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In the last SPOTLIGHT issue, two new high-quality L-shaped R120 waveguide rotary joints (BN 635725 and 635726) with a design particularly adapted to the use with Ku-band satellite communication systems within a tight budget were presented. Due to the high demand for rotary joints for such types of application, further models have been now designed both for use with the C-band and the Ku-band. All models have a precise and yet cost-optimized design, using plain chromatised casings made from a seawater-resistant aluminium alloy. Identification of all stated models is made by means of abrasion-resistant laser engraving. As with the models BN 635725 and 635726, this rotary joint only makes use of selected parts and tightly tolerated, contactless coupling systems. Thanks to precise and careful assembly, the excellent RF parameters and the lowest possible series variations are achieved. These models, including those in the SPINNER rotary joint product range from now on, are individually presented below.
This rotary joint is a versatile I-shaped R120 waveguide rotary joint for Ku-band satellite communication systems. Its basic design is mainly similar to BN 635725. This rotary joint also offers IP40 protection and is intended for use within closed casings or internal spaces.
Compared to the L-shaped rotary joint BN 635725, it proved possible for the usable frequency range of this rotary joint to be extended to 10.75 to 14.50 GHz so that the transmission and receiving frequency ranges are covered equally. The minimization of critical contact locations results in a particularly low insertion loss that is typically below 0.1 dB, as well as excellent series stability and high durability over the full specified temperature range.
This special rotary joint is also designed for use in Ku-band satellite communication systems. Such communication systems make use of the fact that additional isolation between transmit and receive signals can be achieved by an orthogonal polarization of these signals (polarization duplex). Technically, this is realised by circular waveguides operated with two orthogonal H11 modes and a special waveguide coupler (ortho mode transducer, "OMT") for the separation of RX and TX signals.
Being a dual-mode H11 circular waveguide rotary joint, this model is used when fixed dish aerials from VSAT terminals need to be connected to the circular waveguide port of an OMT on a rotary basis, for example. This allows for the swivelling of the OMT around its roll axis so that the rotary or swivelling OMT can always be aligned with the corresponding polarization level of the aerial signal. For this, an additional rectangular waveguide rotary joint such as 635725 or 635730 would be required at the axial TX input port of the OMT.
The design of the contactless joint system and the precise bearing allows for a significantly increased stability of all RF parameters over rotation compared to the products of other manufacturers, as well as for a highly improved intermodulation behaviour and an extraordinary separation of the orthogonal H11 waves usually totalling more than 60 dB. The typical values for VSWR are below 1.1; the insertion loss is usually below 0.05 dB.
The conical design of the circular waveguide (19.05 mm on 17.42 mm) allows for a low-reflection combination of standard OMTs with a waveguide diameter of 19.05 mm and aerials with a lower waveguide diameter without any discontinuities. And it goes without saying that any corresponding customer-specific adjustments, such as assembly flanges or waveguide diameters, can be realised without any problem.
BN 634915 & BN 634915C0001
In response to several customer requests, two further C-band rotary joints have been created in addition to the Ku-band rotary joints stated above. These I-shaped waveguide rotary joints are equipped with R70 waveguide flanges (CPR137/G) and cover the frequency range between 5.8-7.0GHz. These models are a cost-reducing supplement to the well-known standard rotary joint BN 634912 and can be used for applications where the extreme average power rating and tightness offered by the BN 634912 are not required. Nevertheless, these IP40-protected models offer extraordinary technical parameters, high manufacturing consistency and the extremely high stability of all RF parameters during rotation.
The only difference between the two models is in the design of the casing. The BN 634915 is equipped with an assembly flange, while the BN 634915C0001 version features identical internal equipment but without a flange.
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