Discussion in 'VHF/UHF - 50Mhz and Beyond' started by W9EAM, Aug 26, 2021.
Can you co-phase to dishes?
Certainly! Radio astronomers make use of radio interferometers usually on very large scales. Several smaller dishes are combined together to give the same performance as one large dish. For example the Very Large Array in New Mexico takes advantage of this technique. See link: https://www.britannica.com/topic/Very-Large-Array
From an amateur astronomer or ham radio standpoint, you can co-phase a couple of Direct-TV dishes together. The beam width will be narrower and the pointing of the dishes will be more critical, but the gain and resolution will be improved.
"Co phase" is a weird expression, but putting antennas in phase and aimed in the same direction works.
And it's "two."
But anyway, of course you can. The trick with dish antennas is to be effective (have substantial gain) they are extremely directional with very narrow beamwidth, so finding the correct way to phase them for added gain takes complex mathematics and a really good understanding of each dish's aperture, which is directly related to its gain.
"Co-Phased Antennas" was the catch phrase back in the 70's. Truckers loved their co-phased "Big Mommas" on the mirrors of their trucks. Co-Phase antennas even had a draw for home use
Gosh, I just love this tech-talk! Can we discuss SWAR's next? Huh? Can we?
A pair of similar dishes still has the ~ 3dB gain of a pair of dipoles.
I wonder what drives you to ask this question? Understanding your goal may allow us to provide you with guidance that you may not have considered.
For example, combining two dish antennas will provide 3dB of gain in a perfect world, however in practical terms...at microwave frequencies you are likely to lose at least 1 dB (and probably more) in the harness that you would use.
On the other hand, you will get a true 3dB simply by using a dish that is 50% larger. You get 6dB by using a dish that is 2x in size. Both will be significantly less complex than "phasing" two independent dish antennas.
I can't think of any reason to do this except maybe EME. I used to work in point to point long haul microwave and have never heard of it being done. Usually any microwave path has enough "fade margin" that 3 dB either way isn't much of a factor. What's the application? In theory I don't see any reason it wouldn't work if the waves at the receiving end are in phase. I guess I can think of a few applications, like hooking up two similar 2.4 or 5.8 antennas for a slightly better path, but I think the benefit would be marginal. I agree with W2EV.
I stacked and split 6M Squaloes using the RG9 coax to rematch the Z of two ants to one coax feedline. .Got 3dB Omnidirectional gain