Unique Fabrication Technique for Waveguide below Cut off High Pass Filters

This paper describes a method of fabricating waveguide below cut off high pass filters from sections of waveguide without the use of special jigs, molds, or mandrels and eliminates the requirement for welding. This technique employs a slot cut along the centerline of the top and bottom of the waveguide for a length of approximately 12 wavelengths. The waveguide is then squeezed to close the slot for approximately seven wavelengths. This narrows the width of the waveguide and raises its cut off frequency. Squeezing the waveguide only in the middle portion produces gradual tapers on each end reducing the standing wave ratio and insertion loss caused by an abrupt change in waveguide width. The width of the slot will determine the final width of the waveguide which is critical for a specific cut off frequency. Since the slot is cut on the center line of the top and bottom of the waveguide it does not affect the performance of the filter. Top and bottom plates are epoxied in place to maintain the proper waveguide dimensions and seal the waveguide for pressurization. Precise adjustment of the cut off frequency, the attenuation rate below cut off, and adjustment of the VSWR over a particular frequency range are easily controlled since RF sweep generators and monitoring devices can be employed to monitor all these characteristics during the squeezing process.