For example: Agilent E4440A or Anritsu 68369
YIG Oscillator
Yttrium iron garnet spheres (YIG spheres) serve as magnetically tunable filters and resonators for microwave frequencies
Keysight / Agilent 5086-7903
HP Agilent Keysight 5086-7903 YIG Oscillator
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Manufacturer: Keysight / Agilent