For satellite broadcasting applications, the reflector antenna has proven to be a reliable solution and is therefore the preferred choice for most missions. For contoured beam applications, a single shaped reflector is usually used, whereas for multiple beam applications, multi-aperture reflector farms are used. The cost associated to these antenna solutions is high, and means to reduce the cost and schedule are of great interest.
Printed reflectarrays provide an alternative way to realize low-cost high-gain antennas and many of the recurring costs associated with the reflector technology can be circumvented. Consequently, ESA has been recently promoting reflectarray R&D activities oriented towards telecommunication applications. Despite several advantages, reflectarrays still exhibit limited performance compared to traditional reflector solutions.
The objective of this project is to develop a curved reflectarray that can provide RF performance comparable to conventional reflector solutions while offering advantages in terms of cost, accommodation, versatility, and ability define the coverage late in the development plan.
From an RF design point of view, the challenge is to design a curved reflectarray that is capable of providing RF performance comparable to existing reflector solutions.
From a mechanical point of view, the manufacturing of a curved reflectarray is challenging and requires a non-conventional manufacturing approach.
A curved reflectarray has several distinct advantages.
For contoured beam applications, the curvature of the reflectarray can be used to enhance the bandwidth of the reflectarray resulting in performances that are comparable of the shaped reflector. Furthermore, a curved reflectarray is attractive compared to traditional shaped reflectors due to the possibility of reusing a standard parabolic mould for multiple coverages and missions, thereby reducing cost and delivery time.
For multiple spot beam missions, the curvature provides ways to reduce the number of main apertures required in a reflector farm. In the typical 4-color frequency polarization re-use scheme, it is possible using a curved reflectarray to radiate more than one beam type in the re-use scheme, enabling the possibility of reducing the number of main apertures from four to two for both transmit/receive operations, while maintaining the simplicity of the single-feed-per-beam operation.
The main feature of the reflectarray antenna is that the array elements are printed on a doubly curved surface. The use of a curved surface is a necessity to realize a reflectarray antenna that is competitive to existing reflector solutions.
The curved reflectarray can be designed to radiate a contoured beam, or to be used in a multiple beam antenna farm for spot beam applications.
For the design of the curved reflectarray, a direct optimization approach is used, providing additional control of the reflectarray performance as compared to existing synthesis methods.
The antenna system consists of a single offset curved reflectarray based on a single metallization layer configuration. For contoured beam applications, the reflectarray is illuminated by a single feed whereas a feed cluster is used for multiple spot beam applications.
The project is divided into two phases:
- The first phase deals with the preliminary design of curved contoured beam reflectarrays and curved multiple spot beam reflectarrays.
In the second phase, the detailed design of a curved multiple spot beam reflectarray in Ka-band is conducted, including experimental validation by means of breadboard manufacturing and RF testing.
The activity has been completed with the successful manufacturing and RF testing of the curved reflectarray. Excellent agreement between simulations and measurements were obtained, confirming the proposed concept.