In literature, generalized waveguide connections to other circuits are represented similar to Z_in and Z_out in figure a) which is from M.S Khalil et al. 2012(1). Does Circuitikz have a similar element? How would you go about creating such an element to add to a diagram?
(1) M. S. Khalil, M. J. A. Stoutimore, F. C. Wellstood, and K. D. Osborn , "An analysis method for asymmetric resonator transmission applied to superconducting devices", Journal of Applied Physics 111, 054510 (2012) https://doi.org/10.1063/1.3692073


tlineandtlinestub(see the manual at page 126 and following, about RF components; there is an example also on how to change relative size). Try it and if you have problems, add the code to the question and we'll try to help. – Rmano Apr 18 '23 at 20:45