Towards optics design for the next generation very large array

This paper will discuss some options for the optics design of the antenna taking into account performance, cost, accessibility to the receivers for maintenance purposes, and receiver distribution in the focal plane. The baseline design will use an 18-meter parabolic main reflector. For the secondary reflector, an off-axis design is being considered. In addition to the advantages of higher gain, low near-in sidelobes, lower antenna temperature, minimized standing waves, etc., this design will provide sufficient real estate for accommodating the receiver cryostats. In an on-axis design, it may not be possible to install all the receivers within the subreflector profile on an 18-m antenna such as being proposed. The importance of size, opening angle of the subreflector and its impact on the types and sizes of feeds will be discussed. The pros and cons of different geometries of dual-offset reflector designs will be presented with performance comparisons.