1055497-1 Datasheet, PDF (281/320 Pages) Tyco Electronics – RF Coax Products

RF Coax Connectors
Appendix C - Intermodulation in RF Coaxial Connectors
Product Facts
■ High quality plating to 6µm
for IM-sensitive products
■ Restrict materials to copper
and its alloys
■ Avoid the use of stainless
steel, nickel, ferrites, etc.
in the signal path
■ Quality machining
■ Ensure, by design, a prop-
erly defined contact inter-
face at connector, panel and
contact interfaces
■ Avoidance of crimps
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The increased demand from the mobile
communication industry to provide greater
channel capacity coupled with the increased
sensitivity of receivers has exposed a condi-
tion within RF Coaxial Connectors referred to
as Intermodulation Distortion (IMD). This
condition occurs when non-linearities within
the connectors act as imperfect diodes to
generate other frequencies known as
Intermodulation Products (IMP). Some of
these frequencies appear within the receive
band and effectively block the channel. The
purpose of this application note is to outline
the basic causes of Intermodulation and the
techniques Tyco Electronics has undertaken
to minimize this condition.
IM Basics
Modern developments in base stations for
GSM, DCS 1800 and PCS 1900 have
necessitated the use of “7-16”, “4.1/9.5”
and “N” connectors due to the increased
power requirements. The requirements for
performance are typically in the order of -
160 dBc to -163dBc (when working in dBc)
or -120dBm (when working in dBm), both
with 2 x (+43dBm) tones. The requirement
is so stringent because the connectors are
used in post-filtering sections of the transmit
path (between the diplexer and the
antenna) and also because the system is a
full duplex system where the multiple-carrier
transmit path is also the receive path. In a
truly linear system, the output is directly
proportional to the input, following the form
of y=mx+c (see fig. 2). Coaxial connectors
have traditionally been viewed as following
this pattern. In reality, there have always
been non-linearities present in coaxial con-
nectors. These were not readily apparent as
the resultant IM products were significantly
below the noise floor of the system due to
relatively weak carrier signals. This situation
becomes apparent when the incident power
is raised above 30 dBm.
The small non-linearities have a character-
istic similar to a square-law (see Fig 3). The
distortion to the waveform is evident, the
Fig. 2
12 _Linear
10
8
6
4
2
0
Linear vs. Non-linear Response
Fig. 3
120 _Non-linear
100
80
60
40
20
0
Catalog 1307191
Revised 3-07
www.tycoelectronics.com
Dimensions are in millimeters
and inches unless otherwise
specified. Values in brackets
are standard equivalents.
Dimensions are shown for
reference purposes only.
Specifications subject
to change.
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Canada: 1-905-470-4425
Mexico: 01-800-733-8926
C. America: 52-55-1106-0803
281
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