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.

How to reduce the Q value of the antenna?

Status
Not open for further replies.

051021031

Newbie level 5
Joined
Dec 17, 2008
Messages
10
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,368
Hello, Everyone,


I want to ask if I can reduce the Q value of the antenna. Because usually for the narrowband antenna, it has quite high Q value (I think it should be larger than 20, some maybe 40 or 60).
Now I want to reduce the Q value of the antenna, and further increase the antenna bandwidth. For example, if I can add a resistor in parallel with the antenna to reduce the Q value of antenna? Now I have a narrowband antenna, but I want to measurement some wideband signal, I want to improve the bandwidth of the antenna in PCB.

If it is possible to do it. Thanks in advance.

Jack
 

karesz

Advanced Member level 5
Joined
Apr 13, 2008
Messages
2,332
Helped
327
Reputation
654
Reaction score
52
Trophy points
1,328
Location
EU
Activity points
14,612
Hi 051021031,
yes, so is it.
Usually you have ca. 20Kohm (with the IC parallel), you can apply some other smaller value, discrete, resistor_maybe up to ca. 1KOhm, but dont forget your signal/reader distance will be smaller/shorter too....
In all cases it is not a verysimple problem, than you have usually a impedance matching circuit too.
007:)_ alias Karesz
 

biff44

Advanced Member level 5
Joined
Dec 24, 2004
Messages
4,928
Helped
1,363
Reputation
2,722
Reaction score
1,043
Trophy points
1,393
Location
New England, USA
Activity points
37,041
Adding a resistor might make it "look" like there is more bandwidth, but you are just decreasing the overall efficiency of the antenna to make it look that way. Another way would be to modify the structure to look more "lumped element" in nature. For example, if the antenna is a quarter wave long, if you add a lumped capacitor to the end and instead used an 1/8th wave element, you would have more bandwidth. That is why you see strange "top hat" structures on the top of some antennas.
 

051021031

Newbie level 5
Joined
Dec 17, 2008
Messages
10
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Activity points
1,368
Thank you very much for your reply.

Actually at present, I don't care how much the efficiency of the antenna is dropped. My target is improving the bandwidth of the antenna.

I am quite new in the field of antenna. Would you please give me some reference about the relationship between the bandwidth and the efficiency, and the methods to do it?

I the bandwidth is increased for the narrow-band antenna, the power efficiency should be dropped, I think there should be some equations to explain the principle.

Thank you again for your comments.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top