Thank you for such detailed reply!

And sorry for Akismet 🙂

The chinese flat panel antenna is indeed a mystery. Many things seem to be going on here. First the individual elements, if they do indeed transform a left or right handed polarized wave into a current in the probes on cavity side, the phase of that current in the probe will be dependant on the rotational orientation of the individual element. This only matters relative to adjacent probes. So you can
have any phase you want with respect to other probes by simply turning the element.

If this antenna is being illuminated on axis by a left or right polarized wave which these elements are sensitive and all the elements
were oriented to say twelve oclock, All the probes in the cavity side would be in phase. That would be useful if the probes were attached to an efficient combining network. Such network would be hugely expensive.

Lets not call the thing on the back a cavity, it’s too lossy around the edge anyway and would have tuning issues too. Lets call it
a pie shaped wave guide. Think of each radial pie section as a distributed feed wave guide where the probes contribute some power to a traveling wave. A wave which travels and gets stronger as it passes each probe till the energy is extracted from the
guide by the central probe which is connected to the LNA.

For this to work out each probe must be in phase with the wave that is propagating under it in that sector. That is aranged by orienting (rotating) each element to get the desired phase at it’s radial distance from central, output probe.

One more thing, while there is a wave coherently building toward the center of the pie there can be waves going outward and being lost from the signal by the action of all of those elemenal probes. The radial spacing of the elemental probes is an engineering
choice and can give rise to driving a radially outward propagating wave which won’t feed the central probe and produce useful output.

Since these pie shaped wave guide segments have no real constraint for guiding waves in the radial direction, it is possible to propagate waves in other than radially inward directions if the layout of the elemenents is not optimal or the antenna is used at
different than designed frequency.

Back to your blog picture, it looks like the element orientations at each radial distance from the center do not show a common orentation, as in the hands of an ensemble of clocks, so it appears that the probe phases inside the wave guide at each radial
location are not the same, which would be bad. This could happen in the transit from china or the people preparing this array
during manufacture had a bad day or were unaware of the phase matching problem and that the phase of each element, determined by rotational orientation, is significant.

There might be ways to ‘align’ this antenna. I use the word align because the word relates to tuning a distributed amplifier.
You mentioned getting no signal during testing. Do you suppose you could set the thing up again with the circuler polarized input beam impinging exactly normal to the plane of the antenna and orient the first ring of elements to the same clock angle. This should
put all six of the first ring in phase with each other at that radial distance from the output probe at the center of the antenna. With
six probes in phase you should get a reading on your power meter. Then orient the next ring of 12 elements to an arbritrary clock position and see if this new ring of elements is helping or hindering the output power. Next advance the clock angle of all 12
elements incrementally if the power out goes up, try another increment of rotation or turn the other way if power goes down. Continue until you get max power for that ring.

To really get the concept of how a circularly polarized element works, consider this: If you rotate a cp antenna around it’s axis at the rate of one turn per second, this will shift the received frequency by one hertz. Rotating physically the other direction will shift the received frequency one hertz the other way. A circularly polarized antenna is a perfect phase shifter. Turn the thing 30 degrees
and the output phase will shift 30 degrees. So an array of elements in a plane will all have the same phase if their rotational datum points in the same direction as the hand of many clocks on a wall. For these elements the datum could be taken as the little arm’s pointing direction or just as well where the loops wire slightly overlap direction from the center.

On with the allignment: Go to the next ring of elements from the center and carry out the same optimization procedure. Since each ring of elements are approximately the same incremental distance from the center, one should expect the required phase shift to be about the same for each step out. This means you should orient all the elements in the ring by about the same angle to get close to the correct orientation. Small rotations of all the elements of the ring of elements should quickly peak the power detected.

Keep moving out to the next ring and optimizing before moving out to the next ring of elements.

As each element should contribute about the same amount of power to the load and each ring of elements from the center has more elements. It should be easy to see improvements as each ring of elements coherently adds power to the load.

These are just some ideas that you inspired me to write down. They may be correct.

On a different topic: Earlier in your blog you state:

“Now let’s talk about circular polarization. This type of polarization happens when there is a 90 degree phase shift between the E and H component of the electromagnetic wave. With the different sigh of the phase shift we might get Left or Right circular polarization.”

It’s my understanding that for a linearly polarized wave propagating in free space, the E field maxima and minima are exactly in phase with the H field maxima and minima, That they are welded at the hip, so to speak.

A circularly polarized electromagnetic wave in free space is exactly equivlent to two linearly polarized electromagnetic waves of the same frequency, one vertically polarized E field, the other horizontally polarized E field, propagating in the same direction. The two waves phase shifted + or – 90 degrees. As you show in your disection of LNB cp antennas, The dipoles are orthogonal as required to make two independent linear E field polarizations, orthogonal and spaced one ahead of the other by 90 degrees of electrical phase. The H field, welded to the hip of the E field, just goes along for the ride.

Thanks again for getting me to think about this stuff and show me a very interesting and cleaver antenna and crazy traveling wave combiner. I might have described it corectly. Somebody probably wrote a paper on it 50 years ago!

eric-

WN7WNL, 73

Thanks i send email to you.

Hello. Sure, I checked some photos of this LNB.
Looks like quite standard construction of a feed horn, should be no problems to convert this LNB.
Can you show me your construction?

Hello,
It’s here: https://olegkutkov.me/2020/09/22/mysterious-flat-satellite-antenna-from-china/