Making Measurements 3
Making a Reflection Calibration Measurement
The following procedure makes a reflection measurement using a coupler or directional bridge to measure the return loss of a filter. This example uses a 370 MHz low- pass filter as the DUT.
The calibration standard for reflection measurements is usually a short circuit connected at the reference plane (the point at which the device under test (DUT) is connected.) See Figure
19.A short circuit has a reflection coefficient of 1 (0 dB return loss). It reflects all incident power and provides a convenient 0 dB reference.
1Connect the DUT to the directional bridge or coupler as shown below. Terminate the unconnected port of the DUT.
Figure 20 Reflection Measurement Short Calibration Test Setup
Short Circuit
Or
DUT
Coupled |
Port |
N9340A
1 | 2 | 3 |
4 | 5 | 6 |
7 | 8 | 9 |
| 0 |
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| If possible, use a coupler or bridge with the correct test |
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N O T E |
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port connector for both calibrating and measuring. Any |
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| adapter between the test port and DUT degrades |
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| coupler/bridge directivity and system source match. |
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| Ideally, you should use the same adapter for the |
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| calibration and the measurement. Be sure to terminate the | |
| second port of a two port device. |
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N9340A User’s Guide | 51 | |
