This is my first post, I would like to say hello to everyone on the forum.

Is it possible to join two folded dipoles with specific twin lead cable length to retransmit on the other end a signal 180 out of phase? Preferrably without two circulators and 2 amplifiers. How would one calculate the length of the cable? Both antennas would be in the field of view of the transmitter. When the signal comes to the first dipole and starts to travel via cable is there any phase change on the transmitted wave of the other antenna other than the delay because of slower speed in cable(velocity factor)?

 

The short answer is NO.

If You would explain what it is that You are trying to accomplish
it might be possible to provide more constructive answers.
.
.
.

 

Welcome to AAC.

You might be thinking of the case of a phasing harness used to stack gain antennas. The problem is that although phase is involved in this, it is a mechanism for impedance matching not phase shifting. Trying to use the technique to put antennas out of phase would make them unmatched for impedance.

In any case, you seem to want to make the equivalent of a "silence machine" as appears in the Arthur Clarke short story "Silence Please". In it, an engineer creates a device that uses destructive interference to block all sound. Clarke knew it wouldn't work, it was a humorous idea (the machine in his story worked, until it exploded violently which as the story has it was due to the "condensers (capacitors) becoming overloaded because they energy had to go somewhere").

But you face the problem that was faced by Clarke's invention. Out of phase according to what observer? The fading caused by multipath interference, where one or more reflections or a signal and the primary arrive at an antenna a the same time, but out of phase, was a very familiar effect in the days of simple auto FM radios.

It could happen because of buildings or, quite amazingly, if a passenger jet flew over. But, it was a flutter, a sine-wave like attenuation with a variable frequency because there is no way to hold the phase constant once the signal leaves the antenna. Phase and polarity of a radio signal in the real world outside the anechoic chamber is a crap shoot. You have no control.

But, as @LowQCab said, if you could describe the problem you are trying to solve, there might be other approaches, even passive ones. No guarantees, mind you, but without understanding the actual problem I guarantee we can't help.

 

Thank you for the answer. I know it is not possible to cancel the signal. I was
thinking about attenuation. So in your opinion a receiver behind a Van Atta ref
lector array would still receive same strength signal. The reflector would not s
hield the receiver like if it was behind a mirror.

 

Putting-up Aluminum-Window-Screening between the 2 will have the same results.

If there was a Light-Bulb burning on the opposite side of a square piece of Cardboard,
could You tell if the Light-Bulb was On or Off ?
.
.
.

 

And in the UHF where the signals bend? I don't understand how the distance between Van Atta array elements are calculated and also how to calculate the cable distance. Is it related to phase? Does the reflection happen only in the near field? Is the principle similar to phased arrays?
I was hoping that destructive interference would be possible. For example even if i don't match the phase of two antennas exactly, that there would be less energy in the remaining space. What really hapens when i connect the antennas that way?
So it is not possible to attenuate the signal other than polyurethane foam with grapite/graphene filler? Are these materials used only for canceling reflection inside faraday cages because of transmitters or can they be used for attenuation of outside signals from penetrating inside the cage? Why are they used when you can ground a faraday cage, wouldn't that cancel the reflections?
I don't have any specific project in mind, just would like to know more.

 

Thank you for the answer. I know it is not possible to cancel the signal. I was
thinking about attenuation. So in your opinion a receiver behind a Van Atta ref
lector array would still receive same strength signal. The reflector would not s
hield the receiver like if it was behind a mirror.

Depending on the wavelength of the signal, the same sort of “picket fence” effect caused by FM broadcast multipath, or some other version of fading and not some fixed attenuation, would be my expectation.

I understood that you didn’t expect to make the RSSI 0dB but the method of destructive interference is also equally capable of constructive interference and maintaining phase once the signal is “in the air” is not possible.

We know it works, though, because of the common experience of nulls or dead spots in mobile phone or WiFi coverage that are very constrained and due to fixed objects that tend to reflect in a way that causes a particular area of weak signal. But these depend on extremely hard to control factors and are not general at all.

 

And in the UHF where the signals bend? I don't understand how the distance between Van Atta array elements are calculated and also how to calculate the cable distance. Is it related to phase? Does the reflection happen only in the near field? Is the principle similar to phased arrays?
I was hoping that destructive interference would be possible. For example even if i don't match the phase of two antennas exactly, that there would be less energy in the remaining space. What really hapens when i connect the antennas that way?
So it is not possible to attenuate the signal other than polyurethane foam with grapite/graphene filler? Are these materials used only for canceling reflection inside faraday cages because of transmitters or can they be used for attenuation of outside signals from penetrating inside the cage? Why are they used when you can ground a faraday cage, wouldn't that cancel the reflections?
I don't have any specific project in mind, just would like to know more.

A Van Atta array works because of local effects of the phasing causing constructive and destructive interference. This is very distinct from placing a pair of antennas somewhere between transmitter and receiver.

There are engineered materials that can cause a phase shift. It’s a new area of research. You can probably find papers.