About RF Layout Design

[Kazuhira]

Hello All,

I've been trying to learn about RF circuit design. I have been using AWR and CST so far.
I sometimes try to remake the boards designed by others.
But they seem very specific to be designed in such softwares.
So I have few questions.

1) What are those discontinuities at the sides of the matching network?

2) What is that triangle at the output of the diode mixer?

3) What kind of filter is this?


But the ultimate question is how are these designed and tested?
Are they prototyped then cut by knife on PCB? Or do they use copper tapes?
What is the design and tuning process?

 

[dick_freebird]

The tools can tell you the outcome of your choices,
but it won't make those choices for you. RF is one of
the last "artsy" segments of chip design (analog used
to be, but now it's mostly regular FETs and lots of 'em
doing correction, of ugly things that used to be art).

A RFIC designer ought to be looking up (at better
performing higher frequency designs, the how and
the why and the tried-and-discarded) and to the side
(RF modules and PCBs made of discretes, have been
fighting the same fight at the frequencies RFICs are
just starting to touch) for the "Easter eggs" that will
fill your clue-basket, and make you a designer who
doesn't need to crack a book or watch a video every
time something new lands on your project-pile.

I'd imagine that you could sketch up these layouts
you show in one of your fave analytical tools, and
run it alongside a copy where you start "removing
things you don't understand" (like Mad Man Muntz)
and learn what and why to keep, by the outcomes
you see. Then later, next time you see the same
undesired result "feature", you'll have some ideas
around what would help.

If you think this looks like it will require lifetime
learning to get and stay good at it, you'd be right.

 

[volker@muehlhaus]

3) What kind of filter is this?

This is an elliptic low pass filter. With the C in parallel to the L, you can insert additional zeros.

 

[BigBoss]

1-They are not discontinuities, the designer put these optional copper patterns for tuning purposes. During fine tuning, some additional elements can be soldered to get a better result.
2-It's another optional copper track for fine tuning purpose. If it's necessary, the designer will cut the track.
3-The answer is above.

 

[Kazuhira]

1-They are not discontinuities, the designer put these optional copper patterns for tuning purposes. During fine tuning, some additional elements can be soldered to get a better result.
2-It's another optional copper track for fine tuning purpose. If it's necessary, the designer will cut the track.
3-The answer is above.

Thank you all, can you help me with the last question? How can I design such different layouts? I am a student, read pozar, steer but I couldnt find a way except very basic ones such stubs etc. Is there a way to learn this? Or a book?

 

[BigBoss]

Thank you all, can you help me with the last question? How can I design such different layouts? I am a student, read pozar, steer but I couldnt find a way except very basic ones such stubs etc. Is there a way to learn this? Or a book?

This layout is generally produced by a Filter Design Program. It's possible to achieve such layout manually but the necessary precision cannot be obtained.
Finally, this layout and peripheral elements are simulated in a EM simulator such as ADS Momentum, Sonnet etc. But this requires strong experiences and practicing works. These techniques are not mentioned in introductory textbooks. After having basic knowledge, you can refer to advanced topics.

 

[Kazuhira]

This layout is generally produced by a Filter Design Program. It's possible to achieve such layout manually but the necessary precision cannot be obtained.
Finally, this layout and peripheral elements are simulated in a EM simulator such as ADS Momentum, Sonnet etc. But this requires strong experiences and practicing works. These techniques are not mentioned in introductory textbooks. After having basic knowledge, you can refer to advanced topics.

I use AWR, but it seems not possible for such to do so, can I mail you smh?

 

[Kazuhira]

This layout is generally produced by a Filter Design Program. It's possible to achieve such layout manually but the necessary precision cannot be obtained.
Finally, this layout and peripheral elements are simulated in a EM simulator such as ADS Momentum, Sonnet etc. But this requires strong experiences and practicing works. These techniques are not mentioned in introductory textbooks. After having basic knowledge, you can refer to advanced topics.

or can you tell me a program that you call "filter design software"

 

[BigBoss]

or can you tell me a program that you call "filter design software"

Ansys NuHertz Filter Design Software.

 

[volker@muehlhaus]

Long ago, I designed a similar low pass manually, starting from the regular lumped element low pass, then replacing the series L by microstrip line segments (narrow width), then adding C parallel to these printed inductors to add transmission zeros. It's no rocket science, you can go step by step.

 

[Kazuhira]

Long ago, I designed a similar low pass manually, starting from the regular lumped element low pass, then replacing the series L by microstrip line segments (narrow width), then adding C parallel to these printed inductors to add transmission zeros. It's no rocket science, you can go step by step.

Well they arent rocket science but the triangle one seems like one. For the first pic, I couldnt find a way to connect the transistor to the bottom of the transmission line, the programs only have regular bends, mlines but those on mixer seems different. I can not tell what is what there. Why a thick transmission line?