We describe a method for the measurement and alignment of reflector surfaces of radio telescopes with high precision. The scheme is based on antenna gain measurements under a series of active surface perturbations in terms of a set of orthogonal basis functions. Both local and global basis functions can be employed, resulting in different spatial resolution and different requirements on signal-to-noise ratio. Both theoretical studies and numerical simulations are presented, and demonstration experiments on a 1.2-m submillimeter antenna are reported. Practical considerations, including the effects of antenna mispointing and near field operation, are also discussed.
A novel wavefront-based algorithm for the beam simulation of both reflective and refractive optics in a complicated quasi-optical system is proposed. The algorithm can be regarded as the extension to the conventional Physical Optics algorithm to handle dielectrics. Internal reflections are modeled in an accurate fashion, and coating and flossy materials can be treated in a straightforward manner. A parallel implementation of the algorithm has been developed and numerical examples show that the algorithm yields sufficient accuracy by comparing with experimental results, while the computational complexity is much less than the full-wave methods. The algorithm offers an alternative approach to the modeling of quasi-optical systems in addition to the Geometrical Optics modeling and full-wave methods.