Here we use the example of equivalent 10-dB broadwall couplers in C-band and Ka-band to demonstrate that the decision on which frequency band to use for a particular project need no longer be driven by cost considerations, and can be determined largely by technical and mechanical criteria such as bandwidth, link budget, atmospheric performance and space outline.
In the past the significant difference in cost between C-band and Ka-band components has been justified by the higher machining tolerances required for smaller waveguide sizes, coupled with the relatively higher complexity of the millimetre-wave design process. Indeed for many years millimetre-wave design had a reputation for being a ‘black art’, because much of it could not be simulated accurately and required an empirical approach and an experienced touch – or a degree of good luck. Military and high-cost professional applications were able to absorb this cost differential, but the move towards employing higher frequencies for commercial communications has brought about pressure to bring down component costs, while at the same time the issues that led to higher costs for millimetre-wave components have largely been resolved. Figure 1 gives a summary comparison of selling price and manufacturing costs of a 10-dB waveguide broadwall coupler in WR-137 for C-band and WR-28 for Ka-band, which are analysed further in this article.
Figure 1: Comparison of selling price and manufacturing costs for a 10-dB broadwall coupler in WR-137 and WR-28.