Cascaded loops directional filter with transmission zeroes for multiplexing applications

In this paper, a new design of a traveling wave loop directional filter allowing for realization of transmission zeroes has been proposed. In order to introduce transmission zeroes to bandpass branch of the filter, two loops have been cascaded using transmission line sections. Theoretical analysis of the circuit has been provided giving the insight into behavior of the appearing transmission zeroes related to electrical lengths of the loops' connecting segment. Performance of the presented approach has been verified by the design and measurements of an exemplary cascaded single-loops directional filter with two symmetrically placed transmission zeroes covering ISM 2.4 GHz band. The obtained results prove the usefulness of the presented approach.

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