(Note: change all parameters with mil unit to mm). By click on tools then choose line calculation we get microstrip calculator as shown in figure 13. Figure12 11) Now we want to implement our design example so, we need to get the values of width and length using microstrip line calculator provided by qucs. Figure11 10) Click on insert then choose insert Equation and drop it to the page as shown in figure 12. Figure10 9) Choose S parameter simulation from simulation library as shown in figure 11. Figure9 8) Choose substrate from transmission lines as shown in figure 10. Figure8 7) Connect power sources to the circuit using wire then insert ground to each source as shown in figure9. Figure7 6) Select wire as shown in figure 7 to connect the microstrip lines, Click the bottom as shown in figure 8 and choose sources, and select power source then place one in input port and another one in output port. Figure6 5) In our design we need 6 microstrip lines so we copy it or insert it 6 times as shown in figure 7. Figure5 4) Drag the microstrip line to the blank page from transmission lines library as shown in figure 6. 2) Click the new button as shown in Figure 4 Figure4 3) Click the button as shown in figure 5, and choose transmission lines. You will see a layout similar to that shown in Figure1. Table1: Element values for maximally flat low-pass filter prototypes Thus, g1 = 0.517 = C1 g2 = 1.414 = L2 g3 = 1.932 = C3 g4 = 1.932 = L4 g5 = 1.414 = C5 g6 = 0.517 = L6 Figure1: Low pass filter prototype circuit We want to implement this on a microstrip substrate with a thickness h = 1.58 mm, and a dielectric constant Єr= 4.6. Solution: First, we need to get filter element values. Implement the filter using only microstrip with the highest and lowest practical impedance values of 120 Ω and 20 Ω. Design Example: Design a 6th order low-pass filter with a maximally flat response and a cutoff frequency of 2.5 GHz. We will explain Qucs through that design example. In this tutorial we are not concerned about the design of this low-pass filter and we will focus our attention on using Qucs to simulate the structure and obtain its parameters. The low-pass filter is fabricated on substrate with the dielectric constant of 4.6. Simulation of a 2.5 GHz low-pass filter with a maximally flat response using Qucs a Tutorial by Mahmoud Sadat Hesham Sadat Arab Academy for Science & Technology & Maritime Transport Collage of Engineering and Technology In this brief tutorial, we use Qucs to simulate a 2.5 GHz low-pass filter with a maximally flat response.

Qucs frequency sweep tutorial