In October 2017 I began my PhD and every time I answer the question, “What do you do?”, the next question would be, “What is your subject?”
The first time I answered whilst quoting the e-mail describing the job, “My PhD is part of the REVOLVE project which is a European initiative dealing with the study of the Smart Reflector Surfaces with processing capability based on actuated flexible thin organic large area surfaces.”
The second question, ‘What is your subject?’ took me by surprise and led me to create my PhD title: ‘Mechanically Reconfigurable Antennas.’ At this moment I was very proud of myself as I had finally found a way to explain what I will do using a title that people can understand. I looked at the eyes of my interlocutor and I understood that what I had described was not very clear. Describing or explaining something is much more difficult than trying to find a title, even more when you already have read a lot of papers about the subject area and when you try to interest people. It is my purpose on the blog to try and do this so do not hesitate to comment or to ask questions – I am still learning!
The first step to clarify a subject is to know more about the general context.
What is the context of the ESR5 ?
The REVOLVE project is a European initiative aimed at developing new solutions for future satellite systems. It will aim to investigate new technologies that will make the satellites easier to build and cheaper thus gaining time and reducing costs which is very important for industries. Moreover, the growth of the technical improvement is very fast and it is important to adapt in order to be competitive in the market.
The second is to understand a subject, and it is important to know the meaning of each word used :’ Smart Reflector Surfaces with processing capability based on actuated flexible thin organic large area surfaces’.
What is a Smart Reflector Surfaces for antenna?
In this PhD, the ‘Smart Reflector Surfaces’ will be a reflectarray. What is a reflectarray ? It combines some features of reflectors and of array antennas. A reflector antenna is a device that reflects electromagnetic waves while the array antennas is composed of groups of radiating elements which are distributed and oriented in a specific configuration. I have described two interesting experiments around Smart Reflector Surfaces for Antenna below:-
Take one curved mirror and a flashlight. Turn off every light. Illuminate the curved mirror with the flashlight, you will see on the wall in front of the mirror a circular lighted zone : it is the same process for the reflector antenna. The light rays are replaced by the electromagnetic waves which are directed on a precise zone on the Earth (see below)…
Take four plane mirrors and a flashlight. Turn off every light. Gather all the mirrors together but give them different orientation. Illuminate all the mirrors simultaneously with the same flashlight, you will see on the wall in front of the mirrors a lighted zone : it is the same process for the array antenna. Same as before, the light rays are replaced by the electromagnetic waves which are directed on a precise zone on the Earth. Nevertheless, it is important to note that the impact of the given incidence of the miror is equivalent of the array radiating elements geometry.
In conclusion, the reflectarray combines the simplicity of the reflector antenna with the performances of the array type. In fact, the reflectarray is a planar reflecting surface with a lot of radiating elements.
What is the meaning of processing capabilities?
As it is presented before, the technologies and the market change continuously and it is important to have an overview of all the possible applications a system could manage. For an antenna it could be : radio applications, space tracking or communications.
Furthermore, the main goal of this subject is to be able to reconfigure the antenna. We could say that for one mission, for exemple a satellite place at 500km of altitude which as to cover France, the antenna has one fixed shape and the satellite will be design and product during approximately 10 to 15 years. In conclusion what we ask now will be in-orbit in 2028-2033, it is too long as regard of the needs growth.
The figure below presents one cell phone of the year 2003:
What is TOLAE (Thin Organic Large Area Surface)?
It is an emerging technology and is the goal is to have a large area electronics that are thin, light weight, flexible and/or stretchable, suitable for large market sectors.
Why do we need TOLAE?
To reconfigure an antenna we could do it electromagnetically or mechanically. In my PhD we will try to do it with the second possibility in order to increase the fiability of the final system. If we take the hypothesis presented before : one shape of the antenna for one mission. So if we change the shape we change the mission and so the targeted zone on Earth, but it is quite more complicate.
To simplify the reflectarray is made of two layers separated by vacuum. On the upper layer you have the radiating elements which are illuminated by a feed (the flashlight). The electromagnetic waves will pass through this layer and be re-radiated by the second layer (the ground plane) in one direction.
Using the principle of the second experience presented before, if we modify the shape of the second layer, we will change the specification of the missions. To do it we could use some actuators which will push on this second layer at different zones and that is why we need a flexible surface.
In conclusion, the main purpose of my PhD is to find a mechanical way to change in-orbit the mission’s specifications which has to be lightweight, cheap and simple.