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Trying to understand this feed structure, and have questions in mind.

It clearly seems that two 180 degree couplers and one 90 degree coupler utilized to get the antenna circularly polarized.

Since this's a dipole antenna, I see two feed points on each pole on the left pic for balanced fed configuration.

What's that red circle part exactly? How it's fed as balanced? I don't see a balun, coax cable seems like have two inner conductor?

enter image description here

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    \$\begingroup\$ This isn't a dipole! This very much seems to be designed as an aperture antenna array with coupled (resonant, maybe?) patches. Don't know how you call this a dipole? If it were, it would be a single thin conductor only interrupted in the middle, where it is fed. I see none of these features! \$\endgroup\$
    – mmmm
    Commented Jun 12, 2021 at 9:20
  • \$\begingroup\$ @mmmm this's generally called as crossed bow tie dipole antenna \$\endgroup\$
    – Xant
    Commented Jun 12, 2021 at 9:26
  • \$\begingroup\$ Wow! Didn't know that! Thanks, @antfellow. But that name then suggests that the opposite "wings" are analogous to the two halves of a dipole, and not that the two feeds on the same wing are dipole-ish (I hope I understand your question correctly). \$\endgroup\$
    – mmmm
    Commented Jun 12, 2021 at 9:42
  • \$\begingroup\$ @mmmm Welcome, yes, the 'wings' can be considered as the two halves of a dipole. I literally think that there're two feed points on each halve, and that's because of balanced fed. However, I don't understand the red circle, where I only see a coax comes from the 180 degree coupler. There are like two connector jack, I don't know. maybe coax just has two inner conductor and each inner conductor soldered over there. ? \$\endgroup\$
    – Xant
    Commented Jun 12, 2021 at 9:53

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During my early EE days (we're talking 1970's) one of my tasks was analyzing the antennas on captured military equipment. Here's my take on this antenna.

As @mmmm has suggested, it's a crossed bowtie, and it's cavity-backed. It's a rough prototype built by sticking copper tape to a dielectric and connecting up 90 and 180 degree hybrids to create four feeds at 0, 90, 180, and 270 degrees phase.

The builder was faced with how to connect the output of those four feeds, as coaxial cables, to the copper-tape bowties. I think he/she punched holes in the dielectric sheet -- one near each feedpoint -- and fed a hairpin of some ordinary copper wire through. On the antenna side, he/she folded the ends flat and stuck down the copper tape element, counting on the conductive adhesive of the tape to make contact. The folded end of the hairpin stuck down through the dielectric. Here, he/she stripped the end of the coax, soldered the shield to the copper housing, and soldered the center conductor to the hairpin wire sticking down through. This conglomeration is what you've circled in red. It's just a quick and dirty way to get the signal from the center conductor of each coax cable to its corresponding bowtie element.

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  • \$\begingroup\$ Thank you, Mark. So I get that what makes this feed network is balanced is because of the designer fed each halves. Right? \$\endgroup\$
    – Xant
    Commented Jun 13, 2021 at 12:44
  • \$\begingroup\$ Let's clarify more. Each trapezoidal element is fed like a monopole, from the coax center conductor. By itself, it's not a dipole. It's the pair of trapezoidal elements, on each side of the center of the antenna, that make up a dipole. That dipole is balanced because the feeds to the two elements are 180 degrees out of phase with each other. \$\endgroup\$ Commented Jun 13, 2021 at 16:00
  • \$\begingroup\$ Thank you, I really appreciated \$\endgroup\$
    – Xant
    Commented Jun 13, 2021 at 17:59

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