WiFi

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Wireless Network

Wireless network equipment uses the 2.4 GHz ISM (Industrial, Scientific and Medical) band to operate and is split into 10 to 14 channels, depending on the continent. Ranging from 2412 Mhz to 2484 MHz in 5 MHz intervals. Each channel extends in both directions by 11 MHz and can overlap upto four other channels. If two systems operate on channels close each other they will probably interfere and the performance will suffer. When building antennas it's recommended to use the middle-most frequency of the band to calculate the wavelength, 2437 Mhz (channel 6).

Wavelength

The optimal wavelength for the 2.4 GHz band is around 123 mm.

Wavelength = Lightspeed / Frequency in megahertz
300 000 Km/sec / 2 437 GHz = 123.10 mm = 12.31 cm

Antenna length should be in whole halves, quarters, eighths etc, for best signal reception. The most common antennas are built on a 1/4 or lower size, this makes them very small but still performs very well.

External Conductor Square Frame = Wavelength / Size
123 mm / 4 = 30,75 mm

Various 2.4 Ghz frequencies and the full wavelength:

#	Countries	Frequency (GHz)	Full wavelength
1	Europe, USA Japan	2.412	124.38 mm
2	Europe, USA Japan	2.417	124.12 mm
3	Europe, USA Japan	2.422	123.87 mm
4	Europe, USA Japan	2.427	123.61 mm
5	Europe, USA Japan	2.432	123.36 mm
6	Europe, USA Japan (Center channel for US)	2.437	123.10 mm
7	Europe, USA Japan (Center channel for EUROPE)	2.442	122.85 mm
8	Europe, USA Japan	2.447	122.60 mm
9	Europe, USA Japan	2.452	122.35 mm
10	Europe, USA Japan, France, Spain	2.457	122.10 mm
11	Europe, USA Japan, France, Spain	2.462	121.85 mm
12	Europe, Japan, France, Spain	2.467	121.61 mm
13	Europe, Japan, France, Spain	2.472	121.36 mm
14	Japan	2.484	120.77 mm

Basic notes

Avoid bending the coax cable too much if possible.
Shortcuits are possible since RF energy isn't true current, i.e. element on BiQuad.
Use as few connectors and cables as possible between the device and the antenna, keep the loss low.
Protect the center conductor of the coax cable as much as possible before it connects the the antenna element, it's carring the signal.
Cover the connectors with UV-resistant tape to avoid noise from the sun. It's also a good idea to cover the antenna if any bare metal is exposed.
Every connection should be soldered (properly) to maximize the signal flow.

Cabling

ANTENNA -> N-FEMALE CONNECTOR -> N-MALE == RP-SMA FEMALE [OR N MALE] -> RP-SMA MALE [OR N FEMALE -> DEVICE [OR PIGTAIL CABLE]

Antenna connector:
1. 30 cm Belden H1000 cable (below) with N Female Solder Connector (ELFA 46-086-34) and heat-shrink tube (ELFA 55-080-07) for protection on both ends (antenna backside og connector). Additional melt adhesives recommended (ELFA 80-915-22).
3. Or, N Connector Female Socket (ELFA 46-104-73)
(optional) N Male Solder Connector (ELFA 46-071-64), for antenna cable end - same diameter as RG-8 and RG-213
(optional) 3 - 5 m Belden H1000, low loss coaxial cable (0,218 dB/meter at 2320 MHz) (ELFA 55-914-25)
(optional) N Female Solder Connector (ELFA 46-086-34), for pigtail cable end - same diameter as RG-8 and RG-213
(optional) N Male pigtail cable from WLAN card (RP-SMA, RP-TNC, MMCX, MC-Card), under 50 cm recommended.

Different cable diameters: