What are RF Pick-Off Tees?

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. 

A Pick-Off Tee is an essential tool for signal monitoring in high-frequency applications. It enables the extraction of a small portion of the signal from the main transmission line, diverting it to the pick-off port for monitoring purposes, all without significantly affecting the integrity of the original signal.