| 主权项 |
1. An apparatus comprising:
a mode filter that provides a low-loss transmission path for RF signals propagating in a first mode, while substantially suppressing at least one second mode, the mode filter comprising:
a proximal port and a distal port, having a respective characteristic cross sectional dimension Dp1 and Dp2; andan electrically conductive hollow tube having a longitudinal axis and extending a length L between a distal end of the proximal port to a proximal end of the distal port, wherein a cross section transverse to the longitudinal axis is non-uniform along length L and has a minimum internal characteristic dimension Dmin at least at a first longitudinal position and a maximum internal characteristic dimension Dmax at least at a second longitudinal position, Dmin being substantially different from Dmax; wherein
the mode filter is configured to suppress the at least one second mode by at least 5 dB, and Dmax is less than 2.5 times the greater of Dp1 and Dp2. |
