Flexible Waveguide

Summary of the construction, applications and limitations of flexible waveguide or flex waveguide.

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Waveguide Tutorial Includes:
Waveguide basics Waveguide modes Waveguide impedance & matching Waveguide cut-off-frequency Waveguide flanges Waveguide junctions Waveguide bends Flexible waveguide Waveguide types & sizes

Flexible waveguide is often used to connect two elements using rigid waveguide systems together, especially when they cannot be accurately located or positioned.. For example, flexible waveguide is often used to connect antenna systems, especially when they may not be fixed, to the base transmitter receiver system.

Flexible waveguide may not have the same level of performance that is provided by rigid waveguide, but the mechanical advantages offered normally well outweigh the electrical performance limitations.

Flexible waveguide is also used to allow for mechanical movement. Often flexible waveguide may be used to allow for thermal expansion and contraction, or it may be used to allow for mechanical vibration.

Flexible waveguide construction

Flexible waveguide is available in a variety of different forms. Each type has its own advantages and disadvantages;

The flexible waveguide may be made from flat ribbons would on a rectangular mandrel. The edges are then convoluted or folded in and interlocked. The convoluted flexible waveguide may be left unsoldered or it may be soldered - the flexibility of the waveguide results from the flexing of each arm and not the relative sliding of the ribbons. However if it is soldered it does loose some flexibility and it is not able to be twisted to any degree.
A form of corrugated flexible waveguide may be constructed. It is manufactured by shaping thin wall rectangular tubing. It may also be made by bending and soldering corrugated sheet metal.
It is also possible to construct a bellows-style flexible waveguide using a flexible alloy.
Another common form of flexible waveguide construction is to use a helically wound system. This form of flexible waveguide is manufactured by a process of helical winding a silver coated, brass strip to form a continuous, uniform rectangular tube.

In general flexible waveguide is jacketed in Neoprene, Silicone, Viton, Devcon or other similar materials to provide additional protection from mechanical damage while still allowing flexibility.

Limitations of flexible waveguide

As might be expected the performance of flexible waveguide is not as good as rigid waveguide. Some reductions in performance may be noticed in the following areas:

Increased loss: The walls of the flexible waveguide will not be able to provide the same level of conductivity as that provided by solid / rigid waveguide. As the waveguide attenuation and loss will depend upon the conductivity, the performance of the flexible waveguide will inferior to that of the rigid style.
Possible introduction of passive intermodulation products: As some types of flexible waveguide have jointed sections, these can allow any corrosion to form non-linear joints that can give rise to low levels of passive intermodulation products. These can be of great importance on systems such as full duplex satcom or other systems when the diplexer is situated close to the antenna and one feeder is used. Any passive intermodulation products generated by the transmitter could fall within the receive band and impair the receive performance.
Minimum bend radius: There will be a minimum bend radius specification for the flexible waveguide. This should not be exceeded otherwise there permanent damage to the waveguide.

Flexible waveguide is an essential item for many waveguide installations. The flexible waveguide provides the required degree of flexibility to enable a degree of mechanical movement either for vibration, allow for other movement, or just to take up the mechanical tolerances which might otherwise not be possible. However care must be taken when using flexible waveguide as losses are higher, it can be expensive and it may have higher levels of passive intermodulation distortion. As a result, most lengths of flexible waveguide are relatively short.