Historically C-band and X-band components were routinely machined to tolerances of ±0.05 mm, or even as high as ±0.1 mm, since special skills and exceptional care in setting up tools was required to achieve better results. Due to the smaller waveguide size, Ka-band components demand tolerances of ±0.02 mm, so both machining and assembly costs were higher because of the greater accuracy required. Now the latest CNC machines are able to routinely achieve tolerances of ±0.02 mm or better, which means that not only are the lower frequency components now produced more accurately but also Ka-band components need not cost any more to produce. Indeed, as is shown in Figure 1, using the 10-dB broadwall coupler as an example, the actual manufacturing costs for Ku-band are less than for C-band. The same price comparisons are broadly similar for most waveguide components, from transfer switches through waveguide-to-coaxial adaptors to a full antenna subsystem.
Figure 2: Comparison of dimensions of WR-137 and WR-28.
The material cost for a WR-28 coupler is only around 60% of that for an equivalent coupler in WR-137, as the smaller Ka-band component uses much less metal and produces less scrap. The machining time is lower because fewer machining operations are required. The operations are also smaller and the tool travel distance between operations is much shorter.
The cost savings continue when subsystem assembly is taken into account. Less solder is required, and consequently less heat needs to be applied. Where bolts are used, although these are smaller they are often easier to handle, and fewer bolts are required. Millimetre-wave flanges are frequently aligned using dowel pins, which makes assembly quicker and more accurate.