Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics 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.

antennas -connecting two waveguides of different impedances

Status
Not open for further replies.

max232

Member level 5
Member level 5
Joined
Dec 20, 2002
Messages
89
Helped
2
Reputation
4
Reaction score
1
Trophy points
1,288
Activity points
721
antennas

I have to connect together two air dielectric coaxial cables with same external diameter, but different diameter of the inner conductors.
My question is: how can I simulate this kind of connection?
I have a microwave CAD but unfortunatly the program doesn't work on this kind of component (I think is possible simulate it with a capacity, but I don't know how to relate the capacity to the geometrical dimension of the lines).
Could someone help me?
Thank you.
 

zorro

Advanced Member level 4
Advanced Member level 4
Joined
Sep 6, 2001
Messages
1,130
Helped
357
Reputation
712
Reaction score
298
Trophy points
1,363
Location
Argentina
Activity points
8,909
Hi max,

You have a junction between two lines of different characteristic impedance. If the size of the junction is much less tahn the wavelengths in the lines (this is surely your case), tou can predict theoretically the behaviour of the union (reflections, input impedances, etc) considering ideal lines. You can use formulas or Smith Chart.
Regards

Z
 

loucy

Advanced Member level 1
Advanced Member level 1
Joined
Aug 26, 2001
Messages
414
Helped
24
Reputation
48
Reaction score
11
Trophy points
1,298
Activity points
4,657
Zorro is absolutely correct if you don't need to be concerned with higher order modes, that is, when this junctions is far away from other discontinuities. Otherwise, those 3-D field solvers like MWStudio, HFSS, etc. can simulate your problem accurately.
 

flatulent

Advanced Member level 6
Advanced Member level 6
Joined
Jul 19, 2002
Messages
4,626
Helped
489
Reputation
980
Reaction score
151
Trophy points
1,343
Location
Middle Earth
Activity points
46,689
reflection

Since the impedances of the two cables are differenent (OD/ID ratios different with same dielectric constant) , you will get more reflections from that source than from the small shunt capacitance from the diameter differences.
 

personal

Junior Member level 3
Junior Member level 3
Joined
Nov 29, 2002
Messages
30
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
141
antenna

you may like to try xfdtd or empire...They are good...
 

egliu

Member level 4
Member level 4
Joined
Jan 15, 2003
Messages
71
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
587
if you just care about the junction, you can check some basic formula. I think this is accurate enough for the case with same meterial in two Tl.
 

flatulent

Advanced Member level 6
Advanced Member level 6
Joined
Jul 19, 2002
Messages
4,626
Helped
489
Reputation
980
Reaction score
151
Trophy points
1,343
Location
Middle Earth
Activity points
46,689
I looked it up

I have looked this up in an old 1955 standard text and they say that the effective shunt capacitance will be under 1 pF in even extreme diameter differences and usually much smaller. This will cause a shunt reactance of several thousand Ohms in the VHF region. This will produce less transmission imperfections than the manufacturing tolerances of the cables.
 

yingyang

Full Member level 2
Full Member level 2
Joined
Dec 26, 2002
Messages
126
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,298
Activity points
862
junctions

I think you can also adopt the same techniques as Koul's books on finlines to solve your problem --- mainly mode-matching method....Very easy to write....
 

loucy

Advanced Member level 1
Advanced Member level 1
Joined
Aug 26, 2001
Messages
414
Helped
24
Reputation
48
Reaction score
11
Trophy points
1,298
Activity points
4,657
Mode matching also has its "relative convergence" problem. If there is no other discontinuities, lumped model is the way to go.
 

Lupin

Full Member level 6
Full Member level 6
Joined
Jan 22, 2003
Messages
342
Helped
12
Reputation
24
Reaction score
9
Trophy points
1,298
Location
Italy
Activity points
3,235
I'm looking for design equation about RF losses in squared or rectangular coaxial lines..

Can anyone help me?

Thanks in advance
Lupin
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top