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.

 

[berkeman]

the application is musical and will not affect living beings in any way

I see from your Profile that you are in Germany. I have designed and qualified RF products for use in Germany, and 700-800MHz definitely lies within the regulated frequency bands. What is your strategy for transmitting RF energy in these regulated bands? What ramp shape and duration will you be using to turn on and off your transmitters to avoid generating harmonics in other bands?

What are the receivers for these transmissions? Are you just turning on and off lights or sounds or something with this? If so, why no just use IR transmissions from the transmitter(s) to the receivers to accomplish the same thing without having to do the very involved RF qualification work?

 

[Esquilo]

[Post edited by a Mentor to remove accidental inclusion of the non-translated version of the below text]

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.

The system for detecting the signal is also an antenna as a receiver, the channel width must not exceed a quarter wavelength, my system is similar to the theremin but I would like there to be little interference in case the two signals interfere in space, considering the fact that I will hold the receiving antenna with my hands, and I could alter the diffraction and in some points the wave shortens or lengthens, because obviously it is not always perfect, so in which of the two cases do you get less background noise if there were interference?

 

[Esquilo]

I see from your Profile that you are in Germany. I have designed and qualified RF products for use in Germany, and 700-800MHz definitely lies within the regulated frequency bands. What is your strategy for transmitting RF energy in these regulated bands? What ramp shape and duration will you be using to turn on and off your transmitters to avoid generating harmonics in other bands?

What are the receivers for these transmissions? Are you just turning on and off lights or sounds or something with this? If so, why no just use IR transmissions from the transmitter(s) to the receivers to accomplish the same thing without having to do the very involved RF qualification work?

use a phased array for this very reason, to keep the signal in the Fresnel zone within a meter of the source and thus not interfere with the regulated bands, the pulse rises are pulsed and therefore rectangular, and the receiving system is a similar antenna, but I will pick it up with my hands and these in contact with the 800 MHz could create diffraction problems and therefore shorten the waves which is why they could interfere, so in which case there would be less interference??

 

[berkeman]

What is your planned transmit power in dBm? What is the maximum allowed RF level detected for Germany's Level A and Level B tested at 3 meters in dB?

the pulse rises are pulsed and therefore rectangular,

That is probably not going to work, since you will be generating harmonic noise in other bands.

 

[.Scott]

The system for detecting the signal is also an antenna as a receiver, the channel width must not exceed a quarter wavelength, my system is similar to the theremin but I would like there to be little interference in case the two signals interfere in space, considering the fact that I will hold the receiving antenna with my hands, and I could alter the diffraction and in some points the wave shortens or lengthens, because obviously it is not always perfect, so in which of the two cases do you get less background noise if there were interference?

You need two radio receivers.
Each receiver will include an antenna and some circuitry.

The channel width is described in Hz. So, if one of your receivers is tuned to an 800.1Mhz center frequency, then it will be sensitive to a range of frequencies around 800.1MHz. To make this simple (and it isn't this simple), if your receiver channel width is 80KHz, then when tuned to a center frequency of 800.1MHz, it will respond to signals in the range of 800.06 to 800.14MHz.

A theremin - so one of those two frequencies will be controlling pitch, the other volume. You will have two receivers. I believe theremins are controlled by capacitance - but your will be different.

I don't think we need to get into exactly how you will design your theremin - only on those two radio receivers you will be using.

 

[Esquilo]

What is your planned transmit power in dBm? What is the maximum allowed RF level detected for Germany's Level A and Level B tested at 3 meters in dB?



That is probably not going to work, since you will be generating harmonic noise in other bands.

57 and 47 dbm at 3 meters, yes you are actually right with square signals I have many harmonics and therefore a lot of noise I will have many filters I will see what to do

 

[Esquilo]

You need two radio receivers.
Each receiver will include an antenna and some circuitry.

The channel width is described in Hz. So, if one of your receivers is tuned to an 800.1Mhz center frequency, then it will be sensitive to a range of frequencies around 800.1MHz. To make this simple (and it isn't this simple), if your receiver channel width is 80KHz, then when tuned to a center frequency of 800.1MHz, it will respond to signals in the range of 800.06 to 800.14MHz.

A theremin - so one of those two frequencies will be controlling pitch, the other volume. You will have two receivers. I believe theremins are controlled by capacitance - but your will be different.

I don't think we need to get into exactly how you will design your theremin - only on those two radio receivers you will be using.

yes I should use maybe more than two receivers, I could make a system similar to metal detectors but it would be too difficult, and as berkerman said I would generate too many harmonics with the pulses, so I think my idea is too complicated for me to implement

 

[berkeman]

57 and 47 dbm at 3 meters

Yikes, you may be missing a minus sign or something there...

From a Google search on VDE Level B at 3m test distance:

216 MHz – 960 MHz: 46.0 dBuV/m (Quasi-peak)

So you still need to do the conversion to dBm, but 47dBm is crazy high.

I finally saw that your application is a theremin, so I'm even more confused now but I'll try do some reading about that when I get a chance. If it's all near-field stuff around your hands, you may be able to use a low enough Tx level that you will obey the regulatory requirements for RF transmissions. But I guess I'm still not understanding how 800MHz is good for detecting human hands (or water, etc.). It seems like using the "microwave oven" ISM band would be better for that, but again, I need to do more reading.

 

[renormalize]

I finally saw that your application is a theremin, so I'm even more confused now but I'll try do some reading about that when I get a chance.

A standard Theremin uses 3 oscillators, two working at about 260 kHz and one at 450 khz. Nothing oscillates at nearly a gigahertz. See:
https://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/60.17.html

 

[.Scott]

I finally saw that your application is a theremin, so I'm even more confused now but I'll try do some reading about that when I get a chance. ... But I guess I'm still not understanding how 800MHz is good for detecting human hands (or water, etc.).

I wasn't going to get into his theremin design. But if we do, why would we use a phase array instead of two or three directional antennae? This really looks like a rabbit hole.