Spectrum Elektrotechnik GmbH

INTRODUCTION: There are applications where a stationary RF line needs to be connected to a rotating component.The Rotary Joint has been developed to service these needs, translating the electromagnetic energy from a stationary line to a rotating line. As the Rotary Joint is a dynamic device, the electrical performance depends very much on a reliable mechanical design that is engineered for the satisfaction of the dynamic requirements and the RF performance. The electrical specification of the Rotary Joint is not supposed to change over its guaranteed lifetime.

The Coaxial Line Rotary Joint: The device has coaxial input and output terminals and is using a transmission path that is also a coaxial line.For the electromagnetic propagation the TEM mode is used. The unit can usually cover a wide frequency range. The power handling capability is normally only restricted by the power limits of the connectors.

The Waveguide Rotary Joint: This device is using rectangular waveguide for input and output, and for the transmission line itself. The unit operates in the TE10 mode and can provide low VSWR at high power levels. As coupling for the rotation element, normally a noncontacting choke coupling is employed. The frequency band of operation is limited by the waveguide and in addition by the frequency sensitivity of the coupling choke.

The Waveguide to Coaxial Rotary Joint: For Input and output of the device rectangular waveguide is used, while the transmission line path is provided as coaxial line, connecting to the waveguide sections. The modes of operation are TE10 mode in the waveguide sections and TEM in the coaxial path. The operating frequency is limited by the waveguide, the power is limited by the coaxial part.

The Rectangular to Circular Waveguide Rotary Joint: Input and output of the device are provided as rectangular waveguide, the transmission line uses circular waveguide. The modes of operation are the TE10 mode in the rectangular sections and the TM01 mode in the circular waveguide. As coupling for the rotation element, normally a noncontacting choke coupling is used. The frequency band of operation is limited by the waveguide and in addition by the frequency sensitivity of the coupling choke.

Frequency Range: Spectrum Elektrotechnik GmbH has manufactured units in different frequency bands, usually designed exactly to the customers' specifications. Engineering is currently designing Standard Coaxial Rotary Joints for the frequency ranges DC-2.0 GHz, DC-18.0 GHz and DC-26.5 GHz, operating in a regular environment.
A rather simple design will meet all the requirements at lower frequency ranges, while only a most precise and state-of-the-art unit can be used at higher frequencies.

Rotary Joint Life: The life expectancy will mainly depend on the lifetime of the ball bearings, seals, and contact junctions. Other parameters that are limiting life, are rotational speed, and external mechanical loading, or pressurizing the unit. Harsh environment, subjecting the rotary joint to vibrations, shock, extremely low or high temperatures, humidity, etc. may further shorten the lifetime. It is therefore of utmost importance to identify in detail the environment the device is supposed to operate in.

VSWR:Every microwave component shows reflections and discontinuities within the circuit, as no design can be perfect, and manufacturing tolerances unfortunately do not allow perfect designs. VSWR is the ratio of the reflected signal and the incident signal. Rotary Joints are also characterized by the tendency of having to use a high number of parts. The tolerances on the dimensions need to be as tight as possible, not only for mechanical purposes, but also for electrical reasons, in order to assure that reflections cannot increase after some time of operation.