The Rohde and Schwarz ZVCE Options:
ZVCE50 = 20 kHz to 8 GHz, 3-Channel, Bidirectional, 50 Ohm, Active, Couplers
ZVCE51 = 20 kHz to 8 GHz, 3-Channel, Bidirectional, 50 Ohm, Passive, SWR Bridges
ZVCE52 = 300 kHz to 8 GHz, 3-Channel, Bidirectional, 50 Ohm, Active, SWR Bridges