TWTAs are widely used in satellite communications (as for example repeater payloads) that require important amount of power at very high frequencies (above 4 GHz). While providing power rates of Kwatts with good efficiency, TWTA lack in linearity where up to 6 dB output back off is needed to reduce distortions. This is a huge loss compared to the maximum output power that can be provided by these amplifiers.
In order to overcome this problem, analog predistortion is presented as a very effective linearization method in terms of integration, cost and linearity. In this context, we are aiming to design, manufacture and test a predistortion circuit based on two path configuration. In the non-linear path, the distortion generator can provide an expansion or a compression depending on the biasing of the Schottky diodes. Consequently, the linearizer, with different control circuits (input amplification, attenuator, phase shifter), can nearly fit the reverse function of the amplifier.
The assembled circuit was tested around 5.2 GHz. In CW (Continious Wave) test, an improvement of 1.7 dB of 1dB compression output power was achieved while reducing gain compression to 2.6 dB (down from 7.3 dB) and phase lag to 12 degrees (down from 26) near saturation. At 6 dB output back-off, ACPR with QAM-16 signal and C/I3 were improved by 7 dB and 15 dB respectively. This allowed a gain of 2.5 dB in power output at 40 dBc ACPR.
| Date | 13 Mar 2013 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Ammar B. Kouki (Supervisor) |
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Hadouej, T. (Author),
Kouki (Supervisor),
13 Mar 2013Student thesis: Master's thesis › Master in Engineering: Electrical Engineering