Model XMC2560A-20
Rev B
Available on Tape
and Reel for Pick and
Place Manufacturing.
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Wideband 20 dB Directional Coupler
Military Grade
Description
The XMC2560A-20 is a low profile, high performance 20dB directional coupler
in an easy to use, manufacturing friendly surface mount package. It is
designed primarily for defense applications. The XMC2560A-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 100 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.
Electrical Specifications **
Frequency Mean
Coupling Insertion
Loss VSWR Directivity
MHz dB dB Max Max : 1 dB Min
2500-6000 20.0 ± 0.80 0.20 1.25 18
Frequency
Sensitivity Power ΘJC Operating
Temp.
dB Max Avg. CW Watts ºC/Watt ºC
±1.25 TBD 21.5 -55 to +95
Features:
• 2500 – 6000 MHz
• Defense Applications
• 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
**Specification based on performance of unit properly installed on Anaren Test Board 54606-0003 with small
signal applied. Specifications subject to change without notice. Refer to parameter definitions for details.
Top View
.560±.010
[14.22±0.25]
PIN 4
PIN 1
GND
.254±.004
[6.45±0.10]
.350±.010
[8.89±0.25]
.464±.004
[11.79±0.10]
Bottom View
PIN 3
Side View
PIN 3 PIN 4
4X .025±.004
[.64±0.10]
PIN 2 PIN 2 PIN 1
GND
4X .042±.004 SQ
[1.07±0.10]
DENOTES
ARRAY NUMBER
ORIENTATION
MARKER DENOTES
PIN 1
.065±.014
29 Sep 09
Model XMC2560A-20
Rev B
Directional Coupler Pin Configuration
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Available on Tape and
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Manufacturing.
The XMC2560A-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.
XMC2560A-20 Typical Performance
Return Loss
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
2500 3000 3500 4000 4500 5000 5500 6000
Freq uency [MHz]
Return L o ss [dB]
S11
S22
S33
S44
Coupling
-24.0
-23.0
-22.0
-21.0
-20.0
-19.0
-18.0
-17.0
-16.0
2500 3000 3500 4000 4500 5000 5500 6000
Frequency [MHz]
Coupling [dB]
S41
S32
Mea n
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Model XMC2560A-20
Rev B
Fr equenc y Sensit i vit y
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2500 3000 3500 4000 4500 5000 5500 6000
Frequency [MHz]
Frequency Sensitivity [dB
]
S41
S32
Directivity
-40
-35
-30
-25
-20
-15
-10
-5
0
2500 3000 3500 4000 4500 5000 5500 6000
Frequency [MHz]
Directivity [dB
]
S31-S41
S42-S32
I nse r t i on Loss
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
2500 3000 3500 4000 4500 5000 5500 6000
Frequency [MHz]
Insertion Loss [dB]
S21+S41
S43+S23
29 Sep 09
Model XMC2560A-20
Rev B
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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
Mean coupling is the
average coupling value in
dB of the maximum and
minimum power levels
from the coupled arm..
Mean Coupling (dB) =
0.5 * [CouplingMax (dB) + CouplingMin (dB)]
where
CouplingMax (dB) =10log (PowerMax*)
CouplingMin (dB) =10log (PowerMin*)
* from the coupled arm
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)
Model XMC2560A-20
Rev B
Available on Tape
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Notes on RF Testing and Circuit Layout
The XMC2560A-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
29 Sep 09
Model XMC2560A-20
Rev B
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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
6GHz. 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 may affect the data at frequencies above
6GHz.
Circuit Board Layout
The dimensions for the Anaren test board are shown below. The test board is printed on Rogers RO4003 material
that is 0.020” 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 line width 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 RO4003 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,
Model XMC2560A-20
Rev B
Available on Tape
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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.
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.
Testing Sample Parts Supplied on Anaren Test Bo ards
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
2500 MHz ~ 0.29dB
4000 MHz ~ 0.41dB
6000 MHz ~ 0.57dB
For example, a 4300MHz, 20dB coupler on a test board may measure –20.60dB from input to the coupled port at
frequency F1=4000 MHz. When the loss of the test board is removed, the coupling at F1 becomes -20.19dB (-
20.60dB + 0.41dB). 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.
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.
29 Sep 09
Model XMC2560A-20
Rev B
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
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 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.
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]
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Rev B
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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.
29 Sep 09
Model XMC2560A-20
Rev B
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Figure 5 – Low Temperature Solder Reflow Thermal Profile
Figure 6 – High Temperature Solder Reflow Thermal Profile
Model XMC2560A-20
Rev B
Available on Tape
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Place Manufacturing.
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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.
LOAD
12
34
Reflected
Wave
Vinput
I
VV
R
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
φ
j
ReV Γ+= CTCD
Eq. ap.n.1-1
and
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.
29 Sep 09
Model XMC2560A-20
Rev B
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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 XMC2560A-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 (please contact Anaren for corresponding parts).
Model XMC2560A-20
Rev B
Available on Tape
and Reel for Pick and
Place Manufacturing.
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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.
29 Sep 09
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Toll Free:
Europe:
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Available on Tape and
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Manufacturing.
Model XMC2560A-20
Rev B
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
XMC
0405 = 400-500
0825 = 800-2500
0525 = 500-2500
1720 = 1700-2000
2325 = 2300-2500
3338 = 3300-3800
2560 = 2500-6000
A = 0.56 x 0.35
B = 1.00 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
XXX XXXX X - XX X
