The Importance of
Low PIM Components
Author Tony Ramsden, President of Microlab
Why are Low PIM Components Important
• What is PIM, and what causes it?
• What is the effect of PIM?
• What can be done to control it?
What is Intermodulation?
• Intended Intermodulation
– Interaction of 2 or more signals
to produce new signals, such as
in a mixer which is designed to
be a non-linear device.
– Signals at frequencies A and B mix to produce new
signals at frequencies (A+B) and (A-B).
– If harmonics are also present at 2A and 2B, we’ll also
see signals at 2A+B, 2A-B, A+2B and A-2B.
What is PIM (Passive Intermodulation)?
• PIM is simply Intermodulation caused by
passive components such as:
– Coaxial Cable and Jumpers
– Filters, Power Dividers, Couplers, etc.
– Any RF signal path discontinuity, especially connectors
and connections
– In fact, whenever the RF signal sees a non-linearity,
Intermodulation will be produced.
Why should PIM be important?
• The spurious produced by a passive source
must be so low level, so why does it matter?
• The problem occurs in wireless systems
because Tx and Rx signals frequently share
the same signal path.
• This means that 2 large Tx signals can mix
and produce a spurious in the Rx band where
even a very, very small Tx PIM signal can
look like an Rx signal.
Primary Effect of PIM
• Unfortunately, the receiver, looking for the
true Rx signal sees the spurious as real.
• If the spurious signal is stronger than the
true, then the receiver desensitizes and the
call is dropped.
• As ‘Dropped Calls’ increase, revenue falls,
and Customer Churn increases.
!
Controlling Passive Intermodulation
• Starts by having Low PIM components
whenever signal levels are large, say >3W
– Connectors and cables need to be low PIM
– Signal Combiners should be Low PIM Hybrid
Couplers/Matrices or Diplexers
– Cavity Filters for narrow band Duplexer functions
– All Attenuators and Terminations must be Low PIM
• Controlled Installation – Torque wrenches!
• Available in-service signal monitoring and
alarms, particularly of dropped calls
Critical PIM Areas
• Signal Combining Systems
– Neutral Host Combiners
– Broadband Antenna Signal Combiners
• High Power Distribution
– Initial Signal Splitters for In-Building
– Surge Protection Components
• High Power Attenuation/Termination
– Prevent PIM being reflected back
So where does Microlab Fit In?
• Microlab has developed the ‘know-how’
to design and produce low PIM products
• In design
– Choosing the right materials
– Using PIM friendly interfaces, connectors
– Minimizing all metal-to-metal contact
• In manufacture
– Following processes explicitly, no short cuts!
– Testing 100% for PIM performance
Low PIM Products from Microlab
• Splitters, Couplers & Tappers
– Reactive styles using air dielectric are the low PIM choice
– Stripline, if designed properly, can be low PIM
– Wilkinson designs are inherently poor PIM, as they
include carbon resistor elements
• Low PIM Attenuators and Terminations
– Terminator/Attenuator Powers from 10 to 100W
– Portable Loads for troubleshooting PIM problems
Low PIM Signal Combining Products
• Broadband Diplexers
– Combine Wireless Bands without appreciable loss
• Hybrid Derivatives
– 2 x 2, 3 x 3 and 4 x 4 Hybrid Couplers
– Simultaneously combine and split signal with
minimal loss
• Neutral Host Combining Systems
– Assemblies of Diplexers and Hybrids
Diplexers to Join Wireless Bands
• Planar or Cavity?
– Planar are broadband, low PIM
friendly
– Broadband = Common Off-theShelf Designs for Tetra/P25,
Cellular, PCS, UMTS, LTE, WiFi
including 5.8 GHz
– Cavity are suited to narrowband
needs
– Narrowband = Usually task specific
– Difficult to achieve low PIM
New Diplexer 80–960/1710-2700 MHz
Ultra Wideband for Combining Band Extremities
BK-12N
Diplexer adds Tetra/LMR to Wideband
• Adds 80 – 520 MHz to 700 – 2700 MHz
– Low loss, <0.3/0.5 dB low band/high band
– High Isolation, >50 dB
– Low PIM
LTE-2600 Low PIM Diplexer Filters
Combine to 80 – 2170 MHz
Add to 1710 – 2170 MHz
Add to 698 – 960 MHz
• Inject LTE-2600 to existing bands
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50 dB Isolation
80W – 250W/input power
Minimal Path Loss
PIM <-150 dBc; -160 dBc typ.
Small, lightweight
Diplexers for WiMAX/WiFi 3.3 – 5.9 GHz
Coming Soon
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0.38-2.7 / 3.3-6.0 GHz
>50 dB Input Isolation
Low PIM, <-150 dBc
Average Power:
>50W Low and >5W High
Band
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2.4-3.8 / 5.15-5.9 GHz
>50 dB Input Isolation
Low PIM, <-150 dBc
Average Power:
>20W Low and High Bands
700/850 MHz LTE/Cellular Combiner
Diplexer Combines 698 – 793
MHz with 824-894 MHz
Triplexer adds 1710 – 2170 MHz
Low PIM Hybrid Couplers
• Microlab is the World Leader in Hybrid Couplers for
Wireless
– 2 x 2 is the standard, 4 x 4 is well appreciated
– 3 x 3 is now becoming known; Also 4:2, 3:1, etc.
• Hybrids are the Signal Combining Building Block
– Signals can be very close to each other and yet do not interfere with
each other
– Hybrids do not have the negative aspects of filters
– Hybrids can be used to enhance filter systems
• Microlab Hybrids are all High Isolation and Low PIM
• Combined with low PIM Loads they are an effective way
of adding signals which are close together
3dB Hybrid Couplers/Combiners
Micro Base
Stations
A+B
2
System A
Hybrid
Coupler
System B
A+B
2
Hybrid Coupler allows sharing of antenna distribution
network between signals/service providers
Basic 2 x 2 Multi-Band Hybrid Couplers
Standard for Highest Isolation,
160W for 698 – 2700 MHz
Ultra Broadband
Now 350 – 6000 MHz
Hybrids with Exceptional Performance
698 – 2700 MHz with >30 dB Isolation
Narrow and Broad Bandwidths
<-150 dBc PIM standard
400W for 698 - 2700 MHz
Multi Casting Matrix: MCM
4 Hybrids become an MCM
• New 4 x 4 Hybrid series
• up to 30 dB isolation
• Low Loss, Low PIM
• Cover 350-2700 MHz
• common connector
spacing!
Then a 4 x 4 Matrix
Wideband 3 x 3 Hybrid Matrices
698 – 2700 MHz
25 dB Isolation
Low Loss, Low PIM
The General Purpose Combiner Box
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4 Low Band (698 – 960MHz) Inputs
4 High Band (1710 – 2700 MHz) Inputs
High Isolation (>22 dB in-band; >55 dB intra-band)
4 Combined Outputs, PIM <-142 dBc (+43 dBm x 2)
Broadband Combiner Box – KM-90
Expanding the Capability with Tetra
Adding Four 380-520 MHz Inputs with no additional Loss
How do we do it?
We can even expand up and down!
Adding Four 380-520 MHz and Four LTE-2600 Inputs with
No Additional Loss for 16 Channels
16 Inputs To Each Of Four Outputs
TETRA Combining Box
• Combines Public and 1 Private Tetra to All Mobile
Channels, 698 – 2700 MHz
Alternate could be:
One Tetra
One GSM-850
One UMTS-2100
One LTE-2600
…feeding to two outputs
Low PIM Terminations
Portable 50W
Dual DIN model
• Hermetic Cable Loads at 10, 30 & 100W
• Exceptionally low PIM, <-160 dBc
• <1.1:1 VSWR (>27 dB Return Loss)
Hybrid Combiners for Low Powers
• 2:1, 3:1 & 4:1 Hybrids
• 698-2700 MHz Band
• Integrated Loads from 3W
to 25W
• Low PIM if required
Low PIM Hermetic Hybrid Combiners
• 80W Broadband Combiner
• 25 dB Isolation
• Higher Powers and Isolations for narrower bands
• Single and dual versions, IP67
Low PIM Attenuators (698–2700 MHz)
100W
30W
In-Out now on
Opposite Faces
New 1 & 1.8 dB
Attenuation
Values
N or 7-16 mm
• Hermetic Attenuators from 1 to 30 dB
• Powers from 30 to 150W
• Exceptionally low PIM, <-160 dBc
• <1.2:1 VSWR (>21 dB Return Loss)
So Why Do We Need Low PIM?
• Remember, the receiver, looks for the true Rx
signal and sees the spurious as real.
• If the spurious is stronger than the true, then the
receiver desensitizes and the call is dropped.
• As ‘Dropped Calls’ increase, revenue falls, and
Customer Churn increases.
The Solution: Use Low PIM Components
From Microlab, of course!

WTG Regional Technical Contacts
for Additional Questions
• Mr. James Lim - JLim@wtcom.com
• Mr. Tony Lin - Shanghai, China - TLin@wtcom.com
• Mr. Steven Shaw - Manchester, UK - SShaw@wtcom.com
• Mr. Bob Muro - Parsippany, NJ - RMuro@wtcom.com