The LMX1204EVM has slightly elevated phase noise compared to both the cascaded LMX1204 design and SMA100B as shown in Figure 2-3. As the cascaded LMX1204 design matches the SMA100B at low frequency offsets (< 100 Hz), the inconsistency at those low frequency offsets is likely due to PCB layout related differences.

All three sources match to around the 400-kHz offset frequency range before diverging. At this point, the SMA100B begins to drop beneath the -160 dc/Hz noise floor shown by the LMX1204 devices. There is minimal separation between the single and dual stage LMX1204 configurations, indicating the added phase noise by the second LMX1204 is negligible at 1 GHz.