When waveguide pieces or components are joined together, the coupling is generally by means of some
sort of flange. The function of such a flange is to ensure a smooth mechanical junction and suitable
electrical characteristics, particularly low external radiation and low internal reflections. The same
applies to rotational coupling, except that the mechanical construction of it is more complicated.
A waveguide coupler provides a means of sampling the energy travelling within a waveguide, and as
most couplers are directional in nature, sampling energy travelling in one direction, they are called
waveguide directional couplers.
Waveguide couplers are available that sample the energy travelling in both directions - these are known
as waveguide bi-directional couplers.
1.1.1. FLANGES
Atypical piece of waveguide will have a flange at either end. When two pieces are joined, the flanges are
bolted together; care must be taken to ensure perfect mechanical alignment. This prevents an
unwanted bend, step, either which would produce undesirable reflections. It follows that the guide ends
and flanges must be smoothly finished to avoid discontinuities at the junction.
a) Waveguide flange leakage
One aspect of waveguide flanges that is of particular importance is the leakage that occurs across the
joint. As the joints across the waveguide flanges are metal to metal contact, and they may not be
completely flat and perfect some leakage will always occur.
In order to improve the waveguide flange leakage caused by imperfect metal surfaces joining together,
many waveguide flanges incorporate a grove cut in either surface so that a gasket can be added.
The measurement of the actual leakage from a waveguide flange is very difficult. To attain a level of
consistency across measurements a standard procedure with defined test equipment and a given
environment need to be adopted.
However it is found that in general measurements made of the fields made using probes show a sharp
peak around the edge of the waveguide flange connection. Levels are typically around -130dBc, which
indicates a low level of leakage. To achieve this, the waveguide flange surfaces must be clean and bolts
must be tightened to the required torque level. Good RF gaskets also ensure these levels are maintained
or improved upon.
b) Waveguide flange insertion loss
As is likely to be anticipated there will always be some loss, even if small, caused by the introduction of a
joint, including the flange.
The waveguide flange insertion loss will arise mainly from two main factors:
Loss arising from leakage: The leakage through the joint between two waveguide flanges is
normally small, but in some instances a poor joint may give rise to measurable levels of loss due to
leakage.
Loss arising from flange resistance: If the two waveguide flanges are not bolted together tightly
enough, there will be resistance between the flanges. As the waveguide relies on the conduction in
the surface of the waveguide for its transmission, the resistance between the two waveguide
sort of flange. The function of such a flange is to ensure a smooth mechanical junction and suitable
electrical characteristics, particularly low external radiation and low internal reflections. The same
applies to rotational coupling, except that the mechanical construction of it is more complicated.
A waveguide coupler provides a means of sampling the energy travelling within a waveguide, and as
most couplers are directional in nature, sampling energy travelling in one direction, they are called
waveguide directional couplers.
Waveguide couplers are available that sample the energy travelling in both directions - these are known
as waveguide bi-directional couplers.
1.1.1. FLANGES
Atypical piece of waveguide will have a flange at either end. When two pieces are joined, the flanges are
bolted together; care must be taken to ensure perfect mechanical alignment. This prevents an
unwanted bend, step, either which would produce undesirable reflections. It follows that the guide ends
and flanges must be smoothly finished to avoid discontinuities at the junction.
a) Waveguide flange leakage
One aspect of waveguide flanges that is of particular importance is the leakage that occurs across the
joint. As the joints across the waveguide flanges are metal to metal contact, and they may not be
completely flat and perfect some leakage will always occur.
In order to improve the waveguide flange leakage caused by imperfect metal surfaces joining together,
many waveguide flanges incorporate a grove cut in either surface so that a gasket can be added.
The measurement of the actual leakage from a waveguide flange is very difficult. To attain a level of
consistency across measurements a standard procedure with defined test equipment and a given
environment need to be adopted.
However it is found that in general measurements made of the fields made using probes show a sharp
peak around the edge of the waveguide flange connection. Levels are typically around -130dBc, which
indicates a low level of leakage. To achieve this, the waveguide flange surfaces must be clean and bolts
must be tightened to the required torque level. Good RF gaskets also ensure these levels are maintained
or improved upon.
b) Waveguide flange insertion loss
As is likely to be anticipated there will always be some loss, even if small, caused by the introduction of a
joint, including the flange.
The waveguide flange insertion loss will arise mainly from two main factors:
Loss arising from leakage: The leakage through the joint between two waveguide flanges is
normally small, but in some instances a poor joint may give rise to measurable levels of loss due to
leakage.
Loss arising from flange resistance: If the two waveguide flanges are not bolted together tightly
enough, there will be resistance between the flanges. As the waveguide relies on the conduction in
the surface of the waveguide for its transmission, the resistance between the two waveguide
