How to Minimise near field

Hi,
How can the length of the near field of a microstrip antenna be reduced?
The wevelength is 403MHz, the microstrip resonates at 1/4 lamda, the substrate has an Er=35.
The near field at the moment is too large, can it be reduced?
Thank you.
Kind Regards.

You are pretty much hemmed in by the physics of the situation. The antenna has to be a certain size to have the proper impedance (especially no reactive component). This sets the current and voltage distribution. Physics takes over and sets the three fields ( 1/r^3 1/r^2 and 1/r) the first is the reactive field, the second is the near field and the third is the far field.

For a particular wavelength, the only way to reduce the near field (reactive or radiating) is to reduce the physical dimension of the antenna (at the expense of losing efficiency).

Would a high Er superstrate cover help?
Also, if I thin the antenna down, could I not find the impedance match buy moving the side feed around the periphery until a match was found?
Thank you.

Added after 39 seconds:

flatulent said:

You are pretty much hemmed in by the physics of the situation. The antenna has to be a certain size to have the proper impedance (especially no reactive component). This sets the current and voltage distribution. Physics takes over and sets the three fields ( 1/r^3 1/r^2 and 1/r) the first is the reactive field, the second is the near field and the third is the far field.

Click to expand...

Would a high Er superstrate cover help?
Also, if I thin the antenna down, could I not find the impedance match buy moving the side feed around the periphery until a match was found?
Thank you.

Added after 54 seconds:

vfone said:

For a particular wavelength, the only way to reduce the near field (reactive or radiating) is to reduce the physical dimension of the antenna (at the expense of losing efficiency).

Click to expand...

Would a high dielectric constant cover help?

Thank you.

What do you mean by near field? I suspect you mean the reactive (non-radiating) field of the antenna. Near-field can also refer to the radiating field close to the antenna. If you mean the reactive field, this will tend to concentrate in any dielectric loading you have so this will certainly work for you. the problem is that this will likely alter the impedance and pattern of your antenna so you need to design the antenna with the loading in mind. You can also load the antenna with a magneto-dielectric (both dielectric and magnetic) loading. This will tend not to affect the impedance as much, but will still concentrate your reactive field.

You could also use a short wavelength if that is possible.

You may be able to tolerate having a larger reactive field if it is magnetic instead of electric. Current based antennas like loops have mostly a magnetic reactive field that doesn't interact strongly with dielectrics in close proximity. You'll see these antennas in wearable electronics for that reason.

-Tip