Micris was approached by a company based in the Netherlands, who had a requirement for a radome that could house a portable satellite communication system that operated over the Ka frequency band, the main requirements were:
- Portability – panels needed to be packed into cases and lightweight
- Quick assembly
- Watertight to IP65
- Frequency performance over the Ka band to be <-0.75 Db
- UV stable exterior finish
We have never been involved in trying to design a portable radome, and we looked into the radome market to see if there was already any innovative designs we could base this radome on, but from our research we did not find any that seemed to suit this requirement. We decided to have meetings with both the client who was our customer, but we also wanted to include the end customer so we could fully understand how this radome needed to be deployed and the environment it was going to be used.
From the meetings we were able to start and put together some design intents so that the team could review and eventually come up with the optimum panel size and weight, that would still meet the required build time.
We also had to take into account some further requirements that came out of the meetings, the radome needed to have an access hatch that could allow components the system inside the radome to be removed and / or replaced, this also needed to be a quick release type of system, but also very robust. Some of the panels needed to have air ducts built into them, as in some situations, as it was felt that air conditioning units would also be needed in certain situations
All the above was very different to the radome currently manufactured by Micris and other manufacturers, and using a new type of pre-preg composite system, we knew this was going to take a fresh look at current radome design.
To allow the manufacture of this radome, firstly we need to choose the best materials to get the RF performance, structure stability and keep within the weight criteria.
After reviewing the various manufacturing processes and materials available on the market, it was decided to start with an epoxy pre preg system. The reasons for this choice were as follows:
- Precise layer thickness could be achieved, which is critical for the frequency band
- We can use an open cell core material which will aid in the weight saving
- Good structural stability
- A UV stable outer coating can be applied to the material.
Using software, we designed the ply lay up to optimise the ply book and allow samples to be manufacture for testing, we looked at A sandwich and C sandwich for the RF performance.
From these results we decided to validate the 2mm and 3mm pre preg C sandwich options, as they gave the optimum RF performance with the structural integrity we required.
All the RF testing was conducted at the University of Liverpool in the Electrical department head up by Dr Yi Huang.
We manufactured the required samples for testing and had the test conducted.
The report is attached for reference.
From the test reports, which in the main validated our predictive work, the C sandwich 2mm Nomex was chosen for the construction of the radome.
The next stage was to design the radome, considering the design criteria of the portability, and ease of construction. We also had to consider, that due to the material decision, that the radome panels had to be manufactured under vacuum and heated up to a temperature of 120 deg C.
Using our 3D CAD software various designs were produced and discussed with the client, to ensure it met all the needs, we also had to validate that the end radome design could accommodate the system being used by the client.
Below are some of the designs that were under consideration
This was an 8-petal design using a 3-tier configuration.
Mockup of the system to be used inside the radome, this was used to validate the required swept volume.#
Another idea in the designing stage.
As stated in the brief, the hatch had to be a completely new design, which was easy to use, large enough to allow the removal of parts from the system inside the radome, and be very easy to open and close, also maintaining the water integrity
A key area to the design of the hatch would be the closing mechanism, in the past we had used a simple quick quarter turn device, but it was felt that this would not be a robust solution for this application, so we had to research different types of available catches that were readily available. We were finding that catches that would be the optimum of this application would ultimately not work with our usual hatch design, and that this would also require a complete re-design
Below shows the final design including the catches that were chosen.
The final and approved design, and accepted client working drawings.
Once the design of the radome had been completed, the next stage was the tooling design.
This also gave a new problem, as we were using a product that required the process to manufactured not only at temperature, it needed to be under vacuum. The shape of the designed panels had undercuts, that would not allow the final product to be removed from the tooling without having removable flanges. This gave us the problem of having 2-part tooling that needed to be air tight on the joint line to allow the vacuum to be formed over the tooling using a bag.
We came up with the design for the cnc masters to have a 1-piece flange system that could accommodate a sealing system on the final tooling.
Micris uses an outsourced company to manufacture the CNC tooling, but the tooling design is completed by Micris.
All the designs are submitted in a 3D format to the CNC company who validate the cad data to ensure it will translate onto the CAM software.
Some pictures of the CNC masters designed by Micris.
From the CNC masters, production tooling is manufactured, this is done inhouse so we can control the quality and time scales, the tooling is manufacture from a composite resin tooling system and was designed to be subjected to the processing temperature
Below, some picture of the composite tooling in manufacture.
To allow the manufacture of this radome, and through the choice of materials, Micris needed to invest into additional equipment, the main requirement was a processing oven that was large enough, and had the required controls and safety requirements that would allow the oven to operate over night, and therefor using the down time of the factory to process the materials and be ready for production in the morning.
The final design and type of oven was made after consultations with companies who had the relevant experience to advise us.
We installed a 4m x 4m x 2.1m gas fired oven, (we also had to increase the gas supply into the works, as this was insufficient to both the oven and factory heating) the oven is programable to allow a wide range of materials to be used.
Below is a picture of the completed radome.