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

Claim 2

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.

Claim 3

A directional coupler arrangement according to claim 1, characterized in that said terminal impedance (12) comprises two parallel connected branches, the impedance of said first branch is alterable to be made smaller or larger than the impedance of the second branch by means of said control signal.

Claim 4

A directional coupler arrangement according to claim 2, characterized in that said first branch comprises a PIN diode (D1) whose bias voltage is said control signal.

Claim 5

A directional coupler arrangement according to claim 3, characterized in that said control circuit comprises a transistor (Q1) for controlling the bias voltage of the PIN diode (D1).

Claim 6

A directional coupler arrangement according to claim 4, characterized in that said transistor (Q1) is a bipolar transistor having a base connected to the output port of said detector element (4), a collector connected to a positive potential (Vcc) and an emitter connected to an anode of said PIN diode (D1).

Claim 7

A directional coupler arrangement according to claim 3, characterized in that said directional coupler arrangement further comprises a capacitor (C2), wherein a cathode of said PIN diode (D1) is connected to the second end of the second element (2) of the directional coupler and an anode of said PIN diode (D1) is connected via said capacitor (C2) to the earth potential.

Claim 8

A directional coupler arrangement according to claim 3, characterized in that an anode of said PIN diode (D1) is connected to the second end of the second element (2) of the directional coupler and a cathode of said PIN diode (D1) is connected to the earth potential.

Claim 9

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.

Claim 10

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.

Claim 13

A method according to claim 9, further comprising the steps of: forming a control signal from the output signal which is based upon the detected power level of the first branch; and varying the control signal in response to changes in the output signal, wherein the control signal electrically alters the impedance value of the terminal impedance of the directional coupler.

Claim 14

A method according to claim 10, wherein the step of varying the control signal in response to changes in the output signal reduces the impedance value of the terminal impedance of the directional coupler when the value of the output signal increases, and increases the impedance value of the terminal impedance of the directional coupler when the value of the output signal diminishes.

Claim 15

A method according to claim 10, wherein the terminal impedance of the directional coupler is driven by a PIN diode (D1) disposed on the second branch between the second end of the second conductor and the earth potential, wherein the step of varying the control signal in response to chances in the output signal forward biases the PIN diode (D1) when the value of the output signal increases, and when the value of said output signal diminishes, the forward biasing of the PIN diode (D1) is reduced towards zero biasing.

Claim 16

A method according to claim 10, wherein the terminal impedance of the directional coupler is driven by a PIN diode (D1) disposed on the second branch between the second end of the second conductor and the earth potential, wherein the step of varying the control signal in response to changes in the output signal forward biases the PIN diode (D1) when the value of the output signal increases, and when the value of the output signal diminishes, the PIN diode (D1) is reverse biased.

Claim 17

A method according to claim 9, wherein the directional coupler arrangement includes a reference signal for controlling the power level, wherein the step of electrically altering the impedance value of the terminal impedance is performed by the reference signal.

Claim 18

A method according to claim 9, wherein the step of electrically altering the impedance value of the terminal impedance of the directional coupler is performed by an electrical signal formed by a processor that controls an operation of the directional coupler arrangement.