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.

Register Log in

About matching between antenna and LNA

Status
Not open for further replies.

pavel_adameyko

Full Member level 4
Joined
Jun 23, 2010
Messages
190
Helped
52
Reputation
104
Reaction score
37
Trophy points
1,308
Location
Belarus
Activity points
2,338
Dear all
Imagine the folllowing: we have passive antenna which feeds receiver's LNA input without any filter between them. It appears that S21,S12,S22 and NF of LNA are good, but S11 is very poor. I wonder if we would observe any negative effects due to poor LNA matching in such receiver.
Any opinions would be appreciated:)
 

BigBoss

Advanced Member level 5
Joined
Nov 17, 2001
Messages
4,837
Helped
1,465
Reputation
2,928
Reaction score
1,312
Trophy points
1,393
Location
Turkey
Activity points
29,183
The overall sensitivity of the receiver will drop because the energy coming from antenna will return back to antenna due to poor S11..
 

pavel_adameyko

Full Member level 4
Joined
Jun 23, 2010
Messages
190
Helped
52
Reputation
104
Reaction score
37
Trophy points
1,308
Location
Belarus
Activity points
2,338
The overall sensitivity of the receiver will drop because the energy coming from antenna will return back to antenna due to poor S11..
Hi BigBoss
As i know the overall sensitivity is determined by NF of receiver. Surely we can improve NF of receiver by matching input of LNA, so S21 would increase, therefore the noise contribution of subsequenr stages to overall NF would decrease. But what if we have acceptable overall NF even with poor matching at input?

One negative effect i think up reading your post is that antenna would re-radiate the signal, so it would disturb another receivers working near the one we discussed. Did anybody face such effects?
 

tony_lth

Advanced Member level 5
Joined
Jul 28, 2010
Messages
2,004
Helped
375
Reputation
752
Reaction score
367
Trophy points
1,363
Location
Beijing
Activity points
11,867
You can calculate the reverse radiation.
In telecomm system, there is same channel interference and adjecent channel interference, and the specification is about -30dB, if I remember correctly.
So you need to judge whether it is a problem or not.
 

vfone

Advanced Member level 5
Joined
Oct 10, 2001
Messages
5,110
Helped
1,520
Reputation
3,041
Reaction score
1,119
Trophy points
1,393
Activity points
32,329
I would recomend to do first a conducted system sensitivity (without antenna) and after that do a radiated sensitivity using the antenna in place.
For radiated test you need some knowledge how to calibrate the setup.
After that you can compare the results and decide if the system needs or not NF improvements (matching the LNA input for best NF when antenna is connected).
 

pavel_adameyko

Full Member level 4
Joined
Jun 23, 2010
Messages
190
Helped
52
Reputation
104
Reaction score
37
Trophy points
1,308
Location
Belarus
Activity points
2,338
Hi, vfone
Could you explain more about conducted system sensitivity and radiated one? Or any links ?
Thanks
 

Status
Not open for further replies.
Toggle Sidebar

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top