Microwave communications

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

Try this one:

Best Regards, Andreas

a écrit dans le message de news: snipped-for-privacy@q28g2000prh.googlegroups.com...

Mimix has some chips for the 24GHz band (U1010, etc). Hittite too.

Cheers, Robert

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

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.

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 ?

Components made for 2.4 or 5.7 GHz WLAN systems should be of interest.

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