Hi All,
I am working on the design of an S band continuous wave high power amplifier based on 64QAM signal.
The major bottleneck for the time being is the selection of a suitable amplifier/ combination of amplifiers (LDMOS/ GAN based) and using them in such a way that I am able to obtain a high signal linearity with minimum distortion (might utilize some pre-distortion techniques), and am able to achieve a low bit error rate and phase distortion within a band of approx 300-400MHz.
I am initially targeting a power of 300-400watts which I will at the later stage increase using an array of transmitting antennas.
Any guidelines/ suitable research material would be highly appreciated.
Regards
Anum
It seems efficiency is not important for your design. If you use single stage (not doherty or ourphasing), you need to operate at deep back-off power to achieve high linearity. Although linearity of the LDMOS devices are better, they usually have internal matching structures (matchng circuit in the package) which can cause some design issues for wideband operation. High power GaN products are suitable to achieve 300-400 W output power. You can check companies reference designs for wideband. But you need to optimize videobandwidth and RF bandwidth to have a successful DPD.
Perfectly explained by Osman Ceylan , LDMOS devices have better linearity, but will give you less efficiency plus u have to be more careful abt harmonic control with GaN.
Optimization of RF bandwidth. For wide band operations you have to choose the perfect GaN. LDMOS have less efficiency, LDMOS based on Class F amplifier will be fine. Pre-distorted signal measurement is very useful case in this experiment to get an adaptive DPD.
Follow these ref. :
Ma, G.; Qiang Chen; Tornblad, O.; Tao Wei; Ahrens, C. and Gerlach, R. (2005). High Frequency Power LDMOS Technologies for Base Station Applications Status, Potential, and Benchmarking, Electron Devices Meeting, 2005. IEDM Technical Digest. IEEE International, pp. 361 – 364, ISBN 0-7803-9268-X, Washington DC, USA, 5 Dec. 2005
Aflaki, P.; Negra, R. and Ghannouchi, F. M. (2009). Enhanced Architecture for Microwave Current Mode Class-D Amplifiers Applied to the Design of an S-Band GaN-Based PA, IET Microwave Antenna & Propagation, Vol.3, No. 6, pp.997–1006, Sep. 2009, doi:10.1049/iet-map.2008.0282
Goto, S.; Kunii, T.; Inoue, A.; Izawa, K.; Ishikawa, T. and Matsuda, Y.; Efficiency enhancement of Doherty amplifier with combination of class-F and inverse class-F schemes for S-band base station application, 2004 IEEE MTT-S International Microwave Symposium Digest, Vol.2, pp. 839 – 842, ISSN 0149-645X
Kikkawa, T.; Maniwa, T.; Hayashi, H.; Kanamura, M.; Yokokawa, S.; Nishi, M.; Adachi, N.; Yokoyama, M.; Tateno, Y.; Joshin, K. (2004). An Over 200-W Output Power GaN HEMT Push-Pull Amplifier with High Reliability, 2004 IEEE MTT-S International Microwave Symposium Digest, Vol.3, pp. 1347 – 1350, 6-11 June 2004, ISSN 0149-645X
Dear Anum,
To achieve the highest linearity you may use class A transformer coupled amplifier that has the highest efficiency of 50 %. To achieve higher efficiency you may go to class AB amplifier. You need to design wide band LC band pass filter to from the output of the amplifier to the load MATCHING and for selectivity. You can use a wide band common emitter amplifier as driver. Basically you will build your amplifier as two stage amplifier one driver stage and one end amplifier stage with captive coupling.
You can use bipolar silicon transistors with the suitable rating.
There are vendors producing such amplifier with specifications that match your amplifier specifications. You can follow them as they have experience in designing microwave components.
Best wishes
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