Question SMA connectors pads

[Marios91]

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

 

[barry]

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

 

[jiripolivka]

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.

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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.

 

[Marios91]

@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.

 

[jiripolivka]

@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.

At the 10 MHz input the mismatch would not cause a problem, but at UWB output, rather yes.

 

[hagster]

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.