Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

A question on the microwave reflection

Status
Not open for further replies.

bingjiang99

Advanced Member level 4
Joined
Apr 27, 2005
Messages
116
Helped
5
Reputation
10
Reaction score
0
Trophy points
1,296
Activity points
2,307
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

Full Member level 4
Joined
Jul 28, 2002
Messages
229
Helped
44
Reputation
88
Reaction score
2
Trophy points
1,298
Activity points
4,642
bingjiang99 said:
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

Advanced Member level 4
Joined
Apr 27, 2005
Messages
116
Helped
5
Reputation
10
Reaction score
0
Trophy points
1,296
Activity points
2,307
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,
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top