an even number values of z rf less than 1 ohm are predicted which provides a good short circuit waveguide stub 12 is typically a hollow tube with a rectangular cross section in the 300 600 ghz band the dimensions of the rectangular cross section of waveguide stub 12 are on the order of 500 u03bcm u00d7 250 u03bcm at these high frequencies high impedance sections 26 28 30 and 32 become too thin to fabricate and conventional noncontacting waveguide backshort 22 is no longer strong enough to slide snugly in waveguide stub 12 this is a serious limitation because it limits the development of waveguide circuits for high frequencies a more rugged alternative is provided by the present invention as shown in fig3 through 5 referring now to fig3 noncontacting waveguide backshort 40 is shown in cross section view in accordance with the present invention noncontacting waveguide backshort 40 includes low impedance metallic bar 42 sheathed within mylar insulator 44 insulator 44 serves the same general purpose as insulator 24 shown in fig2 the thickness t of metallic bar 42 is chosen so that together with mylar insulator 44 they will fit snugly but movably within waveguide stub 12 the equivalent of the periodic impedance variations provided by high and low impedance sections 26 28 30 32 34 35 36 and 38 of conventional backshort 22 shown in fig2 are provided by holes 46 48 and 50 in low impedance metallic bar 42 in accordance with the present invention holes 46 48 and 50 are spaced apart an equal spacing distance s which provides a portion of low.