I have got a PCB sample from Rogers corporation in order to make my VSWR-meter. Nonetheless I have got some trouble to "translate" figures from maths to real lines on the PCB.....

I worked with this calculator:

http://www1.sphere.ne.jp/i-lab/ilab/tool/ms_line_e.htm

As an example I have got these figures for a RF4 PCB :

Operating frequency : 2450.000 MHz
Dielectric constant :5.4

Substrate thickness : 1.600 mm

Microstripline impedance : 50 ohms
Microstripline physical width : 2.53 mm
One wavelength (360°) : 61.6 mm

Quarter wavelength (90°) : 15.4 mm

Hence my questions below ==>

It leads to a lambda= 15.4 x 4= 61.6 mm inthe PCB instead of 300/24.5 (122.4 mm) in the air, right ?

Does it means that the velocity factor is 61.6/122.4 = 0.503 ?

Is the length of the 50 Ohm line on the PCB a mandatory request or its length is pointless ?

In other words may the line be of any length ?

About the forward and the backward lines:

Do they have a 5O Ohm impedance as well or they could be of any width ?

Do they have any length or they must be as long as the main line ?

What is the depth of  the gap  between the main line and the backward and forward ones ?

Could anyone tell me where I could find some theorical work about this concern ?

I would like to make my own VSWR-meter to "refresh" a bit my knowledge in the field of RF since I didn't make anything for a lot of years in this field. I feel like an idiot.....

Thanks a lot to you all and, above all,

HAPPY NEW YEAR

Richard

Hello Richard,

Based on the questions you have put forth, It looks like you might be missing a little bit on your understanding of RF theory.  Radio propagation is a little different then low frequency theory.   Velocity should not be something you need to consider.  However the length of the trace might be an issue depending on a variety of factors.

It might not be a good idea to build this board without some help.   The devil is in the details.    If you like I am available for the next month or so until I start my next project in March.  I can give you a hand reviewing your design and helping you get on the right track.

Give me a call or drop me an email if you are interested.   www.pinterec.ca

Contact:  Chris Pinter   http://www.pinterec.ca/contact-us/

Hello Richard,

Based on the questions you have put forth, It looks like you might be missing a little bit on your understanding of RF theory.  Radio propagation is a little different then low frequency theory.   Velocity should not be something you need to consider.  However the length of the trace might be an issue depending on a variety of factors.

It might not be a good idea to build this board without some help.   The devil is in the details.    If you like I am available for the next month or so until I start my next project in March.  I can give you a hand reviewing your design and helping you get on the right track.

Give me a call or drop me an email if you are interested.   www.pinterec.ca

Contact:  Chris Pinter   http://www.pinterec.ca/contact-us/

Richard - Take a look at the book:

Foundations of Interconnect and Microstrip Design

By: TC Edwards

On Amazon you can search the table of contents and it has a nummber of chapters and presents Coupler Design Equations.

HTH - Steve H.