The phase continuous mode can be enabled in the "Phase Continuous Frequency Settings" section of the "Frequency" dialog. In this mode, the output sinewave is phase continuous, that means there is no phase discontinuity or glitch when changing the frequency.
At the transition from one frequency to another an intermediate frequency (switching transient) occurs, which causes spurs (see figure below). The transient is due to changes of the synthesizer settings (e.g. dividers, filters, phase detectors).

The phase continuous mode freezes the settings of the synthesizer (for example dividers, filters, phase detectors) which could generate phase discontinuities when changed. The frequency change is effectively performed by changing the fine resolution synthesizer. This allows a phase continuous change from one frequency to another without any transients (see figure below).

The available frequency range for phase continuous settings is limited by the fine resolution synthesizer used and varies with the RF frequency setting at the point of activating the phase continuous mode.
Depending on the instrument equipment - with or without option R&S SMA-B22 - the fine resolution synthesizer used is a DDS (Direct Digital Synthesizer, with option R&S SMA-B22) or a Fractional N-Synthesizer (without option R&S SMA-B22). The DDS provides generally a wider frequency range for phase continuous settings. In addition, two modes (narrow and wide) allow a selection either in favor of higher signal quality or in favor of an especially wide frequency range.
![]() | When phase continuous frequency setting is active, data sheet values no longer apply Activating frequency or phase modulation deactivates phase continuous settings and vice versa. |
In the "RF Frequency Sweep" Menu, if the sweep is active, switch it off.
In the "RF Frequency" Menu under the "Phase Continuous Frequency Settings" dialog
If the "Phase Continuous Frequency Mode" is Active, switch it off
Set "Frequency Range" to “Narrow”
Select the RF frequency
Check displayed Frequency Range
If the "Frequency Range" corresponds to the selected frequency range, check the "Phase Continuous Active" box
If "Frequency Range" in Narrow Mode does not, select “Wide” for the Frequency Range and check the Phase Continuous Active box
In the "RF Frequency Sweep" dialog
Modify the "Start Freq" and "Stop Freq" or "Center Frequency" and "Span" as needed.
Set the RF frequency sweep State to “ON”.
In the "RF Frequency Sweep" dialog there are some settings that will improve the phase continuous sweep results for both "Narrow" and "Wide" mode choices.
"Step Lin": low step size
In order to get the best spur performance during frequency change, it is recommended to reduce the step size and (if necessary) increase the sweep speed by decreasing the Dwell Time. Effectively, the sweep will be performed in the same amount of time, but with smaller step sizes.
"Shape": Triangle sweep
The triangle sweep offers a uniform forward sweep and return to the beginning frequency. The saw tooth sweep produces a uniform forward sweep with an abrupt reset to the starting frequency. The abrupt reset can generate spurs.
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