High Gain Yagi Wi-Fi Antenna >>

Build this wi-fi antenna to build when you want results FAST and have just a few inexpensive tools and supplies available. It will greatly extend your wi-fi range - well beyond the limits of the dipoles that accompany most routers and some wireless adapters. When connected to a USB wireless adapter the performance is excellent. When connected to a high powered wi-fi adapter, the performance is astounding! Forget about building those overly hyped wi-fi cantennas - they don't perform anywhere close to the yagi antennas depicted here.
Sometimes the perfect wi-fi antenna is the one that can be made in an hour's time, from inexpensive parts, and yet enables connections over moderate to long distances. The yagi wi-fi antenna design depicted here is exactly that! It is computer designed, made of wood and wire, and provides high gain and directivity. It is directional - favoring wi-fi signals in one direction and rejecting interference from the sides or behind the antenna. The 15 element wi-fi antenna provides over 15 dB of gain (multiplying your effective radiated power by 31), while the larger 20 element wi-fi antenna provides over 17 dB of gain (multiplying your effective radiated power power by 51). Front to back ratio for both antennas is about 22 dB.
Yagi wi-fi antennas can be rather difficult to make - elements must be precisely cutto the proper length, and spaced at the correct distance from otherelements, or the antenna doesn't work. Before good computer tools were available, a designer used various charts and tables to determine antenna dimensions. These days, however, much of the mind numbing calculation can be carried out in a split second. One excellent tool for crunching design numbers is the yagi antenna modeler, created by Kevin Schmidt (W9CF) and Michael Lee Electronics Circuit Application

  The 15 element yagi wi-fi Antenna                           The antenna modeler also
lists element lengths and positions                               dimensions in the W9CF java applet   


The on-line antenna modeler initially starts with several examples tailored for operation in the amateur radio bands. One of the best designs is the classic K1FO yagi. By following a few steps, the antenna can be scaled for the 2.4 Ghz wi-fi 802.11 b/g/n frequencies:

1. Start with the 15 or 20 element K1FO 70cm example.
2. In the "units" menu, select "Radians."
3. In the "conductivity" menu, select "Copper"
4. In the "frequency" field, enter 2450 (MHz) for the center of the wi-fi networking band.
5. For "Element Diameter", enter 0.08729 (radians).
6. Click the "calculate" button.
7. In the "units" menu, select "millimeters."
8. Note that the element diameter perfectly matches 14 gauge wire!
9. In the file menu, select "list elements."

The elements list will show each element, from the reflector (element 1, position zero mm), to the last director. Any changes in element diameter, metal type, or design frequency will need recalculation and the new elements list checked. These dimensions work quite well:

Element data for the 15 Element Yagi Wi-Fi Antenna.

Element	Length (mm)	Position (mm)
1 (Reflector)	59.61	0.00
2 (Driven Element)	58.55	18.34
3 (Director)	55.20	25.75
4 (Director)	53.62	39.51
5 (Director)	52.38	58.55
6 (Director)	51.68	82.19
7 (Director)	50.97	109.70
8 (Director)	50.62	140.74
9 (Director)	50.26	174.60
10 (Director)	49.91	210.94
11 (Director)	49.56	249.38
12 (Director)	49.21	289.60
13 (Director)	48.85	331.39
14 (Director)	48.68	374.25
15 (Director)	48.50	418.52

Element data for the 20 Element Yagi Wi-Fi Antenna.

Element	Length (mm)	Position (mm)
1 (Reflector)	59.96	0.00
2 (Driven Element)	58.91	18.34
3 (Director)	55.56	25.75
4 (Director)	53.97	39.51
5 (Director)	52.73	58.55
6 (Director)	52.03	82.19
7 (Director)	51.32	109.70
8 (Director)	50.97	140.74
9 (Director)	50.61	174.60
10 (Director)	50.26	210.94
11 (Director)	49.91	249.38
12 (Director)	49.56	289.60
13 (Director)	49.21	331.39
14 (Director)	49.03	374.25
15 (Director)	48.85	418.52
16 (Director)	48.68	463.67
17 (Director)	48.50	509.70
18 (Director)	48.32	556.26
19 (Director)	48.15	603.53
20 (Director)	47.97	651.32

Below is a graphic, meticulously adapted by AB9IL from the modeler, which shows element lengths and positions along the boom, measured from the reflector (location zero millimeters). Note that the driven element is depicted in green, and for the wi-fi yagi project, will be a folded dipole. Why a folded dipole? It provides a good impedance match to coaxial cable when used as the yagi wi-fi antenna's driven element. In free space, a folded dipole has a 300 ohm impedance at resonance, but the impedance drops drastically when parasitic elements are brought into close proximity. Electronics Circuit Application

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