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RF Power Divider Design

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • An RF power divider is a three-port device that provides RF power division or RF power combining. 

  • RF power dividers are extensively employed in measurement systems, radars, high-power amplifiers, phased array antennae, etc.

  • The Wilkinson RF power divider is a robust circuit topology among the various RF power dividers.

RF power divider design

RF power divider designers need to consider the bandwidth, amplitude, and phase characteristics of the divided power

In RF systems, power division is required in power amplifiers, active circulators, mixers, phased array antennas, etc. RF power divider designers must consider the bandwidth, amplitude, and phase characteristics of the divided power. 

Dividing and Combining RF Power

In electrical and electronics engineering, there are numerous instances where it is required to divide or combine electromagnetic signals. In RF systems, power division and recombination are required functionalities, and both are considered fundamental signal processes.

In RF electronics, different tools and devices are available to enable RF power division and recombination. Power dividers are the most commonly used RF circuits for RF power division and combination.

RF Power Dividers/Combiners

Generally, an RF power divider is a three-port device that provides RF power division or RF power combining. Usually, RF power dividers are specified along with the term ‘combiner’. The specification RF power divider or combiner indicates the reciprocity of the device.

RF power divider/combiner

Almost all power dividers are reciprocal. They can combine as well as divide power, depending on where and how many inputs are given. A reciprocal RF power divider can divide the power either equally or unequally between channels. The same RF divider can also be employed to combine the power from two or more channels, as shown in the figure above. 

The Goal of RF Power Dividers

An ideal power divider/combiner divides the power input to port 1 equally between the output ports 2 and 3, or vice versa for power recombination. RF power dividers are extensively employed in measurement systems, radars, high-power amplifiers, phased array antennae, etc.  

RF power divider goals

RF Power Divider Functionalities

  • Addition and subtraction of signals

  • Multi-in-phase output signal production

  • Multiple outputs from a single input

  • Combining signals from multi-ports and obtaining a single output

  • Obtaining RF logic arrangements

Performance Indices of RF Power Dividers

  • Splitting ratio or coupling ratio

  • Relative phase shift

  • Amplitude balance

  • Amplitude ripple

  • Phase balance

  • Phase ripple

  • Insertion loss

  • Power divider isolation

  • Return loss of VSWR

Couplers vs. RF Power Dividers

RF Power Divider

Coupler

Divides the power equally or unequally

Sample off a small portion of the input power to the output port for monitoring purposes

No phase shift between outputs, ideally

A phase shift between output signals

Insertion loss in the power divider = additional losses created by the power division process 

Insertion loss in coupler = total attenuation from the input port to the output port

Number of ports - 3

Number of ports - 4

No isolated ports present

One of the output ports is isolated

RF Power Divider Topologies 

RF Power Divider Topology

Circuit Diagram

Description

T-Junction RF power divider

T-junction RF power divider

  • Splits the RF power to two reduced amplitude signals

  • No impedance matching at ports

  • No port-to-port isolation

Resistive RF power divider

Resistive RF power divider
  • Simple circuit to divide RF power
  • Absorbs power
  • High Insertion loss
  • No port-to-pot isolation

Wilkinson RF power divider

Wilkinson RF power divider
  • Two-way RF power divider
  • Broad bandwidth
  • Equal phase characteristics at output ports

Wilkinson RF Power Divider Design

Wilkinson RF power dividers are a robust circuit topology among various RF power dividers. Compared to T-function RF power dividers, Wilkinson RF power dividers offer isolation between output ports, and the output ports are impedance matched. The Wilkinson RF power divider dissipates reflected power.

Wilkinson RF power design steps:

  1. Select the dielectric substrate material and the effective permittivity that suits the operating frequency.

  2. Determine the length of the quarter wave transmission lines in Wilkinson RF power dividers.

  3. Design quarter-wave transformers operating at application frequency with an impedance greater than the characteristic impedance of the port 1 transmission line.

  4. Chose terminal resistors to match the input impedance at port 1 to the characteristic impedance.

RF power divider designers must consider not only the operating frequency, amplitude, and phase characteristics but also the insertion loss, return loss, impedance matching, etc. Using sophisticated simulation software can help in gauging the various characteristics of RF power divider designs. The Cadence AWR design environment platform offers simulation technology and design automation to help RF engineers develop RF power dividers, amplifiers, and circulators.

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