When implementing RF circuits in rectangular waveguide, we use stubs/screws/iris to realise capacitance, inductance. What what are the dimension we should choose for particular Capacitance and inductance values?
From a research paper i came to know that the ratio of the post diameter to the wide side of waveguide should be less than 0.25 (diameter of post/a < 0.25), But how to determine exact dimension for respective capacitance and inductance values.
When a metallic post/ screw in inserted in to broader side of waveguide, it functions as iris in a waveguide and it is equivalent to an iris in the cross section of waveguide. It detailed qualitative analysis is given the chapter 5, Waveguide Handbook," MIT Radiation Laboratory Series, vol. 10, McGraw-Hill Book Company, Inc., New York, 1951.
However a subjective/descriptive analysis is given below
When depth of penetration of screw is less the quarter wave length at operating frequency, then it behave like a capacitive reactance on the other hand, when depth of penetration is more than the quarter wave length at operating frequency then it behave like inductive reactance. A shown in figure (Attached )below horizontal-axis indicate depth of penetration. Form figure we can note that, as depth of penetration of screw/post increases from zero to quarter lambda, during this path capacitance increases from zero to maximum. Now if we continue to increase up to opposite broad wall, the it behave like an inductive reactance and it is maximum at quarter lambda depth subsequently it start decrease and it attend minimum value for inactive reactance when post/screw touches opposite broad wall.
Hope above information may helpful to you.
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