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Advantages of Orthomode Transducer | Disadvantages of OMT

This page covers advantages and disadvantages of Orthomode Transducer (OMT). It mentions benefits or advantages of Orthomode Transducer and drawbacks or disadvantages of Orthomode Transducer.

What is Orthomode Transducer (OMT) ?

It is a three port waveguide component which combines horizontally polarized signal and vertically polarized signal to circularly polarized or elliptically polarized signal. As there are total three ports each of these signals are available on one port each. It can also receive circular polarized signal and divides it into horizontal and vertical plane with different polarizations. Due to its functions, it is also known as polarization duplexer. It is commonly used in terrestrial microwave radio links and ground based satellite systems.

OMT - Orthomode Transducer

The figure depicts one such C band orthomode transducer (OMT) used in VSAT system. It is mounted along with feed horn antenna at the centre of VSAT disc. Circular port is coupled with circular horn antenna and other two ports are coupled with two rectangular waveguides. As shown, transmit port is connected with output of power amplifier (PA) after RF up conversion or it can be directly connected with BUC (Block Up converter). BUC contains both PA and RF Up converter. Receive port is connected with LNA (Low Noise Amplifier) or LNB (Low Noise Block Converter). LNB contains both LNA and RF Down Converter. Refer design and development of RF Transceiver >> and design guidelines of RF Frequency Converter >>.

Orthomode transducers are available for different frequency bands which can easily be employed as per application usage. Common frequency bands for which OMTs are designed include C band, X band, Ku band, K band and Ka band.

In summary, we can derive two major functions of Orthomode Transducer (OMT).
• It separates and directs signals of two different polarities.
• It acts as T-junction device which provides connectivity between two rectangular and one circular waveguide.
• It determines isolation required for circular polarization.

C/Ku band OMT serves two terminals at C band and Ku band simultaneously. It separates incoming signals based on polarization and frequency and delivers signals to two distinct ports for further processing by respective C/Ku band modules. One such C/Ku band OMT has been developed by Space Applications Center division of ISRO Ahmedabad, INDIA.

Benefits or advantages of Orthomode Transducer (OMT)

Following are the benefits or advantages of Orthomode Transducer i.e. OMT :
➨It helps to use same VSAT for simultaneous transmission and reception by acting as polarization duplexing device. Hence it increases satellite capacity by allowing frequency re-use at different polarizations.
➨Polarization adjustments are not required in circular polarized antenna system as it is fixed by OMT.
➨It offers superior cross polarization performance.
➨It is very small in size. Hence it does not block RF signal.
➨It is very light in weight which can easily be fixed by single RF technician. It can be installed in less time.
➨Latest OMTs such as C/Ku Orthomode transducer allows combination of separate C band VSAT terminal and Ku band VSAT terminal into a single system. This saves considerable amount of cost savings due to minimization of infrastructure hardware.
➨It offers low insertion loss, good return loss and good isolation at appropriate ports as desired.

Drawbacks or disadvantages of Orthomode Transducer (OMT)

There are not many drawbacks or disadvantages of Orthomode Transducer i.e. OMT as such.
➨Use of OMT in the wireless system increases cost of the overall antenna system. This factor has become negligible after advancement in manufacturing techniques.
➨While selecting OMT, return loss of all the three ports and isolation between ports should be chosen better. Poor return loss and isolation degrades performance of the wireless satellite system housing OMT.

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