Ring focus antenna system with an ultra-wide bandwidth
A ring focus antenna system has an ultra-wide bandwidth for receiving and transmitting electromagnetic (EM) signals. The system includes a main reflector having an axis of rotation and a splash plate feed assembly consisting of a waveguide and a sub-reflector which is substantially aligned with the axis of rotation. The sub-reflector has surfaces that include segments of a displaced ellipse, having a first focal point which coincides with an ISO phase center located inside the waveguide and a second focal point located on a ring focus of the main reflector. A dielectric support for the sub-reflector has a shaped boundary which eliminates refraction at the dielectric-air interface. In one embodiment, the ultra-wide bandwidth includes EM frequencies belonging to Ku-band and Ka-band communication frequencies. The waveguide may be configured as a quad-ridged polarizing waveguide.
1. A ring focus antenna system having an ultra-wide bandwidth for receiving and transmitting electromagnetic (EM) signals, the system comprising
a main reflector having an axis of rotation; and
a splash plate feed assembly;
wherein,
the splash plate feed assembly comprises an EM waveguide and a sub-reflector which is substantially aligned with the axis of rotation;
the sub-reflector comprises surfaces that include segments of a displaced ellipse having a first focal point which coincides with an ISO phase center located inside the waveguide and a second focal point located on a ring focus of the main reflector; and
the sub-reflector is mated to a dielectric support having a shaped boundary which includes a portion of a circle whose center is at the second focal point.
2. The system of claim 1 wherein the EM waveguide is a quad-ridged polarizing (QRP) waveguide having the ultra-wide bandwidth and a central axis.
3. The system of claim 1 wherein the shaped boundary is configured so that EM rays cross perpendicular to the shaped boundary.
4. The system of claim 1 wherein the ultra-wide bandwidth includes EM frequencies belonging to Ku-band and Ka-band communication frequencies.
5. The system of claim 1 wherein the main reflector has a parabolic surface.
6. The system of claim 1 wherein the splash plate feed assembly comprises a splash plate feed cone.
7. The system of claim 6 wherein the feed cone has rotational grooves.
8. The system of claim 2 wherein the QRP waveguide comprises a pair of conducting horizontal ridges, a pair of conducting vertical ridges, and a dielectric central portion.
9. The system of claim 8 wherein the ridges comprise a plurality of steps whose dimensions vary with position along the central axis.
10. The system of claim 8 wherein the ridges comprise a metallic material selected from a group consisting of aluminium, magnesium, zinc, titanium, chromium, gold, and steel.
11. The system of claim 8 wherein the horizontal ridges are arranged at an oblique angle to the vertical ridges.
12. The system of claim 8 wherein the dielectric central portion is configured to have two slabs arranged in a cross-hair shape.
13. The system of claim 1 wherein a far-field radiation pattern has a first sidelobe level off peak gain of less than −20 dB for EM frequencies within the ultra-wide bandwidth.
14. The system of claim 1 wherein an aperture efficiency is greater than 70% for EM frequencies within the ultra-wide bandwidth.
15. The system of claim 1 operationally connected to a receiver and a transmitter in a communication system.