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UBC Theses and Dissertations

Investigation of a frequency multiplexer design for band splitting in a wideband feed antenna Moazen, Nima


This thesis describes the design of a frequency multiplexer for band splitting in a wideband feed antenna. The work is motivated by the design of a 1-8 GHz coaxial waveguide feed antenna intended for radio astronomy applications in the square kilometer array (SKA) project. The feed antenna consists of three nested coaxial waveguides each designed to operate over an octave bandwidth. The bands are 1-2 GHz, 2-4 GHz and 4-8 GHz, and a frequency multiplexer is required to connect a common input terminal and split the signal into three contiguous frequency bands. The common input terminal must be matched over the entire frequency range while the output ports are connected to coaxial waveguides. The requirements for the multiplexer are challenging and a design is proposed based on the theory of complementary diplexers. Complementary diplexers are three port filter networks which are matched at the input port and whose output ports are split into two complementary and contiguous bands. By cascading two complementary diplexers, a design can be realized that meets the SKA requirements. Different design concepts were evaluated using electromagnetic simulation tools and an important conclusion from the work is that compact capacitor structures are required to obtain broadband stop band responses in the diplexers. Two compact capacitor designs were fabricated and tested in diplexer configurations. One design uses interdigital capacitors and in another design thin dielectric metal insulator metal capacitors are used. Experimental prototypes were fabricated to compare with simulation results and the results are in good agreement. The research shows that complementary diplexer filter concepts can be used to realize broadband multiplexers for the SKA antenna feed.

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