To overcome the constraints of a single subarray, multiple subarrays can be produced with a topology, such as shown in figure 6. In this topology the low noise amplifier (LNA) outputs are split to many analog beamformers where N number of elements can produce M number of analog subarray beams.
Each analog beamformer is programmed for a different antenna pattern. By repeating the figure 6 topology across an array, digitally beamformed patterns can be created at widely disparate angles.
This topology is one type of hybrid architecture that can provide the benefits of every element digital system, but with a reduced waveform generator and receiver count. The trade-off in this case is the analog beamformer complexity. Traditional analog beamformers would have required a single function GaAs phase shifter and single function GaAs attenuator for each antenna element. More advanced approaches integrate the phase shifter and attenuator into a single GaAs front-end IC, that includes the power amplifier (PA), LNA, and switch. Analog Devices' integrated analog beamformer chips achieve significant integration in SiGe BiCMOS technology, that incorporate four channels into a single IC with a reduced footprint, and less power dissipation.
The front-end modules, sometimes called transmit/receive (T/R) modules, provide the interface to the antenna element. The front-end module is critical in terms of transmit power and efficiency, as well as receiver noise. The high power amplifiers (HPA) set the output power. The LNA establishes the system noise performance. Many systems require provisions for calibration or additional filters, and an example front-end module block diagram is shown in figure 7.
Digital beamforming phased arrays are now common, and rapid proliferation is expected with a huge range of frequencies and architectures being developed from L-band through to W-band. Analog Devices is enabling new system developments with SiGe beamformers, microwave frequency conversion, front-end modules, and high speed converters. Our beamforming solutions combined with our power amplifiers, low noise amplifiers, and switch technology enable Analog Devices to be the only antenna-to-bits supplier in the market, offering optimized solutions to our customers’ complex system problems at both the semiconductor and integrated subsystem level.
About the author:
Peter Delos is a technical lead at Analog Devices, in the Aerospace and Defense Group – www.analog.com