where could i possibly buy high-valued inductors ( tens of uH) with an
SFR close to 3GHz.this will serve as my rf choke in conjuction of a
decoupling cap of 100nF...thanks
murata has good high frequency inductors but the problem is i cant find
one with high SFR..
thanks!

www.coilcraft.com

Regards,

Frank


"mazerom" wrote in message
oups.com...
where could i possibly buy high-valued inductors ( tens of uH) with an
SFR close to 3GHz.this will serve as my rf choke in conjuction of a
decoupling cap of 100nF...thanks
murata has good high frequency inductors but the problem is i cant find
one with high SFR..
thanks!

Your best hope would be to cascade a small inductance and a larger one.
An alternative is to use a ferrite which looks more like a resistance
than an inductance at high frequencies, though I suppose that's not
really what you are trying to accomplish. (In general it's better to
post more about what you are wanting to do in a more global sense,
because sometimes the best solution is different than what you've
assumed.) Note that an 0.1uF capacitor is very unlikely to look much
like a capacitor above a few MHz, let alone up to 3GHz.

Cheers,
Tom

mazerom wrote:

where could i possibly buy high-valued inductors ( tens of uH) with an
SFR close to 3GHz.this will serve as my rf choke in conjuction of a
decoupling cap of 100nF...thanks
murata has good high frequency inductors but the problem is i cant find
one with high SFR..
thanks!


Look at www.CoilCraft.com


They have a new series of inductors based on conical shaped coilbase which
makes the coil a conical spiral coil. Some types of these are happy all the
way up to 40 GHz.

Cheers

Dan / M0DFI

thanks.
my applications is this:
1.im designing an antenna switching array of four quarter wavelengths
equally spaced apart in a circular manner @2.4 ISM band.
2.this is a doppler antenna system in which i switch(discrete lines
from a microcontroller)) the antennas using rf pin diode(above 3GHz)
around 30-50khz repetition rate .
3.from the discrete lines, i put a decoupling cap of 100nF to filter
out high frequency generated by my micro(5th harmonics) and series it
with an RF choke(choke the 2.4ghz signal coming from the antenna)
direct to my switch(series) then a DC blck cap then the antenna. i have
4 arrays of these.also, i plan to have a DC feed after my antenna but
could hardly find high-valued inductors with sfr about 2.4GHz hence i
omitted it.

questions:
1.i doubt my isolation level for this setup.also,my reverse bias is
only logic zero '0V'.would you recommend another setup with higher
isolation at the same time cost-wise?
2.any recommendations on my possible pcb board layout with regards to
ground/power planes?

thanks!

So, why is it that you need "tens of microhenries"?? Having built
(after doing some redesign on it) a doppler-scanning antenna before,
I'm having a hard time seeing why you would need that sort of
inductance in your antenna switch. I guess you better use some low
capacitance PIN diodes, and resonate them with inductances to reflect a
high impedance back to the "off" antennas...and I can see a need for RF
chokes that represent a couple hundred ohms reactance at 2.4GHz, but
that's only a few nanohenries, not tens of microhenries.

You should be able to have one diode forward biased and the rest
reverse biased by the remainder of your logic voltage level...if you
want more (why?), use high voltage open collector gates as drivers, or
just four discrete transistors.

Layout: make it very symmetrical, so each antenna behaves the same
way. Standard microstrip techniques should work fine. If you're not
used to working with this stuff, I highly recommend enlisting help from
someone with experience, at least to give you occasional guidance.
In-person help will be much more useful than what you get on r.r.a.a.

Cheers,
Tom

Surely 100nF would kill yoru swithcing waveform at 30-50kHz.
Also the value of choke needed for 2.4GHz is in the nano Henys range
not the micro Henrys
It you wish the docouple lower frequencies then cascade L/C pairs,
keeping the high SRF items at the 2.4GHZ end

73
Jeff

ive got some miscalculations as with regards to the impedance at
2.4ghz..
thanks.

i need more negative bias because the pin diode im using maximum Vr is
in -50V. reversing it with higher voltage will increase its isolation
capability as compared to a logic 0 volt level.

With reverse bias, the PIN diode looks like a capacitance. Resonate
that capacitance with a parallel inductor, and you'll do more for
isolation than you will by increasing the reverse bias from 5V to 40V.
I assume you're not dealing with signals that are several volts in
amplitude...