# What is the advantage of multiple antenna in receiver in energy harvesting ?harvested more power?

What is the advantage of multiple antenna in receiver in energy harvesting ?

Assume there are $$3$$ transmitted antennas in the A device,and $$1$$ received antenna in the B device,now assume A device use beamforming with $$3$$ antenna to transmit some signal to B device,and B device harvest $$0.1W$$ power from the signal.

Now if i add one more received antenna to device B,that is, there are $$2$$ antennas in B device now,and assume these two antennas are very closed,how much power will device B harvest now? still $$0.1W$$? or $$0.1W\times2$$ ?

I am confused about this question,because if device B still harvest $$0.1W$$,then what is the advantage of multiple antenna in receiver in energy harvesting ?

If device B harvest $$0.1W\times2$$,and this mean if i want to create power,i just use $$1$$ antenna to transmit 1W RF power to a receiver with $$\infty$$ antennas receiver,then i can get $$0.1W\times \infty$$ power ,but it is impossible .

• The harvested power would improve with more receive antennas, but I am not sure by how much exactly. You cannot use $\infty$ antennas at the receiver because of physical limitations, like device's size, and sometimes computational limitations. Also, after a certain number of antennas, the improvement may not be significant, as it's the case with receive diversity, for example. – BlackMath Nov 9 '19 at 12:39
• So if the antenna number of B become 2,will the harvested power become $0.1 \times 2$? if the device A just transmit the one signal to B – Sylvindrunner Nov 9 '19 at 13:22
• @BlackMath I have add my thinking in the answer,do you accept my thinking? – Sylvindrunner Nov 9 '19 at 13:30
• These questions are valid, but need research and mathematical derivations. I haven't worked on this topic before, but there should be improvement. The only thing to proof is by how much. I suggest to get a paper on the topic and read it. – BlackMath Nov 9 '19 at 19:22

After thinking,i think when the antenna number of device B become 2,the harvested power of B will not become $$0.1W \times 2$$,WHY?
However,if the antenna number become two,device A has to let both of two antenna of B receive or harvest the signal,so the beamforming direction has to change,maybe the middle of these two antenna,so now first antenna will harvest about $$0.05W$$,and the other will receive $$0.05W$$ as well.Or perhaps $$0.06W$$ and $$0.04W$$,but the total power will not be larger than 0.1W
• "first antenna will harvest about $0.05 \text{ W}$, and the other will receive $0.05 \text{ W}$ as well". That is not true. Maybe you're thinking along the lines of conservation of energy so everything should equal out, but that is not true. Most simple counter example is think of two receive antennas at equidistant points from the transmitter in free space, then why wouldn't each receive the transmit power minus the path loss? – Engineer Dec 3 '20 at 18:06