IEC 61580-4:1997 pdf download – Methods of measurement for waveguides -Part 4: Attenuation of waveguide and waveguide assemblies

IEC 61580-4:1997 pdf download – Methods of measurement for waveguides -Part 4: Attenuation of waveguide and waveguide assemblies.
This part of IEC 61580 is applicable to attenuation of waveguides and waveguides assemblies. The objective of the test procedures given below is to characterize the attenuation.
2 General
The swept frequency method may be used to determine the attenuation.
The conditions tot attenuation measurements on waveguides are characterized by access to only one end or a very low loss to be measured or else by both together.
Four methods are presented hereinafter in order to cover each case:
Method 1: insertion method using swept frequency. It is used for general purposes.
Method 2: reflection method using swept frequency. It is used when only one end is available but there may be some limitations on the insertion loss values that may be measured.
Method 3: reflection method using discrete frequencies. Ills used when low attenuation Is to be measured and where one end only is available.
Method 4: uses an automatic network analyser. The use of an automatic network analyser requires that, for measurement on long lengths of waveguide, particular attention must be given to the number of frequencies and the frequency sweep rate selected. Care must be taken to ensure that any sharp peaks or troughs In the amplitude response are not effectively smoothed out to produce an erroneous result.
3 Test equipment
Suitable test set-ups are shown in figures I, 2 and 3. Other equivalent set-ups can be used by agreement between customer and supplier.
a) Sweep RF generator: the sweep rate should be slow enough to allow the chart recorder or plotter to reproduce the peak values faithfully.
b) Isolator: an isolator or an attenuator is included to prevent reflected waves affecting the output level of the generator.
C) Low.pass filter: a low-pass filter or a band-pass filter is included to eliminate spurious harmonic frequencies. In the case where the return loss of the low-pass filter is not good enou9h. it should be connected before the isolator providing the RF source is not adversely affected. Alternatively, if enough RF power is available, the filter match could be Improved by using a suitable well-matched attenuator.
d) Coupler: the error signal at the coupler(s) delector ports shall be insignificant compared to the signal level being measured. The error signal can be reduced by ensuring that the coupler ports (including adaptors) are well-matched and that the coupler has a high value of directivity (typically better than 45dB). Coupling values are usually 10dB to 20dB with a flat response across the required frequency band.
e) Calibrated attenuators: attenuators shall be Calibrated in the frequency band of the test.