Design and analysis of multi-band transmitters for wireless communications
[Examensarbete på avancerad nivå]
The purpose of this thesis is to analyze a transistor under multi-band operation and investigate how termination of the intermodulation products affect device performance. A multi-band active load-pull system is used for device measurements, and the two frequencies of interest are 2.14 GHz and 2.65 GHz, which represent two LTE bands. From measured results, two amplifiers are designed, fabricated and evaluated. The first amplifier is a dual-band power amplifier (DBPA) while the other is designed as a concurrent dual-band power amplifier (CDBPA) and implements proper intermodulation termination. It is shown that the optimal load reflection coefficient for highest efficiency changes between single band transmission and concurrent band transmission for the two frequencies. Depending on the termination of the intermodulation products, located at 1.63 GHz and 3.16 GHz, the efficiency varies between 41.5% and 46%. The fabricated amplifiers show peak efficiencies of 54% and 45% at concurrent transmission for the DBPA and CDBPA, respectively. Using a 5 MHz OFDM signal, the amplifiers show average efficiencies of 26% and 20%, respectively.
Nyckelord: Microwave, Power Amplifier, Load-Pull, Multi-Band