STZ series full waveguide band noise sources are silicon IMPATT diode based solid state noise sources. These noise sources implement high performance diode and propriety circuit design to offer high ENR with extreme flatness in entire waveguide bandwidth in the frequency range of 26.5 to 170 GHz in eight waveguide bands. The standard noise sources have integrated Faraday isolators to improve port VSWR which results in more reliable noise figure measurements. The operating voltage range of the standard noise sources is from +18 to +28 VDC via a BNC (F) connector which offers immediate interface requirements with industry standard noise meters, such as Keysight Model 8970 or N8975A. In addition, the noise sources can work in either CW or pulse AM operation modes. The AM modulation mode is triggered by TTL control signal via an SMA (F) connector.
The outline drawing of the W band waveguide noise source with integrated Faraday isolator is shown in Figure 2.
The Triggering Port (female SMA connector) of the noise source is provided to turn the noise source on and off via a TTL control signal any time when the Bias is applied. The switching frequency is limited to 1 kHz. While the AM modulation rate of the standard model is at limited at 1 kHz, the higher modulation rate up to 1 MHz is offered under custom models.
The Power/Triggering Inversion Switch of the noise source is provided to manually turn the noise source on and off any time when the Bias is applied. When the switch is in “ON” position, the LED light will be illuminated, which indicates that the noise source is on (Hot).
How is the noise figure tested?
To test the noise figure of the mixer, the low noise amplifier or the receiver, the “Y-Factor” method is commonly used. The output noise power of these devices is measured when the input port is terminated with a known “Hot” or a known “Cold” temperature termination. The noise figure of the device under test (DUT) can be calculated with the following equations. Where “Phot” and “Pcold” are the output power of the DUT when the input is terminated with “Hot” and “Cold” terminations, respectively.
The Y-Factor = Phot / Pcold
The STZ series full waveguide band noise sources are used as “Hot” or “Cold” temperature terminations by switching the noise source “ON” and “OFF” with the known ENR. Based on that, the noise figure of DUT can be obtained by following equation.
NF = ENR –10 Log (Y-1) (dB)
How is the Noise Source Calibrated and What is the Uncertainty?
The key uncertainty of the noise figure measurement is the noise source’s ENR. Here is the calibration method used for the series STZ noise sources.
- A “Hot” matching termination (295K) and a “Cold” liquid matching termination (77K) are used to calibrate a receiver Noise Figure (NFreceiver) as reference.
- Then, the known noise figure receiver is used to calibrate the noise source by switching it “ON” and “OFF” to obtain the ENRnoise source.
Repeat above steps for five times to obtain five independent sets of NFreceiver and ENRnoise source to remove the uncertainties. From a typical chart below, the uncertainty of the ENR of the noise source can be obtained. For a W band noise source, the uncertainty is 1 dB approximately.