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First, apologies if my terminology is wrong - by sleeved balun and plain whip 2.4GHz antennas, I mean:

Sleeved balun Plain whip
sleeved balun plain whip
Taoglas CBD01.07.0100C TTM 66089-2406

If you buy 2.4GHz drone receivers they often come with sleeved balun antennas rather than just a plain whip antenna.

But does a sleeved balun really confer any noticeable improvement for these short (typically 15cm at most) 2.4GHz antennas?

The reason I'm doubtful is not due to an understanding of the physics but due to the fact that it seems near impossible to buy such antennas from name-brand suppliers.

If they were really significantly better, wouldn't suppliers like Digikey carry a large range of them? But they don't so I'm suspicious it's just a gimmick started by one manufacturer of these RXs that the others felt obliged to copy.

Note: it's not that Digikey don't have any (e.g. they have this one), it's just that they have a huge range of plain whip antenna and almost none of the sleeved balun style. Even given that the sleeved balun style must be more expensive to produce, I wouldn't expect this discrepancy in choice unless the advantage of the sleeved balun is so minimal as to be worthless relative to the additional cost.

I've also checked Reichelt (big in Europe) and other suppliers - same story.

Note: most of the whip antennas on Digikey are this style (rather than the bare antenna shown above) but I'm assuming they're fundamentally the same:

whip antenna with plastic casing

[ The antenna above is a Pulse W1049B030. ]

If you're curious, this is the kind of drone RX that I was referring to above that often comes with sleeved balun antennas (and operates in the 2.4GHz band):

FrSky TW SR12

[ The RX above is an FrSky TW SR12. ]

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  • \$\begingroup\$ From Mark Leavitt's answer, it's clear that I was misinterpreting the term "whip antenna", used by sites like Digikey, as always meaning a simple monopole antenna. \$\endgroup\$ Apr 9 at 19:39

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Yes, there are advantages to the "sleeved balun" antenna designs (which are more commonly called coaxial dipoles), and that is that they are "ground-independent". This means their radiation pattern and impedance is relatively independent of the length of their feedline and the configuration of the RF device feeding them.

The "whip" antennas you show (at the top of your post) are monopoles, and as such their pattern and impedance depends considerably on what ground plane is provided. Only if the ground plane is conductive, large, and spreads out at right angles to the antenna will they perform the same as the dipole. Mounted on a metal case, the performance will be fine too. Without a ground plane or metal case, RF currents can flow on the feedline to create unpredictable irregularities in the radiation pattern. They may also radiate energy into, or pickup energy from, nearby circuitry causing interference.

You can see why the coaxial dipoles may be a preferred choice for plastic-bodied drones with RF-sensitive circuitry. For many other designs with a metal case, the simple whip is adequate and cheaper.

Added note: the Pulse 1049B030 you called a "whip" is more likely a coaxial dipole. It's just hidden inside the plastic cover. This is a very popular design for 2.4 GHz antennas.

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  • \$\begingroup\$ Thanks for a super clear explanation as to why the coaxial dipole antenna would work so much better than a monopole for something case-less like a drone. Given that there is such a clear difference between these styles of antenna, I'm really surprised that it's not one of the fundamental characteristics that Digikey lets one filter on (they certainly support filtering on enough other attributes). I had to look at the datasheet for the W1049BXXX to see that yes, its type is dipole. \$\endgroup\$ Apr 9 at 19:28
  • \$\begingroup\$ Thanks again for the answer Mark, I've asked a follow-up question here - I suspect you'd know the answer to it also if you have time to take a look. \$\endgroup\$ Apr 10 at 17:55

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