RF Selectivity using first and second set of 90 degree phase shift coupling means and at least one pair of resonating means

摘要

Apparatus allowing radio frequency selectivity for use in a wireless communication system for the passage of one or more receiving and/or transmission frequency signals includes at least a first set 204 of first and second 90 degree phase shift coupling means (3dB hybrid couplers) 206, 208, and at least one pair of resonating means 210, 212 coupled between the at least first and second 90 degree phase shift coupling means. The apparatus includes at least one further set 214 of first and second 90 degree phase shift coupling means 216, 218 which are cascaded, either directly or indirectly, with said at least first set 204 of first and second 90 degree phase shift coupling means, with or without at least one pair of resonating means located between the first and second 90 degree phase shift coupling means of the at least one further set. This arrangement allows transmission zeros to be created in the filter transfer function of the combiner apparatus without a requirement of cross coupling to be provided between resonators. As such, smaller sized combiner apparatus can be provided of reduced cost. In addition, as there is no direct coupling between pairs of resonators, different types or different Q technology resonators can be used within the same combiner apparatus.