Wavelength Dependency in RF Propagation?

Started by Randy Yates May 26, 2018
In an article in a recent issue of Microwaves & RF magazine, Jack
Browne makes the following statement:

  Frequency plays a part in any link budget, especially for longer links,
  since long-distance links require the LONGER PROPAGATION DISTANCES of
  larger-wave-length, lower-frequency signals rather than
  smaller-wavelength, higher-frequency signals.

(emphasis mine). 

I was miffed initially by this statement since, as far as I know, there
is nothing inherent in wavelength that impacts how RF waves travel
through space.

But I guess this was just a way (a confusing one, IMO) of referring to
the wavelength dependency of antenna aperture, as explained nicely
in this article on the Friis equation? 

  http://www.antenna-theory.com/basics/friis.php

@article{microwaves-and-rf-difference-between-long-and-short-haul-links,
  title = "What's the Difference Between Long- and Short-Haul Links?",
  author = "Jack Browne",
  journal = "Microwaves \& RF Magazine",
  month = "April",
  year = "2018"}
-- 
Randy Yates, DSP/Embedded Firmware Developer
Digital Signal Labs
http://www.digitalsignallabs.com
On 26.05.18 07.40, Randy Yates wrote:
> I was miffed initially by this statement since, as far as I know, there > is nothing inherent in wavelength that impacts how RF waves travel > through space.
If you are talking about vacuum then yes. In all other media the velocity of propagation depends on the frequency. E.g. water molecules in the air interact frequency dependent.
> But I guess this was just a way (a confusing one, IMO) of referring to > the wavelength dependency of antenna aperture, as explained nicely > in this article on the Friis equation?
The coupling of the antenna to the free space also introduces a frequency dependent group delay. And last but not least a short distance link has some frequencies with poor performance due to eigenvalues of the overall geometry. Marcel
On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
<yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack >Browne makes the following statement: > > Frequency plays a part in any link budget, especially for longer links, > since long-distance links require the LONGER PROPAGATION DISTANCES of > larger-wave-length, lower-frequency signals rather than > smaller-wavelength, higher-frequency signals. > >(emphasis mine). > >I was miffed initially by this statement since, as far as I know, there >is nothing inherent in wavelength that impacts how RF waves travel >through space. > >But I guess this was just a way (a confusing one, IMO) of referring to >the wavelength dependency of antenna aperture, as explained nicely >in this article on the Friis equation? > > http://www.antenna-theory.com/basics/friis.php > >@article{microwaves-and-rf-difference-between-long-and-short-haul-links, > title = "What's the Difference Between Long- and Short-Haul Links?", > author = "Jack Browne", > journal = "Microwaves \& RF Magazine", > month = "April", > year = "2018"}
I don't suppose he could have been referring to ground wave or ionospheric propagation associated with low frequency transmissions ?..... Or, how higher frequencies have more of a line of site characteristic ? boB
Hi Marcel,

Thank you for responding and discussing.

Marcel Mueller <news.5.maazl@spamgourmet.org> writes:

> On 26.05.18 07.40, Randy Yates wrote: >> I was miffed initially by this statement since, as far as I know, there >> is nothing inherent in wavelength that impacts how RF waves travel >> through space. > > If you are talking about vacuum then yes. In all other media the > velocity of propagation depends on the frequency. E.g. water molecules > in the air interact frequency dependent.
Does the velocity of propagation affect path loss/attenuation?
>> But I guess this was just a way (a confusing one, IMO) of referring to >> the wavelength dependency of antenna aperture, as explained nicely >> in this article on the Friis equation? > > The coupling of the antenna to the free space also introduces a > frequency dependent group delay.
I didn't know that. I can certainly see that group delay impacts the overall response (namely, the phase response), but it doesn't cause attenuatation. I was mainly interested in attenutation.
> And last but not least a short distance link has some frequencies with > poor performance due to eigenvalues of the overall geometry.
I love it! Applying linear algebra to wave propagation! Do you have a reference (hopefully easy to read)? -- Randy Yates, DSP/Embedded Firmware Developer Digital Signal Labs http://www.digitalsignallabs.com
On Sat, 26 May 2018 01:40:39 -0400, Randy Yates
<yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack >Browne makes the following statement: > > Frequency plays a part in any link budget, especially for longer links, > since long-distance links require the LONGER PROPAGATION DISTANCES of > larger-wave-length, lower-frequency signals rather than > smaller-wavelength, higher-frequency signals. > >(emphasis mine). > >I was miffed initially by this statement since, as far as I know, there >is nothing inherent in wavelength that impacts how RF waves travel >through space. > >But I guess this was just a way (a confusing one, IMO) of referring to >the wavelength dependency of antenna aperture, as explained nicely >in this article on the Friis equation? > > http://www.antenna-theory.com/basics/friis.php >
For the most part you're right, the frequency effects are predominantly associated with antenna characteristics. I wrote and article about it about a decade ago: https://www.dsprelated.com/showarticle/62.php There are some atmospheric effects, etc., that are frequency dependent, and materials penetration/reflection is frequency dependent, but for the most part free space propagation is independent of frequency.
Randy Yates  <yates@digitalsignallabs.com> wrote:

>In an article in a recent issue of Microwaves & RF magazine, Jack >Browne makes the following statement:
> Frequency plays a part in any link budget, especially for longer links, > since long-distance links require the LONGER PROPAGATION DISTANCES of > larger-wave-length, lower-frequency signals rather than > smaller-wavelength, higher-frequency signals. > >(emphasis mine). > >I was miffed initially by this statement since, as far as I know, there >is nothing inherent in wavelength that impacts how RF waves travel >through space. > >But I guess this was just a way (a confusing one, IMO) of referring to >the wavelength dependency of antenna aperture, as explained nicely >in this article on the Friis equation?
It's a pretty sloppy statement at best. The Friis pathloss assumes 0 dBi antennas, and the aperture of a 0 dBi antenna is about 0.05 times the wavelength squared. (Some sources say 0.07.) The aperture of a parabolic dish is roughly the area of the dish, so a given size dish has more gain (in dBi) at shorter wavelengths. This is why space communications uses short wavelengths. The (perfectly executed) New Horizon mission to Pluto operated at 6 GHz. I'm betting Jack Bronwe never worked on a space datalink? That or they just slipped up when they wrote this. Steve
Marcel Mueller wrote:
> On 26.05.18 07.40, Randy Yates wrote: >> I was miffed initially by this statement since, as far as I know, >> there is nothing inherent in wavelength that impacts how RF waves >> travel through space. > > If you are talking about vacuum then yes. In all other media the > velocity of propagation depends on the frequency. E.g. water > molecules in the air interact frequency dependent. > >> But I guess this was just a way (a confusing one, IMO) of referring >> to the wavelength dependency of antenna aperture, as explained >> nicely in this article on the Friis equation? > > The coupling of the antenna to the free space also introduces a > frequency dependent group delay.
All necessary apologies in advance. All group delay is inherently frequency dependent: " Group delay is the actual transit time of a signal through a device under test as a function of frequency." http://na.support.keysight.com/pna/help/latest/Tutorials/Group_Delay6_5.htm A reasonable definition. I have the conceit that I'm not picking nits here so much as heading off one potentially confusing interpretation of that sentence :) The "quantifiers" for "a group delay" sort of leaves the phrase "for all group delay" dangling.
> And last but not least a short > distance link has some frequencies with poor performance due to > eigenvalues of the overall geometry. >
Aka comb filtering/multipath/cosite interference?
> > Marcel
-- Les Cargill