The Control and Ultilization of Dual Orthogonal Modes in a Rectangular Cavity

We here calculate the discontinuity impedance of the aperture with metallic grid. bars to set up the complete equivalent circuit of the cavity resonator with a symmetrical aperture lined with metallic grid bars, the two orthogonal modes inside the cavity are excited so that one mode is to be perturbed by an external body near the aperture, this mode is called the working mode while the other mode is not affected, this mode is called the reference mode. By measuring the difference of the resonant frequencies of these two modes ¿ f=f1-f2 and that of the external Q´s of these same two modes ¿ Q= QL1-QL2 we can determine two parameters of the property of the perturbing external body, for instance, the moisture content and the thickness of the external body. The advantage of this method for measurement of the parameters characterizing the external body lies in that we ultilize two modes so that we can have the self-compensation on the effect of external environment such as the changes in humidity and in temperature(see fig.(6) for the self-compensation action). Thus an instrument built on this principle will work in adverse industrial environment.