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whip antenna with plastic casing

I'm confused, Digikey has a huge range of antennas, that look like the one above, which they characterize as "whip antennas".

Wikipedia says here that a "whip antenna is a form of monopole antenna." So, I assumed all the antennas that Digikey is calling "whip antennas" were monopoles. But this isn't the case (as @MarkLeavitt pointed out to me), e.g. the datasheet for the antenna shown above clearly says it's a dipole antenna.

Hence my confusion.

It seems other people call this style of antenna a "swivel antenna" or a "rod antenna".

First, is one of the terms (whip/swivel/rod) the more clearly correct/common one? And second, are swivel/rod antennas always dipole antennas? If not, what clues/indicators are there that a given model, of this style of antenna, is a monopole or dipole if it's not explicitly stated?

E.g. I've found several datasheets like this one where many characteristics are listed but no specific mention is made of monopole or dipole:

Parameter Specification
Frequency Bands, MHz 2400-2500
VSWR (Max) 3.0:1
Peak Gain, dBi (Typ) Up to 2.81
Nominal Impedance 50 Ω
Max Power (ambient temp of 25°C) 10 Watts
Azimuth Beam Width (deg) Omnidirectional
Polarization Linear, Omnidirectional

If they don't advertise the fact that it's a dipole do I just assume it's a monopole?

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  • \$\begingroup\$ The dipole is made up of two rigid metal branches separated in the center by a gap, connected to the RF source or receiver, from one end to the other the length is λ/2 and is also called Hertzian dipole. Another elementary type which originates from the previous one is the one which considers a grounded branch for which the actual antenna is λ/4 long and is of the Marconian type. ect.., ect., \$\endgroup\$
    – Franc
    Commented Apr 10 at 19:11

2 Answers 2

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The confusion arises because terms that describe the external appearance of the antenna -- such as whip/swivel/rod -- are not standardized. Furthermore, they do not necessarily correspond with the internal, electrical design of the antenna -- such as monopole, dipole, coaxial dipole, and many others.

Always demand a datasheet if you want to understand an antenna you're specifying for your design.

Lacking that, you can make some guesses. If the antenna is 1/4 wavelength long at the operating frequency, and is a thin rod of uniform length, it's probably a monopole (and depends on a ground plane). If it's 1/2 wavelength and has a thick and thin part, it may be a coaxial dipole (and is ground independent). There are many exceptions to this rule of thumb, as antennas can be made physically longer or shorter than these lengths, may operate over multiple bands, etc.

For more complex antennas such as Yagis, helices, log-periodics, etc, the physical structure usually makes the electrical design obvious.

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  • \$\begingroup\$ That's annoying that there's not more clarity about this :( But I guess if even the datasheet - like the one for an antenna I bought recently (a 134mm - so full wavelength - 2.4GHz antenna with the thick and thin parts you mention) doesn't bother mentioning monopole, dipole or coaxial dipole then they're not aiming their product at very discerning market. I.e. I should treat it as a hobbyist product for people like me who (at least until recently) didn't know anything about these distinctions. \$\endgroup\$ Commented Apr 11 at 7:54
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'A monopole antenna is a type of dipole antenna formed by replacing one half of the dipole antenna with the ground plane at a right angle to the remaining half. If the ground plane is large enough, the monopole behaves exactly like a dipole because its reflection in the ground plane forms the missing half of the dipole.'

Courtesy: sciencedirect.com

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