Product Feature
Rotary Joints
for SatCom
Applications
Executive Interview Series
MWJ speaks with Klaus-Dieter Beck, Head of Sales and Marketing, Radar and
Satellite Division, Spinner GmbH.
Visit www.mwjournal.com to read this in-depth interview.
M
s Fig. 1
odern mobile satellite communication systems provide bidirectional
broadband network access for moving
ground, maritime and airborne terminals. Applications enabled by mobile SatCom systems
include broadband Internet access, video conferencing and data transmission. Currently such
systems—commonly called SatCom on-themove—are being introduced on a large scale
all over the world for commercial as well as for
governmental (civilian and military) use. For
mobile SatCom equipment the commercial Kuband is often chosen since this frequency range
offers a trade-off between reduction of antenna
size on the one hand, and reasonable resistance
to adverse weather conditions on the other.
A moving satellite terminal requires a highly
sophisticated beam steering system in order to
continuously track the satellite during operation. There are two basic technologies that can be employed
for pointing an antenna beam:
The electronically phased-array
antenna and the mechanically
steered pencil beam antenna.
When the latter system is
used, the strong space restricU- and L-shaped variants of the
tions imposed by a mobile Sat-
new Ku-band rotary joint family.
106
Com terminal require the adoption of a small
aperture antenna together with a low-profile
pedestal. Likewise the rotary joints employed
for signal transmission along the mechanical
steering axes need to be small and often shaped
specifically for the application.
Therefore, in order to provide equipment
manufacturers with rotary joints tailored to the
specific requirements of fixed and mobile SatCom systems, Spinner has developed two new
rotary joint product families—single channel
waveguide rotary joints for Ku-band, and dual
channel coaxial rotary joints, which are suitable
for Ku-band and intermediate frequency applications.
Both product lines follow a common design philosophy that is characterized by wellthought-out modularity that allows a large variety of solutions with a minimum number of different piece parts and excellent electrical and
mechanical performance, allied to a simple and
highly reliable design.
SINGLE CHANNEL ROTARY JOINTS
Figure 1 shows the U-shaped and L-shaped
Spinner GmbH
Munich, Germany
MICROWAVE JOURNAL n AUGUST 2009
Product Feature
0
–5
–10
–15
–20
–25
–30
–35
–40
10
s Fig. 2
0
–0.1
–0.2
–0.3
DL
UL
–0.4
–0.5
–0.6
–0.7
–0.8
14 15
11
12 13
FREQUENCY (GHz)
Typical frequency response of the
new Ku-band rotary joint family.
108
TABLE I
KU-BAND SINGLE CHANNEL WAVEGUIDE ROTARY JOINTS
Model
Case style
Interface center
distance(s)
BN 635710
BN 635709
I
L
U
65 mm / 22 mm
52 mm / 22 mm
Frequency range
10.7 to 14.5 GHz
Return loss, min./typ.
20 dB / 23 dB (see Figure 2)
Insertion loss, max./typ.
0.2 dB / 0.1 dB (see Figure 2)
Insertion loss variation,
max./typ.
0.1 dB / 0.02 dB
Peak power, max.
Average power, max.
Interfaces
the low insertion loss and the method
of construction, with large cross-section metallic parts that allow for efficient axial heat removal towards both
ends of the joint.
Besides good RF performance the
Ku-band rotary joints are characterized by a dust-tight design that is protected against water jets (protection
level to IP65) by the inclusion of a dy-
s Fig. 3
I- and L-shaped variants of the
new dual channel rotary joint family.
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BN 635707
74 mm
INSERTION LOSS (dB)
RETURN LOSS (dB)
members of the product family, while
the main characteristics of the Kuband waveguide rotary joints are
summarized in Table 1. Although
realized in a non-contacting design,
the Ku-band family is characterized
by wide frequency coverage (relative
bandwidth of 30 percent and above).
An advanced electromagnetic design
employing two stepped impedance
transformers makes it possible to cover the full satellite band portion of the
Ku-band with a high return loss and
low insertion loss (see Figure 2).
These rotary joints are suitable for
downlink frequencies (10.70 to 12.75
GHz) and uplink frequencies (13.75
to 14.50 GHz) as well as for the guard
band in between. This last feature is being demanded by more and more customers. Figure 2 shows that any parasitic resonances are placed clearly outside
the specified transmission band.
Another significant feature of the
single channel rotary joints is that they
are able to handle high average power
levels safely. This feature is a result of
5 kW
600 W
PBR120 and/or UBR120 mod.
namic seal. In order to accommodate
this seal the torque is increased and
the housing slightly lengthened, but
both are kept to a minimum.
DUAL CHANNEL ROTARY JOINTS
The newly introduced dual channel rotary joints belong to a universal
product family that covers different
preferential frequency ranges, different case styles and flanges. The predecessor to this family is the multipurpose rotary joint BN153118 that is
shown on the left of Figure 3.
Its main characteristics are summarized in Table 2. This dual band rotary
joint and its derivatives are realized
with galvanic contacts at the center and
outer conductors. As a result of this design each channel enables combined
RF and DC transmission. This DC
MICROWAVE JOURNAL n AUGUST 2009
Product Feature
TABLE II
BN 153118 MULTI-PURPOSE DUAL-CHANNEL ROTARY JOINT, I-STYLE
Channel
Frequency range
VSWR, max.
VSWR variation, max.
Insertion loss, max.
Insertion loss variation,
max.
CH1
CH2
DC to 18 GHz
DC to 18 GHz
1.35 @ DC to 8 GHz
1.5 @ 8 to 18 GHz
2.0 @ DC to 4 GHz
2.5 @ 4 to 8 GHz
3.5 @ 8 to 12 GHz
4.5 @ 12 to 18 GHz
0.1
0.1 @ DC to 4 GHz
0.4 @ 4 to 8 GHz
0.8 @ 8 to 12 GHz
2.0 @ 12 to 18 GHz
0.4 dB @ DC to 8 GHz
1.0 dB @ 8 to 18 GHz
0.5 dB @ DC to 4 GHz
1.0 dB @ 4 to 8 GHz
1.5 dB @ 8 to 12 GHz
3.5 dB @ 12 to 18 GHz
0.06 dB
0.1 dB @ DC to 4 GHz
0.35 dB @ 4 to 8 GHz
0.7 dB @ 8 to 12 GHz
1.5 dB @ 12 to 18 GHz
Isolation, min.
Interfaces
Size
50 dB
1.5-3.5 female, fully compatible to SMA
45 mm flange dia. x 32 mm OD x 56 mm length
transmission makes it possible to supply active components on the rotating
part of a platform (e.g. an LNA).
Besides the I-shaped models like the
one shown on the left in Figure 3, the
new product family also includes rotary
joints with L-shaped (shown on the
right in Figure 3) and U-shaped housings that allow for a space-saving antenna pedestal design. These L-shaped
and U-shaped variants significantly
simplify the integration of the rotary
joint. In order to cover a large variety
of customer needs, the different basic
case styles are available with standard
and custom specific mounting flanges.
The different housing variants described above are just one advantage.
Moreover, specialized versions are
available that incorporate application
specific tuning of the second channel
in order to fulfill more stringent performance requirements within a dedicated frequency range. The L-shaped
rotary joint BN 153146 shown on the
right side of Figure 3 is an example of
a variant optimized for SatCom use.
As a result of this optimization channel, CH2 of BN 153146 clearly outperforms channel CH2 of BN 153118
with respect to all RF parameters. At
the expense of a narrower usable frequency range, channel CH2 of BN
153146 does now comply with a VSWR
below 2.0 (compared to 3.5), a VSWR
variation during rotation less than 0.5
(compared to 0.8), an insertion loss below 1.0 dB (compared to 1.5 dB) and a
110
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s Fig. 4
Custom specific combination of
a dual channel rotary joint with a slip ring
assembly.
maximum insertion loss variation of 0.4
dB (compared to 0.8 dB).
For applications that require a contacting transmission of supply power
(DC, AC) or low frequency signals
(analog, data), the dual channel rotary
joints are also available in combination
with standard and customer specific
slip ring assemblies. Figure 4 shows a
typical combination of an I-style rotary
joint mounted within such an assembly.
CONCLUSION
These two new SatCom rotary
joints that have been introduced by
Spinner define a reference standard
in electrical and mechanical performance. The Ku-band single channel
waveguide rotary joints stand out due
to their extremely wide transmission
band. The dual channel rotary joint
family features a unique variety of
shapes in conjunction with its excellent RF data.
Spinner GmbH, Munich, Germany
+49 89 12601 1160,
info@spinner.de.
RS No. 301
MICROWAVE JOURNAL n AUGUST 2009