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Commercial success of future broadband interactive satellite networks depends in part on low user-terminal cost. Waveguide components used in these terminals require high dimensional accuracy and are costly when made with traditional machining methods which increases the cost of the terminal.
Previous studies have shown that injection-molded and metallized polymer components have the potential for both low-cost production and high performance from 10-30GHz. The main objective of this project is to determine the suitability and applicability of polymer technology for critical passive front-end components of low-cost satellite user terminals. The critical components include filters, orthomode transducers, and antenna feedhorns.
We seek to find the optimum combination of materials, component design and fabrication technology that can deliver the specified performance at the lowest cost in high-volume production and thus lower the total user terminal cost.
The key issue addressed in this project is lower-cost production methods for Ka band waveguide components that satisfy all the functional, mechanical and environmental requirements.
The project will contribute to the evolution of DVB-RCS terminals by:
This work is concerned with the waveguide portion of the terminal which may be divided into three main functions corresponding to three waveguide components; the feedhorn, the circular polarizer and the OMT and filter component.
The OMT and filters are used to a) isolate the transmitter and receiver from each other and b) to combine or separate the transmitter and receiver signals at the common port based on orthogonal linear polarization. The polarizer component converts the linear polarized signals at the OMT common port to or from circular polarization. The feedhorn illuminates the main reflector.
Note that all three components are dual-band and must work as specified at two widely seperated frequency bands. The project began with the intention of demonstrating a linearly polarized Ka band front-end but the program was modified in Phase 2 to add the circular polarizer as a third component to the front-end.
The project was organized into six tasks whereby Tasks 1 – 3 comprised Phase 1 and Tasks 4 – 6 comprised Phase 2.
The project began in May 2003 and was completed in November 2009. Phase 1 concerns technology selection, evaluation, and risk reduction. Phase 2 concerns the design, fabrication, and test of a complete 'proof-of-concept' front-end structure using the most promising metallized polymer technology.
This project is now complete. The overall objective of this technology development project was to determine the suitability and applicability of polymer technology for satellite user terminals.
Phase 1 was completed successfully. We demonstrated fabrication of the transmitter bandpass filter at 30GHz without tuning using metallized, injection molded polymer technology. The geometric reproducibility (standard deviation) was a few micro-meters which was much better than the value required (i.e. 10μm) for good yield.
Phase 2 was partially successful. The major challenges encountered in this project were:
a) maintaining accurate circular symmetry (relevant to the horn and polarizer),
b) achieving good contact quality (relevant to the polarizer and OMT),
c) insufficient performance of the particular overmolding assembly design (relevant to the polarizer and OMT) and
d) insufficient mold tooling fabrication and measurement capabilities (in Phase 2 but not in Phase 1).
These areas could benefit from further work.
The major successes of the project were:
a) the selected polymer and metallization combination worked well together,
b) very good surface qualilty in the polymer parts was possible when the tooling was polished,
c) geometric reproducibility was very good (standard deviation typically 4μm for the polymer parts and 7μm for the metallized parts),
d) mold tuning was successful as demonstrated with the polarizer,
e) demonstration that reliable, reproducible low-cost production of wave-guide components is feasible when the tooling is correct and
f) the polarizer and feedhorn worked almost perfectly.
Prototype Ka band front-end assembled from overmolded polymer waveguide components using auxillary flanges and a transition block for connection to the rectangular waveguide ports.
Further work is needed in tooling fabrication, measurement and modification. The mechanical design of the parts and the joining method (overmolding) was adequate in some cases (polarizer) but not others (OMT) but can certainly be improved. There are some possibilities for further cost reduction. Overall we conclude that, with this additional work, the technology is suitable for low-cost, high-volume, precision fabrication of waveguide components.