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Model XC0900A-20
Rev G
t
20 dB Directional Coupler
Description
The XC0900A-20 is a low profile, high performance 20dB directional
coupler in a new easy to use, manufacturing friendly surface mount
package. It is designed for AMPS band applications. The XC0900A-20 is
designed particularly for power and frequency detection, as well as for
VSWR monitoring, where tightly controlled coupling and low insertion loss
is required. It can be used in high power applications up to 200 Watts.
Parts have been subjected to rigorous qualification testing and they are
manufactured using materials with coefficients of thermal expansion (CTE)
compatible with common substrates such as FR4, G-10, RF-35, RO4350
and polyimide. Available in both 5 of 6 tin lead (XC0900A-20P) and 6 of 6
tin immersion (XC0900A-20S) RoHS compliant finishes.
Electrical Specifications **
Features:
• 800 – 1000 MHz
• AMPS
• High Power
• Very Low Loss
• Tight Coupling
• High Directivity
• Production Friendly
• Tape and Reel
• Available in Lead-Free (as
illustrated) or Tin-Lead
• Reliable, FIT=0.41
Frequency Mean
Coupling Insertion
Loss VSWR Directivity
MHz dB dB Max Max : 1 dB Min
800 - 1000 20.1 ± 0.60 0.18 1.15 23
700 – 800 20.7 ± 1.00 0.16 1.28 18
869 - 894 20.2 ± 0.60 0.14 1.12 23
925 - 960 20.2 ± 0.60 0.14 1.12 23
Frequency
Sensitivity Power ΘJC Operating
Temp.
dB Max Avg. CW Watts ºC/Watt ºC
± 0.20 150 16 -55 to +95
± 0.40 200 16 -55 to +95
± 0.05 200 16 -55 to +95
± 0.05 200 16 -55 to +95
**Specification based on performance of unit properly installed on Anaren Test Board 54606-0003. Refer to
Specifications subject to change without notice. Refer to parameter definitions for details.
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Tolerances are Non-Cumulative
XC0900A-20* Mechanical Outline
Dimensions are in Inches [Millimeters]
Side View
.060±.012
[1.52±0.30]
Bottom View (Far-Side)
Top View (Near-Side)
Denotes
Array Number
4X .040±.004
[1.02±0.10]
4X .059±.004 SQ
[1.50±0.10]
.430±.004
[10.92±0.10]
.220±.004
[5.59±0.10]
GND
GND
Pin 1 Pin 2
Pin 3
Pin 4
Pin 1
Pin 2
Pin 4
Pin 3
.560±.010
[14.22±0.25]
.350±.010
[8.89±0.25]
Orientation
Marker Denotes
Pin 1
*For RoHS Compliant Versions order with S suffix
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Directional Coupler Pin Configuration
The XC0900A-20 has an orientation marker to denote Pin 1. Once port one has been identified the other ports are
known automatically. Please see the chart below for clarification:
20dB Coupler Pin Configuration
Pin 1 Pin 2 Pin 3 Pin 4
Input Direct Isolated Coupled
Direct Input Coupled Isolated
Note: The direct port has a DC connection to the input port and the coupled port has a DC connection to the
isolated port. For optimum performance use Pin 1 or Pin 2 as inputs.
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Rev G
Insertion Loss and Power Derating Curv es
Insertion Loss Derating:
The insertion loss, at a given frequency, of a group of
couplers is measured at 25°C and then averaged. The
measurements are performed under small signal
conditions (i.e. using a Vector Network Analyzer). The
process is repeated at 95°C, 150°C, and 200°C. A best-
fit line for the measured data is computed and then
plotted from -55°C to 300°C.
Power Derating:
The power handling and corresponding power derating
plots are a function of the thermal resistance, mounting
surface temperature (base plate temperature),
maximum continuous operating temperature of the
coupler, and the thermal insertion loss. The thermal
insertion loss is defined in the Power Handling section of
the data sheet.
As the mounting interface temperature approaches the
maximum continuous operating temperature, the power
handling decreases to zero.
-100 -50 050 100 150 200 250 300 350
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
Temperature of the Part (ºC)
Insertion Loss (dB)
Typical Insertion Loss Derating Curve for XC0900A-20
typical insertion loss (f=894MHz)
typical insertion loss (f=960MHz)
typical insertion loss (f=1000MHz)
025 50 75 100 125 150 175 200 225 250 275 300
0
25
50
75
100
125
150
175
200
225
250
275
Base Plate Temperature (ºC)
P ow er (W atts )
Power Derating Curve for XC0900A -20
power handling at 894MHz
power handling at 960MHz
power handling at 1000MHz
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Typical Performance (-55°C, 25°C and 95°C): 800-1000 MHz
800 820 840 860 880 900 920 940 960 980 1000
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (MHz)
R eturn Los s (dB )
Return Loss for XC0900A-20 (Feeding Port 1)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (MHz)
R eturn Los s (dB )
Return Loss for XC0900A-20 (Feeding Port 2)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (MHz)
R eturn Los s (dB )
Return Loss for XC0900A-20 (Feeding Port 3)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (MHz)
R eturn Los s (dB )
Return Loss for XC0900A-20 (Feeding Port 4)
- 55ºC
25ºC
95ºC
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Typical Performance (-55°C, 25°C and 95°C): 800-1000 MHz
800 820 840 860 880 900 920 940 960 980 1000
-21
-20.8
-20.6
-20.4
-20.2
-20
-19.8
-19.6
-19.4
-19.2
-19
Frequency (MHz)
Coupling (dB)
Coupling for XC0900A-20 (Feeding Port 1)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Frequency (MHz)
D irec tiv ity (dB )
Directivity for XC0900A-20 (Feeding Port 1)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
Frequency (MHz)
Insertion Loss (dB)
Insertion Loss for XC0900A-20 (Feeding Port 1)
- 55ºC
25ºC
95ºC
800 820 840 860 880 900 920 940 960 980 1000
-0.2
-0.18
-0.16
-0.14
-0.12
-0.1
-0.08
-0.06
-0.04
-0.02
0
Frequency (MHz)
Transm ission Loss (dB )
Transmission Loss for XC0900A-20 (Feeding Port 1)
- 55ºC
25ºC
95ºC
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Definition of Measured Specifica tions
Parameter Definition Mathematical Representation
VSWR
(Voltage Standing Wave Ratio )
The impedance match of
the coupler to a 50Ω
system. A VSWR of 1:1 is
optimal.
VSWR = min
max
V
V
Vmax = voltage maxima of a standing wave
Vmin = voltage minima of a standing wave
Return Loss
The impedance match of
the coupler to a 50Ω
system. Return Loss is
an alternate means to
express VSWR.
Return Loss (dB)= 20log 1-VSW
R
1VSWR
+
Mean Coupling
At a given frequency (ωn),
coupling is the input
power divided by the
power at the coupled
port. Mean coupling is
the average value of the
coupling values in the
band. N is the number of
frequencies in the band.
Coupling (dB) = ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=)( )(
log10)(
ncpl
nin
nP
P
C
ω
ω
ω
Mean Coupling (dB) =
N
C
N
nn
∑
=1)(
ω
Insertion Loss The input power divided
by the sum of the power
at the two output ports.
10log direct cpl
in
PP P
+
Transmission Loss The input power divided
by the power at the direct
port.
10log direct
in
P
P
Directivity
The power at the
coupled port divided by
the power at the isolated
port.
10log iso
cpl
P
P
Frequency Sensitiv ity
The decibel difference
between the maximum in
band coupling value and
the mean coupling, and
the decibel difference
between the minimum in
band coupling value and
the mean coupling.
Max Coupling (dB) – Mean Coupling (dB)
and
Min Coupling (dB) – Mean Coupling (dB)
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Notes on RF Testing and Circuit Layout
The XC0900A-20 Surface Mount Couplers require the use of a test fixture for verification of RF performance. This test
fixture is designed to evaluate the coupler in the same environment that is recommended for installation. Enclosed
inside the test fixture, is a circuit board that is fabricated using the recommended footprint. The part being tested is
placed into the test fixture and pressure is applied to the top of the device using a pneumatic piston. A four port Vector
Network Analyzer is connected to the fixture and is used to measure the S-parameters of the part. Worst case values
for each parameter are found and compared to the specification. These worst case values are reported to the test
equipment operator along with a Pass or Fail flag. See the illustrations below.
3 & 5 dB
Test Board 10 & 20 dB
Test Board Test Board
In Fixture
Test Station
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The effects of the test fixture on the measured data must be minimized in order to accurately determine the
performance of the device under test. If the line impedance is anything other than 50Ω and/or there is a discontinuity
at the microstrip to SMA interface, there will be errors in the data for the device under test. The test environment can
never be “perfect”, but the procedure used to build and evaluate the test boards (outlined below) demonstrates an
attempt to minimize the errors associated with testing these devices. The lower the signal level that is being
measured, the more impact the fixture errors will have on the data. Parameters such as Return Loss and
Isolation/Directivity, which are specified as low as 27dB and typically measure at much lower levels, will present the
greatest measurement challenge.
The test fixture errors introduce an uncertainty to the measured data. Fixture errors can make the performance of the
device under test look better or worse than it actually is. For example, if a device has a known return loss of 30dB and
a discontinuity with a magnitude of –35dB is introduced into the measurement path, the new measured Return Loss
data could read anywhere between –26dB and –37dB. This same discontinuity could introduce an insertion phase
error of up to 1°.
There are different techniques used throughout the industry to minimize the affects of the test fixture on the
measurement data. Anaren uses the following design and de-embedding criteria:
• Test boards have been designed and parameters specified to provide trace impedances of 50
±1Ω. Furthermore, discontinuities at the SMA to microstrip interface are required to be less than
–35dB and insertion phase errors (due to differences in the connector interface discontinuities
and the electrical line length) should be less than ±0.25° from the median value of the four
paths.
• A “Thru” circuit board is built. This is a two port, microstrip board that uses the same SMA to
microstrip interface and has the same total length (insertion phase) as the actual test board. The
“Thru” board must meet the same stringent requirements as the test board. The insertion loss
and insertion phase of the “Thru” board are measured and stored. This data is used to
completely de-embed the device under test from the test fixture. The de-embedded data is
available in S-parameter form on the Anaren website (www.anaren.com).
Note: The S-parameter files that are available on the anaren.com website include data for frequencies that are
outside of the specified band. It is important to note that the test fixture is designed for optimum performance through
2.3GHz. Some degradation in the test fixture performance will occur above this frequency and connector interface
discontinuities of –25dB or more can be expected. This larger discontinuity will affect the data at frequencies above
2.3GHz.
Circuit Board Layout
The dimensions for the Anaren test board are shown below. The test board is printed on Rogers RO4350 material
that is 0.030” thick. Consider the case when a different material is used. First, the pad size must remain the same to
accommodate the part. But, if the material thickness or dielectric constant (or both) changes, the reactance at the
interface to the coupler will also change. Second, the linewidth required for 50Ω will be different and this will introduce
a step in the line at the pad where the coupler interfaces with the printed microstrip trace. Both of these conditions will
affect the performance of the part. To achieve the specified performance, serious attention must be given to the
design and layout of the circuit environment in which this component will be used.
If a different circuit board material is used, an attempt should be made to achieve the same interface pad reactance
that is present on the Anaren RO4350 test board. When thinner circuit board material is used, the ground plane will
be closer to the pad yielding more capacitance for the same size interface pad. The same is true if the dielectric
constant of the circuit board material is higher than is used on the Anaren test board. In both of these cases,
narrowing the line before the interface pad will introduce a series inductance, which, when properly tuned, will
compensate for the extra capacitive reactance. If a thicker circuit board or one with a lower dielectric constant is used,
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the interface pad will have less capacitive reactance than the Anaren test board. In this case, a wider section of line
before the interface pad (or a larger interface pad) will introduce a shunt capacitance and when properly tuned will
match the performance of the Anaren test board.
Notice that the board layout for the 3dB and 5dB couplers is different from that of the 10dB and 20dB couplers. The
test board for the 3dB and 5dB couplers has all four traces interfacing with the coupler at the same angle. The test
board for the 10dB and 20dB couplers has two traces approaching at one angle and the other two traces at a different
angle. The entry angle of the traces has a significant impact on the RF performance and these parts have
been optimized for the layout used on the test boards sho wn below.
10 & 20dB Test Board 3 & 5dB Test Board
Testing Sample Parts Supplied on Anaren Test Boards
If you have received a coupler installed on an Anaren produced microstrip test board, please remember to remove the
loss of the test board from the measured data. The loss is small enough that it is not of concern for Return Loss and
Isolation/Directivity, but it should certainly be considered when measuring coupling and calculating the insertion loss
of the coupler. An S-parameter file for a “Thru” board (see description of “Thru” board above) will be supplied upon
request. As a first order approximation, one should consider the following loss estimates:
Frequency Band Avg. Ins. Loss of Test Board @ 25°C
800 – 1000 MHz ~ 0.07dB
1700 – 2300 MHz ~ 0.12dB
For example, a 1900MHz, 10dB coupler on a test board may measure –10.30dB from input to the coupled port at
some frequency, F1. When the loss of the test board is removed, the coupling at F1 becomes -10.18dB (-10.30dB +
0.12dB). This compensation must be made to both the coupled and direct path measurements when calculating
insertion loss.
The loss estimates in the table above come from room temperature measurements. It is important to note that the
loss of the test board will change with temperature. This fact must be considered if the coupler is to be evaluated at
other temperatures.
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Peak Power Handling
High-Pot testing of these couplers during the qualification procedure resulted in a minimum breakdown voltage of
1.7KV (minimum recorded value). This voltage level corresponds to a breakdown resistance capable of handling at
least 12dB peaks over average power levels, for very short durations. The breakdown location consistently occurred
across the air interface at the coupler contact pads (see illustration below). The breakdown levels at these points will
be affected by any contamination in the gap area around these pads. These areas must be kept clean for optimum
performance. It is recommended that the user test for voltage breakdown under the maximum operating conditions
and over worst case modulation induced power peaking. This evaluation should also include extreme environmental
conditions (such as high humidity).
Orientation Marker
A printed circular feature appears on the top surface of the coupler to designate Pin 1. This orientation marker is not
intended to limit the use of the symmetry that these couplers exhibit but rather to facilitate consistent placement of
these parts into the tape and reel package. This ensures that the components are always delivered with the same
orientation. Refer to the table on page 2 of the data sheet for allowable pin configurations.
Test Plan
Xinger II couplers are manufactured in large panels and then separated. A sample population of parts is RF small
signal tested at room temperature in the fixture described above. All parts are DC tested for shorts/opens. (See
“Qualification Flow Chart” section for details on the accelerated life test procedures.)
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Power Handling
The average power handling (total input power) of a Xinger coupler is a function of:
• Internal circuit temperature.
• Unit mounting interface temperature.
• Unit thermal resistance
• Power dissipated within the unit.
All thermal calculations are based on the following assumptions:
• The unit has reached a steady state operating condition.
• Maximum mounting interface temperature is 95oC.
• Conduction Heat Transfer through the mounting interface.
• No Convection Heat Transfer.
• No Radiation Heat Transfer.
• The material properties are constant over the operating temperature range.
Finite element simulations are made for each unit. The simulation results are used to calculate the unit thermal
resistance. The finite element simulation requires the following inputs:
• Unit material stack-up.
• Material properties.
• Circuit geometry.
• Mounting interface temperature.
• Thermal load (dissipated power).
The classical definition for dissipated power is temperature delta (ΔT) divided by thermal resistance (R). The
dissipated power (Pdis) can also be calculated as a function of the total input power (Pin) and the thermal insertion loss
(ILtherm):
)(101 10 WP
R
T
Ptherm
IL
indis ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−⋅=
Δ
=
−
(1)
Power flow and nomenclature for an “H” style coupler is shown in Figure 1.
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Pin 1
Pin 4
Input Port
Coupled Port Isolated Port
Direct Port
PIn POut(RL) POut(DC)
POut(CPL) POut(ISO)
Figure 1
The coupler is excited at the input port with Pin (watts) of power. Assuming the coupler is not ideal, and that there are
no radiation losses, power will exit the coupler at all four ports. Symbolically written, Pout(RL) is the power that is
returned to the source because of impedance mismatch, Pout(ISO) is the power at the isolated port, Pout(CPL) is the
power at the coupled port, and Pout(DC) is the power at the direct port.
At Anaren, insertion loss is defined as the log of the input power divided by the sum of the power at the coupled and
direct ports:
Note: in this document, insertion loss is taken to be a positive number. In many places, insertion loss is written as a
negative number. Obviously, a mere sign change equates the two quantities.
)dB(
PP P
log10IL
)DC(out)CPL(out
in
10 ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
⋅= (2)
In terms of S-parameters, IL can be computed as follows:
)dB(SSlog10IL 2
41
2
3110 ⎟
⎠
⎞
⎜
⎝
⎛+⋅−= (3)
We notice that this insertion loss value includes the power lost because of return loss as well as power lost to the
isolated port.
For thermal calculations, we are only interested in the power lost “inside” the coupler. Since Pout(RL) is lost in the
source termination and Pout(ISO) is lost in an external termination, they are not be included in the insertion loss for
thermal calculations. Therefore, we define a new insertion loss value solely to be used for thermal calculations:
)(log10
)()()()(
10 dB
PPPP P
IL
RLoutISOoutDCoutCPLout
in
therm ⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+++
⋅= (4)
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In terms of S-parameters, ILtherm can be computed as follows:
)(log10 2
41
2
31
2
21
2
1110 dBSSSSILtherm ⎟
⎠
⎞
⎜
⎝
⎛+++⋅−= (5)
The thermal resistance and power dissipated within the unit are then used to calculate the average total input power
of the unit. The average total steady state input power (Pin) therefore is:
)(
101101 1010
W
R
T
P
Pthermtherm ILIL
dis
in
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−
Δ
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛−
=−− (6)
Where the temperature delta is the circuit temperature (Tcirc) minus the mounting interface temperature (Tmnt):
)( CTTT o
mntcirc −=Δ (7)
The maximum allowable circuit temperature is defined by the properties of the materials used to construct the unit.
Multiple material combinations and bonding techniques are used within the Xinger II product family to optimize RF
performance. Consequently the maximum allowable circuit temperature varies. Please note that the circuit
temperature is not a function of the Xinger case (top surface) temperature. Therefore, the case temperature cannot
be used as a boundary condition for power handling calculations.
Due to the numerous board materials and mounting configurations used in specific customer configurations, it is the
end users responsibility to ensure that the Xinger II coupler mounting interface temperature is maintained within the
limits defined on the power derating plots for the required average power handling. Additionally appropriate solder
composition is required to prevent reflow or fatigue failure at the RF ports. Finally, reliability is improved when the
mounting interface and RF port temperatures are kept to a minimum.
The power-derating curve illustrates how changes in the mounting interface temperature result in converse changes
of the power handling of the coupler.
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Mounting
In order for Xinger surface mount couplers to work
optimally, there must be 50Ω transmission lines leading
to and from all of the RF ports. Also, there must be a
very good ground plane underneath the part to ensure
proper electrical performance. If either of these two
conditions is not satisfied, insertion loss, coupling, VSWR
and isolation may not meet published specifications.
Overall ground is improved if a dense population of
plated through holes connect the top and bottom ground
layers of the PCB. This minimizes ground inductance
and improves ground continuity. All of the Xinger hybrid
and directional couplers are constructed from ceramic
filled PTFE composites which possess excellent electrical
and mechanical stability having X and Y thermal
coefficient of expansion (CTE) of 17-25 ppm/oC.
When a surface mount hybrid coupler is mounted to a
printed circuit board, the primary concerns are; ensuring
the RF pads of the device are in contact with the circuit
trace of the PCB and insuring the ground plane of neither
the component nor the PCB is in contact with the RF
signal.
Mounting Footprint
To ensure proper electrical and thermal performance
there must be a ground plane with 100%
solder connection underneath the part
Dimensions are in Inches [Millimeters]
XC0900A-20* Mounting Footprint
.220
[5.59]
4X .066 SQ
[1.65] 4X 50 Ω
Transmission
Line
4X .040
[1.02]
Multiple
plated thru holes
to ground
.430
[10.92]
Coupler Mounting Process
The process for assembling this component is a
conventional surface mount process as shown in Figure
1. This process is conducive to both low and high volume
usage.
Figure 1: Surface Mounting Process Steps
Storage of Components: The Xinger II products are
available in either an immersion tin or tin-lead finish.
Commonly used storage procedures used to control
oxidation should be followed for these surface mount
components. The storage temperatures should be held
between 15OC and 60OC.
Substrate: Depending upon the particular component,
the circuit material has an x and y coefficient of thermal
expansion of between 17 and 25 ppm/°C. This coefficient
minimizes solder joint stresses due to similar expansion
rates of most commonly used board substrates such as
RF35, RO4350, FR4, polyimide and G-10 materials.
Mounting to “hard” substrates (alumina etc.) is possible
depending upon operational temperature requirements.
The solder surfaces of the coupler are all copper plated
with either an immersion tin or tin-lead exterior finish.
Solder Paste: All conventional solder paste formulations
will work well with Anaren’s Xinger II surface mount
components. Solder paste can be applied with stencils or
syringe dispensers. An example of a stenciled solder
paste deposit is shown in Figure 2. As shown in the
figure solder paste is applied to the four RF pads and the
entire ground plane underneath the body of the part.
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Model XC0900A-20
Rev G
Figure 2: Solder Paste Application
Coupler Positioning: The surface mount coupler can
be placed manually or with automatic pick and place
mechanisms. Couplers should be placed (see Figure 3
and 4) onto wet paste with common surface mount
techniques and parameters. Pick and place systems
must supply adequate vacuum to hold a 0.50-0.55
gram coupler.
Figure 3: Component Placement
Figure 4: Mounting Features Example
Reflow: The surface mount coupler is conducive to most of
today’s conventional reflow methods. A low and high
temperature thermal reflow profile are shown in Figures 5
and 6, respectively. Manual soldering of these components
can be done with conventional surface mount non-contact
hot air soldering tools. Board pre-heating is highly
recommended for these selective hot air soldering
methods. Manual soldering with conventional irons should
be avoided.
Available on Tape
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Place Manufacturing.
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Model XC0900A-20
Rev G
Figure 5 – Low Temperature Solder Reflow Thermal Profile
Figure 6 – High Temperature Solder Reflow Thermal Profile
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Model XC0900A-20
Rev G
Qualification Flow Chart
Available on Tape
and Reel for Pick and
Place Manufacturing.
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Model XC0900A-20
Rev G
USA/Canada:
Toll Free:
Europe:
(315) 432-8909
(800) 411-6596
+44 2392-232392
Available on Tape and
Reel for Pick and Place
Manufacturing.
Model XC0900A-20
Rev G
Application Information
Directional Couplers and Sampling
Directional couplers are often used in circuits that require the sampling of an arbitrary signal. Because they are
passive, non-linear devices, Anaren directional couplers do not perturb the characteristics of the signal to be sampled,
and can be used for frequency monitoring and/or measurement of RF power. An example of a sampling circuit is the
reflectometer. The purpose of the reflectometer is to isolate and sample the incident and reflected signals from a
mismatched load. A basic reflectometer circuit is shown in Figure ap.n.1-1.
Figure ap.n.1-1. A Reflectometer Circuit Schematic
If the directional coupler has perfect directivity, then it is clear that VI is strictly a sample of the incident voltage Vinput,
and VR is strictly a sample of the wave that is reflected from the load. Since directivity is never perfect in practice, both
VI and VR will contain samples of the input signal as well as the reflected signal. In that case,
θ
j
IeV Γ+= CDTC Eq. ap.n.1-1
and
φ
j
ReV Γ+= CTCD Eq. ap.n.1-2
where C is the coupling, D is the directivity, Γ is the complex reflection coefficient of the load, T is the transmission
coefficient, and φ and θ are unknown phase delay differences caused by the interconnect lines on the test board. If we
know VI and VR, we can easily calculate the reflection coefficient of the load. One should notice that in order to make
forward and reverse measurements using only one coupler, the directivity must be really low. In specific customer
applications, the preferred method for forward and reverse sampling is shown in Figure ap.n.1-2.
LOAD
12
34
Reflected
Wave
Vinput
I
VV
R
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Model XC0900A-20
Rev G
LOAD
12
34
Reflected
Wave
INPUT
ISOLATOR
REVERSE
MEASUREMENT
MEASUREMENT
FORWARD
RFP-500500A6Z50150
RFP-375375A6Z5050
RFP-250375A4Z5015
RFP-060120A15Z50
8
MODELPower (Watts)
** RECOMMENDED TERMINATIONS
**TERMINATION
Figure ap.n.1-2. Forward and Reverse Sampling
The isolator in Figure ap.n.1-2 prevents the reflected wave from exciting the directional coupler. A list of recommended
terminations is shown in the figure.
Directional Couplers in Feed-Forward Amplifier Applications
Feed-forward amplifiers are widely used to reduce distortion due to nonlinearities in power amplifiers. Although the
level and complexity of feed-forward amplifiers varies from one manufacturer to another, the basic building block for this
linearization scheme remains the same. A basic feed-forward schematic is shown in Figure ap.n.2-1. The input signal
is split in two using a hybrid coupler or power divider. The output of the main amplifier is sampled with a 20dB-30dB
directional coupler. The XC0900A-20 is an excellent candidate for this sampling since it provides great return loss and
directivity. The sampled signal, which consists of a sample of the original input signal plus some distortion, is inverted
and then combined with the output of the first delay line. This procedure subtracts (through destructive interference) the
sample of the original input signal, leaving only the distortion or error component. The error component is then
amplified and combined with the output of the second delay line using another directional coupler. In many cases, a
10dB coupler is used to combine the two signals. The XC0900A-10 is a perfect choice for this injection because it has
tight coupling, superior directivity, and excellent match.
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Available on Tape and
Reel for Pick and Place
Manufacturing.
Model XC0900A-20
Rev G
RFP-500500A6Z50
RFP-375375A6Z5050
RFP-250375A4Z5015
RFP-060120A15Z508
MODELPower (W atts)
50 Ohm ** (see table below)
** RECOMMENDED TERMINATIONS
TERMINATIONS
COUPLER
HYBRID
3dB
10dB
DIRECTIONAL
COUPLER
COUPLER
DIRECTIONAL
20dB -- 30dB
OUTPUT
INPUT
ERROR
AMPLIFIER
CANCELLATION
CARRIER
DELAY
DELAY
AMPLIFIER
MAIN
100
Figure ap.n.2-1. Generic Feed Forward Circuit Schematic
Both directional couplers in the Figure ap.n.2-1 have one port terminated with a 50Ω resistor. In order to achieve
optimum performance, the termination must be chosen carefully. It is important to remember that a good termination
will not only produce a good match at the input of the coupler, but will also maximize the isolation between the input port
and isolated port. Furthermore, since the termination can potentially absorb high levels of power, its maximum power
rating should be chosen accordingly. A list of recommended terminations is shown in Figure ap.n.2-1. For an ideal
lossless directional coupler, the power at the coupled and direct ports can be written as:
Watts
dB
10
)(Coupling
input
coupled
10
P
P=Eq. ap.n.2-1
Watts
dB
10
)(Coupling
input
inputdirect 10
P
PP −= Eq. ap.n.2-2
where Pinput is the input power in Watts, and Coupling(dB) is the coupling value in dB.
Available on Tape
and Reel for Pick and
Place Manufacturing.
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Toll Free:
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Model XC0900A-20
Rev G
Packaging and Ordering Information
Parts are available in both reel and tube. Packaging follows EIA 481-2. Parts are oriented in tape and reel as
shown below. Minimum order quantities are 2000 per reel and 30 per tube. See Model Numbers below for
further ordering information.
Xinger Coupler Frequency (MHz) Size (Inches) Coupling Value Plating Finish
XC
0450 = 410-480
0900 = 800-1000
1900 = 1700-2000
2100 = 2000-2300
2500 = 2300-2700
3500 = 3300-3700
A = 0.56 x 0.35
B = 1.0 x 0.50
E = 0.56 x 0.20
L = 0.65 x 0.48
M= 0.40 x 0.20
P = 0.25 x 0.20
03 = 3dB
05 = 5dB
10 = 10dB
20 = 20dB
30 = 30dB
P = Tin Lead
S = Immersion Tin
XX XXXX X - XX X
