• Designed a Wilkinson Combiner at 30 GHz using microstrip transmission line and then at 60 GHz using coplanar waveguide. • Simulated the Layout of the testbench using the EM Simulator at RF.

1. ECE 593 Project 1 By: Chien Chun Yao and Karthikvel Rathinavel
Introduction:
This report describes a method to design and layout a Wilkinson combiner by first using a microstip transmission line and
then using a coplanar waveguide. A two way Wilkinson power divider works by dividing the power coming from one port
and splitting it equally into two parts if it splits into a quarter wavelength in both sides and a shunted resistor between the
ports. It can be shown that if the input characteristic impedance is 50 ohms, then for a shunted resistor of 100 ohms the
output transmission lines should have 70.7106 ohms of characteristic impedance.
Final Simulated Results:
Simulated Results Microstrip TL Coplanar Waveguide
Bandwidth (-10dB) Very High 76.8 GHz
Loss -2.415 dB -5.445 dB
Minimum Metal Width (W) 6.187 um 8.038 um
Minimum Metal Spacing (G) - 10 um
Design Approach: The simulated results for our initial design from the EM layout extracted symbol was tested by
constructing a testbench which comprised of a 100 ohm resistor between the open ports and also by adding terminations.
Next we fine-tuned the values of W and L (in the case of microstrip) in order to look at the impact it has to our bandwidth
and loss. Decreasing W and L results in decreasing the overall area of the layout while keeping maintaining the same
impedance of the different parts of the line. Similarly decreasing the metal spacing (G) in the case of coplanar waveguide,
will reduce the area.
Bandwidth Calculation:
To determine the bandwidth of the Wilkinson combiner, the plots of S-parameters, , , , are observed at the
intersection points with -10dB. In fact we can appropriately select certain attenuation (in dB) such that we observe
bandwidth. Since the S parameters for input and output reflection coefficients ( , , never cross -10 dB for
Microstrip Transmission Line, its bandwidth cannot be ascertained. However, if we select -18 dB compression for all
three reflection coefficients, we can estimate bandwidth.
Power Loss Calculation:
The total power loss is calculated by adding the magnitude of insertion loss, isolation loss and the return loss in the
combiner. This is calculated at the center frequency for each case. Using the following equation.
Loss

2. Testbench for extracted EM simulation:

3. A. A single-ended 30GHz Wilkinson Combiner using a mircrostrip transmission line.
Schematic:
Layout:

4. Simulations for loss and bandwidth from extracted EM simulation for Microstrip Transmission Line:
Discussion
To increase the bandwidth, the number of input ports could be increased; stepped multiple sections (Pozar). Increasing
numbers of input ports leads to high power loss, which implies larger bandwidth. Area could be further decreased by
decreasing the length of each MLIN. This could be done by decreasing the angle while for the same line impedance by
performing lincalc.

5. B. A single-ended 60GHz Wilkinson Combiner using a coplanar waveguide transmission line.
Schematic
Layout

6. Simulations for loss and bandwidth
Discussion
In order to further decrease the area, the metal spacing can be reduced. As a result our bandwidth will increase. In
addition we can increase the bandwidth with a series of coupling holes (Pozar) ie. By increasing the number of input
coupling ports. By reducing the phase of the input CPWGs we can reduce the length of the transmission line for the same
impedance which reduces the area.
References:
(1) Pozar