Near field antenna
Near field antenna
(OP)
Hello guys,
I am looking for UHF (915 MHZ) near field antenna. Can anybody help me regarding what are the possible types like one possiblity is small dipole antenna. Can we design a microstrip patch antenna for near field response.
It will really help me if you guys can give links to some material about near field antenna design.
thanks alot
I am looking for UHF (915 MHZ) near field antenna. Can anybody help me regarding what are the possible types like one possiblity is small dipole antenna. Can we design a microstrip patch antenna for near field response.
It will really help me if you guys can give links to some material about near field antenna design.
thanks alot





RE: Near field antenna
RE: Near field antenna
VSWR changes greatly only when dipoles get about 1/4-1/2 wavelength from metal, which is pretty close.
Explain the application please. Heating? probing, reduction in snoring?
kch
PS re: snoring, (not a joke, latest Microwave magazine shows snoring is stopped by nearfield microwave heating to form a deep scar in tissue stopping nighttime vibrations)
RE: Near field antenna
thanks for the reply.
I am trying to design UHF RFID near field reader antenna, from what I understand, when you make dipole with much less lenth than required half wavelenth and able to match the impedance, that dipole antenna can acts as a good near field antenna than the far field antenna. May be iam wrong in my opinion. For the reader should I use microstrip patch antenna or dipole. Which one gives the better performance in the near field.
thanks
RE: Near field antenna
What are your size restrictions? i.e. what's your frequency and what physical size is your maximum for this antenna?
Patch antennas are more easily shrunk than dipoles.
kch
RE: Near field antenna
I dont have any restriction on antenna size, it can be any size but I need a good antenna for near field reading.
thanks again
RE: Near field antenna
Just about any antenna that's 1/4 wavelength having good VSWR will be efficient. You will not see much variation in results unless you have some metal environment, then placement of the antenna will change the results. If you compare the antenna I described to a perfect dipole or patch, they will probably be very similar.
kch
RE: Near field antenna
The 0.25 wavelength dipole he suggested would work OK or you could bend it into a loop, soldering the center conductor back to the braid. The loop will have a poorer VSWR but a more localised reception pattern and might be better in the near field.
RE: Near field antenna
Really thanks for the reply.
I am trying to design near field antenna for UHF RFID reader. We need some kind of coupling in near field for RFID system to work. HF RFID systems use magnetic coupling with the help of two electrically small loop antennas ( one in reader and one in tag). But for UHF RFID system we already have elctrically small dipole antenna for tag, so I am looking for reader antenna, which I can use for communication between reader antenna and tag antenna. I think, if I use loop antenna with an dipole antenna on the other end do you think is there any kind coupling between them in the near field? can we use dipole antennas for capacitive coupling?
RE: Near field antenna
For this reason it is difficult to calculate what the near field coupling will be and I would take a practical approach to this and try it on a spectrum analyser. Measure the signal from each antenna with the ID tag held nearby in all sorts of attitudes. You need signal strength - and capacitive coupling will be effective very close in.
RE: Near field antenna
RE: Near field antenna
kch