This document lists the common RF measurements that can be performed by the CASSINI ATE and provides a brief description of each.
The measurements are categorized into 4 categories: VNA measurements, Testhead measurements, Receiver measurements, and Noise measurements.
VNA Measurements
The VNA measurements are all vector error corrected. Like the testhead, the VNA performs 8 measurements to get the 4 s-parameters. The VNA measurements assume the input and output frequencies to be the same, using the input frequency for the error correction.
VNA Measurements:
 Button | Units | Comments |
S Parameters | Complex Voltage | Measures all 4 s-parameters, vector error-corrected. Individual s-parameters must then be extracted using single-input calc buttons. |
S11 Only | Complex Voltage | Measures S11 using reflection-only error correction. Full error correction could degrade accuracy if the other s-parameters are invalid, so this should be used when the other s-parameters are invalid, such as on one-port devices. |
S11 | Complex Voltage | Returns S11. All 4 s-parameters are measured with full error correction. Then, only S11 is returned. |
Input VSWR | N/A | Returns S11 as a VSWR. All 4 s-parameters are measured with full error correction. Then, S11 is extracted and converted to VSWR. |
Gain | Volts | Returns the magnitude only for S21. All 4 s-parameters are measured with full error correction. Then, S21 is extracted and converted to voltage gain. |
Phase | Degrees | Returns the phase only for S21. All 4 s-parameters are measured with full error correction. Then, S21 is extracted and converted to phase. |
Testhead measurements
The testhead measurements are all based on the wave parameter measurements, taking 8 receiver voltage measurements to produce the requested result. If the testhead's s-parameter mode (SPAR MODE) is bidirectional, the measurements are taken in a traditional VNA method that reverses the signal through the DUT. In the unidirectional mode (recommended for most measurements), Roos' unique unidirectional process using a bi-state load is used. This process acquires all 8 measurements without reversing the signal through the DUT.
Some of the testhead buttons are very similar to VNA buttons. The main differences are: 1) In the testhead measurements the input and output frequencies are independently specified, whereas the VNA measurements (discussed later) assume the input and output frequencies to be the same. 2) Both measurements are vector error corrected, but the VNA measurements use more sophisticated error correction.
Testhead Measurements:
Button | Units | Comments |
Wave Param at xxx Freq(1) | N/A | The 'Wave Param at xxx Freq buttons are not exactly high-level measurement buttons. They produce raw measurements that can then be manipulated using calc buttons. |
Input Power | Watts | Measures power into the DUT with error correction at the input frequency |
Output Power | Watts | Measures power out of the DUT with error correction at the output frequency |
Conversion Gain | Linear Pwr Ratio | The 'Conversion Gain' button measures the ratio of output power to input power. |
Harmonics | Linear Pwr Ratio | The 'Harmonics' button measures the ratio of power at the receiver frequency to output power. |
(1) xxx Freq is the input frequency, the output frequency, or the receiver frequency.
- For the input frequency, the system attempts to find the source that is being used based on the Testhead and Src12Output settings. (It does not look at the sources' power or on/off settings.) Whenever the result is ambiguous, it assumes source 1.
- For the output frequency, the system uses the 'FREQ REFERENCE', 'OUT FREQ OFFSET' and 'OUT FREQ SCALE' buttons from the 'System' panel.
- For receiver frequency, the system uses the receiver's actual frequency.
Receiver Measurements
The receiver measurements can be thought of as 'low level' measurements. They are the raw measurements that form the basis for the higher-level testhead, VNA and noise figure measurements (described later). The receiver measurements do not have vector error correction. Except for the 'relative' measurements, they have scalar path loss correction.
Measurement | Detector | P/L (2) | Units (3) | Typical Use | Comments |
Voltage (4) | Complex | Y | Complex Voltage | Measure any synchronous signal. (All system components, except noise, are synchronized.) | Use Voltage for most measurements except noise. |
Relative Voltage | Complex | N | Complex Voltage | Only used for system service plans. | Same as Voltage but without path loss correction. |
Power (4) | Complex | Y | Watts | Measure non-synchronous signals. | |
Relative Power | Complex | N | Watts | Only used for system service plans. | Same as Power but without path loss correction. |
RMS Power | RMS | Y | Watts | Scalar measurement of low level signals. | No compensation for bandwidth. |
Noise Power | RMS | Y | Watts/Hz | Noise close to the noise floor. | Assumes 4 MHz IF BW (Not valid for 7 kHz BW) Compensates for BW. Corrects for system noise floor |
Relative Noise Pwr | RMS | N | Watts/Hz | Only used for system service plans. | Same as Noise Power but without path loss correction. |
Phase Noise | Both(5) | Y | Watts/Hz | Phase noise measurements | Compensates for bandwidth. |
(2) P/L means path loss correction. If 'Y' then path loss correction is applied. If 'N', path loss correction is not applied. Measurements without path loss correction are only used for system service plans. Note that receiver correction (IF gain, etc.) are always applied. Only the path loss is removed.
(3) Complex voltage is returned as a pair of numbers representing the real and imaginary number. Units returned can be converted to other compatible units using single-input calc buttons.
(4) For a single average, 'Voltage' and 'Power' return the same result. Only the units are changed. However when averages >1 are selected, they act differently. 'Voltage' performs a complex average, taking into account the phase as well as the amplitude of the measurement. For a non-synchronous signal, such as noise, enough averages will return a result of zero. 'Voltage' is useful for measuring a signal in the presence of noise or spurious signals, because averages will effectively reduce the noise while not affecting the desired (synchronous) signal. 'Power' performs a scalar average, which means it will return the average power of all the signals getting to the complex detector. If the goal is to measure noise or to measure a non-synchronous signal with the complex detector, then power is used.
(5) For phase noise measurements, if the receiver IF BW is in the 4 MHz state, the RMS detector is used. If the IF BW is in the 7 kHz state, the complex detector is used.