| Summary: | Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2007. === This dissertation presents a technique for the design of N-way conical line power combiners,
which offers significant advantages over existing axially symmetric combining techniques.
A full analytical study of conical transmission lines is done, and evaluated results are presented.
These include a proof of the cutoff frequency equation, and plots of the field patterns, of higher
order modes which are unavailable in literature.
A coaxial fed conical line combiner for 10 inputs is proposed, designed and evaluated. The
design technique relies on the uniform transmission line characteristics of the conical lines to
eliminate the need for complex full wave optimisation, typically needed in the design of the more
commonly used radial line combiners. Circuit models are instead employed to achieve a wide
matched bandwidth by using optimised stepped impedance coaxial lines to feed the combining
structure. The prototype developed at X-band displays more than an octave bandwidth with
a return loss of better than -14.5 dB. Using tapered line matching sections increases the power
handling capability of the combiner by eliminating sharp edges, and allows for tolerance insensitive
manufacture of the structure by widening conductor spacings. Such a 10-way prototype
is developed at X-band which displays a -18.7 dB return loss bandwidth of 47% with very low
losses.
A study is done to determine the limitations on the design of general N-way combiners, and
the results are incorporated into the design technique. The full process is demonstrated by
the design and simulation of a 30-way combiner at Ku-band which displays a simulated -20 dB
return loss bandwidth of 34%.
The design technique is simple to execute and requires very little full wave analysis. Results
obtained with the manufactured combiners are better than those of any previously published
axially symmetric combiners.
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