Dual-Band Filters for Base Station Multi-Band Combiners

In this paper a synthesis technique for dual band filters to be used in base station multi-band combiners is presented. The topology of the dual band filters is constituted by two sub-networks connected in parallel, which are obtained from suitable transformations of the lowpass transversal canonical prototype. The two sub-networks synthesized with the novel design technique are characterized by practically feasible couplings even when the separation of the two passbands is very large (the classical dual band synthesis methods may determine in this case too large coupling coefficients for a practical implementation); moreover the overall synthesized dual band filter is more easily tunable with respect to the classical inline topology because the resonators in each sub-network are all tuned in the same passband. The novel method has been applied to the design of a wireless base station combiner for PCS and AWS bands; the measurements on the fabricated prototype have confirmed the effectiveness of the novel synthesis technique.