IEC 62037-5-2021 pdf free download – Passive RF and microwave devices, intermodulation level measurement – Part 5: Measurement of passive intermodulation in filters.
4 General comments on PIM testing of filter assemblies
4.1 Sources of error: back-to-back filters
Testing filter assemblies for PIM can be error prone if certain precautionary guidelines are not followed. Since PIM can be a frequency-dependent phenomenon, mathematically related to the harmonics of the input signals and combinations thereof, consideration should be given not only to the behaviour of the test set-up under fundamental stimulation, but also its harmonic performance. In particular, consider a receive-band PIM test set-up as shown in Figure 1 . As shown, this set-up could be used to measure the PIM in a two-port device under test (DUT); however, the accuracy of the measurement could be in question due to the back-to-back filters (diplexers) used.
While the diplexers certainly appear as a matched load around the fundamental frequencies andreceive-band lM products, they can be very poorly matched at the harmonics of the fundamentals.A poor match will set up a standing wave at the harmonic frequencies which can re-illuminateany PlIM sources within the DUT with higher-than-typical current densities. Furthermore，themeasured lM response will become highly dependent upon the electrical length of the DUTbecause the locations of the peaks and valleys of any standing waves will move with respect tothe PlM sources as the electrical length of the DUT changes.
4.2Environmental and dynamic PIMtesting
Environmental and dynamic PlM testing，which can include placing vibrational or thermalstresses upon filter assemblies while concurrently measuring the PlM produced，may not giveaccurate or repeatable results.There are several significant factors affecting the results of thesetypes of PIM tests.
a) DUT/test system isolation – it is highly desirable that any environmental and dynamic stresses placed upon a DUT be isolated from the test system such that there are nomeasurable residual effects. This not only addresses the practical issues of test systemreliability and maintenance, but it directly affects the issue of measurement repeatability.That is, should a particular piece of the test system require replacement after a set numberof trials, then the results of subsequent measurements may be skewed by the performanceof the replaced part.
b) Measurement repeatability – it should be possible to repeat the results obtained from a particular measurement within a specific precision.However, the inherent sensitivity of thePIM response can prevent a desired precision from being achieved.
c) Stress repeatability – the particular stress placed upon the DUT shall be repeatable both between tests upon the same DUT and tests between different DUTs. However，in theexperience of many, it is likely that the repeatability of the particular stress will be far worsethan that of the particular PlIM test results so that the standard specifying the stress may notbe unnecessarily rigorous.
Based upon these factors, measuring PIM from a filter assembly whilst it undergoes thermal orvibrational stresses is not currently recommended.
A less vigorous form of dynamic testing should be performed on a filter assembly in order todemonstrate that stability of the PIM level is maintained after certain stresses have been applied.This style of dynamic test typically takes the form of striking the assembly with an instrumentthat will not damage the surface of the assembly.The impact of this tapping shall be at leastthat described in lEc 60068-2-75:2014,Clause 7 for the 0,14 J drop, with conditions given inIEC 60068-2-75:2014,Table 1 and Table 2, that is,a 0,25 kg striking element of polyamide(Rockwell hardness: 85<HRR<100) dropped from a height of 56 mm.
The impact shall be applied as close as possible to each of the connectors of the filter,whilestill impacting the filter body.The impact near each connector shall be repeated three times.Also, for any side of the filter that has no connectors, three impacts shall be applied along oneedge of that side. The shape of the striking element shall be the same as described inIEC 60068-2-75, for ≤ 1 J.An example， taken from lEC 60068-2-75:2014,Annex A, is shownFigure 2.IEC 62037-5 pdf download.