New concept of multi-band "Circulator-Antenna" based on ferrite materia – BISTRAU

Communication systems for civil and military applications have become increasingly complex. They tend to agglomerate multiple standards, which often contradicts the miniaturization requirements of terminals. Two essential elements of RF Front End are the antennas and the circulators placed ahead of them. They are usually designed separately and matched to a standard impedance, typically 50 Ohms. Increasing the compactness and the reducting the losses of these devices will be achieved by grouping these two elements together via a joint antenna/circulator design in order to avoid the interconnection stages. Furthermore, the grouping of communication standards on the same Front-End also seems relevant and requires the development of multi-band antennas as well as multi-band circulators.
Finally, circular-polarized transmission and/or reception is/are increasingly required, especially for space applications. Biased ferrite materials are the main element in the design of passive circulators. In addition, they allow the natural generation of circularly polarized waves, which also makes them good candidates for circularly polarized antennas.
The BISTRAU project presented in this document therefore aims to develop a new methodology for the joint design of a compact multi-band "circulantenna" (circulator-antenna association) radiating circular polarization thanks to the specific properties of ferrites. This co-integration will involve the use of a common ferrite substrate consisting of one or two layers (functions stacking). In this framework, a new topology of microstrip dual band circulator will be developed due to its smaller footprint. We will take advantage here of the biased ferrites properties that generate naturally circularly right and left polarized waves. An application in the SatCom band (20-30 GHz) will be targeted. Thus, to summarize, several challenges will be addressed in this project:
• The development and validation, for the first time in the state-of-the-art, of a dual-band circulator in microstrip technology with a f2/f1 ratio of 1.5.
• The design and validation of the first circularly polarized dual-band ferrite antenna with a ratio f2/f1 = 1.5. The control of the frequency ratio is a real challenge.
• Development of a dual-band “circulantenna” co-design method without using 50 Ohms with again a frequency ratio of 1.5.
Microstrip technology will be also chosen. An experimental phase will be carried out.
In addition and to validate the methodology, a comparison of the performance between the joint design and a separate design will be carried out.