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DDSat Technologies wishes Happy Diwali

DDSat Technologies wishes you a very Happy and Prosperous Diwali..

Manufacturer of Satellite Antenna Controller, 3-Axis Satellite Antenna Positioner, Intelligent MDU, PDU, Switched PDU, MDU for Broadcast and IT server room rack power distribution, Automation of Cars, SUVs, Automatic Foot Step, Other customized Automation Products, System Integration, Satellite Communication Training, Project Management, etc

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How to plot Satellite Antenna Transmit Radiation Pattern using Microsoft Excel

This tutorial will help understand use of MS Excel to draw Satellite Antenna Transmit Pattern from the captured .CSV file and superimpose the 29-25LOG(Theta). Once the plots are drawn, 3dB and 15dB beamwidth can be calculated and lastly the antenna Transmit Gain. The .CSV file is saved earlier by rotating the 3.8 meter Prodelin make offset Tx/Rx antenna. This method of drawing 29-25LOG(Theta) can be used where OEM/Proprietary software is not available. Antenna is being tested for Mandatory Performance Verification Test (MPVT) in India by rotating the Satellite Antenna for all three axis. The antenna is said to clear the MPVT when all electrical parameters are within the specified limits. Satellite antenna is then being registered with Indian Regulatory Authority to be used in India for Teleport, Static, DSNG, Flyaway, etc. Other Satellite Operators do not follow this tedious method to get the antenna registered for used on their Satellites Comments are most welcomed.

MESH DISH OR SOLID DISH?

Solid dishes:

Solid dishes offer many advantages over mesh or perforated dishes. Solid dishes are sturdier, they hold their shape and they do not flex in the wind. They are more expensive, but have better value for money. Most popular solid dish is the prime focus one, where the feed/LNB assembly is positioned exactly on the focal point of the dish. Expect solid aluminium dishes to have a useful life of 10 to 20 years. Their efficiency ranges from 60% for dishes greater than 3.0 meters to 75% for smaller dishes.

Solid segmented dishes are also available; segmentation, however, implies reducing shipping costs during transport from one country to the other. Segmenting a parabolic dish causes typically a 10%-20% reduction in efficiency with increased side lobes. There are satellite dishes installed over 20 years ago which are still fully operational in a satisfactory condition.

Mesh or perforated dishes:

Mesh or perforated dishes are more flexible than solid dishes. They move more in the wind – causing the satellite signal to degrade or disappear – and are less durable. Mesh dishes are much less expensive, but need more frequent replacement. Expect mesh or perforated dishes to have a useful life of 3 to 5 years. Other disadvantages of mesh or perforated dishes include poor side lobe rejection of adjacent satellites and the rejection is not consistent from year to year. Furthermore, they have poorer efficiency, typically 35%, since they are improperly segmented. This means that a 2.4 meter solid dish with 70% efficiency performs as good as (if not better than) a 3.4 meter mesh dish!

Offset dishes:

Offset dishes are another type of dish seen on the market. “Offset” means the feed element is purposely kept outside of the “main beam” between the dish and satellite. Offset dishes reduce terrestrial interference and improve the beam shape slightly, but they are more complex to set up and adjust. They have higher efficiencies than prime-focus solid dishes, typically around 75%. However, they are only available in small sizes typically from 60 cm to 2.4 m for TVRO purpose.

Diameter choices come down to one statement: “Bigger is better”. Bigger dishes offer higher gain, they have narrower beamwidths that have better side lobe rejection of adjacent satellites and better rejection of terrestrial interference. Of course this terminology applies only within the same type of dishes, i.e a 3.0 meter solid one piece dish outperforms a 2.4 meter solid one piece antenna. So, theoretically, a 2.4 meter solid one piece dish should perform as good as a 3.4 meter mesh segmented dish. Whist this may be true if the antennas were operated at C band, but believe it or not, experience showed that a 2.4m solid dish outperforms a 5.0m mesh dish at Ku band.

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Satellite Dish (TVRO) Antenna Selection Criteria

When choosing a new antenna, diameter and gain may no longer be the most important parameters. Side-lobe rejection is also now important. Many antennas were sold with a “two degree compliant” sales pitch. This indicates that the side-lobe rejection curve for this antenna meets specified Side-lobe characteristics. This specification alone may not be good enough for reliable operation in a real-world two degree spaced environment.

Mesh or perforated dishes are more flexible than solid dishes. They move more in the wind and are less durable. Mesh dishes are less expensive, but need more frequent replacement. Expect mesh or perforated dishes to have a useful life of 4 to 5 years. Other disadvantages of mesh or perforated dishes include poor side lobe rejection of adjacent satellites and the rejection is not consistent from year to year. Due to less gain efficiency it occupies more roof space compared to solid dishes.  Gain of 16 feet mesh is considered equivalent to 4.5 mtr (14.76 feet) solid dish.

Solid dishes offer many advantages over mesh or perforated dishes. Solid dishes are sturdier, they hold their shape better and they flex less in the wind. They are more expensive, but have a better value for the investment. Expect solid dishes to have a useful life of 10 to 15 years. DDSat recommends using only solid dishes.

Diameter choices come down to one statement: “Bigger is better”. Bigger dishes offer higher gain, they have a narrower “beam” that has better side lobe rejection of adjacent satellites and better rejection of terrestrial interference. DDSat¬†recommends a minimum dish diameter of 3.8 meters. A dish as large as 4.5 meters virtually guarantees headache-free operation for 15 years or more.

Mounting choices are several and you must select very carefully. An improperly mounted dish will move in the wind. Inexpensive mounts may be less durable. Single pole mounts work best when braced with diagonal members also anchored to the foundation. Purchase a high-wind brace kit if it is available for your dish.