MEASUREMENT ERRQRS

L

Unknown

pg659d

Figure 6-42. Bhjor Sources of Error

The transmission coefficient is measured by taking the ratio of the incident signal (I) and the transmitted signal (‘I) (see F’igure 6-43). Ideally, (I) consists only of power delivered by the source, and (T) consists only of power emerging at the test device output.

(1) ) CT) * Forward S2,M

‘ZIA’ ETF

(+ !T) + (I) Reverse S,2M

?2M 0-1S12A =

E TR

‘12AETR

pg660d

Figure 6-43. Transmission Coetllcient

As in the reflection model, source match can cause the incident signal to vary as a function of test device &A. Also, since the test setup transmission return port is never exactly the characteristic impedance, some of the transmitted signal is reflected from the test set port 2, and from other mismatches between the test device output and the receiver input, to return to the test device. A portion of this signal may be re-reflected at port 2, thus affecting &M, or part may be transmitted through the device in the reverse direction to appear at port 1, thus affecting Sll~. This error term, which causes the magnitude and phase of the transmitted signal to vary as a function of $ZA, is called load match, ELF (see Figure 6-44).

Application and Operation Concepts 6-67