antenna-theory.com

[pascualhr]

Hi everyone,

I have one question which confuse me a lot. Here I go:

Let's consider an ideal isotropic antenna which radiates 10dBm (Ptx0 = 5dBm; Gtx = 5dB) and taking into account path losses at 0.5m of distance, we have a signal level of -14dBm.



Now, in the receiver part we have a 2x2 planar array antenna and my question is the following. Is each one of the 4 patches receiving -14dBm? Or is the whole system which is receiving this power and hence the power received at each element would be -14dBm splitted by 4?

If apart from the answer you could explain me why that would be great.

Thank you so much in advance guys.

[hagster]

Firstly if you have an ideal isotropic antenna its gain will be 0dBi not 5dBi(noting you missed off the unit). Maybe you mean omni directional which could have a gain of 5dBi.

Your pathloss figure is only true for a specific frequency. From my calculations it is about 800MHz? This tells me that your 0.5 meter seperation is still in the near field. Hence in the rral world we are not dealinng with a plane wave and potrntially there are mutual coupling effcts between the tx and rx antennas.

Your 2x2 array (assuming its pointed in the right direction and with a matching polorisation) will have its own gain figue. This is the number you use to work out the total received power in dBm. Then assuming it it 100% efficient, you can divide this by 4(remember you are in dB so you really just subtract ~6dB).

You can also think of the same problem in terms of power density over the receiving sphere. In this case you need to be thinking about the effective appertures of your antennas not gain figures.