Some common questions asked by phased array designers are:
- Should I use an analog beamforming phased array?
- And, what are the benefits and drawbacks of analog beamforming?
It is important to answer these questions because the result may drive decisions in your system design. Therefore, this blog describes analog beamforming and some of the benefits and drawbacks.
For several decades, analog beamforming has been the dominate approach for systems requiring phased array antennas. Analog beamformed phased arrays will likely continue to be used and developed for several decades. The competing technology to analog beamforming is digital beamforming which will be used in O-RAN 5G systems that will be developed and deployed over the next 8-12 years.
What is an analog beamforming array? The answer can be found by looking at the typical block diagram of an analog beamforming array as shown in the figure below. It shows a simple 8 element phased array with an analog beamformer behind the transmit/receive (T/R) modules. In this instance, the analog beamforming is simply a series of power dividers/combiners that split the signal to/from each of the T/R modules.
The configuration shown supports one antenna beam. In the simplest case, for each additional beam, the electronics behind each element in the array need to be repeated.
Given this description, what are the benefits and drawbacks of analog beamforming phased arrays? The table below describes three benefits and three drawbacks of analog beamforming.
A driving factor in several of the benefits and drawbacks is the divider/combiner circuit. This is because it can drive the size/weight and a separate divider/combiner is required for each simultaneous beam. Despite the drawbacks of analog beamforming, it will continue to be used for many years to come.
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1) Simplicity: Single beam arrays are regarded by some as the simplest architecture to implement.
2) Centralized Digital Sampling: The digital sampling occurs after the beamformer, and only one sampler set is required for a simple beam antenna.
3) Less Power Consumption: All things being equal, the use of only one digital sampling stage is lower power than digital sampling at each element in the array as with digital beamformed arrays.
1) Mass: The weight of the analog beamforming power divider/combiners can be significant especially if multiple simultaneous beams are required.
2) RF Interconnects: The beamformer requires the use of interconnects that operate at the frequency of the system which can be challenging and costly.
3) Simultaneous Beam Challenge: It is difficult to achieve more than 3 simultaneous beams in analog beamforming phased arrays due to the electronic packaging challenge.
Block diagram of an 8 element analog phased array showing the antennas, T/R modules, analog beamformer,digital receiver/exciter (DAC/ADC), digital signal processing, and the user interface/rest of the system.