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I'm working on a project involving RF. I have a pretty good understanding of "HAM Radio" style RF engineering, but not at a professional level.

I'm trying to find a commercially available dipole antenna for a high altitude balloon. I have no available ground plane, and so my first though was to look for dipole antennas on DigiKey. As I understand it, a 1/2 wave dipole (two 1/4 wave wires -> Balun -> SMA) is the optimal isotropic antenna. I am not interested in directional gain. I'm interested in both 2.4Ghz and 433Mhz. I'd like to spec an antenna for each.

My issue is that none of these antenna types are recognizable to me:
pcb ant duck ?
I've found lots of PCB antennas. Some look like dipoles, but are connected to coax with no balun. Some are "rubber-ducky" style, which I don't fully understand. How can they work without a ground plane? How do handheld Baofeng radio antennas work? Some others are just wire, with various twists. Is there a reason there aren't any normal Dipoles? Assuming cost is not a barrier, what's the best (most efficient?) isotropic antenna style?

I was envisioning something like a rubber ducky, but with two arms coming off the feed point. I found one like that (RPSMA sadly):
enter image description here
But per the datasheet it's 14.5cm total, and for 433Mhz it should be 35cm! link here

I can build my own dipole from wire and measure its performance on a VNA. Why are so few products available along those lines? Help me understand my shopping confusion.

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    \$\begingroup\$ A dipole (or monopole or any practical antenna) is NOT isotropic. \$\endgroup\$ – Andy aka Dec 9 '19 at 10:57
  • \$\begingroup\$ Of course, but a dipole is rather isotropic, right? I'm not sure if it's the most isotropic, but I don't know anything better. \$\endgroup\$ – Tim Vrakas Dec 9 '19 at 11:01
  • \$\begingroup\$ No such thing; it's like saying that a biscuit is somewhat like a cake. \$\endgroup\$ – Andy aka Dec 9 '19 at 11:02
  • \$\begingroup\$ I'll be rigorous. If we sample the gain pattern at 1000 random (or equally distributed) directions, the standard deviation of the gain patterns of a dipole is significantly less than that of Yagi, Patch, dish, Helix, etc. By that metric, is a dipole is the most isotropic? \$\endgroup\$ – Tim Vrakas Dec 9 '19 at 11:07
  • \$\begingroup\$ Antennas with less directionality have a wider field of view but, spread their energy out thinner (transmitting) or pick up more noise (receiving). I'm not sure what you are trying to say or want. \$\endgroup\$ – Andy aka Dec 9 '19 at 11:13
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Why are so few products available along those lines?

As a general rule, if it's easy to build, doesn't have a huge market share, and every customer will want something a bit different, then it won't be available off the shelf.

This was the case in the 1980's and 1990's for power inductors -- every switching supply design was unique, and inductors are easy to wind. So you could get every kind of inductor core off the shelf, and just about every moderate-sized technical center (e.g. Portland Oregon) had several coil winding companies that would custom wind you coils -- but the actual selection of off-the-shelf coils designed for switching applications was just not there. Contrast that with today, where the introduction of cheap, easy to apply switching ICs has made the coil choice abundant.

Build your own, once you choose the right wire for the antenna and dielectric for the center support, there's not much to screw up.

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My issue is that none of these antenna types are recognizable to me: [...]

Don‘t let you disguise by the way these antennas look like.

Although all of them look like monopoles that would need a gnd plane, they are actually dipol types. There‘s a a special buildup magic involved here (think of a wire that goes from bottom to tip and back to bottom)

They are shorter than lambda/2 because they also have electrical components (caps/inductors) inside that make them electrical lambda/2 but physically much smaller.

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  • \$\begingroup\$ Does this improve, or hurt, their performance? How can I measure their performance, or determine from a datasheet? \$\endgroup\$ – Tim Vrakas Dec 10 '19 at 2:15
  • \$\begingroup\$ Most datasheets for antennas show performance figures. \$\endgroup\$ – Stefan Wyss Dec 10 '19 at 18:21
  • \$\begingroup\$ Most show dBi, and VSWR. A high gain antenna is not what I want, and low VSWR indicates a good impedence match, not a good efficiency or aperture. \$\endgroup\$ – Tim Vrakas Dec 10 '19 at 22:01
  • \$\begingroup\$ The dipole antennas that you show in your pictures certainly do not provide high directivity. Normally they have not more than +5dBi in the main direction. So these might fit perfectly for your use case. \$\endgroup\$ – Stefan Wyss Dec 14 '19 at 10:52

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