Keysight / Agilent / HP 8721A Directional Bridge

The Keysight 8721A Directional Bridge is a precision instrument for accurate impedance and reflection coefficient measurements across RF and microwave frequencies. It enables return-loss, insertion-loss, and isolation measurements while serving as a power-monitoring device for both source and load conditions. The bridge delivers the directivity and frequency response required for component characterization, filter analysis, and impedance matching in swept-source and network analyzer configurations.

Technical Specifications

Frequency Range: 100 kHz to 100 MHz

Impedance: 50 Ω (75 Ω optional)

Insertion Loss: 6 dB

Coupling to Auxiliary Arm: 6 dB

Frequency Response: ±0.5 dB (0.1 to 110 MHz)

Directivity: Greater than 40 dB (1 to 110 MHz)

Load-Port Return Loss: Greater than 30 dB

Maximum Input Power: +20 dBm

Weight: 1 lbs

Key Features

Monitors source power under load and power delivered to remote loads with 6 dB attenuation in both bridge arms

Directivity exceeding 40 dB enables precise separation of incident and reflected signals

Flat frequency response of ±0.5 dB maintains measurement accuracy across the operating band

Compatible with both 50 Ω and 75 Ω systems

Typical Applications

Return-loss characterization of RF and microwave components

Impedance measurement and validation

Transmission and reflection analysis with tracking generators and spectrum analyzers

Power-level monitoring in multi-port systems

Filter and matching network evaluation

Compatibility & Integration The 8721A integrates with the HP 11652A Transmission/Reflection Kit and operates with swept sources including tracking generators and spectrum analyzers. It pairs with network analyzers such as the HP 8407A and with vector voltmeters like the HP 8405A for CW transmission and reflection measurements.