For example: Agilent E4440A or Anritsu 68369
Transmission Test Kit
Keysight / Agilent 85046B
S-Parameter Test Set, 75 Ohms, 300 kHz to 2 GHz
Manufacturer: Keysight / Agilent
Keysight / Agilent 87511B
S-Parameter Test Set, 75 Ohm 100 KHz- 500 MHz
Manufacturer: Keysight / Agilent