IEC 62037-1-2021 pdf free download – Passive RF and microwave devices, intermodulation level measurement – Part 1: General requirements and measuring methods.
4Characteristics of intermodulation products
PIM interference is caused by sources of non-linearity of mostly unknown nature, location andbehaviour. A few examples are inter-metallic contacts, choice of materials,corrosion products,dirt,etc.Most of these effects are subject to changes over time due to mechanical stress,temperature changes,variations in material characteristics (cold flow， etc.) and climaticchanges.
The generation of intermodulation products originates from point sources inside a DUT andpropagates equally in all available directions.
The generation of passive intermodulation (PIM) products does not necessarily follow the lawof the usual non-linear equation of quadratic form. Therefore，accurate calculation to otherpower levels causing the intermodulation is not possible and PIM comparisons should be madeat the same power level.
Furthermore, PlM generation can be frequency dependent. When PlM generation is frequencydependent, the PlM performance shall be investigated over the specified frequency band.
5 Principle of test procedure
Test signals of frequencies f， and f2 with equal specified test port power levels are combinedand fed to the DUT. The test signals should contain a harmonic or self-intermodulation signallevel at least 10 dB lower than the expected level generated in the DUT.
The PIM is measured over the specified frequency range.The intermodulation products of order(2f1±82).(2f2 ±f1), etc., are measured.
In most cases,the third order intermodulation signals represent the worst-case condition ofunwanted signals generated;therefore, the measurement of these signals characterizes theDUT in a sufficient way.However, the test set-ups given in Clause 6 are suitable for measuringother intermodulation products.
ln other systems (such as CATV), the third order may not be as applicable in characterizing theDUT.
lIntermodulation can be measured in the reverse and forward direction.Reverse and forwardrefer to the direction of propagation of the most powerful carrier.
6Test set-up
6.1General
Experience shows that the generation of intermodulation products originates from point sourcesinside a device under test (DUT) and propagates equally in all available directions. Therefore,either the reverse (reflected) or the forward (transmitted) intermodulation signal can bemeasured.
Two different test set-ups are described in Figure 1 and Figure 2 and are for reference only.Other topologies are possible.
Set-up 1 is for measuring the reverse (reflected) intermodulation signal only, and set-up 2 is formeasuring the forward (transmitted) intermodulation signal.The measurement method (reverseor forward) is dependent upon the DUT. The set-ups may be assembled from standardmicrowave or radio link hardware selected for this particular application.All components shallbe checked for lowest self-intermodulation generation.
Experience shows that devices containing magnetic materials (circulators,isolators, etc.) canbe prominent sources of intermodulation signal generation.
See Annex B for additional set-up considerations.
6.2Test equipment
6.2.1General
Two signal sources or signal generators with power amplifiers are required to reach thespecified test port power.The combining and diplexing device can comprise a circulator, hybridjunction，coupler or filter network.
The test set-up self-intermodulation generated (including contribution of the load) should be atleast 10 dB below the level to be measured on the DUT.The associated error may be obtainedfrom the graph in Figure 3.
The DUT shall be terminated by a load for the specified power if necessary.The receivingbandpass filter, tuned for the desired intermodulation signal, is followed by a low noise amplifier(if required) and a receiver.
See Annex B for additional set-up considerations.
6.2.2Set-up 1
This set-up is for measuring the reverse (reflected)lM-product and is therefore suitable for one-port and multi-port DUTs.On multi-port DUTs, the unused ports shall be connected to a lineartermination.See Annex A for information on low PIM terminations.
a) Generators
The generators shall provide continuous wave (cW) signals of the specified test port power.They shall have sufficient frequency stability to ensure that the lM-product can be detectedproperly by the receiver.The generators may be pulsed on and off while testing to reducepower consumption.
Some limitations apply when using pulsed generators. See Annex B for test procedureconsiderations when using equipment with pulsed generators.
b) Transmit-filters
The filters are bandpass filters tuned to the particular frequencies. They isolate thegenerators from each other and filter out the harmonics of f and f2-IEC 62037-1 pdf download.