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參數資料
| 型號： | AD8302-EVAL |
| 廠商： | Analog Devices, Inc. |
| 英文描述： | LF.2.7 GHz RF/IF Gain and Phase Detector |
| 中文描述： | LF.2.7 GHz射頻/中頻增益和相位檢波器 |
| 文件頁數： | 20/24頁 |
| 文件大?。?/td> | 533K |
| 代理商： | AD8302-EVAL |
REV. 0
AD8302
–20–
The measurement accuracy can be compromised if board
level details are not addressed. Minimize the physical distance
between the series connected couplers since the extra path
length adds phase error to . Keep the paths from the couplers
to the AD8302 as well matched as possible since any differences
introduce measurement errors. The finite directivity, D, of the
couplers sets the minimum detectable reflection coefficient, i.e.,
|G
MIN
(dB)|<|D(dB)|.
SOURCE
1dB
C1
C4
C6
C5
VP
C7
R4
R1
R2
20dB
INCIDENT
WAVE
REFLECTED
WAVE
Z
LOAD
R5
R6
1
COMM
MFLT
14
INPA
VMAG
2
13
OFSA
MSET
3
12
VPOS
VREF
4
11
OFSB
PSET
5
10
INPB
VPHS
6
9
COMM
PFLT
7
8
AD8302
C2
C8
C3
Figure 13. Using the AD8302 to Measure the Vector
Reflection Coefficient Off an Arbitrary Load
Reflectometer
The AD8302 can be configured to measure the magnitude ratio
and phase difference of signals that are incident on and reflected
from a load. The vector reflection coefficient, is defined as,
=
Reflected Voltage
/
Incident Voltage
= (
Z
L
–
Z
O
)/(
Z
L
+
Z
O
), (16)
where
Z
L
is the complex load impedance and
Z
O
is the charac-
teristic system impedance.
The measured reflection coefficient can be used to calculate the
level of impedance mismatch or standing wave ratio (SWR) of a
particular load condition. This proves particularly useful in diag-
nosing varying load impedances such as antennas that can degrade
performance and even cause physical damage. The vector
reflectometer arrangement given in Figure 13 consists of a pair
of directional couplers that sample the incident and reflected sig-
nals. The attenuators reposition the two signal levels within the
dynamic range of the AD8302. In analogy to Equations 14 and
15, the attenuation factors and coupling coefficients are given by,
C
B
+
L
B
=
P
IN
–
P
OPT
C
A
+
L
A
=
P
IN
+
where
negative for passive loads. Consider the case where the incident
signal is 10 dBm and the nominal reflection coefficient is –19 dB.
As shown in Figure 13, using 20 dB couplers on both sides and
–30 dBm for P
OPT
, the attenuators for Channel A and B paths are
1 dB and 20 dB, respectively. The magnitude and phase of the
reflection coefficient are available at the VMAG and VPHS pins
scaled to 30 mV/dB and 10 mV/degree. When is –19 dB, the
VMAG output is 900 mV.
(17)
(18)
NOM
–
P
OPT
NOM
is the nominal reflection coefficient in dB and is
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