The design of the antenna was proposed in 2007 by the Serbian radio amateur Dragoslav Dobričić (YU1AW). He also named this antenna Amos. The prototype of this antenna is the collinear antenna, also known as the Franklin's antenna.
However, the Franklin name rather evokes associations not with the inventor of this antenna, but with his namesake - one of the founding fathers of the United States, whose image we can see on a $100 bill. This Franklin had a favorite hand mouse named Amos, and the antenna is named after her.
The Amos antenna has a wide radiation beam in the horizontal plane - more than 120° at -3 dB level and almost 180° at -6 dB level, but due to the narrowing of the major lobe in the vertical plane (about 15°) - a pretty decent gain - about 12-14 dBi. The figure shows a 3D model of the sectoral antenna pattern.
The antenna is quite broadband, which is its undoubted advantage when used in digital networks 3G-4G and Wi-Fi. As you can see in the graph below, the antenna bandwidth overlaps the entire Wi-Fi range with a margin:
The antenna is made from two segments of copper wire with a 2-2.3 mm diameter. You can use 4 mm2 wire from the electric wiring. Antenna dimensions can be calculated using the Amos antenna online calculator. As a reflector, you can use any suitable metal plate - PCB, aluminum, galvanized sheet. The wire is bent into two radiating elements fixed above the reflector. As a holder, you can use the internal polyethylene insulation from a thick coaxial cable. The braid and the central conductor must be removed.
The antenna input impedance at the connection point is about 200 ohms and for matching with a 50 ohm feeder, one can use a 4:1 half-wave coax balun.
In addition to impedance matching, the loop performs the function of balancing, preventing high-frequency current from flowing to the outer side of the feeder braid. At the microwave frequencies the dimensions of such a loop are too small, so it should be done very carefully. The outstanding ends of the central conductor and braid should not be more than 2 mm. The loop with the main coax feeder is soldered to the connection point and this place is sealed with silicone for weather protection.
Here is what the finished Wi-Fi antenna looks like:
In the image, the antenna is on the table. To get a vertically polarized wave, it must be positioned vertically.
Due to its relative broadband, the antenna has good repeatability and does not need further tuning, unlike the multi-element Yagi-Uda. Therefore, it can be used as a good alternative to the more well-known BiQuad antenna.
Links with detailed photos of designs:
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