Malcolm White thank you for your answer, but in my case i am working on microwave planar circuits, i dont know if LTSpice support this kind of measurments.
Define the frequency range for the simulation. This can be done by either setting a single frequency or a range of frequencies. To set a single frequency, go to the Transient Solver settings and set the Start Frequency and Stop Frequency to the same value. To set a range of frequencies, set the Start Frequency and Stop Frequency to the desired values.
Set the number of samples for the simulation. This can be done by going to the Transient Solver settings and setting the Number of Samples to the desired value. The number of samples will determine the resolution of the voltage gain plot.
Add a voltage monitor to the circuit. This can be done by going to the Design pane and clicking on the Add Monitor button. In the Add Monitor dialog box, select Voltage from the Monitor Type drop-down list and then click on the OK button.
Position the voltage monitor at the desired location in the circuit. This can be done by clicking and dragging the voltage monitor to the desired location.
Run the simulation. This can be done by clicking on the Run button in the Simulation pane.
Plot the voltage gain. This can be done by going to the Results pane and clicking on the Field Monitors tab. In the Field Monitors tab, select the voltage monitor that you added in step 3 and then click on the Plot button.
The voltage gain plot will be displayed in the Plot pane. The x-axis of the plot will represent the frequency and the y-axis of the plot will represent the voltage gain.
Here are some additional tips for plotting voltage gain in CST:
You can use the Plot Settings dialog box to customize the appearance of the voltage gain plot.
You can save the voltage gain plot to a file by clicking on the Save button in the Plot pane.
You can plot the voltage gain for multiple frequencies by setting the Start Frequency and Stop Frequency to different values and then running the simulation multiple times.