Corrugated coaxial cable vs other shielding methods

[matthuszagh]

What are the applications of corrugated shielding for coaxial cable in comparison with other forms of shielding? Wikipedia (https://en.wikipedia.org/wiki/Coaxial_cable#Construction) has the following to say about coaxial cable with a corrugated shield:

For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor is corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. One brand name for such cable is Heliax.

But, when I was looking on Pasternack I found for example this (https://www.pasternack.com/50-ohm-low-loss-corrugated-1-4-superflexible-helical-coax-pe-1-4sfhc-p.aspx). It supports a max frequency of 20.4 GHz, which is well above the 1 GHz mentioned by Wikipedia.

I would assume this solid outer conductive shield would reduce the flexibility of the cable, but this cable has a minimum repeated bend radius of 1 in., which seems pretty good. The rest of the specs also seem good and the price is in the middle of the range compared to some of their other cables.

What are the drawbacks of this cable? When would I not want to use it? For example, is cable assembly more difficult with this cable (I only care about this with respect to a manual crimping process).

The cable outer diameter is a bit on the large side, so maybe this is the main drawback?

[T3sl4co1l]

Maximum frequency is set by acceptable losses, and "breakup" caused by additional non-TEM0 modes.  Wiki is probably erroneous.  Maybe their source explains in better detail (anyone got that edition handbook?), or maybe it's also erroneous.

Losses are determined by construction, generally with larger build having lower loss, and also smoother metal faces (especially silver plated), and higher-Q dielectric (or the lack thereof -- as with foam, spiral or other sparse supports).  The design choice is generally to use the largest line you can, up to the TEM cutoff, given cost, loss budget, and other considerations like available space, flexibility, etc.

"Cutoff" is not that it stops transmitting signals, but that it stops being as well-behaved of a medium -- specifically what happens is, as higher order (waveguide) modes come into play, their impedances and velocities are all different, and so the signal arrives at its destination over a range of times -- it becomes smeared out, dispersed; hence the property is called dispersion (when velocity depends on frequency).

Tim

[Bassman59]

What are the applications of corrugated shielding for coaxial cable in comparison with other forms of shielding? Wikipedia (https://en.wikipedia.org/wiki/Coaxial_cable#Construction) has the following to say about coaxial cable with a corrugated shield

Back when I was doing work with high power microwave transmitters, we used 25 mm-thick Andrew Heliax cables from the amplifiers to the antennas. This cable had corrugated shields.

Why? These transmitters were powerful and the cable had to handle the power with as low loss as possible. That dictates the cable geometry and the shield thickness. But the cables had to be transported (on big spools) and installed, which meant that they had to be flexible to some degree. A solid shield that could handle the power won't flex. Hence the use of corrugated shields. The shields are like an armadillo's shell.

[David Hess]

The cutoff frequency is the first higher order mode.  Applications which do not excite the higher order modes or are tolerant of them can operate above this frequency.  Increasing the cutoff frequency means using smaller diameter cable with a greater loss.

Corrugations in the inner and outer conductor, and non-uniform support of the inner conductor as with helical construction, and bends cause distortions in the group delay.  Sharp bends are worse than gradual bends.