of interest in the present invention for the te 01 mode equ3 where b is the inside radius of waveguide 100 u03c9 is the angular frequency 2 u03c0f u03bc 0 is the permeability of free space 4 u03c0 u00d7 10 7 henry meter h m u03c3 is the conductivity of the material used to construct waveguide 100 and x k c k 0 k c being the cutoff number of waveguide 100 that is equal to p 39 01 b p 39 01 being a constant 3 83171 for the te 01 mode u03b2 j is the complex portion of the propagation constant and is computed in the following manner for each j th region a radial cross section of waveguide 100 includes a dielectric region and an air region note that there is no air region associated with plug region 31 by way of example one such radial cross section has been taken along line 5 5 and is shown in fig5 where a is the radius of tuning region 35 b is the radius of waveguide 100 and the air region lies between tuning region 35 and waveguide 100 u03b2 is solved for by computing the electric and magnetic fields in each.