A question on the microwave reflection

[bingjiang99]

Dear all,

Today, when I was working on my microwave circuits, I suddenly got a question. If we have an ideal inductor/capacitor connected to the RF source (a source with 50 ohm resistor), we will get reflection due to the mismatching effect.
Statement 1): If the inductor/capacitor is not infinit, we will not get a complete reflection.
Statement 2): Since only the resistor can dissipate energy, and the energy will not be dissipated by the inductor/capacitor, we will have a complete reflection in this circuit.

So, anyone has a idea how to solve this confliction?

Thanks,

 

[xxargs]

Dear all,

Today, when I was working on my microwave circuits, I suddenly got a question. If we have an ideal inductor/capacitor connected to the RF source (a source with 50 ohm resistor), we will get reflection due to the mismatching effect.
Statement 1): If the inductor/capacitor is not infinit, we will not get a complete reflection.
Statement 2): Since only the resistor can dissipate energy, and the energy will not be dissipated by the inductor/capacitor, we will have a complete reflection in this circuit.

So, anyone has a idea how to solve this confliction?

Thanks,

Statment 1 is wrong if you mean non infinit is same as inductance/capacitans have value lower than infinity value. You have total reflection even using 1 nH or 10 pF ideal reactive terminate - result only change phase angle between voltage and current of reflected wave depend of end ind/cap terminators storing and giving back energy.

statment 1 is correct and disspate part of energy if non infinit means same as inpure ind/cap with real part (resistance) and is non conflict with statment 2


Perfectly open and perfectly shorted end working in real axis (zero and infinity Ohm) still get total reflection and wave travel back and dissepate in generators real part of impedance - but current is 180 degree compare to voltage depend if end is open or shorted.

Ideal inductance or capacitance giving only different phase angle on reflected wave depend of value, ie. Xc = 50 Ohm terminate give 90 degree current before voltage and Xl = 50 Ohm terminate give 90 degree voltage before current in 50 Ohm system - plus angle shift depend of transmissions line length compare to source phase angle.


Xc = - 1/(2*PI*f*C)
Xl = 2*PI*f*L

f = frequency in Hertz

quarter wave length of transmission line can transforming open end to shorted end, reactive terminator of Xc= 50 Ohm to Xl = 50 Ohm etc.



Hmm...

I have not english enough to describe this more understable, so better you read book on transmissions line and working on smitchart to understud more...

 

[bingjiang99]

Thanks. I made a mistake. I thought the reflection factor is not 1 when I put an inductor/capacitor there. You are right, only the phase is changed.

Thanks a lot,