Satellite Dish

Real Summit Network offers a comprehensive portfolio of high performance customizable satellite terminals and accessories to meet the needs of customers anywhere in the world.

To start with, what is a satellite dish?

A satellite dish is a dish-shaped type of parabolic antenna designed to receive microwaves from communications satellites, which transmit data transmissions or broadcasts, such as satellite television.

It is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam.

The dish on the receiving end can't transmit information; it can only receive it. The receiving dish works in the exact opposite way of the transmitter. When a beam hits the curved dish, the parabola shape reflects the radio signal inward onto a particular point, just like a concave mirror focuses light onto a particular point.

In this case, the point is the dish's feed horn, which passes the signal on to the receiving equipment. In an ideal setup, there aren't any major obstacles between the satellite and the dish, so the dish receives a clear signal.

In some systems, the dish needs to pick up signals from two or more satellites at the same time. The satellites may be close enough together that a regular dish with a single horn can pick up signals from both. This compromises quality somewhat, because the dish isn't aimed directly at one or more of the satellites. A new dish design uses two or more horns to pick up different satellite signals. As the beams from different satellites hit the curved dish, they reflect at different angles so that one beam hits one of the horns and another beam hits a different horn.

The central element in the feed horn is the low noise blockdown converter, or LNB. The LNB amplifies the radio signal bouncing off the dish and filters out the noise (radio signals not carrying programming). The LNB passes the amplified, filtered signal to the satellite receiver inside the viewer's house.

Principle of operation

Schematics of reflection principles used in parabolic antennas.

The parabolic shape of a dish reflects the signal to the dish’s focal point. Mounted on brackets at the dish’s focal point is a device called a feedhorn. This feedhorn is essentially the front-end of a waveguide that gathers the signals at or near the focal point and ‘conducts’ them to a low-noise block downconverter or LNB. The LNB converts the signals from electromagnetic or radio waves to electrical signals and shifts the signals from the downlinked C-band and/or Ku-band to the L-band range. Direct broadcast satellite dishes use an LNBF, which integrates the feedhorn with the LNB. (A new form of omnidirectional satellite antenna, which does not use a directed parabolic dish and can be used on a mobile platform.

The theoretical gain (directive gain) of a dish increases as the frequency increases. The actual gain depends on many factors including surface finish, accuracy of shape, feedhorn matching. A typical value for a consumer type 60 cm satellite dish at 11.75 GHz is 37.50 dB.

With lower frequencies, C-band for example, dish designers have a wider choice of materials. The large size of dish required for lower frequencies led to the dishes being constructed from metal mesh on a metal framework. At higher frequencies, mesh type designs are rarer though some designs have used a solid dish withperforations                                                           

Modern dishes intended for home television use are generally 43 cm (18 in) to 80 cm (31 in) in diameter, and are fixed in one position, for Ku-band reception from one orbital position. Prior to the existence of direct broadcast satellite services, home users would generally have a motorized C-band dish of up to 3 metres in diameter for reception of channels from different satellites. Overly small dishes can still cause problems, however, including rain fade and interference from adjacent satellites.

Our satellite terminals are:

• Available in C band, X band, Ku band and Ka band
• VSAT

A common type of dish is the very small aperture terminal (VSAT). This provides two way satellite internet communications for both consumers and private networks for organizations. Today most VSATs operate in Ku band; C band is restricted to less populated regions of the world. There is a move which started in 2005 towards new Ku band satellites operating at higher frequencies, offering greater performance at lower cost. These antennas vary from 74 to 120 cm (29 to 47 in) in most applications though C-band VSATs may be as large as 4 m (13 ft.).

• Individual dishes serving one dwelling: Direct to Home (DTH).
• Collective dishes, shared by several dwellings: satellite master antenna television (SMATV) or communal antenna broadcast distribution (CABD).
• Automatic Tracking Satellite Dish
• Big dish

The LNBF

LNB’s sit in front of the actual parabola of the satellite dish, at the end of the arm projecting from the dish itself. Their purpose is to receive, amplify and down convert the required ‘blocks’ of microwave frequencies to lower 950MHz to 1.45GHz L-band frequency signals; these are then sent to the satellite TV receiver or IRD (integrated receiver decoder), via a coaxial cable (more information on RF coaxial cables is available at Real Summit Office.)

The number of LNBs determines the number of satellites a satellite dish can ‘see’ since a separate LNB is required to receive signals from satellites in different orbital positions. Satellite TV service providers use multiple satellites to deliver their content, hence the need for multiple LNBs to receive the full range of satellite TV programming.

LNB’s use an antenna probe inside the feedhorn to pick up the signal focused by the satellite dish. The probe has to be aligned mechanically in a vertical or horizontal direction (or left and right hand circular polarization for DBS satellites), in line with the polarization of the signal transmitted by the satellite transponders. This dual polarization is used by satellites to avoid interference between adjacent channels, and is achieved by assigning even and odd transponders on the satellite different polarization.

LNBF’s employ a dual antenna probe setup inside the throat of the feedhorn with one aligned vertically and the other horizontally (or left and right). Switching to the correct polarized probe is carried out electronically via a voltage sent up the coaxial cable by the receiver.

Satellite Dish Receiver

 The satellite dish receiver is the end component of your satellite television equipment. There are four basic tasks that are performed by your satellite dish receiver:

The satellite receiver unscrambles the encrypted signal sent via radio waves. The signal is encrypted to protect against people illegally accessing satellite television. A decoder chip within the satellite receiver unscrambles that signal so you can view the television programming.

 The satellite receiver keeps track of any pay-per-view programs and sends the information to your satellite television provider for billing purposes.

The satellite receiver also converts the video format for the signal. The signal is sent to your satellite dish in a digital MPEG-2 or MPEG-4 format, which standard televisions cannot use. The satellite receiver converts the digital signal into a format recognized by your television. In the United States, it would be converted to National Television Systems Committee (NTSC) format. It can also convert it to a high-definition signal.

The satellite receiver also extracts individual channels from the larger satellite signal. As a subscriber to a certain provider (DirecTV, DISH Network, Mytv, Dstv etc.), you only have access to channels they offer at the plan you pay for. The satellite receiver extracts the correct channels from the larger bulk of channels. In addition, whenever you change the channel on your TV, the satellite receiver changes which channel it extracts from the signal.