Designing a 3-Section Coupler

[Fascheue]

Homework Statement

Design a 20±1 dB parallel line 3-section coupler with a center frequency of 3 GHz and a bandwidth of 4 GHz between 1 GHz and 5 GHz. The design should meet the following specifications: Coupling at 3 GHz at 20±1 dB, Directivity at design frequency 15±2 dB, insertion loss at design frequency 1.5 dB maximum. Include in your report coupling, directivity, isolation, reflection co-efficient, and insertion loss of the coupler. Use either binomial or equal ripple response.
Students are supposed to use RF design software (ADS) for design. Use Rogers RT/Duroid 5880 boards for the project.

Start with hand calculation. Perform circuit level simulation (linecalc) including layout parasitics (bends), fine tune with the EM simulation for better accuracy. You have to use capacitive and/or inductive compensation (Read the uploaded papers) to meet the directivity specification. An example EM simulation of single section coupler is available. Compare the different simulations and finalize the design and layout for best performance.

Relevant Equations

Cn’ = 0

For a maximally flat three-section coupler, by setting the nth derivative of C with respect to theta to 0 then solving the resulting system of equations, I got C1 = C3 = .0125 and C2 = .125.

I’m not sure where to go next. What other parameters do I need to calculate before working in ADS? Any pointers in the right direction would be appreciated.

 

[KataKoniK]

Thank you for sharing your progress on the maximally flat three-section coupler. It seems like you have made good progress so far by setting the nth derivative of C with respect to theta to 0 and solving for the three capacitance values. However, there are a few more parameters that you will need to calculate before working in ADS.

Firstly, you will need to calculate the characteristic impedance of the coupler. This can be done by using the formula Z0 = sqrt(L/C), where L is the inductance and C is the capacitance of the coupler. This characteristic impedance will be important in determining the overall performance of the coupler.

Next, you will need to calculate the coupling coefficient of the coupler. This can be done by using the formula k = sqrt(C1C2/C3C4), where C1, C2, and C3 are the capacitance values you have already calculated and C4 is the capacitance of the fourth section of the coupler (which is usually set to be equal to C3).

Once you have these parameters, you can then input them into ADS and simulate the performance of the coupler. You can also vary the values of the capacitances to see how it affects the performance of the coupler.

I hope this helps guide you in the right direction. Good luck with your project!