An “M”-shaped beam producing dual stacked reflector antenna for GPS satellite applications

The global positioning system (GPS) satellite borne, L-band array antenna pattern is shaped to deliver an equal strength signal to any arbitrary location on earth. The resulting satellite antenna pattern is a figure of rotation of an ldquoMrdquo-shaped main beam plus side lobes. The shape of the main beam is akin to the inside of a bowl as the ldquodimplerdquo at the center gradually rises and attains a ring peak along the rim that corresponds to the edge-of-earth (EOE) conic angle. The outside of the EOE is an empty space, in essence, devoid of any radiated power and filled by side lobes. This paper proposes a dual stacked reflector fed by a single backfire monofilar feed as a viable alternative to the existing array antenna. The structure of this reflector antenna is simple, compact and lightweight. Moreover, the cost of this antenna is expected to be well under 1/10th the cost of the current array antenna. Analysis shows that this antenna can provide similar or better performance over a 30% bandwidth. Chamber test results from a 1/3-scale prototype antenna have confirmed an excellent M-shaped beam forming capability over the equivalent frequency band, thereby confirming the viability of the concept and validity of the overall design.