There are many orbital locations where linear and circularly polarised satellites are or could be in the future co-located. An LNB that can receive from both types of satellites could therefore significantly stimulate the use of space capacity for new services from existing locations through ease of reception for the consumer market.
This LNB will be capable of receiving four polarisations simultaneously, these being vertical linear, horizontal linear, right hand circular, and left hand circular. Currently an LNB with this capability is not available on the market and development of this product will require a new approach to LNB design.
These requirements combine to generate a need for a four output LNB, broadly similar to the Quads used in the European Markets.
The Integrated Dual Linear and Circular Polarisation LNB will be designed as a Quad LNB, that is to say, an LNB with 4 outputs allowing the reception of all polarisations simultaneously.
The unit will be designed to receive circularly polarised signals of either polarity in the frequency band 12.2-12.7 GHz Ku band from current orbital locations and also receive linear polarised signals of either polarity in the frequency band 11.7-12.2GHz in the Ku band from the collocated satellites.
1 Feed Horn
For reflectors designed to give high adjacent satellite isolation, the reflector profile is typically elliptic, and therefore an elliptic radiation pattern is required from the feed horn.
This development requires that the phase of the probe outputs is maintained close to 90 degrees over the frequency of operation.
The majority of engineering effort will be spent on examining techniques which will allow phase adjustment during assembly and test.
The theoretical response of the a 3dB split with 90 degrees of differential phase shift cannot be obtained, even theoretically, over finite bandwidth.
From the design point of view, the most gains are likely to be made from an evaluation of alternative geometries.
The alternative solution offered by other satellite operators is a service using two separate LNB's. This solution would require the design of an external IF switch network to combine the outputs of the two LNB's into four IF cables for routing to the Digital Video Recorder and any additional Set Top Boxes within the customer's home. There is a high risk in the implementation complexity and a significant increase in cost of the outdoor reception equipment.
The proposed development and production of this LNB adds value to existing satellite service business by stimulating additional demand for new services including HDTV. At the domestic end of the equipment market, a new set-top box is required. This is being developed specially for the application by a major manufacturer. The signals received by the box will come from the proposed LNB. This is installed on a reflector which is likely to be an item already on the market. However, the extra transmissions will also stimulate demand for further extra capacity.
The unit will be designed to receive circularly polarised signals of either polarity in the frequency band 12.2-12.7 GHz Ku band from current orbital locations and also receive linear polarised signals of either polarity in the frequency band 11.7-12.2GHz in the Ku band from co-located satellites.
The proposed method of carrying this out is to detect the power present within the waveguide in all polarisations with a pair of linear waveguide probes. The probes will be aligned to the horizontal and vertically polarised transmissions from the satellite. The analogue signal-processing will take the horizontal and vertically polarised components and split them into two channels. The first channel represents the linearly polarised signals, H and V, and these are then output directly to the next stage of the LNB where mixing to the IF occurs.
However, the other two channels, one each from the horizontal and vertical probes, are combined in a hybrid coupler to produce Right Hand circular polarisation and Left Hand circular polarisation. The proposed block diagram is shown in figure 1 below.
The complete LNB will be manufactured with an integrated feed horn and waveguide.
The difficulty is in carrying this out while maintaining the necessary phase and amplitude balance required for the circular polarisation to be received. This is because circular polarisation is only perfectly achieved when horizontal and vertical polarisations are of exactly the same amplitude, and separated in phase by exactly 90 degrees.
These two channels
The project is divided into 10 Work Packages. These are :
- RF Board Design,
- LO Board Design,
- Power Supply Design,
- Waveguide Design,
- Feed Horn Design,
- Administration and Management,
- Pre-production Sample,
- Environmental Test
It is anticipated that three design cycles are required for each Work Package.
A significant amount of resources are devoted to ensuring that the design will be viable as a production unit by producing castings with actual draft angles and difficult to produce features.
An additional aspect of this is the relative movement of RF boards to the castings over temperature which may cause performance degradations.
These two activities will allow tolerance analysis to be undertaken at the design phase.
All the aforementioned technical developments and design issues raised during the design phase were solved and project was completed within the required time-scales, however the original cost budgeted for the design portion of the project was exceeded. This cost over run being entirely supported by additional funds from Invacom. A number of unique inventive steps have been carried out and these have now been filed as patents to protect the technology.
Following the success of the design phase of this project, we have completed an engineering test build of 300 units to prove that the unit can be manufactured in volume.
The test results from these units has in particular shown that the cross polar performance of the design is stable with temperature, a major concern at the start of the design phase. The Noise Figure of the LNB is within specification and is hence shown to be unaffected, relative to a Dual Polar LNB by the addition of the Quad Polar Circuits.
The new waveguide structure has shown to be manufacturable in volume and that the production set-up adjustment systems designed into the circuits and waveguide are able to remove the effects of any variations in both waveguide performance and electronic part variations. The variation and spread in component performance through a build of 300 units has enabled us to verify that the batch to batch component variations are not any issue with the design and the future builds will still be within specification.
A significant number of these units have subsequently been sent to multiple distributors, magazine reviewers and other test houses throughout the world for independent testing and evaluation. So far the feedback on the tests has all been positive and the LNB has demonstrated that it meets the technical requirements of the customer.
The overall response from the market has been very positive, and Invacom is now able to enter into volume manufacture with a proven high volume product. Invacom has orders for the first planned production build of the product and continues to find new markets for the product now that awareness of the new technology and its capabilities has being raised.
The process of developing spin of products has now begun and others are continually being identified.
The 300 units that have been built so far demonstrate that the design exceeds the original technical design brief and specification.
The samples sent out for review have all been accepted as demonstrating that the LNB is a high performance product that generally exceeds the performance of standard single polar CP or LP products in the field from other manufacturers. The units are also seen as a major breakthrough in LNB design and performance.
The LNB is being supplied to a number of US distributors and DBS operators. This has generated significant interest in a new area of technology that enables DBS operators a further degree of flexibility in transponder frequency and polarization planing both during the operation and selection of satellites to deliver both DBS and data services to their customers.
The units have been presented a recent DBS manufacturers exhibition and conference in the USA and as a result won awards from both the press as best new product, and the overall award for the best product at show.