how to fix a schottky diode in a microstrip

[haseb_09]

im want to fix schottky diode in a microstrip line using a microwave office friends plz help

 

[biff44]

Unclear, your question is.

 

[Ice Lord]

i have the same problem...

we have to protect the input of our device and now we are using PIN diodes.
Now we have the problem that the capacitance destroy our VSWR.

How can i simulate this problem in Microwave office?!
I cant find PIN diodes or something like that, and i dont want to use a normal Cap!
We have RO4350 with a 530um microstripline...

 

[biff44]

There are two reasons a schottky diode will fail:
1) static damage
2) high microwave power

For static damage, a small value series cap that only passes microwaves, and a shunt inductance to ground (or if narrowband, a quarterwave stub to ground) will probably fix it.

If it is high microwave power, you have to differentiate from situations where you know ahead of time that the power it rising (like you have a 10 watt transmitter sharing the antenna, and know when you are going to turn it on)...or situations where you do not know when high power will arrive (like taxiing around an airport surface and getting blasted by someone elses radar pulse).

For times when you know there is high power coming, a simple pin diode switch, turned to isolation mode before the pulse comes, will do it. They can be designed to handle very high power levels without much insertion loss.

For times when you do not know a pulse is coming, you will need a passive limiter. A thin PIN diode will turn on all by itself (assuming there is a DC path to ground for self bias currents). But it has some capacitance that is a bother at higher frequencies. Matching with series inductors to form a lowpass structure (bond wires make good inductors!) is one way. Using a thicker PIN diode (less capacitance) and a detector diode scheme to provide bias to it is possibly a better way. Another scheme is to use two PIN diodes, a thick one up front, and a thinner one quarter wave further down the line, works too.

Rich

 

[Ice Lord]

For times when you do not know a pulse is coming, you will need a passive limiter. A thin PIN diode will turn on all by itself (assuming there is a DC path to ground for self bias currents). But it has some capacitance that is a bother at higher frequencies. Matching with series inductors to form a lowpass structure (bond wires make good inductors!) is one way. Using a thicker PIN diode (less capacitance) and a detector diode scheme to provide bias to it is possibly a better way. Another scheme is to use two PIN diodes, a thick one up front, and a thinner one quarter wave further down the line, works too.

Rich

Thats the case we have.
We want to use the PIN Limiter Diode 4700 from microsemi, and this one has C=0,15pF.
THe matching trick with smaller wires is ok, but we are looking for a better solution.

We have to design them antiparallel so we have 2 Diodes parallel, now u said that i have to place the 2nd Diode one quarter wave further down the line -> could u explain me why?!
Our bandwith is DC to 6 GHz, could u tell me which wavelenght i have to use to reach the best solution?!

Thx for your reply...

 

[mesohaib]

same problem..please do tell me that what type of schottky diode i fix inside the microstrip line so that it detects millimeter waves..?pls do tell me its reply...