Flexible and Efficient Microwave Power Amplifier for Future Remote Radio Head Applications
Fig. 1: Circuit of the dual-band class-D PA for 0.8/1.8 GHz.
Fig. 2: Realized module of the dual band class-D PA.
Today's mobile communication infrastructure demands for high flexibility, low cost, and high efficiency. As a consequence, the RF power amplifier (PA) as a key part in the transmitter architecture needs to be optimized further. A particular challenge is multi-band capability – a lot of efforts have been devoted to this issue in the last years. Most of the realizations use linear PA concepts and/or their combinations. When targeting a transmitter with increased digital contents – and thus higher efficiency and capability – the class-S and class-D type of amplifiers have proven to be suitable candidates. However, in the microwave frequency range only single-band realizations have been published so far.
At FBH, the first dual-band power amplifier of this type has been realized. It combines a voltage-mode GaN digital PA and a filter with SMD elements at the output for the 0.8/1.8 GHz LTE frequency bands, the 4th generation mobile communications standard. This results in a very compact and highly flexible amplifier module, which is important for future remote radio-head installations. Such installations are particularly robust and compact assemblies that are mounted directly at the antenna mast. They require only a small form factor comprising power supply, transmitter, receiver as well as output amplifier. By placing the module close to the antenna, a lower transmission power is necessary with peak output powers in the 10 W range; the efficiency significantly increases. Fig. 1 shows the concept and Fig. 2 the realized PA module:
The amplifier achieves maximum output powers of 5.4 W and 4.3 W at 850 MHz and 1.8 GHz, respectively. At these output powers a large-signal gain of 23 dB (850 MHz) and 22 dB (1.8 GHz) has been achieved. Maximum drain efficiencies of the final stage reach 84% at 850 MHz and 54% at 1.8 GHz, in the full-scale case. At 12 dB back-off efficiency decreases to 20% and 10% for 850 MHz and 1.8 GHz signal frequency, respectively.
This is the first demonstration of a pulse-modulation based S-class dual-band PA in the microwave frequency range at output powers beyond 1 W. At the same time, the FBH voltage-mode class-D approach offers full flexibility of the input signal and facilitates integration into the next-generation digital transmitter architectures. The results confirm FBH's leading role in this field of research. They were presented at the IEEE International Microwave Symposium in Seattle.
Publication:
A. Wentzel, S. Chevtchenko, P. Kurpas, W. Heinrich, "A Dual-Band Voltage-Mode Class-D PA for 0.8/1.8 GHz Applications", IEEE MTT-S Int. Microw. Symp. Dig., Seattle, USA, Jun 2-7, TH3A-3 (2013).
FBH research: 17.07.2013