How many carriers for phased array?

[Esquilo]

Good morning, I haven't been to the forum in a while and I've been having problems with my email. I hope everything is fine now. As per the title, I'd like to create pulses (5Hz - 8Hz) in specific regions of space. For example, 5Hz arrives in one area, and 8Hz is nearby. To create this effect, I'd like to use phased arrays with 16 patch antennas, but I'm unsure whether to use a single carrier frequency of 800MHz and then pulse at 5Hz and 8Hz, or use two carrier frequencies to avoid interference between the spaces. So, how many carriers should I use to avoid interference between the spaces

 

[.Scott]

I think you might as well go with two carrier frequencies. Either way, you will need two beam-forming circuits that are independently gated then added together. Especially with only 16 elements, you should get fewer artifacts with separate frequencies - you will avoid regions of unintended persistent constructive or destructive interference..

 

[berkeman]

So, how many carriers should I use to avoid interference between the spaces

Can you say more about the application? How "nearby" are the two areas, and how far are the areas from your antenna array? Why have you chosen 800MHz as the carrier frequency? What sort of receiving things are in the two areas?

 

[Esquilo]

I think you might as well go with two carrier frequencies. Either way, you will need two beam-forming circuits that are independently gated then added together. Especially with only 16 elements, you should get fewer artifacts with separate frequencies - you will avoid regions of unintended persistent constructive or destructive interference..

Thanks for your reply, using two carriers, one 800 MHz pulsed at 5 Hz pointing to one area and one 700 MHz pulsed at 8 Hz pointing to another area, if the two waves interfere in a space of a few centimetres I get the beating of the carriers (100 MHz) and the beating of the pulses (8,3,5,13 Hz) so too much interference

 

[Esquilo]

Can you say more about the application? How "nearby" are the two areas, and how far are the areas from your antenna array? Why have you chosen 800MHz as the carrier frequency? What sort of receiving things are in the two areas?

chose the 800 MHz frequencies because they are more manageable as a technology and also have a fairly wide half-wavelength of about 23 cm, so the areas to be focused are half the wavelength of the 800 MHz carrier, the application is musical and will not affect living beings in any way, I do not want interference (or as little as possible) when the two areas interfere, so to have the least interference I have to use one carrier or two carriers??

 

[.Scott]

Perhaps I don't understand exactly what you are aiming for, but the "beating of the carriers (100 MHz)" isn't commonly considered a problem. In fact, I thought you would want to stay in a narrow band - so I was thinking something like 800MHz and 800.1 MHz.
And now that you are posting that you are concerned about this beating showing up in the audio - it should be of no concern. You should have a low pass filter that will kill anything above 20KHz.

 

[Esquilo]

Perhaps I don't understand exactly what you are aiming for, but the "beating of the carriers (100 MHz)" isn't commonly considered a problem. In fact, I thought you would want to stay in a narrow band - so I was thinking something like 800MHz and 800.1 MHz.
And now that you are posting that you are concerned about this beating showing up in the audio - it should be of no concern. You should have a low pass filter that will kill anything above 20KHz.

800 MHz and 800.1 MHz are always two carriers, it's not the difference that interests me, I would just like to understand in which situation there is less interference using two beams, in the first case we have two beams with equal carriers and each different pulse, and in the second case we have two beams with different carriers and also different pulses, in which of these two cases there is less confusion or noise using a phased array

 

[Baluncore]

There is a way to compute a minimum hardware solution to the problem.

I think you must first specify a map of the target area, with the critical signal and separation levels that must be met. That mapped space should be specified by angles in azimuth and elevation, centred on the bore-sight of the array.

Once you have specified the critical levels in dB, in the places that matter, and maximum floor where it does not matter, the map can be deconvoluted using 2D FFTs to give the minimum source phased array, that will generate the required target fields, when excited by the two carriers.

An alternative for a narrow field, would be to use monopulse like design, where you have two elements, one on each side of the focus of a parabolic dish. Each element is then driven by a separate carrier, with dish size and element separation causing inter-fingering of the far fields.

You have presented a problem that is 100 years old. How to build a blind landing system for aircraft, or generate a beam navigation system for bombing your enemy.
https://en.wikipedia.org/wiki/Lorenz_beam
https://en.wikipedia.org/wiki/Battle_of_the_Beams#Knickebein

 

[.Scott]

800 MHz and 800.1 MHz are always two carriers, it's not the difference that interests me, I would just like to understand in which situation there is less interference using two beams, in the first case we have two beams with equal carriers and each different pulse, and in the second case we have two beams with different carriers and also different pulses, in which of these two cases there is less confusion or noise using a phased array

What device are you using to detect these pulses?
Can that device be tuned to either carrier frequency?
When you device is tuned to a carrier frequency, how wide is the channel that it is receiving? Since that frequency channel does not have an abrupt low and high limit, it is usually plotted out or described in more detail.

If the two receivers are able to reject signals that are 50KHz away from their center carrier frequency, then there will be no cross-channel interference. Each receiver will hear it pulses and not hear the other pulses.

About that 800MHz:
I am guessing that you will be implementing this with delay lines that are simply coax cable lengths.
Your wavelength will be 37.5cm and you will be doing your beam forming by pre-calculating the phase differences and cutting the 16 cables for each frequency by hand. Your patch antenna elements should be spaced out in 18cm intervals.