Method for improving power measurement implemented with a directional coupler at low power levels

A directional coupler arrangement for measuring radio frequency power, which directional coupler arrangement comprises a directional coupler comprising a first conductor element (1) and a second conductor element (2), both of which comprise a first end and a second end,

• a detector element (4) for detecting a level of power coupled from the first conductor element (1) to the second conductor element (2) and for providing an output signal as a response to said power level, which detector element comprises an input port and an output port and whose input port is connected to the first end of the second element (2), and
• a terminal impedance (12), which is connected between the second end of the second conductor element (2) and an earth potential,
• characterized in that
• the impedance value of said terminal impedance (12) is altered electrically by means of a control signal fed to it, and further characterized in that said directional coupler arrangement comprises a control circuit (11) between said detector element (4) and said terminal impedance (12) for forming said control signal on the basis of the output signal of the detector element.

A method for measuring the radio frequency power of a transmitter with a directional coupler arrangement, wherein the directional coupler arrangement comprises a directional coupler having a first conductor element and a second conductor element, the first conductor element being disposed within a transmission path of the transmitter, the second conductor element having a first end and a second end, the first end of the second conductor element being electrically connected to the transmitter and defining a first branch, the second end of the second conductor being electrically terminated at an earth potential and defining a second branch, the method comprising the steps of:

• detecting a power level at the first branch using a detector disposed between the first end of the second conductor and the transmitter;
• forming an output signal based upon the detected power level of the first branch;
• and
• electrically altering an impedance value of a terminal impedance of the directional coupler measured at the second end of the second conductor.