Path Loss Model for short range and low antenna height ? - RF Cafe Forums

 Post subject: Path Loss Model for short range and low antenna height ?

Posted: Mon Feb 09, 2009 12:51 pm 

Any suggestions for a simple 'Generic' model for estimating path loss over short range (less than 1km) and with antennas at 1m.

I was very surprised to find that the old faithfuls for example the Hata-Okumura just don't cut the mustard for this scenario. The Hata-Okumura is not valid below 1km and it base station antenna height minimum is 30m. Similar range and or antenna height limits seem to be quite the norm for many other models.

The only model I could find was the log distance model. Thats fine but it has no consideration for antenna height at all and I have no idea where the table of path loss exponents that are often cited with this model originally come from? More painfully though the path loss exponents dont cover suburban or rural.

Any takers?

Steve

Posted: Mon Feb 09, 2009 12:51 pm 

Oops forgot to mention the frequency...... Around 900 MHz would be useful?

 Post subject: Re: Path Loss Model for short range and low antenna height ?

Posted: Tue Feb 10, 2009 3:50 am 

I think you need to look into Airy's analysis of the diffraction shadow zone.
When radio was demonstrated late in the 19th century, many physicists and math dudes were consulted to try and analyze and thus predict signal levels in the diffraction zone. The curves given in the ITU-R tomes (I forget the reference numbers until I get back to base) for signal level vs distance over a smoothly curved earth are heavily based on the work of Airy, who seems to have been the most successful of the many who looked into the problem.
I believe the mechanism is a two-component dielectric trapped wave, that propagates partly in the high dielectric constant medium (the ground) and partly in the air (k=1) immediately above it. There has also been some work done in the last 15 years for the same mechanism but between sea water and the air. However, as it relates to clandestine submarine communications, it is still classified as far as I know.

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 Post subject: Re: Path Loss Model for short range and low antenna height ?

Posted: Tue Feb 10, 2009 6:20 am 

Thanks for the tip, I will check that out.

Steve

 Post subject: Re: Path Loss Model for short range and low antenna height ?

Posted: Tue May 19, 2009 8:56 am 

Hi steve,

Please have you been able to solve the issues of antenna heights and the right propagation model to use? I'm currently experiencing the same problem. I need to analyze the link between two mobile stations of 1.5m height transmitting in a direct mode. Please could you share your findings with me? Thanks in advance.

Deolah