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Figure 6-34. Effective Directivity EDF

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Since the measurement system test port is never exactly the characteristic impedance

(50 ohms), some of the reflected signal bounces off the test port, or other impedance transitions further down the line, and back to the unknown, adding to the original incident signal (I). This effect causes the magnitude and phase of the incident signal to vary as a function of &A and frequency. Leveling the source to produce a constant incident signal (I) reduces this error, but since the source cannot be exactly leveled at the test device input, leveling cannot eliminate all power variations. This re-reflection effect and the resultant incident power variation are caused by the source match error, ESF (see F’igure 6-35).

 

 

 

 

 

1

 

 

 

 

 

S o u r c e

Match

 

 

 

 

 

I

 

 

 

 

 

 

 

EDF

\I s 1 I A

 

 

 

 

 

 

 

 

 

 

 

 

R

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

L

 

U n k n o w n

 

 

 

 

 

 

 

 

,

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Figure 6-35. Source Match ESF

Frequency response (tracking) error is caused by variations in magnitude and phase flatness versus frequency between the test and reference signal paths. These are due mainly to coupler roll off, imperfectly matched samplers, and differences in length and loss between the incident and test signal paths. The vector sum of these variations is the reflection signal path tracking error, EFW (see Figure 6-36).

6-62 Application and Operation Concepts

Page 343
Image 343
HP 8753E manual Effective Directivity EDF