Method for non-destructive estimation of waveguide directional coupler dimensions

A method for estimating the size and location of couplings within a waveguide directional coupler is provided. The method is applied to a waveguide directional coupler having a main transmission waveguide connected to an auxiliary transmission waveguide by a number of bore hold couplings. The bore hold couplings are in the interior of the waveguide directional coupler and, therefore, are not easily measurable. The method generally includes the steps of applying a two-sided tape to a member, inserting and securing the member within the main transmission waveguide, pouring a fine particulate substance such as talc into the auxiliary transmission waveguide such that a portion of the talc enters the bore hole couplings and adheres to the two-sided tape, and withdrawing the member such that the size and location of the bore hole couplings can be determined by measuring the size and location of marks on the two-sided tape caused by the fine particular substance adhering to the two-sided tape.