What is a matching network ?

Can someone tell me what is meant by matching network ?

I designed a 2 array rectangular patch antenna with er=2.33, 14.8Ghz.
So length and breadth comes out to be 8mm and 6.3mm..
I used IE3D software to simulate the structure and found the bandwidth.


Now.. using the same structure.. I have changed the dielectric constant to er=2.1. But i'm not sure if the circuit is matched properly or not.. How can i find it.. or else.. what shud i do so that the circuit is matched properly..

Thanks

Re: Machting network

Try Here
http://www.circuitsage.com/matching.html

Re: Machting network

it confused me more..

Re: Machting network

to check the matching , get the input impedance of ur structure , and check ur feeding impedance

or simply in ur simulator measure the S11 , if it is in the target bandwidth is under -10 dB , then ur structure is matched

khouly

Re: Machting network

thanks.. using S11 paramter seems easier to me..
i'm a very slow learner so pl bear with me.

so the thing is:
i checked S11 parameters.. the problem is this:
The central frequency shifts when i change the dielectric constant.

For eg. original structure: er=2.33, central freq = 14.8GHz (it goes below -10dB)
bandwidth = 0.3230 GHz (i have taken the difference between the points where the S11 curve crosses -10db on the 2 sides of the central freq, ie S11 curve crosses -10dB at 14.63GHz then reaches a max. at 14.8GHz and then again crosses the -10bd at 14.96 GHz)


Now.. i change the dielectric constant to er = 2.1
Then, i simulate using IE3D.
I observe that central freq has shifted to 15.6 GHz. (it goes below -10dB... at 15.41GHz and 15.79GHz)
bandwidth for this case = 0.3783 (difference between 15.79 and 15.41)

1. Since central freq has shifted from 14.8 to 15.6 GHz... I'm not sure if i can say this antenna system is matched properly or not.. or can I ? can u explain..

2. However, if i consider this er=2.1 and 15.6Ghz as a new antenna system (and neglect the original design with er=2.33 and 14.8GHz).. this means that the antenna is matched .. right ? because S11 parameter goes below -10db value..
So i can say that if er=2.1 and operating freq is 15.6 GHz then the antenna is properly matched to 50ohm feedline. Am i correct saying this ?

3. But if i consider that 14.8 GHz should be the only operating freq,, then this shift of 14.8 to 15.6 makes the input impedance mismatched for the new antenna (With er=2.1) because instead of operating at 14.8GHz it is operating at 15.6 GHZ right ?
So does it mean my antenna is mismatched ?

Re: Machting network

for orignal sturctutes it is matched as ur discribe

for the second when u change the er of the dielectric for sure the frequency will shift , so u need to readjust ur patch dimenssions to be operate in the orignal center frequency ,

to get the impedance make a graph a, d plot S11 on smith chart , or make IE3d plot the input impedance , after dembedeing the reffernce plan to the input of the strusture

khouly

Machting network

is there some tutrial about matching techniques , i heared about a one from agilent but i could't find it, can anyone provid a one for matching in case of inputand output

Re: Machting network

there are any resiurses on the net about matching techniques
check **broken link removed**

the amplifier design tutorial , and there are here many books about lumped and distributed matching techniques


khouly

Re: Machting network

Am i correct by saying the following things:
(1). Conside the case that the original structure is matched.
By Matched means - that after designing the microstrip patch, we design the lenght and width and the position of the 50 ohm feedline.
This structure will be operating at a certain frequency.
Actually.. what is matching to a 50 ohm feedline mean?

(2). when i change the dielectric constant (er), the resonating/central frequency will shift. So in order to have the same resonating/central frequency, i should change the patch dimensions. The feedline(length, width) and the feeline position doesnt play any role in this changing back to the original resonating frequency. Only thing to change is the patch dimensions (its length and width) so that it again starts operating at the original resonating/central frequency.

(3). If the original structure is matched propely(1), then after i do (2), I get back a matched circuit for 50 ohm feedline. Ie. I change the patch dimensions but let the stripline to be of the same width/length etc.

(4) If i dont change the dimensions of the patch.. and simulate and see that S11 parameters are below -10dB for a central frequency far off from the orginal frequency, then that means this structure is not matched to 50 ohm stripline but to some other.

Also..
Is there any step by step formulas that i can see for the design of a microstrip patch antenna with a stripline that is lambda/4 in length.
I saw book by pozar and antenna theory by balanis. but still not clear .. damn.. is there some easier book than this..

Re: Machting network

By changing the Dielectric you have changed the length/width that
will be needed to be 50 Ohms/ Characteristic impedance.

As you saw Fo went up in freq, that's because as the dielectric gets
smaller the "same" trace gets smaller with respect to the wave length.
So you have the old design dimensions but with the new dielectric
it's like you shrunk the dimensions by some (?) % of your design.
I would just multiply all your dimensions by ~ 1.05 and you should see
Fo come down in freq.

Re: Machting network

1) the matching to 50 ohm feed line means , that the input impedance of the structure is equal to 50 ohm ,so when u connet the 50 ohm line , there is no discontinuty in impedance

2) the feedline have no effect on the resonanse frequency "the patch dimenssions only have"

3) after u have change the patch dimessions to get the acutal reonsnace frequency , u should measure the impedance of the struture and then see if it 50 ohm , conect the feed line directly , but if it is not , u need to design a matching section

4) to design a simple matching use λ/4 transformer , which z0=√(z1*z2)
this means if u have z1 is the impedance of the patch , z2 is 50 , then z0 is the impedance of the line u need to draw betweeen the patch and 50 ohm line
and it is length is λg/4 in the freqency of operation

khouly