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Question SMA connectors pads

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Marios91

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Hello fellow designers,
i have designed a UWB gaussian pulse generator . The input is 10 MHz -1.5/1.5 square pulse and the output is a gaussian pulse which has a duration of 200 psec. I have to design the pcb now and i have some concerns regarding the sma connectors. I have chose to use edge mounted connectors whose signal pin has a diameter of 0.36 mm.Do i have to use a 50 Ohm microstrip line to mount the sma? The frequency input is relatively low so i don't expect to have reflection problems. A 50 ohm microstrip line has a width of 3.7 mm given the substrate i use, which is big in comparison to the line widths in the main circuits.
Thanks in advance :)
 

You need a 3.7mm trace for 50 ohms? What's your dielectric, wood? I think you need to go back and recalculate something.
 

Try to design your stripline for 50 Ohms to match the SMA connector. Then its response will be as wideband as needed for UWB application.

- - - Updated - - -

BTW. SMA connectors have center conductors with a diameter close to 1 mm. 0.36 mm will not match 50 Ohms.. If needed, use a taper and check your UWB response.
 

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@barry , I use the ROG4003C substrate with Er=3.55 . The problem is caused by the substrate height(i chose 1.524 mm) .

@jiripovlika. The input frequency is only 10 MHz , is the possible mismatch going to cause problems?

Sorry if my questions seem naive but this is my very first PCB.
 

Marios91 said:
@barry , I use the ROG4003C substrate with Er=3.55 . The problem is caused by the substrate height(i chose 1.524 mm) .

@jiripovlika. The input frequency is only 10 MHz , is the possible mismatch going to cause problems?

Sorry if my questions seem naive but this is my very first PCB.
Click to expand...

At the 10 MHz input the mismatch would not cause a problem, but at UWB output, rather yes.
 
Remember 10MHz is just the lowest frequency of your square wave. Its the harmonics that make it square.

Also check your impedence calculations. I tried a few online calculators and get 3.4mm not 3.7. The difference is only a few ohms but worth checking.
 

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