Also, the layers can move relative to each
other during high-temperature assembly
processes, because the fibers in different
layers are oriented in different directions.
This may substantially reduce performance,
or even be catastrophic, for the high-precision
structures and placement necessary for
automated millimeter-wave assembly.
In the multilayer circuit board mentioned
earlier, MMIC Solutions uses new liquidcrystal
polymer (LCP) materials from Rogers. They eliminate such effects and enable
high-yield automated assembly of MMIC
chips and surface-mount components into
modules operating at 60 GHz and above.
Passive imaging at 100 GHz requires
very good receiver sensitivity, usually
specified as the noise equivalent temperature
difference (NETD), which is the
smallest detectable difference in wideband
noise, of around 0.7K. This requires a low
receiver noise figure (around 5 dB at 100
GHz) and very low high-frequency loss in
the module circuit board.
MMIC Solutions measures less than 0.2
dB/mm loss for a buried stripline in the
multi-layer LCP substrate of its MSi102
product for W-band imaging. The MSi102
mates to a standard WR-10 mechanical
interface, also formed in the module substrate.
The waveguide termination (backshort)
is formed by the lid used to encapsulate
the MMIC devices (Fig. 4).
In imaging, the packing density of an
array of receivers is additionally important in
determining the resolution of the image and,
therefore, in the system’s ability to detect
small objects that could be a threat. For this
reason, imaging arrays are perhaps the most
demanding of all millimeter-wave applications
on the small size of the module.
Using the latest multilayer substrates to
reduce size, MMIC Solutions developed
its latest MSi200 series receivers for imaging
systems. The modules are 18 mm long
by 8.5 mm wide by 5. 5mm high, and they
measure less than 850 mm3 in volume.
SUMMARY
Not all systems working in the millimeter-
wave band need small size, low weight,
and reduced cost to support increasing
volumes. Some military, aerospace, and
research radio and radar apps are inherently
small quantity-wise, for which “hand-tuning
by experts” is an appropriate solution.
But increasing demand to use the large
available bandwidth at millimeter-wave
frequencies for commercial systems and
services drives the need for new solutions.
Smaller, lighter components than the milled
metal blocks are welcomed by almost all
and demanded by some applications.