For example: Agilent E4440A or Anritsu 68369

Filter

Passive or active filters

Manufacturers: Keysight / Agilent, Ballantine, Fluke Networks, Stanford Research Systems, Trilithic, K&L Microwave, Krohn-Hite, Wavetek, Wiltron, Anritsu, Keytek, Amplifier Research, Avantek, Rohde and Schwarz, Mini-Circuits