# What will be antenna impedance of a dipole antenna when it is kept lambda/2 away from the transmitter

I understand that half-wave dipole antenna, which is in far-field, impedance is around 73 ohms. If I keep same antenna in near-fied at distnace lambda/2 from the 1.25 lambda length tranmiter?

• Your question is not clear. Can you explain in more detail what the arrangement of wires looks like? One 0.5 wave, one 1.25, 0.5 wavelengths apart? What's connected to each feed point? Where do you want to know the impedance? This will help us give a useful answer. Sep 28, 2015 at 14:22
• The tranmitter is a 5 db, 10 cm lenght dipole antenna. The receiving antenna is a half wave dipole antenna, which is a part of rectenna, is kept lambda/2 distance from the transmitting antenna. I am trying design a matching circuit for which I need to know receiving half wave dipole antenna source impedance to match it with rectifier input impedance. I am thinking that since receiving antenna is located in the near-filed radiating region (2.4 GHz operating freq), its impedance is not 73 ohms. Oct 2, 2015 at 22:10
• You need the formula for the mutual impedance of two parallel dipoles, it's not too complicated. Search the internet or try this paper as an example. You should probably assume that the source antenna is a simple dipole, for this calculation. Oct 4, 2015 at 6:39
• Otherwise, it might be easier to simulate it, in NEC or FEKO. This will help you adjust the position of the two antennas for maximum coupling too. Oct 4, 2015 at 6:41
• Thank you tomnexus. I will try and let you know. Thanks again. Oct 4, 2015 at 17:22