The goal of the antenna design was to produce something that was low cost and easy to build with the fabrication facilities provided by the College of Engineering and Department of Physics. Additional considerations were that of scale, bandwidth, gain, and directivity. To investigate different designs, the open source computational electromagnetics library NEC++ was used with a C++ wrapper that would generate initial conditions and perform analysis for the expected beam pattern. We began working on constructing a genetic algorithm to optimize the parameters of the design, however, due to time considerations, the standard parameters were used with manual optimization for the spacing between antennas. Later design was followed up by duplicating the original design in the computational electromagnetics software FEKO. Structural design and analysis was then conducted in Autodesk Inventor.
The Yagi Antenna
When originally considering antenna designs, we decided to go with something similar to the Cambridge Low Frequency Synthesis Telescope (CLFST), which used a coupled set of 4 Yagi-Uda antennas. Additionally, with the frequency previously chosen of 408 MHz, several constraints were already chosen. With 4 antennas, there are only a few possible orientations, which were all chosen. We concluded that the final configuration provided the best directivity / gain, as well as HPBW of the antenna function.
The Wide Band Antenna
Looking into an interferometer design, we concluded that we should consider building hardware for a wider spectral band, allowing us to work with both the 408 MHz region, as well as those allocated to 21cm HI observations and the 18cm OH observations. The resulting design was a prime-focus dish (with various diameters – 1.9 meters was used as a standard), containing a cylindrical feed horn at the focus. The cylindrical feed horn contains a “tree” of dipole antennas, which have their lengths and distances of separation manually optimized. This tree pattern looks like a plus from above, and a poorly constructed Christmas tree from the side (see below), allowing for both X and Y polarization pickup at four different bands. The design was explored, and optimized using FEKO.
After much planning, my student organization and I have come up with a design for the internal antenna structure, and the feed in general. The design will involve 3D printing several spacers, gaskets, and supports, in an effort to effectively electrically isolate the system. Additionally, an adjustable feed mount has been designed, to allow for us to focus the feed in the positive z-axis. This adjustment is done via three threaded rods in a triangle formation located above the horn itself. These designs can be seen in the following figures.