The present invention relates generally to microwave antennas. More particularly, my invention relates to microwave antennas that are designed for receiving satellite broadcasts and that are heated to eliminate ice and snow buildup that otherwise causes signal loss. Further, this invention relates to auxiliary heaters for microwave receiving systems that may be retrofitted to existing antennas.
In the prior art a variety of large (i.e., larger than one meter in diameter) microwave and UHF dish antennas have been proposed. Relatively recently direct satellite broadcasting has become popular. Digital systems (i.e., systems sold under the trademark DSS.TM. have become popular. Satellites orbiting the earth at approximately 23,500 miles operate in the KU microwave band in the broadcast satellite service. Such satellites transmit digital, compressed television signals that can be received by relatively smaller dishes. The relatively small dishes typically employed to receive KU band signals are approximately eighteen to twenty inches in diameter, unlike the larger and more cumbersome antennas of the older C-band, which can be seven to twelve feet in diameter. Satellites in the direct satellite broadcast service transmit at approximately 120 watts rather than five watts, so a smaller antenna can be used successfully. KU-band satellites can be spaced apart at approximately nine degrees, allowing the antennas to aim at particular satellites with less mechanical movement.
Sophisticated digital signal processing techniques are used in direct broadcast satellite transmission. Digitization of the signal enhances bandwidth, and compression techniques enhance throughput. For example, direct satellite broadcasting systems employ MPEG (i.e., "Motion Picture Expert Group") compression. MPEG-2 is the new standard. Bandwidth is increased approximately seven fold over the older C-band analog systems. Further, adjacent channel selectivity is enhanced because of the technique.
Another advantage of modern direct broadcast KU-band satellite systems is that they employ circular polarization. With older antenna technologies the installer must tediously align the antenna elements responsive to horizontal and vertical components of the polarized signals to be received. Circular polarization techniques of the direct broadcast satellite service makes it much easier to aim and install the antenna. Additionally, better signal attenuation between adjacent satellites is realized.
Thus the smaller satellite dishes employed by the direct broadcasting satellite service are advantageous. They are widely gaining in popularity as users find that installation is quick and easy. Most importantly, since the satellite receiving antennas are relatively small, they do not create an eye sore, and they are less objectionable esthetically.
However, the band upon which such devices operate can be severely affected by various weather elements. In fact, during periods of heavy rain or snow, signal attenuation can be noted between the satellite and the receiver. More particularly, when ice or snow accumulates upon the antenna or the low noise broad band amplifier (i.e., the LNB), tremendous signal degradation is experienced. Particularly in northern climates, signal degradation of 20-30 db. can result from the accumulation of snow or ice upon the antenna. Snow or ice can accumulate directly upon the antenna in an uneven fashion, primarily distributed upon the bottom third of the dish. Snow or ice can also accumulate directly upon the LNB, degrading the ability of the waveguide to properly receive signals reflected by the dish.
Therefore, I have proposed a system for heating microwave antennas, particularly satellite dishes for the direct satellite broadcast service. A viable de-icing system must be easily incorporated into existing designs. Moreover, the system, should be capable of retrofitting. More particularly, a viable system must not interfere or degrade with signal transmission characteristics and must not alter the mechanical configuration or strength of the antenna. Such a system must be integrated into existing antennas without degrading the esthetics or ornamental appearance of the device and the system must function automatically without viewer attention or maintenance.