Influence of Manufacturing Tolerancies on Central Frequency of a Narrow Band E-Plane Waveguide Filter

The aim of this work is to master the design of a narrow band waveguide E-plane filter for Ku band that will not need to be adjusted in serial production, therefore its center frequency should be exact. This paper presents the procedure for designing a filter with inserted metal septa and investigates the repeatability of its characteristics with respect to tolerances of both the waveguide housing and the metal septa. It has been shown that longer waveguide's dimension (a) has the greatest influence upon filter's central frequency and it has to be precise within limits of 0.1mm. It has also been found that other influences (waveguide's height tolerances (b), unequal dimensions of the halves (a/2), as well as unsymmetrical fitting of waveguide's halves along E-field direction) could be neglected. These findings have been used to obtain the filter that has the center frequency fc=12.764GHz, which is only 1MHz less then demanded. Measured insertion loss in passband is 0.55dB.