XC1900A-03P - Anaren Microwave, Inc.

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Model XC0450A-03

Rev B

Hybrid Coupler

3 dB, 90°

Description

The XC0450A-03 is a low profile, high performance 3dB hybrid coupler

in a new easy to use, manufacturing friendly surface mount package. It is

designed for NMT band applications. The XC0450A-03 is designed

particularly for balanced power and low noise amplifiers, plus signal

distribution and other applications where low insertion loss and tight

amplitude and phase balance is required. It can be used in high power

applications up to 45 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 (XC0450A-03P) and 6 of 6

RoHS compliant tin immersion (XC0450A-03S).

Electrical Specifications **

Frequency Isolation Insertion

Loss VSWR Amplitude

Balance

MHz dB Min dB Max Max : 1 dB Max

410-480 23 0.36 1.22 ± 0.15

Phase

Balance Power ΘJC Operating

Temp.

Degrees Avg. CW Watts ºC/Watt ºC

90 ± 3.5 45 27 -55 to +95

Features:

• 410 – 480 MHz

• NMT

• Very Low Loss

• Tight Amplitude Balance

• High Isolation

• Production Friendly

• Tape and Reel

• Available in Lead-Free (as

illustrated) or Tin-Lead

• Reliable, FIT= 0.53

**Specification based on performance of unit properly installed on Anaren Test Board 58481-0001 with small

signal applied. Specifications subject to change without notice. Refer to parameter definitions for details.

Mechanical Outline

.072±.014

[1.82±0.37]

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

Pin 1 Pin 2

Pin 3

Pin 4

Pin 2

Pin 4

Pin 3

.560±.010

[14.22±0.25]

.350±.010

[8.89±0.25]

Orientation

Marker Denotes

Pin 1

4X .040±.004

[1.02±0.10]

Pin 1

GND

Dimensions are in Inches [Millimeters]

XC0450A-03* Mechanical Outline

* For RoHS compliant versions order with S suffix

Tolerances are non-cumulative

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Model XC0450A-03

Rev B

Hybrid Coupler Pin Configuration

The XC0450A-03 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:

Configuration Pin 1 Pin 2 Pin 3 Pin 4

Splitter Input Isolated

-3dB 90

−

∠

-3dB

∠

Splitter Isolated Input

-3dB

∠

-3dB 90

−

∠

Splitter -3dB 90

−

∠

-3dB

∠

Input Isolated

Splitter -3dB

∠ -3dB 90

−

∠

Isolated Input

*Combiner A90−∠

∠

Isolated Output

*Combiner A

∠ A90

−

∠

Output Isolated

*Combiner Isolated Output

A90

−

∠

*Combiner Output Isolated A

∠

−

∠

*Note: “A” is the amplitude of the applied signals. When two quadrature signals with equal amplitudes are

applied to the coupler as described in the table, they will combine at the output port. If the amplitudes are

not equal, some of the applied energy will be directed to the isolated port.

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Model XC0450A-03

Rev B

Insertion Loss and Power Derating Curv es

-50 050 100 150 200 250 300

-0.5

-0.45

-0.4

-0.35

-0.3

-0.25

-0.2

-0.15

Temperature of the Part ( °C)

Insertion Loss (dB)

Typical Insertion Loss Derating Curve for XC0450A-03

typical insertion loss(f=480Mhz)

025 50 75 100 125 150 175 200 225

Base Plate Temperature (°C)

Power (Watts)

Power Derating Curve for XC0450E-03

power handling (f=480MHz)

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 -55°C and 95°C. Based on

copper as well as dielectric losses, the insertion loss is

computed 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.

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Rev B

Typical Performance (-55°C, 25°C and 95°C): 410-480 MHz

410 420 430 440 450 460 470 480

-60

-50

-40

-30

-20

-10

Frequency (MHz)

Return Loss (dB)

Return Loss for XC0450A-03(Feeding Port1)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

-60

-50

-40

-30

-20

-10

Frequency (MHz)

Return Loss (dB)

Return Loss for XC0450A-03(Feeding Port2)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

-60

-50

-40

-30

-20

-10

Frequency (MHz)

Return Loss (dB)

Return Loss for XC0450A-03(Feeding Port3)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

-60

-50

-40

-30

-20

-10

Frequency (MHz)

Return Loss (dB)

Return Loss for XC0450A-03(Feeding Port4)

-55 °C

25 °C

95 °C

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Typical Performance (-55°C, 25°C and 95°C): 410-480 MHz

410 420 430 440 450 460 470 480

-3.4

-3.3

-3.2

-3.1

-3

-2.9

-2.8

Frequency (MHz)

Coupling (dB)

Coupling for XC0450A-03(Feeding Port1)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

-0.3

-0.25

-0.2

-0.15

-0.1

-0.05

Frequency (MHz)

Insertion Loss (dB)

Insertion Loss for XC0450A-03(Feeding Port1)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

Frequency (MHz)

Phase Balance (degree)

Phase Balance for XC0450A-03(Feeding Port1)

-55 °C

25 °C

95 °C

410 420 430 440 450 460 470 480

-60

-50

-40

-30

-20

-10

Frequency (MHz)

Isolation (dB)

Isolation for XC0450A-03(Feeding Port1)

-55 °C

25 °C

95 °C

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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

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

1VSWR

Insertion Loss The input power divided

by the sum of the power

at the two output ports.

Insertion Loss(dB)= 10log

direct cpl

Isolation The input power divided

by the power at the

isolated port.

Isolation(dB)= 10log

iso

Phase Balance The difference in phase

angle between the two

output ports.

Phase at coupled port – Phase at direct port

Amplitude Balance The power at each output

divided by the average

power of the two outputs.

10log

⎟

⎠

⎞

⎜

⎝

⎛+

directcpl

cpl and 10log

⎟

⎠

⎞

⎜

⎝

⎛+

directcpl

direct

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Rev B

Notes on RF Testing and Circuit Layout

The XC0450A-03 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

410 – 480 MHz ~ 0.03dB

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

Ptherm

indis ⎟

⎟

⎠

⎞

⎜

⎝

⎛−⋅=

−

(1)

Power flow and nomenclature for an “X” style coupler is shown in Figure 1.

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Pin 1

Pin 4

Input Port

Coupled Port Direct Port

Isolated Port

PIn POut(RL) POut(ISO)

POut(CPL) POut(DC)

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(

log10IL

)DC(out)CPL(out

10 ⎟

⎟

⎠

⎞

⎜

⎝

⎛

⋅= (2)

In terms of S-parameters, IL can be computed as follows:

)dB(SSlog10IL 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

RLoutISOoutDCoutCPLout

therm ⎟

⎟

⎠

⎞

⎜

⎝

⎛

+++

⋅= (4)

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In terms of S-parameters, ILtherm can be computed as follows:

)(log10 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

Pthermtherm ILIL

dis

⎟

⎠

⎞

⎜

⎝

⎛−

⎟

⎠

⎞

⎜

⎝

⎛−

=−− (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 50 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, electrical performance 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]

XC0450A-03* Mounting Footprint

.220

[5.59]

.430

[10.92]

4X .065 SQ

[1.65] 4X 50 Ω

Transmission

Line

4X .040

[1.02]

Multiple

plated thru holes

to ground

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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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.

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Rev B

Figure 5 – Low Temperature Solder Reflow Thermal Profile

Figure 6 – High Temperature Solder Reflow Thermal Profile

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Model XC0450A-03

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Qualification Flow Chart

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Electrical testing at room

temperature S-parameter

n=50

Visual Inspection

n=25

Mechanical Inspection

n=25

Microsection

3 test units and 1 control

High Power Test

n=2

Life Testing XXX watts Input XXX°C

base plate temperature 96 hours 3 in

series n=6

Visual Inspection

n=16

Electrical Testing at room temperature

and over temperature S-parameter

n=6

Microsection

2 Life, 1 high power and 1

control

Visual Inspection

n=50

Bake parts for 1 hour at 100°C

n=40

Electrical testing at room

temperature S-parameter

n=50

Moisture Resistance Testing -25° to 65° C for 2 hrs.

@ 90% humidity. Increase to 95% humidity and

soak for 4 hrs. ramp temp to 25° C in 2 hrs. repeat

for 10 cycles and then soak -10° C hour 3 hrs. n=40

Electrical testing at room

temperature s-parameter n=50

Visual Inspection

n=50

Control Units

n=10

Control Units

n=10

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Application Information

The XC0450A-03 is an “X” style 3dB (hybrid) coupler. Port configurations are defined in the table on page 2 of this data

sheet and an example driving port 1 is shown below.

Ideal 3dB Coupler Splitter Operation

1V 0.707V

∠

(

-3dB

)

0.707V

∠

-90

(

-3dB

)

Isolated Port

The hybrid coupler can also be used to combine two signals that are applied with equal amplitudes and phase

quadrature (90º phase difference). An example of this function is illustrated below.

Ideal 3dB Coupler Combiner Operation

2 1V∠Φ

0.707V∠θ

0.707V ∠θ -90

Isolated Port

3dB couplers have applications in circuits which require splitting an applied signal into 2, 4, 8 and higher binary

outputs. The couplers can also be used to combine multiple signals (inputs) at one output port. Some splitting and

combining schemes are illustrated below:

2-Way Splitter/Com biner Network

Amplitude and

Phase tracking

Devices

* 50Ω

Termination

* 50

Termination

Output

Input

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4-Way Splitter/Com biner Network

Output

* 50Ω

Termination

* 50Ω

Termination

Input

Amplitude and

Phase tracking

Devices

Amplitude and

Phase tracking

Devices

* 50Ω

Termination

* 50Ω

Termination

* 50Ω

Term.

* 50

Term.

The splitter/combiner networks illustrated above use only 3dB (hybrid) couplers and are limited to binary divisions (2 n

number of splits, where n is an integer). Splitter/combiner circuits configured this way are known as “corporate”

networks. When a non-binary number of divisions is required, a “serial” network must be used. Serial networks can be

designed with [3, 4, 5, ….., n] splits, but have a practical limitation of about 8 splits.

A 5dB coupler is used in conjunction with a 3dB coupler to build 3-way splitter/combiner networks. An ideal version of

this network is illustrated below. Note what is required; a 50% split (i.e. 3dB coupler) and a 66% and 33% split (which is

actually a 4.77dB coupler, but due to losses in the system, higher coupler values, such as 5dB, are actually better

suited for this function). The design of this type of circuit requires special attention to the losses and phase lengths of

the components and the interconnecting lines. A more in depth look at serial networks can be found in the article

“Designing In-Line Divider/Combiner Networks” by Samir Tozin, which describes the circuit design in detail and can be

found in the White Papers Section of the Anaren website, www.anaren.com.

3-Way Splitter/Com biner

1/3 Pin

2/3 Pin

1/3 Pin

Pout

2/3 Pin

1/3 Pin

5 dB (4.77)

coupler

3 dB coupler

5 dB (4.77)

coupler

* 50Ω

Termination

* 50Ω

Termination

* 50

Termination

* 50

Termination

*Recommended Terminations

Power (Watts) Model

8 RFP-060120A15Z50

15 RFP-250375A4Z50

50 RFP-375375A6Z50

100 RFP-500500A6Z50

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Reflections From Equal Unmatched Terminations

Referring to the illustration below, consider the following reflection properties of the 3dB coupler. A signal applied to

port 1 is split and appears at the two output ports, ports 3 & 4, with equal amplitude and in phase quadrature. If ports

3 & 4 are not perfectly matched to 50 there will be some signal reflected back into the coupler. If the magnitude and

angle of these reflections are equal, there will be two signals that are equal in amplitude and in phase quadrature (i.e.

the reflected signals) being applied to ports 3 & 4 as inputs. These reflected signals will combine at the isolated port

and will cancel at the input port. So, terminations with the same mismatch placed at the outputs of the 3dB coupler will

not reflect back to the input port and therefore will not affect input return loss.

Γ=

ZZ ZZ

−

0.707V

∠

(

-3dB

)

0.707V

∠

θ -90

(

-3dB

)

Isolated Port

Termination = ZL

Γ× 0.707V ∠θ -90

Γ× 0.707V ∠θ

|Γ (0.5V ∠2θ -90 + 0.5V

∠

-90)| = |Γ|

Γ (0.5V ∠2θ + 0.5V ∠2θ -180) = 0V

Termination = ZL

The reflection property of common mismatches in 3dB couplers is very beneficial to the operation of many networks.

For instance, when splitter/combiner networks are employed to increase output power by paralleling transistors with

similar reflection coefficients, input return loss is not degraded by the match of the transistor circuit. The reflections

from the transistor circuits are directed away from the input to the termination at the isolated port of the coupler.

This example is not limited to Power Amplifiers. In the case of Low Noise Amplifiers (LNA’s), the reflection property of

3dB couplers is again beneficial. The transistor devices used in LNA’s will present different reflection coefficients

depending on the bias level. The bias level that yields the best noise performance does not also provide the best

match to 50 . A circuit that is optimized for both noise performance and return loss can be achieved by combining

two matched LNA transistor devices using 3dB couplers. The devices can be biased for the best noise performance

and the reflection property of the couplers will provide a good match as described above. An example of this circuit is

illustrated below:

LNA Circuit Leveraging the Reflection Property of 3dB Couplers

Amplitude and phase tracking

LNA devices biased for

timum noise

erformance

50Ω

Termination

50Ω

Termination

Output

Input

Energy reflected from LNA

devices biased for optimum

noise

erformance

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Signal Control Circuits Utilizing 3dB Couplers

Variable attenuators and phase shifter are two examples of signal control circuits that can be built using 3dB couplers.

Both of these circuits also use the reflection property of the 3dB coupler as described above. In the variable attenuator

circuit, the two output ports of a 3dB coupler are terminated with PIN diodes, which are basically a voltage variable

resistor at RF frequencies (consult the literature on PIN diodes for a more complete equivalent circuit). By changing the

resistance at the output ports of the 3dB coupler, the reflection coefficient, , will also change and different amounts of

energy will be reflected to the isolated port (note that the resistances must change together so that  is the same for

both output ports). A signal applied to the input of the 3dB coupler will appear at the isolated port and the amplitude of

this signal will be a function of the resistance at the output ports. This circuit is illustrated below:

Variable Attenuator Circuit Utilizing a 3dB Coupler

Vdc

Input

0.707V

∠

(

-3dB

)

0.707V

∠

-90

(

-3dB

)

Output

Γ× 0.707V ∠θ -90

Γ× 0.707V ∠θ

|Γ (0.5V ∠2θ -90 + 0.5V ∠2θ -90)| = |Γ|

and

Out

PIN Diodes

If =0, no energy is reflected from the PIN diodes and S21 = 0 (input to output). If |  | =1, all of the energy is reflected

from the PIN diodes and |S21| = 1 (assuming the ideal case of no loss). The ideal range for  is –1 to 0 or 0 to 1, which

translate to resistances of 0 to 50 and 50 to  respectively. Either range can be selected, although normally 0

to 50 is easier to achieve in practice and produces better results. Many papers have been written on this circuit and

should be consulted for the details of design and operation.

Another very similar circuit is a Variable Phase Shifter (illustrated below). The same theory is applied but instead of PIN

diodes (variable RF resistance), the coupler outputs are terminated with varactors. The ideal varactor is a variable

capacitor with the capacitance value changing as a function of the DC bias. Ideally, the magnitude of the reflection

coefficient is 1 for these devices at all bias levels. However, the angle of the reflected signal does change as the

capacitance changes with bias level. So, ideally all of the energy applied to port 1, in the circuit illustrated below, will be

reflected at the varactors and will sum at port 2 (the isolated port of the coupler). However, the phase angle of the signal

will be variable with the DC bias level. In practice, neither the varactors nor the coupler are ideal and both will have

some losses. Again, many papers have been written on this circuit and should be consulted for the details of design and

operation.

Variable Phase Shifter Circuit Utilizing a 3dB Coupler

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Γ× 0.707V ∠θ -90

Vdc

Input

0.707V

∠

(

-3dB

)

0.707V

∠

θ -90

(

-3dB

)

Output

Γ× 0.707V ∠θ

* |Γ (0.5V ∠2θ -90 + 0.5V ∠2θ -90)| =| Γ|

Varactor Diodes

* The phase angle of the signal exiting port 2 will vary with the phase angle of , which is the reflection

angle from the varactor. The varactors must be matched so that their reflection coefficients are equal.

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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

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