For example: Agilent E4440A or Anritsu 68369
Network Analyzers
A network analyzer is an instrument that measures the network parameters of electrical networks.
Anritsu 37377D
Anritsu 37377D Lightning Series Vector Network Analyzer 40Mhz-50Ghz,

Manufacturer: Anritsu
Keysight / Agilent 41951A
HP Agilent 41951A RF Impedance Test Kit w/ Accessories

Manufacturer: Keysight / Agilent
Keysight / Agilent 4195A
HP Agilent 4195A Network/Spectrum Analyzer, 500MHz

Manufacturer: Keysight / Agilent
Keysight / Agilent 4395A
Agilent 4395A Network/Spectrum/Impedance Analyzer

Manufacturer: Keysight / Agilent
Keysight / Agilent 43961A
HP Agilent 43961A RF Impedance Test Kit w/ 16092A Clip Fixture & Accessories

Manufacturer: Keysight / Agilent
Keysight / Agilent 4396B
1.8GHz Network/Spectrum/Impedance Analyzer

Manufacturer: Keysight / Agilent