Direct analog synthesis modules for an X-band frequency source

Some design considerations of frequency synthesis modules are presented. The module consists of a bank of crystal or SAW resonator stabilized oscillators and frequency multipliers, connected to the output via a multithrow switch. Phase noise performance of SAW oscillators vs. crystal oscillators is compared. It is shown that better spurious signals rejection can be obtained when frequency multipliers are placed before the switch, despite the worse isolation of the switch at higher frequencies. In this configuration, keying the multipliers allows for further isolation improvement.