Millimeter and terahertz waves suffer from attenuation

Millimeter and terahertz waves suffer from attenuation caused by rain and resonant absorption in oxygen and water molecules, so they are unsuitable for long-range radio communications. However, their short wavelengths prove to be an advantage in the transmission of large amounts of data at one time.

1. Substrate Integrated Waveguide components are designed for millimeter wave applications. Most of the applications are for RADAR and IEEE 802.11ad. Then, how are they suitable for long-range radio communications?


Millimeter and terahertz waves also provide high spatial resolution in imaging applications, enabling high-definition images to be obtained, in contrast to the low definition of microwave imaging.

2. How do Millimeter and terahertz waves provide high spatial resolution in imaging applications? which property supports high spatial resolution in imaging applications?

Please clarify.

1) I haven't seen long-range application for mmWave/THz. As you said, they suffer from atomspheric attenuations, they are suitable only for short-range comminications. Do you have example for long range?

2) mmWave/THz have narrower beamwidth, thus they are able to provide higher spatial resolution.

I think several things are being confused here.

'Long range' is a very broad definition, certainly above around 30MHz (it varies considerably) the effects of ionospheric reflection are minimal and radio waves become 'line of sight', that limits them to the distance to the horizon, allowing for antenna height.

At higher frequencies, up to a few GHz, signals travel with relatively little attenuation from the atmosphere.

As the frequency gets higher, generally from around 10GHz and above, the effects of chemical absorbsion start to be more noticable and specific frequencies (according to the type of medium) have higher attenuation or reflectivity.

The speed of data that can be carried on a radio signal is related to the Nyquist theorem (although VMSK is theoretically possible) so for more data a higher carrier frequency is needed.

For imaging, the wavelength is of prime importance. If I draw an analogy, trying to measure tiny distances with a 1M rule is far more difficult than measuring them with a 1nM one. Generally, you want your measuring units to be much smaller than the item you are measuring. Beamwidth has little to do with it except in circumstance where (over long distances) it is easier to focus a signal with shorter wavelength. For example, the beam width attainable from a parabolic reflector is proprtional to it's area relative to wavelength.

Brian.

Hi

Thank You so much.

the antenna - A1 is designed @ 90GHz using substrate Integrated waveguide technology , let D1 be the range it transmits.

the antenna- A2 is designed @ 2.4GHz using substrate Integrated waveguide technology , let D2 be the range it transmits.

Assuming Line of sight, D1 is smaller than D2 ? Please confirm.

But DATA rate in A1 is more than in A2. Am i right? please confirm.

Thanks

Unless something is obstructing or absorbing the signal, and the transmitted power is identical, they should cover the same distance. However, there is more probability of the 90GHz signal being absorbed than the 2.4GHz one.

The data rate is theoretically as much as half the bandwidth so yes, A1 can be greater than A2. In practice, the higher frequency gives you more space to fill with the transmission bandwidth but it would be unusual and impractical to use it all so the data rate is normally much lower than theoretical maximum. Note that the higher frequency doesn't mean the data rate IS higher, only that it CAN BE higher, it's up to you what data rate you actually use.

Brian.

This is an interesting thread.

mm wavelength antennas have significantly reduced beamwidths and increased gain leading to better spatial resolution when aperture size is held constant. The spatial resolution mentioned above I suspect refers to range. There is also angular resolution.

Millimeter band will be used in 5G communication (mainly 28 GHz and 60 GHz band). In 5G, lot of research is going to mitigate this attenuation effect and one emerging technology is FD-MIMO system.

Atmospheric attenuation is "notchy". You have to get
specific about frequency and look at the charts. For
space communications this is a "don't-care" while size
of antenna is a huge deal (and follows wavelength).
Up- and down-links have only a fairly short in-atmosphere
distance compared to terrestrial point-point.

Attenuation is a good thing in cluttered spectrum-space,
the same frequency can be used by other radios at a
reasonable distance of separation. Directionality is
another Good Thing, which at higher frequencies can
be had with smaller antennae.

"Long distance" means different things to different
people. It's a poor question to ask, lacking context
and quantity.