Shielding of microwave leakage in the microwave oven is achieved effectively by using a choke structure. This choke structure is analyzed by using the equivalent circuit representations for a slit discontinuity between two waveguides. An explicit expression for the input admittance of the choke obtained form this analysis is applied to determining the dimensions of the choke periodically slotted choke is even more effective for the shielding of microwave because its periodic slot controls unwanted modes. This periodically slotted choke is analyzed by utilizing Floquet's theorem for the periodic boundary conditions and the circuit representations for the slit discontinuity studied for the choke. The stop bands of the periodic structure may be properly chosen by selecting required periodicity and the impedance of the slit discontinuity.
This stop band for the frequency prohibits the formation of modes in this frequency band that may propagate through the parallel plate gap except one TEM mode propagating perpendicular to the periodic axis.
This TEM wave may be stopped by the choke structure designed to tune only this TEM mode.
The dispersion relation yielding relations between the stopband and the geometrical dimensions of the slotted choke is calculated and plotted by using a computer for various parameter values such as frequency, periodicity and slit width. The practical range of those parameter values is obtained.
