter exhibits an insertion-loss of better than 0.5 dB which is far less than that of commercial dielectric combline filters of the same order. The measured and theoretical frequency responses of the filter are in good agreement.