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| Details for New Generations Right Angle Connectors and Adapters: |
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If there were such a thing as a perfect connector it would consist solely of an outer
conductor, a center conductor and a homogeneous dielectric, forming a perfect 50 .
line. A product that comes close to that perfection is an airline, as used for calibration and
testing with network analyzers. In reality, the regular straight connector is much more complicated,
full of irregularities and a number of capacitive and inductive sections, caused by
the conductors stepping up and/or down, to accommodate dimensional changes.
Also, the captivation of the center conductor with the outer conductor isolates the axial
and rotational forces associated with the coupling  of connectors from the elements to
which the center conductor is attached and maintains the specified dimensions at both
ends of the connector or adapter. Captivation techniques are epoxy, shoulder, single barb
and double barb. Although captivation adds necessary ruggedness, it also causes electrical
disturbance that has to be compensated for. The soldering process also has to be taken into
consideration. It is almost impossible to completely control the solder flow or to compensate
for excessive solder.
As can be seen, making straight connectors with tight tolerances is not easy, so making
parts that go around corners is even more complicated. Basically, angled connectors have
to be made from joining straight pieces together, or the straight components have to be
formed into the angled configuration, or a casting has to be manufactured, which usually
cannot be achieved within tight tolerances. All of these methods were evaluated when Spectrum
Elektrotechnik developed its SA2-Line (Smooth Angle Air) swept angled adapters and
connectors and MA2-Line (Mitered Angle Air) adapters and connectors.
TRADITIONAL METHODS
The swept angled connector (shown in Figure 1) or adapter is often considered to be the
best option, although it does have its drawbacks. One reason being that the outer conductor
is cast, but as liquid metal shrinks when cooling, the surface will never be
 smooth. In addition, the process dimensionally can only be controlled to a certain level.
Therefore, steel balls are forced through the outer conductor to make the surface smoother
and to get the dimensions to an acceptable level. The center conductor and the
dielectric are originally straight and then forced mechanically into the angled
body and through the bend. Also, when the dielectric (Teflon, PTFE or similar) surrounding the
stiff center conductor (usually beryllium copper) is forced through the angled
stainless steel body the ends of the dielectric may be deformed and
need to be machined off — a secondary operation. Additional parts for
the front and/or back end of the dielectric may need to be added as
 well. At the interface the center contact is also normally not completely in
line with the outer conductor. To bend a center conductor into a 90°
angle, it would need to be bent to an angle greater then 90°, depending on
the stiffness of the material. A further aspect that must be taken into consideration
is that the electrical performance of the product may change
over time. Another technique mentioned above is bend tubing, although
this method does not have much advantage over the cast product and is
prone to similar problems.
HIGH PERFORMANCE
Having taken these points into consideration, Spectrum Elektrotechnik
has developed new design and machining techniques to produce a
true mitered angled connector that exhibits superior performance. By
this method the outer conductor of the connector shown in Figure 2 has
been made in one piece, offering both mechanical and  especially electrical
advantages. Also, as parts are not joined mechanically, very tight
tolerances can be set. In fact, tolerances in the important areas at the
outer conductor internally are ±5 µm (±2/10,000 inches). As for the center
conductor and the dielectric, special machining and assembly techniques
are used, employing machined parts with similarly tight tolerances as
those applied to the outer conductor. The improvement of the electrical
performance is measurable, with the adapter, a TNC male to TNC female,
shown in Figure 3, having a VSWR of 1.15 max. up to 18 GHz, and the
typical performance being even better.
Similar performance is achieved with the complete MA2-Line N, TNC and SMA connectors and
adapters using a Teflon dielectric.
AIR DIELECTRIC
A completely different approach is needed to achieve such good performance
for the SA2-Line connector series using air as the dielectric
and a bead for captivation. Figure 4 identifies the different components
that make up the new Spectrum SA2-Line 2.4 mm connector.
 The adapter operates to 50 GHz and exhibits a maximum VSWR of
1.25 up to 50 GHz. The outer conductor is made from
two pieces that fit snuggly together and are designed with perfect alignment
guaranteed. The smooth angled airline section has been milled for optimum
performance and each part is completely finished when leaving the
computerized numerical controlled (CNC) milling machine, with no secondary
operation needed. Even the half threads are made during the primary
operation, guaranteeing that the threads meet and that the male and
female interface parts thread easily. The center contact assembly consists
of five parts, the three-piece center contact and two beads. The
smooth, bent part of the center conductor is the only part in the assembly
requiring a secondary operation. After machining it is bent to an angle
of exactly 90°, using special tooling. The ends are polished to the tolerance
requirement outlined earlier, before the part is sent out for plating.
A FULL RANGE
Figure 5 shows the S-parameter characteristics of the 2.4 mm right
angle adapter. In addition to the 2.4 mm connectors, other airline
adapters in the series include the 2.9 and 3.5 mm versions with a 1.85 mm
adapter currently under development. The adapters are available in
all sex configurations — male-tomale, female-to-female and male-tofemale
for 2.4, 2.9 and 3.5 mm connector configurations. The operating
characteristics of the 2.92 mm adapter are shown in Figure 6.
For these airline connectors and adapters the standard bead allows an
operating temperature of between –54° to +85°C. However, as these bead captivated
airline connectors are being required for higher and higher power applications
 and to operate in harsh environments, the company has developed
a new generation of beads that can operate with no degradation up to 150°C.
This bead is available for some of the connector series used in straight and
right angle configuration products and will be available shortly for all the connector
series from 7 to 2.4 mm. Also, the high power bead has similar electrical
performance as the regular bead, in terms of insertion and return loss.
Furthermore, glass beads have been developed for airline connectors
and adapters for hermetically sealed applications. At present the operating
frequency ranges of these hermetically sealed connectors and adapters,
straight or angled, do not cover the entire possible operating frequency
range of the connector series due to the higher dielectric constant of the
glass currently available.
CONCLUSION
This article began with a discussion of the perfect connector. There is no
such thing, of course, but with its new generation of right angle connectors
and adaptors, Spectrum Elektrotechnik has developed a family of high precision,
high performance components. This has been achieved by using the
latest manufacturing techniques and by working to tight tolerances.
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