A multiplexer includes a first circuit board, a second circuit board, and a third circuit board. The first circuit board includes a first metal layer, a first substrate layer, and a second metal layer sequentially stacked along a first direction. The second circuit board includes a third metal layer, a second substrate layer, and a fourth metal layer sequentially stacked along the first direction. The third circuit board includes a fifth metal layer, a third substrate layer, and a sixth metal layer sequentially stacked along the first direction. The second and third metal layer have same wiring structure, and the second metal layer connects to the third metal layer to form a first signal transmission path structure and a filter structure. The fourth and fifth metal layer have same wiring structure, and the fourth metal layer connects to the fifth metal layer to form a second signal transmission path structure.

A multiplexer includes a first circuit board, a second circuit board, and a third circuit board. The first circuit board includes a first metal layer, a first substrate layer, and a second metal layer sequentially stacked along a first direction. The second circuit board includes a third metal layer, a second substrate layer, and a fourth metal layer sequentially stacked along the first direction. The third circuit board includes a fifth metal layer, a third substrate layer, and a sixth metal layer sequentially stacked along the first direction. The second and third metal layer have same wiring structure, and the second metal layer connects to the third metal layer to form a first signal transmission path structure and a filter structure. The fourth and fifth metal layer have same wiring structure, and the fourth metal layer connects to the fifth metal layer to form a second signal transmission path structure.

A device comprises a loop gap resonator having opposing sides and a central opening therethrough; and at least one exciter board positioned over, and at a preselected distance from, at least one of the opposing sides of the loop gap resonator. The exciter board includes at least one metallized layer and a central hole therethrough. The exciter board has one or more cutouts with respect to the central hole that define a geometric configuration, such that a first portion of the metallized layer borders with the central hole at a first distance from a center point of the central hole. A second portion of the metallized layer borders the one or more cutouts at a second distance from the center point that is greater than the first distance. The exciter board is configured to shift a resonant frequency of the loop gap resonator to match a predetermined resonant frequency.

A device comprises a loop gap resonator having opposing sides and a central opening therethrough; and at least one exciter board positioned over, and at a preselected distance from, at least one of the opposing sides of the loop gap resonator. The exciter board includes at least one metallized layer and a central hole therethrough. The exciter board has one or more cutouts with respect to the central hole that define a geometric configuration, such that a first portion of the metallized layer borders with the central hole at a first distance from a center point of the central hole. A second portion of the metallized layer borders the one or more cutouts at a second distance from the center point that is greater than the first distance. The exciter board is configured to shift a resonant frequency of the loop gap resonator to match a predetermined resonant frequency.

A coupling resonator circuit includes a capacitive portion that includes a capacitive plate having a geometrical shape; and an inductive portion that is coupled to the capacitive portion. The inductive portion includes a transmission line having a first end and a second end, and the transmission line tapers from the first end in the direction of the second end such that a width of the transmission line at the first end is greater than a width of the transmission line at the second end. The coupling resonator circuit is configured to resonate at a desired coupling frequency; and dimensions of the capacitive portion and the inductive portion determines a separation in frequency between the desired coupling frequency and one or more resonant frequencies that are nearest to the desired coupling frequency.

A coupling resonator circuit includes a capacitive portion that includes a capacitive plate having a geometrical shape; and an inductive portion that is coupled to the capacitive portion. The inductive portion includes a transmission line having a first end and a second end, and the transmission line tapers from the first end in the direction of the second end such that a width of the transmission line at the first end is greater than a width of the transmission line at the second end. The coupling resonator circuit is configured to resonate at a desired coupling frequency; and dimensions of the capacitive portion and the inductive portion determines a separation in frequency between the desired coupling frequency and one or more resonant frequencies that are nearest to the desired coupling frequency.