Agilent/HP .1 MHz to 2 GHz 778D Coaxial Dual-Directional Coupler

Agilent/HP .1 MHz to 2 GHz 778D Coaxial Dual-Directional Coupler
Manufacturer: Agilent / HP
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Agilent/HP .1 MHz to 2 GHz 778D Coaxial Dual-Directional Cou


Agilent/HP .1 MHz to 2 GHz 778D Coaxial Dual-Directional Coupler

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   The Agilent 778D is an economical dual-directional coupler designed for swept measurements in the 100 MHz to 2 GHz range. Its high directivity and mean coupling accuracy of ±0.5 dB makes the Agilent 778D ideal for reflectometer applications. The auxiliary arms track very closely, making this coupler particularly useful for reflectometers driven by sweep oscillators.


  • Dual-directional
  • High directivity
  • Excellent mean coupling accuracy
  • Frequency Range: 100 MHz to 2 GHz
  • Nominal Coupling and Variation: 20 ±1.0 dB
  • Directivity: >36dB to 1 GHz
  • Maximum SWR: 1.1
  • Insertion Loss: <0.60 dB
  • Power Rating Average, Peak: 50 W, 500 W

   This dual directional 20 dB coupler has a frequency range extending over 4 octaves from 100 MHz to 2 GHz. The multi-octave capability makes measurements easier¿setup and calibration time are reduced, since normally several couplers are required over this frequency band. The coupling factor increases about 6 dB per octave below 100 MHz; thus, usefulness below this frequency is restricted only by the amount of signal source power and/or the sensitivity of the RF detector connected to the coupler.

   The 778D is ideal for measuring the reflection and transmission characteristics of a device from 100 MHz to 2000 MHz. Figure 2 shows a test configuration in which a 778D dual directional coupler is used to separate and isolate the incident, reflected, and transmitted signals in a swept-frequency measurement. These signals are detected and their ratio displayed on a CRT. This coupler is an ideal companion for the Agilent 8755 frequency response test set, a detection and display system operating from 15 MHz to 18 GHz.

    The high directivity and close tracking of the auxiliary arms of this coupler make it particularly useful for this type of broadband measurement. The high directivity insures accurate measurements by a true separation of the forward and reflected signals. Close tracking of signal variation from the auxiliary arms gives a flat frequency response that makes display readings easy to interpret.

   The 778D is also well suited for measurements of impedance when used with the Agilent 8405A vector voltmeter. The technique is described in Application Note 77-3, Measurement of Complex Impedance, available at your nearest Agilent sales office. Again, a reflectometry technique is used. With the vector voltmeter, however, both magnitude and phase angle of the reflection coefficient can be measured. Data can be read from the two meters of the vector voltmeter and transferred directly to a Smith Chart to provide impedance of such devices as antennas or other passive components.