I am a rookie on both RF and PCB design and I am currently trying to do a 50 ohm 11 watt dummy load project for 100MHz-1GHz.
My calculations are done for the load but I have some questions about designing the PCB.
My new design is as below:
My instructor keeps saying that :
''There is a problem with lining up resistors on a row, because you will see a high impedance with reflections on first resistor, then traveling to the next, and the next ... Try designing so that the signal reaches all resistors at the same time. This is difficult with so many resistors. If the attenuator is then directly connected to the same point your series resistor can be of high impedance without affecting signal, because of the short length.''
I don't know how to do this and out of ideas, I tried to do it as a circle around the connector but still not accepted.
Attenuators written as AT1,AT2,AT3. The other resistors are for the load.
- The power I am trying to terminate is 5-10 watts.
- SMD resistors are 560Nohms 1 watt resistors and the signal strength should not exceed -10dBm that is why I am using an 50dB attenuator, to achieve the desired signal strength.
PCB design Specification:
- Trace Width = 0.5mm
- Dielectric Thickness = 0.3mm
- Trace Thickness = 0.036mm
- Substrate Dielectric (Ɛr) = 4.6
- Total board thickness = 0.39mm
- Size of the resistors (x,y) = (6.4,3.2)mm
- Dimensions of the board are (x,y) = (7.5,10)cm
So I decided to do it as a star or circle shaped design to make the lines equal to each other. Here is what it looks like:
I just draw this schematic to show how my circuit looks like there might be errors.