Steerable satellite antenna assemblies for satellite-to-ground links typically require high gain, low mass, and high reliability. One approach for a steerable satellite antenna assembly is to use a fixed feed source so as to eliminate performance degradations otherwise associated with a moving feed source. Performance degradations for a moving feed source typically include losses due to mechanical rotary joints, RF cable connectors, flexible waveguides, and lengthy cables associated with rotary actuators.
Steerable satellite antenna assemblies also need to avoid the “keyhole effect,” which is a physical limitation due to the orientation of the antenna rotation axis caused by a limited motion range of the actuators. The keyhole effect causes the antenna to momentarily disrupt communications when reaching its physical limitation so as to allow for the actuators to reposition before resuming steering.
One approach for a steerable satellite antenna assembly with a fixed antenna feed is disclosed in U.S. Pat. No. 6,492,955 to Amyotte et al. The antenna assembly includes a subreflector secured to a frame rotatably mounted on a support structure via a first motor, and an antenna feed located at a first focus of the subreflector for illuminating the same. The antenna feed is fixed to the structure and has a feed axis pointing at the subreflector. A parabolic reflector having a focus in common with a second focus of the subreflector to transfer the signal between the same, and a planar reflector is secured to the frame, and has a beam axis. The planar reflector is rotatably mounted on the frame via a second motor to transfer the signal between the parabolic reflector and a target. The antenna assembly includes a controller connected to the motors to steer at the target anywhere within a full spherical angular range.
Another approach for a steerable satellite antenna assembly with a fixed antenna feed is disclosed in U.S. Pat. No. 5,198,827 to Seaton. The antenna assembly includes an antenna feed structure for emitting electromagnetic radiation, and a subreflector for redirecting the emitted radiation. A main antenna reflector projects radiation redirected by the subreflector as an antenna beam. A mechanical arrangement rotates the subreflector about the rotation point.
Even in view of the above steerable satellite antenna assemblies, there is still a need for such assemblies to have a more compact geometry. Continued growth and demand for bandwidth has led to new commercial satellite constellations. For example, the O3b satellite constellation is deployed in a medium earth orbit (MEO) and the OneWeb satellite constellation is to be deployed in a low earth orbit (LEO). A more compact antenna assembly reduces the size and weight of the satellites, as well as costs. In addition, MEO and LEO satellites typically operate at a wider beam scanning range as compared to a traditional geosynchronous orbit. Consequently, another desirable attribute is for the compact antenna assemblies to also operate over a wider scanning range.