TRUNCATION IN MILLIMETER AND SUBMILLIMETER-WAVE OPTICAL-SYSTEMS

We present a technique for determining the power that is lost when the field in a beam waveguide is truncated by an axially-symmetric stop. The technique is based on the principles of multimode Gaussian optics. Although the underlying theory is applicable to any long-focal-length optical system, we concentrate on beam waveguides that are fed by dia gonal horns, corrugated horns, smooth-walled conical horns, and unifor mly-illuminated apertures. The results are summarized in a series of p lots which show truncation loss as a function of normalised aperture s ize and phase slippage. These plots can be used together with single-m ode design techniques to minimize the size of millimeter and submillim eter-wave optical systems.