Compact Monolithic 3D-Printed Wideband Filters Using Pole-Generating Resonant Irises

The design concept of a pole-generating resonant iris is demonstrated in rectangular waveguide filters in this paper. Different from conventional reactive iris, the resonant iris can generate an extra transmission pole without increasing the number of resonant cavities. As a result, several design advantages can be gained: (i) a more compact filter structure; (ii) an ability to realize strong coupling and therefore wide bandwidth; and (iii) a new polarization rotation capability. Two third-order Chebyshev filters are designed and implemented, demonstrating the miniaturization and polarization rotation feature. A fifth-order Chebyshev filter with 20% fractional bandwidth is presented to show the capability of realizing wideband. This also demonstrates the realization of asymmetric coupling between the resonant iris and the cavity resonator on either side. An approach to control and extract the coupling between the iris and the cavity resonator has also been presented. To manufacture the intricate asymmetric iris structure, all the presented filters are printed monolithically using selective laser melting technique. Excellent agreement between the measurements and simulations has been achieved, verifying the design concept as well as the additive manufacturing capability in microwave waveguide devices.