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A two port 3 dB splitter for 13 cm and WLAN

A two port 3 dB splitter for 13 cm and WLAN

The splitter constist of four quaterwave striplines connected at their ends and four terminals (input, ground, output1, output2) connected to the cornes of the square formed by the striplines. The impedance of the terminal leads is 50 Ohm to connect them directly to RF-connectors such as SMA.
Typical applications:

1. Connect two high gain antennas to an access point to cover two directions
2. Connect one omni and one high gain antenna to an access point to provide omni coverage and one link

Stripline length:

The wireless LAN band streches from 2400 to 2485 MHz, center is abt. 2440 MHz. The corresponding wavelenght is 300/2440 meter, or 12.3 cm. A quater wavelenght is 12.3/4= 3.1 cm (in free space). Since we are talking about stripline on FR4 and not in free space, the stripline length has to be multiplied with the “shortening factor” of the PCB. The shortening factor (sf) can be calculated from the dielectric constant (dc). sf = 1 / sqrt (dc). Stripline length is 3.1 cm * 1/sqrt(4.2) = 15 mm

Stripline width:

Calculating the stripline width is a bit more work. Factors like desired impedance (100 Ohm in this case), copper layer thickness, board width and dielectric constant are involved. There are several formulas available, for instance here. An easier way is to let software do the job, for instance Agilent`s AppCad (see screenshot below). AppCad is free and can be downloaded from Agilent`s website. Stripline width is 1.5 mm

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