What are RF Pick-Off Tees?

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Doug Jorgesen - Marki Microwave

Jul 13, 2018

An RF pick off tee is the most basic method of sampling the power on an RF/Microwave transmission line. It consists of two 50 ohm lines- the through line and the coupled line. The through line is connected to the coupled line through a resistor with a high value (relative to 50 ohms), for example 200 ohms. 

The main advantages of this circuit is that it can be extremely broadband; the low frequency extends to DC and the high frequency is only limited by the package and the parasitics of the resistor. It is also extremely easy to design and implement.

The main disadvantage is the lack of directivity, meaning that it cannot discriminate between forward and reverse traveling waves the way that a directional coupler can. This can lead to serious errors in the power measurement. The other disadvantage is that the return loss is limited by the coupling value. The more power is coupled off, the lower the resistor needs to be, and the worse the match is. 


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