N5221A-200: 2 ports, single source, hardware configuration
N5221A-201: 2 ports, single source, with configurable test set
N5221A-210: PNA 2 端口计量选件(选件 210)
N5221A-217: 2 ports, single source, configurable test set, extended power range
N5221A-219: 2 ports, single source, configurable test set, extended power range, bias-tees
N5221A-400: 4 ports, dual source, hardware configuration
N5221A-401: 4 ports, dual source, with configurable test set
N5221A-417: 4 ports, dual source, configurable test set, extended power range
N5221A-419: 4 ports, dual source, configurable test set, extended power range, bias-tees