Printed inductor: is it short circuited or open-circuited stub on the base of BJT?

时间：04-05 整理：3721RD 点击：

Hello!

I can't understand what is inductance of microstrip W=1mm,P=3mm.
I assume that resonant frequency is determined by 0.2pF capacitor and microstrip inductance, and for 6GHz we need inductance:

Code:

L=3.5*10^-9 ' nanohenrysL = 3.5e-9
C=0.2*10^-12 ' picofaradC = 2e-13

F=1/(2*Pi*Sqrt(L*C))F = 6.015491419e9

of 3.5 nanohenrys, that can be made using open or short microstrip:

Code:

short=ATan(omega*L/Z0)short = 6.924628078e1

open=ATan(-Z0/(omega*L))open = -2.075371922e1

open+180Ans = 1.592462808e2

lambda=7.44*4lambda = 2.976e1

lambda*(open+180)/360Ans = 1.316435921e1
lambda*short/360Ans = 5.724359211e0

so it is open 13mm stub or 5.7 short stub for Er eff = 2.82.
Where i am wrong?

Inductors are considered always short circuited.

First of all the circuit presented will never oscillate without feedback capacitors, whatever the series inductor is made by microstrip or lumped. Just put the circuit in a simple simulator for confirmation. Even the circuit is considered a Negative Resistance VCO, would need some feedback components.
Second, the DC current bias of BFP420 (30mA) is set too high, very close to maximum burn out value of 35mA.
For best overall performances (stability, phase noise, harmonics, thermal runaway, etc), the BFP series transistors working as oscillators needs a DC current set to about 5 to 10mA.

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