# A “figure-8” EM field created by a dipole antenna

This question pertains to the EM field of a Pulse W5017 dipole antenna. The data sheet of this antenna can be found here (which contains information regarding the radiation patterns).

There are TWO parts to this question. Edited to remove the second part. Let's see if anyone can answer the first part.

The radiation patterns of the antennas are as shown below (from the datasheet):

Can the 3D view of the radiation pattern (combining information from both horizontal and vertical planes) be visualized as below? (Ignore the horizontal antenna in the picture, just the two lobes are relevant; in fact my antenna is positioned vertically).

What happens to this lobe with distance?

The answer will only be accepted (and the bounty awarded) if a good intuition is provided in the three dimensions. I have removed the second part already since it requires more research.

An insight into the following parameters would be a bonus!

Frequency [MHz]: 868 - 928
Nominal Impedance: [Ω] 50
Return Loss (dB): -8
Gain (dBi): 2
Polarization: Omnidirectional

• Is there no alternative to physically measuring the fields? In the case of a simple dipole antenna, the fields produced are shown by the diagrams above. I even included a 3D model to visualize horizontal and vertical radiation pattern in one picture. Even if I do measure fields, and find out that the intensity around it changes with height above the floor, I still need a reason for that. – U. Muneeb Jul 15 '16 at 18:57
• You can waste your time on endless FDTD simulations, if you like, but personally that wouldn't be my choice. Get yourself a suitable calibrated measurement setup (RSSI is not useful to begin with) and do it right if you actually care to know what is happening in reality rather than in the numerics of somebody else's electromagnetic code. The "reason" for the field configuration are Maxwell's equations. I don't know what that "insight" buys you, though? I suspect this is a multiple scattering problem, so the solution will be ugly, either way. Have you done any control experiments? – CuriousOne Jul 15 '16 at 19:02
• Yes. When placed on floor (and no breach), there is no dip like that in the first picture. With breaches, there are dips, at the correct times. When placed on bench, the output is crap. Repeated both of these to confirm. The observation is correct and I described my guess for it being the way so is described above (the intruder cutting a greater section of the EM field). – U. Muneeb Jul 15 '16 at 19:06
• The floor may be behaving like a virtual ground plane depending on its material composition. You may consider using image theory to find the overall radiation pattern when the antenna is placed at uniform distances from the ground, i.e., at $\lambda_0/1,2,4$. You can find the correct polarization for the image fields in any good engineering E&M book such as Balanis' EM book or Balanis' antenna book. The distance of the antenna from the floor will certainly affect the overall radiation pattern. – Captainj2001 Jul 16 '16 at 19:36
• @Captainj2001, that is a good research direction. Let's see if someone has a solid answer to this. – U. Muneeb Jul 18 '16 at 5:11

A dipole antenna with the main axis vertical will transmit power in the horizontal plane, with less and less power as you go further away (inverse square law). If you measure the power as a function of angle $\theta$ to the horizontal, you will get a $\cos^2\theta$ relationship. The 3D pattern can be found on many sites - it is shown on http://www.antenna-theory.com/antennas/dipole.php as