Forums

Microwave communications

Started by Unknown July 31, 2008
I need to design a system that communicates in the microwave range (>
5GHz) using a horn antenna... Does any body know if there are any off
the shelf chipsets, or can point me in the direction of any reference
designs or manufacturers. The system would be very low power.

Cheers
Ross
On Wed, 30 Jul 2008 23:31:32 -0700 (PDT), ross.g.marchant@gmail.com
wrote:

>I need to design a system that communicates in the microwave range (> >5GHz) using a horn antenna... Does any body know if there are any off >the shelf chipsets, or can point me in the direction of any reference >designs or manufacturers. The system would be very low power.
In which countries should this system operate. Are you prepared to do the type acceptance testing required in some countries ? A horn antenna would suggest line of sight communication and quite high effective radiation power (EiRP), so this would rule out any licence-free bands and a license is required for the system. You did not specify the frequency range, but it is hard to get any chip sets running directly at say 10 GHz. In practice you would have to use a receiver preamplifier on the microwave frequency, then mix down the received microwave signal to a lower intermediate frequency (IF) and then do the processing at a lower frequency. For transmitting, generate the signal at some lower frequency, mix it up with a local oscillator, apply some power amplification before the antenna. Paul
On 31.07.2008 08:31, ross.g.marchant@gmail.com wrote:
> I need to design a system that communicates in the microwave range (> > 5GHz) using a horn antenna... Does any body know if there are any off > the shelf chipsets, or can point me in the direction of any reference > designs or manufacturers. The system would be very low power. > > Cheers > Ross
Try this one: http://www.microwaves101.com/cgi-bin/messageboard/yabb.pl Best Regards, Andreas
<ross.g.marchant@gmail.com> a &#2013265929;crit dans le message de news: 
74d5f1cf-3115-45c0-b38e-7d0154644fbb@q28g2000prh.googlegroups.com...
>I need to design a system that communicates in the microwave range (> > 5GHz) using a horn antenna... Does any body know if there are any off > the shelf chipsets, or can point me in the direction of any reference > designs or manufacturers. The system would be very low power. > > Cheers > Ross
Mimix has some chips for the 24GHz band (U1010, etc). Hittite too. Cheers, Robert www.alciom.com The mixed signal experts
On Jul 31, 5:20=A0pm, Paul Keinanen <keina...@sci.fi> wrote:
> On Wed, 30 Jul 2008 23:31:32 -0700 (PDT), ross.g.march...@gmail.com > wrote: > > >I need to design a system that communicates in the microwave range (> > >5GHz) using a horn antenna... Does any body know if there are any off > >the shelf chipsets, or can point me in the direction of any reference > >designs or manufacturers. The system would be very low power. > > In which countries should this system operate. Are you prepared to do > the type acceptance testing required in some countries ? > > A horn antenna would suggest line of sight communication and quite > high effective radiation power (EiRP), so this would rule out any > licence-free bands and a license is required for the system. > > You did not specify the frequency range, but it is hard to get any > chip sets running directly at say 10 GHz. In practice you would have > to use a receiver preamplifier on the microwave frequency, then mix > down the received microwave signal to a lower intermediate frequency > (IF) and then do the processing at a lower frequency. > > For transmitting, generate the signal at some lower frequency, mix it > up with a local oscillator, apply some power amplification before the > antenna. > > Paul
Thanks for the replies. We are investigating a microwave link through a small steel pipe that is about 3km long. From my basic calculations the cutoff frequency for this waveguide was about 2GHz so I was thinking about >5GHz to minimise transmission losses. I think that a horn antenna would be good to direct the energy, but do they transmit at a particular 'mode'? Would common 2.4GHz stuff like 802.11a / b / g work better? I haven't really looked into this kind of thing before, so I don't really know how much work would be required :) Hmmm gotta get a newsreader... google groups just pasted my email all over the net
On Thu, 31 Jul 2008 20:33:36 -0700 (PDT), geomet
<ross.g.marchant@gmail.com> wrote:

<snip>
> >We are investigating a microwave link through a small steel pipe that >is about 3km long. From my basic calculations the cutoff frequency for >this waveguide was about 2GHz so I was thinking about >5GHz to >minimise transmission losses. I think that a horn antenna would be >good to direct the energy, but do they transmit at a particular >'mode'? Would common 2.4GHz stuff like 802.11a / b / g work better? I >haven't really looked into this kind of thing before, so I don't >really know how much work would be required :) >
Why not just run some fibre thru the pipe? Ought to be a lot easier than messing with microwaves. Probably get a lot better bandwidth, too. -- ArarghMail807 at [drop the 'http://www.' from ->] http://www.arargh.com BCET Basic Compiler Page: http://www.arargh.com/basic/index.html To reply by email, remove the extra stuff from the reply address.
On Thu, 31 Jul 2008 20:33:36 -0700 (PDT), geomet
<ross.g.marchant@gmail.com> wrote:

>We are investigating a microwave link through a small steel pipe that >is about 3km long. From my basic calculations the cutoff frequency for >this waveguide was about 2GHz
If the dielectric constant of the gas significantly differs from that of air, did you take this into consideration when calculating the cut-off frequency ?
>so I was thinking about >5GHz to >minimise transmission losses.
Components made for 2.4 or 5.7 GHz WLAN systems should be of interest.
>I think that a horn antenna would be >good to direct the energy, but do they transmit at a particular >'mode'?
Microwave power is usually connected to the waveguide using an electric or magnetic probe. The magnetic probe might be a better choice, since it can be made smaller, thus causing less resistance to the gas flowing in the tube. There is no need to use a directional horn, since the waveguide is directing the power anyway. The omnidirectional probe will launch power in both directions along the waveguide, but placing a metallic screen (net) at a critical distance from the probe will direct the power in one direction only and thus, increase the signal by 3 dB. Such a small increase might not justify the cost of the screen. At least the fundamental propagation mode does not like sharp bends, frequencies well above the cut-off frequency in some higher propagation mode might propagate better through sharp bends. With a very high frequency signal compared to the waveguide cut-off frequency, there can be multiple propagation modes just like in a multimode optical fiber. In these the maximum _symbol_ rate for a specific distance is limited by the dispersion due to multiple propagation modes having different propagation times. To get around this, WDM (Wavelength Division Multiplexing) is sometimes used on VHF/UHF/SHF OFDM is often used to reduce the symbol rate by sending multiple streams in parallel at different frequencies. With 2 GHz cut-off and 5.7 GHz signal there are only a few possible propagation modes, so you might get away without OFDM, but at least you should be able to change the frequency slightly, if there are some unfavorable propagation modes canceling each other at a specific distance. However, if the dielectric constant of the gas might vary e.g. due to change of temperature, pressure or consistence, the location of nulls might change, calling for frequency changes. To avoid this, OFDM or some wide band spread spectrum system could be used. Paul
On Aug 1, 3:47=A0pm, Paul Keinanen <keina...@sci.fi> wrote:
> On Thu, 31 Jul 2008 20:33:36 -0700 (PDT), geomet > > <ross.g.march...@gmail.com> wrote: > >We are investigating a microwave link through a small steel pipe that > >is about 3km long. From my basic calculations the cutoff frequency for > >this waveguide was about 2GHz > > If the dielectric constant of the gas significantly differs from that > of air, did you take this into consideration when calculating the > cut-off frequency ? > > >so I was thinking about >5GHz to > >minimise transmission losses. > > Components made for 2.4 or 5.7 GHz WLAN systems should be of interest. > > >I think that a horn antenna would be > >good to direct the energy, but do they transmit at a particular > >'mode'? > > Microwave power is usually connected to the waveguide using an > electric or magnetic probe. The magnetic probe might be a better > choice, since it can be made smaller, thus causing less resistance to > the gas flowing in the tube. > > There is no need to use a directional horn, since the waveguide is > directing the power anyway. The omnidirectional probe will launch > power in both directions along the waveguide, but placing a metallic > screen (net) at a critical distance from the probe will direct the > power in one direction only and thus, increase the signal by 3 dB. > Such a small increase might not justify the cost of the screen. > > At least the fundamental propagation mode does not like sharp bends, > frequencies well above the cut-off frequency in some higher > propagation mode might propagate better through sharp bends. > > With a very high frequency signal compared to the waveguide cut-off > frequency, there can be multiple propagation modes just like in a > multimode optical fiber. In these the maximum _symbol_ rate for a > specific distance is limited by the dispersion due to multiple > propagation modes having different propagation times. To get around > this, WDM (Wavelength Division Multiplexing) is sometimes used on > VHF/UHF/SHF OFDM is often used to reduce the symbol rate by sending > multiple streams in parallel at different frequencies. > > With 2 GHz cut-off and 5.7 GHz signal there are only a few possible > propagation modes, so you might get away without OFDM, but at least > you should be able to change the frequency slightly, if there are some > unfavorable propagation modes canceling each other at a specific > distance. > > However, if the dielectric constant of the gas might vary e.g. due to > change of temperature, pressure or consistence, the location of nulls > might change, calling for frequency changes. To avoid this, OFDM or > some wide band spread spectrum system could be used. > > Paul
Thanks for letting me pick your brains :) Actually its not a gas pipe, its used for pumping so it will be full of air, also no sharp bends. I shouldn't give too much away, but we need to send a sensor system to the end of the pipe. Other systems use a cable with power and data, however we are looking at something battery powered with some kind of wireless communications, as cable is both heavy and wears out easily. With the probe, does it need to energise off the waveguide (pipe),? There is do direct connection to the pipe. I see what you mean about the horn - not really needed. I will start looking at the WLAN stuff. Also I saw on wikipedia the 802.15.3a spec is for MB-OFDM so maybe that would work too (actually google says its dead). Would anything using PSK for the modulation be a problem? Anyway, thanks again :)