Multifocus technology in receiving antennas

Something is indisputable: the cable TV signal subscriber has developed what we could call "cable culture", in other words, it now demands quality and variety of programming and therefore the need to be able to have the capacity to receive multiple signals simultaneously from several satellites, it is imperative.

When installing earth stations you can choose one of the following options:

1. The traditional method of using many satellite dishes, an applicable method where factors such as space restriction do not become critical, as well as the number of schedules that can be available. Normally, in most systems with 30 or fewer channels, difficulties will arise when justifying expenses in the implementation of systems in relation to the potential for profitability, so that it is most likely to continue adding parables to the existing ones.
2. The second method is to receive signals from more than one satellite with the same parabola, depending of course on the type of antenna available and the efficiency of the reflector itself. It should be remembered that the vast majority of antennas are designed to see adjacent satellites within a 12° arc, which represents a limitation for all satellite belt use in relation to the number of antennas available.
3. The third option is to receive the signals of all the satellites located in the satellite arc seen from the earth station by using an antenna whose reflector is a combination of surfaces (sphere and parabola) as is the case of Simulsat. This antenna can "see" satellites within a 70+ degree arc, that is, it can receive signals from 35* satellites in the C or Ku bands and in any polarity.

Initially, the number of satellites transmitting commercial programming determined the use of parables. Over time, the offer of entertainment programming multiplied, contributing to a dramatic increase in the number of cable TV operating companies and their penetration rates. Limitations on the number of satellites and operating costs set by the companies that own the transponders, among other factors, have caused programming to disperse along the entire satellite belt. The future launch into orbit of new satellites or the relocation of others causes some confusion for cable operators who permanently try to provide consistent but varied programming to their subscribers.

The ability of subscription television systems to deliver appropriate programming in specific areas of the market can significantly affect long-term profitability. It is evident that in recent years most pay-per-view schedules, teleconferences, special events, can be found on different satellites.

The simple ability to receive signal from several satellites simultaneously, makes the opportunity to obtain economic benefits invaluable. More and more operators recognize the potential profitability of systems when they can have reception along the satellite arc.

Over the next few years, new satellites will be launched and many others will be taken out of service. Existing and available satellite dish technology will continue to produce "antenna farms", a consequence of the limitations already explained. Retrofits (reception of several satellites with a single parabola) will not solve the potential of the markets either. Only the use of multifocuses presents short- and long-term solutions. The fact of being able to access new programming without interrupting the existing ones makes the multifocus (Simulsat case) the antennas to truly "look to the future". Many companies have found that profitability depends not solely on the number of subscribers, but on the ability to retain them.

It is important to understand the difference between the parabolic reflector and that formed by an aesthetic surface. This difference becomes more important now that the FCC, the regulator in the United States, has begun the implementation to reduce the spacing between satellites.

Retrofit systems have practical limitations due to the difference in gain (dB) between the reflector center and the adjacency zones, due to phase problems and above all due to the reduction of the amount of illuminated surface. Figure 1 shows a parabolic reflector operating as a multifocus. The feeder placed on a focal point A receives the beam as indicated. A displacement of the feeder in the transverse plane to receive an adjacent satellite B produces a change in the linear phase through the aperture, thereby changing the direction of the beam. In the opposite direction to that of the beam, degradation problems commonly due to three factors are presented; 1) f/d specific to each antenna, 2) distance from the pointing point, and 3) quality of the antenna surface. In a commercial 5.0 m antenna with f/d=0.38, the targeting degradation is approximately 0.5 dB and 1.8 dB at 8° with a gain of 44 dB. However, a commercial antenna of 5.0 m with f / d = 0.30 will have a behavior of 0.5 to 0.7 dB at 3 ° and 2.7 to 3.0 dB at 8 °, This simple example shows the difference when using retrofits for antennas of the same diameter but different design of f / d.

As illustrated in Figure 2, a feeder only illuminates a portion of the reflector, the area represented by the D aperture. Feeders are placed along the arc in such a way that aperture A produces a beam in that direction, while a feeder pointing to the reflector in segment B, produces a beam in the same direction as B. Thus feeders illuminate the reflector consistently for any end-to-end beam position of the reflector.

Simulsat's "quasi-parabolic" reflector uses the principle of on focus beam in the elevation plane and performs a spherical scan in the azimuth plane. Simulsat is an FCC-approved antenna and receives signals from more than 35 C- and Ku-band satellites with 70°+ aperture.

The advantages of using a reflector of this type among others are: 1) Space saving. A single reflector replaces up to 35 parabolics. 2) Savings in maintenance. They are fixed antennas. 3) Programming changes from one satellite to another can be made from a switch panel. 4) Regular programming and pay per view can be viewed simultaneously. 5) Handling varied programming (Simulsat) can handle just over 1,000).

In the Latin American world of cable, companies such as TV Comunal of Mexico, TL Cable of Puebla, Mexico, Multicanal of Brazil, TV Mundo Visión of Argentina, TV Cable Morón Argentina, TV Cable of Cali, Colombia, among others, have found an effective response to the present and future reception solution, as well as to distribute totally professional signal, when using Simulsat.