Conventional high efficiency feed horns are very useful as elements in phased array antenna and also as feed elements in a multi-beam reflector, in satellite communication systems. A multiple beam reflector has several feed elements that are used for receiving and transmitting multiple beams. Feed horn size is restricted because of the number of feed elements and required beam spacing. A phased array antenna with high efficiency feed horn elements requires 20% less elements, for a desired gain requirement, than that of corrugated feed horns or potter horns that usually have aperture efficiencies of about 70%. The reduction in feed horn elements reduces manufacturing costs, size, and weight of the phased array antenna.
A low efficiency feed horn yields less amplitude taper to a reflector edge for a given feed horn aperture size, which causes high side lobes and spill over loss. High side lobes are not desirable as they cause signal interference between beams. A conventional high efficiency feed horn minimizes spillover loss and interference problems due to its improved edge taper.
Corrugated horns have a disadvantage of a rim, which reduces usable aperture in cases where horn size is limited as with multi-beam antenna. The traditional corrugated horns are therefore not suitable for multi-beam antenna. Antenna packaging is a large driver in designing of multi-spot beam antennas.
Although the high efficiency horns are useful for many applications, they suffer from a limited bandwidth problem. The bandwidth of such feed horns is generally less than 10%. Therefore, separate transmit and receive antennas are required which take up more space and increase costs. Two different phased arrays are used in a phased array antenna, one for a transmitting band and one for a receiving band.
Since feed horn bandwidth decreases as aperture size increases, traditional reflector antennas must limit the horn size. This forces the main reflector aperture to be large in order to minimize spillover loss. Also, large focal lengths are needed to improve scanning performance, which further drives the reflector size to be large.
The above-described problems associated with traditional feed horns result in a trade-off between generally three alternatives; using two single band feed horns, using a dual band feed horn that is large in size relative to single band feed horns, or using a smaller sized dual band feed horn that suffers from interference problems and large spillover loss, which results in poor efficiency.
Additionally, all of the above mentioned feed horns also propagate both transverse electric (TE) modes and transverse magnetic (TM) modes. The propagation of both TE and TM modes further reduces the efficiency of a feed horn.
Therefore, it would be desirable to provide an improved feed horn design that supports dual bands, is smaller in size relative to conventional dual band feed horns, and operates at efficiency levels at least as high as that of conventional high efficiency feed horns with good cross-polarization level.