propagation thru soil
时间：04-09
整理：3721RD
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Lets say I wanted to measure the microwave loss of a signal going thru soil. I was trying to think of how I could set up an experiment to measure actual signal loss, but I am stuck on one thing.
Lets say I got a cardboard tube, maybe 1/3 meter diameter and 1 meter deep, and stand it on its end. I can bury a transmitting antenna at the bottom of the tube pointing up. I can fill the tube with dirt at various heights, and rest the receiving antenna on top of the dirt as it fills up in steps.
So, as I fill up the tube in steps, I can see the total loss (sum of the lossy dirt, plus the 1/r2 or higher theoretical loss of two free space antennas) of the dirt column. However, how do I seperate the two losses? In other words, how do I figure out the ohmic loss of the dirt, and ignore the 1/r2 normal link loss as the antennas get further apart?
I first thought I would measure the two antennas seperated by varying distances with just air between them, and then repeat the test at those same distances with dirt between them. However, it seems like the radiation patterns of the antennas would be severely modified from the free-space to dirt experiments, and therefore the 1/r2 loss component would have a big error. Also, I can tune up the antenna to work with dirt surrounding it, or to work with air surrounding it, but not both simultaneously, so once again the two experiments would have a big error as I retune the antenna for both.
Any ideas?
Lets say I got a cardboard tube, maybe 1/3 meter diameter and 1 meter deep, and stand it on its end. I can bury a transmitting antenna at the bottom of the tube pointing up. I can fill the tube with dirt at various heights, and rest the receiving antenna on top of the dirt as it fills up in steps.
So, as I fill up the tube in steps, I can see the total loss (sum of the lossy dirt, plus the 1/r2 or higher theoretical loss of two free space antennas) of the dirt column. However, how do I seperate the two losses? In other words, how do I figure out the ohmic loss of the dirt, and ignore the 1/r2 normal link loss as the antennas get further apart?
I first thought I would measure the two antennas seperated by varying distances with just air between them, and then repeat the test at those same distances with dirt between them. However, it seems like the radiation patterns of the antennas would be severely modified from the free-space to dirt experiments, and therefore the 1/r2 loss component would have a big error. Also, I can tune up the antenna to work with dirt surrounding it, or to work with air surrounding it, but not both simultaneously, so once again the two experiments would have a big error as I retune the antenna for both.
Any ideas?
While ago I spent some time doing parts of a project for ?Through Wall Detection Radar?.
Just search for documents related to this subject and you will get some answers.
http://ceta.mit.edu/PIER/pier84/02.08052302.pdf
http://pubs.drdc.gc.ca/PDFS/unc36/p518755.pdf
http://uko.tubitak.gov.tr/ToplantiDo...376a8cf6cf.pdf
Here is a bit of history on this. Many years ago, governments made communication systems that were entirely underground, including the antennas, so that an atomic blast would not destroy the equipment. The problem they found was that there were two paths, up in the air and through the ground. These had different propagation velocities which produced a multipath effect and degraded the BER.