High frequency phase reference standard signal

1. A method of providing a pre-characterised high frequency signal, the method comprising the steps of:

a) providing a non-linear circuit,

b) feeding a first signal having a first, fundamental, frequency into the non-linear circuit,

whereby the non-linear circuit generates an output signal comprising components at a plurality of harmonic frequencies, the components of the plurality of harmonic frequencies having stable phase relation relative to each other, and

c) providing information concerning the phase relation of said plurality of harmonic frequency components,

whereby the output signal is in the form of a pre-characterised high frequency multi-tone signal,

wherein

the non-linear circuit includes

d) a first non-linear circuit portion which, if provided with the first signal as its input signal, would generate harmonic components such that the average magnitude of the odd harmonic components would be a first factor higher than the average magnitude of the even harmonic components, and

e) a second non-linear circuit portion which, if provided with the first signal as its input signal, would generate harmonic components such that the average magnitude of the even harmonic components would be a second factor higher than the average magnitude of the odd harmonic components,

and wherein

the first and second non-linear circuit portions are arranged such that the output is a signal which which has odd and even signal components of a similar magnitude;

whereby

the pre-characterised high frequency signal can then he used, within a high-frequency measurement system for measuring the behavior of nonlinear high frequency devices, as a phase reference standard with which absolute phase and magnitude measurements can be obtained.

2. A method according to claim 1 , wherein at least 90% of the power of the harmonic components of the pre-characterised high frequency signal generated by the non-linear circuit is carried by harmonic frequency components at the tenth or lower harmonic frequencies.

3. A method according to claim 1 , wherein the output signal is fed to a vector network analyser and the first signal is generated by a signal generator of the vector network analyser.

4. A method according to claim 1 , comprising a thermally controlled chamber for maintaining the non-linear circuit at a substantially constant and pre-set temperature.

5. A calibration verification method comprising the steps of testing the calibration of a measurement apparatus by means of using the measurement apparatus to measure at least one of (a) the absolute phase relation between different signal components and (b) time domain measurements of a signal component relative to a fixed time, wherein

the signal component(s) so measured are provided by performing the method of claim 1 .

6. A method of measuring the response of an electronic device to a high frequency input signal, the method comprising the steps of:

a) providing an electronic device having a first port and a second port, and applying a high frequency signal to the device,

b) providing a measurement system including a measurement apparatus having a plurality of inputs for measuring high frequency signals from the first and second ports,

c) measuring, at a plurality of different frequencies, and with the use of the plurality of inputs of the measurement apparatus, signals from the first and second ports of the device, and

d) ascertaining at least one of (i) absolute phase information from the signals so measured and (ii) a time domain representation relating to the signals measured by performing the method of claim 1 .

7. A method according to claim 6 , wherein the high frequency signal applied to the device under test is phase-locked with the first signal supplied to the non-linear circuit.

8. A method according to claim 6 , wherein the method is performed to measure the non-linear behaviour of the electronic device.