elec 453 project report

Kaveh Dehno ELEC 453 project report

Wilkinson power divider 1

Table of Contents OBJECTIVES .................................................. 2 INTRODUCTION ............................................ 2

WILKINSON POWER DIVIDER .......................... 2 IDEAL TRANSMISSION LINE ............................ 2 MICROSTRIPS ................................................. 2

PRECEDURE AND RESULTS ...................... 2 IDEAL DESIGN ................................................ 2 MICROSTRIP WITHOUT DISCONTINUITIES ...... 3 MICROSTRIPS WITH DISCONTINUITIES ........... 4 CASE 5 IMPORTED DATA ................................ 5

DISCUSSION ................................................... 5 CONCLUSION ................................................. 6 REFERENCES ................................................. 6

Table of figures Figure 1: Wilkinson power divider [1] ....................... 2 Figure 2: Ideal transmission line schematic ............... 2 Figure 3: Ideal transmission line reflection at port 1 . 2 Figure 4: Reflection coefficient at all other ports ...... 2 Figure 5: Reflection coefficient at all other ports ...... 3 Figure 6: Microstrip design without discontinuities schematic .................................................................... 3 Figure 7: Reflection of microstrip without discontinuities at port 1 .............................................. 3 Figure 8: Microstrip power division .......................... 3 Figure 9: Microstrip without discontinuities reflection at port 2 ...................................................................... 3 Figure 10: Microstrips with discontinuities schematic .................................................................................... 4 Figure 11: Mircostrip with discontinuities reflection at port 1 ...................................................................... 4 Figure 12: Microstrip with discontinuities power division at port 1 ......................................................... 4 Figure 13: Microstrip with discontinuities power division from port 2 .................................................... 4 Figure 14: Microstrip with discontinuity reflection at port 2 .......................................................................... 4 Figure 15: Case 5 and 6 schematic for importing data .................................................................................... 5 Figure 16: Reflection coefficient for case 5 ............... 5 Figure 17: Case 6 reflection coefficient ..................... 5 Figure 18: design with curves .................................... 5 Figure 19: Design with curve reflection ..................... 5



OBJECTIVES • The be able to design a Wilkinson power

divider • To practice the use of ADS program • To examine the ideal and realistic design

differences

INTRODUCTION

Wilkinson power divider Wilkinson power divider is a microwave circuit that divides the power equally to matched loads and is lossless. A picture of a Wilkinson power divider is shown in Figure 1.

Figure 1: Wilkinson power divider [1]

Ideal Transmission line Ideal transmission line is a representation of transmission line without considering any losses due to junctions and discontinuities.

Microstrips Microstrips are a type of transmission lines that are etched on dielectric materials. They occupy very little space and are inexpensive to manufacture compared with other types of transmission lines.

PRECEDURE AND RESULTS

Ideal design At first an ideal transmission line simulation was done to be able to see the behavior of the circuit. The schematic of the ideal transmission line is shown in Figure 2, the reflection coefficient at port 1 in Error! Reference source not found. , the power division from port 1 to all other ports in Figure 4.

Figure 2: Ideal transmission line schematic

Figure 3: Ideal transmission line reflection at port 1

The reflection coefficient at the desired frequency, which is 5.8 GHz is about 31.0623e-6. This means that almost no power is reflected if the input is port 1.

Figure 4: Reflection coefficient at all other ports

The power division simulation shows that the power is equally divided between all ports, which is 0.25 = -6 dB. The reflection coefficient at all other ports is shown in Figure 5.



Figure 5: Reflection coefficient at all other ports

This graph shows that if the input is at ports other than port 1, then there is some power reflected. To compensate for this three resistors are added to the design which is shown in the next step.

Microstrip without discontinuities In this step the design was implemented using microstrips. For this specific design RO3035 substrate was chosen from Roger Corporation. It has a dielectric constant of 3.5 loss tangent of 0.0015, a thickness of 0.13 mm, and the copper cladding is 0.35 um. The microstrip design is shown in Figure 6, and the port 1 reflection coefficient in Figure 7.

Figure 6: Microstrip design without discontinuities schematic

Figure 7: Reflection of microstrip without discontinuities at port 1

The reflection coefficient at port 1 shows almost zero reflection at port 1, which is what is expected. The power division is shown in Figure 8.

Figure 8: Microstrip power division

The power division graph in Figure 8 shows that the power division is close to the ideal case, but there is 0.5 power loss. This could be due to the loss in junctions or the material. The reflection at port 2 is shown in Figure 9.

Figure 9: Microstrip without discontinuities reflection at port 2



The reflection at port 2 shows that there is some power reflected when the input is port 2. To compensate for this issue, three resistors are added to the design.

Microstrips with discontinuities In this design the junctions are added to the microstrip design as well as three resistors for reflection at other ports. The schematic with discontinuities id shown in Figure 10.

Figure 10: Microstrips with discontinuities schematic

The reflection coefficient at port 1 of this design is shown in Figure 11. It shows that even having the microstrips and junction, the reflection is very close to zero at port 1.

Figure 11: Mircostrip with discontinuities reflection at port 1

Figure 12: Microstrip with discontinuities power division at port 1

The power division from port 1 is shown in Figure 12. It shows that discontinuities do not have that much effect on the power division and the power is almost divided equally.

Figure 13: Microstrip with discontinuities power division from port 2

The power division at port 2 in Figure 13 shows that the power is divided evenly even if the input is port 2. This is due to the addition of the resistors.

Figure 14: Microstrip with discontinuity reflection at port 2



Figure 14 shows the reflection at port 2, which is almost zero at 5.8 GHz. This is also due to the addition of the three resistors to the design.

Case 5 imported data The schematic of case 5 and 6 for importing s parameters is shown in Figure 15.

Figure 15: Case 5 and 6 schematic for importing data

The reflection coefficient for case 5 is shown in Figure 16.

Figure 16: Reflection coefficient for case 5

Figure 16 shows that because the loads in case 5 are not matched to 50 ohms we have some reflection at 5.8 GHz.

The reflection coefficient for case 5 is shown in Figure 17.

Figure 17: Case 6 reflection coefficient

Figure 17 shows that the reflection is slightly better for case 6.

DISCUSSION One can continue with the microstrip design and add curves for a better realization. I did some part of it, but left it unfinished du to lack of time. The schematic with curves is shown in Figure 18 and the reflection Figure 19.

Figure 18: design with curves

Figure 19: Design with curve reflection



In addition, the same circuit can be designed only with curves and be compared with respect of size and reflection coefficient.

CONCLUSION In conclusion, a Wilkinson power divider is a circuit that divides the power equally and is lossless and matched at all ports. There should be resistors added to the circuit to make sure that the reflection at all ports is zero independent of the input port. A designer should take into account the discontinuities and curve for the ultimate design. I wish we had the time and ability to physically build and test the circuit, because usually the result of simulations and reality are a bit different.

References

[1] P. M, Microwave engineering, Wiley, 2011.

elec 453 project report

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