3-D Printed Filtering Rat-Race Couplers Using Hemispherical Cavity Resonator

In this article, a new approach for designing 3-D printed single- and dual-band filtering rat-race couplers based on hemispherical cavities is presented, for the first time. By constructing two types of multiplexing multimode topologies in dual-cavity configurations, both single- and dual-band filtering rat-race couplers are developed. In these designs, a pair of TM201 degenerate modes form the passband for single-band operation, while dual-band operation is realized by exciting an additional pair of TE101 degenerate modes. Due to the natural
$E$
-field distributions of these modes, the desired 0° and 180° phase differences and isolations can be realized between output ports without additional matching circuits. By elaborately placing the internal coupling slots and input–output ports, desired filtering responses and phase requirements can be flexibly attained for both single- and dual-band filtering rat-race coupler designs. For demonstration, two prototypes are well implemented as monoblock circuits using 3-D-printing technology. Compared with the up-to-date designs, the proposed works exhibit the merits of compact size, high
$Q$
-factor, lightweight, good single- and dual-band filtering responses with controllable bandwidths and center frequencies, nice phase difference characteristics as well as flexible extendable topologies.