The intention of the proposed development was to design, manufacture and qualify a dual TX/RX C-Band OMT, which would complete the work already initiated two years ago with another ARTES 4 activity: "C-Band Low Mass feed".
This previous activity intended to demonstrate that a significant reduction in mass of C-Band Antenna Feed Horns was achievable. This activity has been successfully completed with the qualification of a C-Band Feed Horn, working at Rx and TX frequencies (3,6-4,2 GHz & 5,925-6,4 GHz), and with a mass of 1,4 Kg. while the currently existing feed horns have a mass around 3 Kg. A high power and low PIM Tx/Rx Diplexer was also successfully developed, manufactured and tested in the frame of this activity.
Now, to complete the previous development , the design and qualification of the polariser for this horn, an OMT, was carried out. It completes a feed that has the same performances than competence feeds with a total mass around 3 Kg. vs. the current existing feeds mass around 6 Kg.
The main challenges of the activity could be summarized in the following points:
- Mass: The mass is the key parameter for the success in the market.
- Design compactness
- Performances in line with market existing designs (state or art).
The design of an OMT covering two frequency bands, with a bandwidth around 10%, separated almost one octave is always a complex exercise. The main difficulty is focused in the necessity to built the Tx OMT area in a symmetric way, to avoid high order mode generation for Rx frequencies. This produce, and mainly in C-band, a complex device geometry, with multiple pieces connection (PIM risk multiplication) and its associate high mass and dimensions.
More than 40% of communication satellites use the C-Band and, only serving North America there are over thirty C-band GEO satellites. Most of this C-band satellites use linear polarization and only a few number of them (e.g. old Intelsat satellites) use circular polarization. Therefore the potential market for the proposed C-Band feeder configuration is very large.
In principle, we could have been in the position of providing this C-Band Feeder if we would have it qualified and it was competitive enough. Under this assumption, the potential initial target market is more than enough to recover the investment and to justify the completion of this C-Band low mass feed development.
The competitors for feed are mainly the own satellite primes, since they are using their own designs, some of them quite obsolete, to cover the lack of potential external suppliers. We count on the close relationship with some of the main primes and we will try to take advantage of that to gain a position in this market as we have done for other equipments in the last five years. RYMSA has also the big advantage of being a horn and polarisers manufacturer so its specialization and expertise its an important competitive advantage which results in very competitive costs. RYMSA has in-home facilities to fully manufacture and test a this low mass feed without subcontracting any recurring activity and this allow us to offer a very competitive schedule and price.
The OMT has four WG inputs and a common circular WG. The OMT consists of junctions and filters running in WG. The common arm (antenna port) is in square WG. The common port is fed by four inputs. (Tx-V, Tx-H, Rx-V and, Rx-H). The OMT inputs operate in fundamental model (TE10) in rectangular WG.
The four OMT Inputs (TE10 single mode) are named as Tx-V / Tx-H / Rx-V / Rx-H. The names are associated to the dominant polarization (V or H) generated in the OMT antenna port, and also to the operating band (Tx or Rx).
The antenna (Common) port is named as AP. AP supports in circular WG two operating modes; TE11 (AP-V and AP-H) in linear polarization.
The requirements stated in the following table have been derived from the total assembly (horn + OMT requirements) requirements and are applicable under operating thermal and temperature conditions and along the device operating life.
|Receive band (Rx)||GHz||5.925-6.425|
|Tx WG interface||---||WR-229|
|Rx WG interface||---||WR-137|
|Return losses||dB||<-20 dB||For any input and output port|
|Tx Insertion losses||dB||<0.25||Any Tx port to AP port|
|Rx Insertion losses||dB||<0.3||Any Rx port to AP port|
|Polarization purity (AP)||dB||>35||For any input port|
|Tx-Isolation||dB||>30||Between Tx-H & Tx-V ports|
|Rx-Isolation||dB||>30||Between Rx-H and Rx-V ports|
|Isolation between Tx-Rx inputs||dB||>30 Tx band
>30 Rx band
|Between Tx-Rx ports of same polarization|
|Tx- power handling||W||350 CW
|Multipactor Margin||dB||6dB||Applicable to Tx ports|
|PIM (at Rx band)||dBm||-140dBc||2 Tx carriers of 100W (6th order)|
|Mass||Kg||1,6||Expected mass 1,4 kg|
|Size||mm||330 (L) x 400 (W) x 300 (H)||Expected: 330 x 400 x 150|
The OMT photograph is shown below:
The Design implementation plan devised for the C-Band OMT pursues as main objective to qualify an EQM of the C-Band OMT which fulfils the goal requirements established in previous section, within the schedule and cost constraints.
The background experience has streamlined the overall development programme in two phases: Design (this phase covers the requirements confirmation, concept selection and detailed design for the C-Band OMT) and Qualification (once the detailed design is completed and the CDR successfully surpassed, the EQM for the OMT will be manufactured and tested).
The design of C-Band OMT was developed and CDR meeting was held on January 2007. An EQM was manufactured and successfully submitted to a complete qualification test campaign.