Lab3_RF_chebysev_filter

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Transcript of Lab3_RF_chebysev_filter

  • 1. RF and Microwave Frequency Circuits and systems RN620 Maximally Flat Microwave Filter Design To design a maximally flat filter with 12dB attenuation at 1.3333 times cutoff frequency of 3.8GHz. We have fc = 3.8 GHz And at 1.3333 times fc Attenuation = 12dB i.e. 10 log PLR = 12 So, PLR = 15.84(Using PLR = 1 + k 2 w / wc N = 4.689 5)2NUsing g0 = gN+1 = 1 And gn = 2 sin [(2n - 1) / 2N]; n = 1, 2... N g1 = 0.618 g2 = 1.618 g3 = 2 g4 = 1.618 g5 = 0.618 And making impedance and frequency scaling with R0 = 50 and c = 2 fc Using L = L n ( R0 / c ) ;L n is normalized inductance And C = C n / ( R0 c ) ;C n is normalized capacitance1

2. RF and Microwave Frequency Circuits and systems RN620 We get2 3. RF and Microwave Frequency Circuits and systems RN620distributed component formFor a capacitance The impedance Z0 = 20 And effective electrical length () = C ( Z0 / R0 ) For inductance The impedance Z0 = 100 And effective electrical length () = L ( R0 / Z0 ) section1 2 3 4 514.16 46.35 45.83 46.35 14.163 4. RF and Microwave Frequency Circuits and systems RN620Magnitude of lumped and distibuted4 5. RF and Microwave Frequency Circuits and systems RN620Also the presence of the capacitance due to junction transition effect was simulated in ADS by using the microstrip step (MSTEP) component. The effect was not included in our calculation but is present in the actual board so we must take it into account if our design is to meet the given specifications.From the figure we can see the effect of using the distributed component instead of the lumped components. Use of distributed component tends to deviate the curve from the lumped component curve at high frequencies. But we still have to make account if the transitional capacitance between microstrip lines. In that case we see there is a change in the attenuation again.5 6. RF and Microwave Frequency Circuits and systems RN620 Now to get as close as possible to the lumped curve, we change the length parameter of all the microstrips proportionally. We had to change the length of each microstrip to about 82% of the actual length required. Final curve after matching is given below.6 7. RF and Microwave Frequency Circuits and systems RN6207