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.