This paper presents an original solution to design a compact dual circularly polarized isoflux antenna for nanosatellite applications. This kind of antenna has been previously designed in our laboratory, for a single circular polarization. This antenna is composed of a dual circularly polarized feed and a choke horn antenna. This feed is a cross-shaped slot in the ground plane, which provides coupling between a patch and a ring microstrip line with two ports. It is located at the center of a choke horn antenna. The simulated antenna presents an axial ratio <3 dB and a realized gain close to 0 dB over a 400 MHz bandwidth (8.0–8.4 GHz) at the limit of coverage, i.e. 65° whatever the azimuth angle (φ) and the port. A 20 dB matching for each port and 13 dB isolation characteristics between the two ports have been achieved on this bandwidth. It has been realized and successfully measured.

This paper presents a solution to reduce the feed complexity and to improve the total efficiency of X-band compact choke horn antenna with circular polarization and isoflux pattern. This kind of antenna had been designed before by our laboratory for nanosatellite applications, but it required a 4-way divider with phase shifter which generates the insertion losses and therefore a lower realized gain (RG). Among several feeds, a uniform circular helix antenna has been used here, which produces a satisfying feed without too much damage for the axial ratio (AR) and the isoflux pattern over a 400 MHz radiation bandwidth (8.0–8.4 GHz). Theoretical and experimental results show an AR lower than 5 dB and a RG higher than 0 dB at the limit of coverage, i.e. 65° whatever the azimuth angle (φ).

This paper presents a tradeoff between isoflux pattern quality and X-band antenna compactness for nanosatellite applications. Having an isoflux radiation and a circular polarization (CP) generally causes a large antenna size which is incompatible for these applications. A new design of an antenna is done with the following maximum antenna dimensions: a diameter of 90 mm and a height of 20 mm above the nanosatellite platform. The isoflux pattern is slightly degraded while a good CP and realized gain are kept. The structure is a compact choke horn. It presents an axial ratio lower than 3 dB and a RG close to 0 dB over a 400 MHz bandwidth (8.0–8.4 GHz). It has been realized and successfully measured.