Microstrip discontinuity and the length of 50 Ohm line

[dienal]

Microstrip Discontinuity

Actually I'm working in a four element microstrip antenna array, but I have a question.
In my patch design, the impedance is 100 ohm and the microstrip line impedance (feed line) is 100 ohm too. In the "middle" of the 100 ohm feed line I have to put an 50 ohm line to match the impedance. (after that must to be an quarter of lambda transformer, etc...) My question is: the longitude of the 50 ohm line is important or not?
If someone give me some advices, i´ll be very gratefully!!

Thanks.
Dienal

 

[sergio mariotti]

Please be more explicit:
1) For You, "match" means 50 Ohm?
2) Does you want connect the 4 antennas together?
In this case an high Zo will help you.

In a general case with Zsource=50+j0Ohm, followed by a line1 (Zo=50Ohm), followed by line2(Zo=70.7Ohm, 1/4Lambda), followed by a line3 (Zo=100Ohm), followed by Zload=100+j0Ohm, The longitude of line2 is NOT IMPORTANT for the matching. ;-) But it is important for the loss, more copper=lower loss).

Give more details
Sergio

 

[goxy]

Re: Microstrip Discontinuity

Misrostrip line is the waveguide and losses are minimal. Shorter line-lower losses in dielecric.

I don't know what type your antenna is it but generally line must be same because phase shifting.

 

[dienal]

Re: Microstrip Discontinuity

The antenna is a array with four patch microstrip elements in 2.4 GHz. Each microstrip patch have 100 ohm in one point of this and I take the Z0 of there. Then the microstrip line is 100 ohm (match with the microstrip patch) and in the midlle of two patch the match is 50 ohm (parallel impedance) and the fed line is 50 ohm, then I have match this to 100 ohm.
My question is if the lenght of the microstrip line of 50 ohm is important.
My dielectric is glassfiber with epsilon of 4.5 because I didn't find other dielectric with specific values in my country. In my country don´t have specific manufactures of dielectrics.
I have in my hands a poliethirene but I don't no what is its dielectric constant.

Thanks,
Dienal

 

[dienal]

Re: Microstrip Discontinuity

In a patch array, the quarter of lambda transformer longitude must to be exactly 30.7 mm ((300/2440)* 1/4), or i need to use the velocity of propagation in the patch? (in the place of the velocity in the free space).

Thank you very much.
Dienal

 

[vfone]

Re: Microstrip Discontinuity

In your case if the 50ohm transmission line it has 50ohms at each end, the length is not important from a radiation point of view. It matter just for the loss. For material that you are using the loss is close to 0.015dB/cm at 2.4GHz.
Polyethylene has Er = 2.25

regards

 

[dienal]

Re: Microstrip Discontinuity

In a microstrip adapter, the quarter of lambda transformer longitude must to be exactly 30.7 mm ((300/2440)* 1/4), or i need to use the velocity of propagation in the formula? (in the place of the velocity in the free space).

Thank you very much.
Dienal

 

[Fantasma]

Re: Microstrip Discontinuity

Deja de preguntar boludeces y agarra los libros!!!


English please!

--
makswell

 

[sergio mariotti]

Microstrip Discontinuity

For my opinion, and if i understow correctly, the leght of the 50 Ohm microstrip il important for the antenna phase syntesis only. ( I.e. the lines should be the same lenght if you want phase=0°). But if you can provide a graphic schematic (JPG, GIF etc.), i should be more accurate.

Me also, i want suggest to you the use of PE (polietylene).
For PE non coloured (semi transparent milk coloured), you may hope that is a pure PE.
Pure PE: er=2.2(+/-0.1) tand=0.002
FR4: (the typical fiberglass for PCB) er=4.5 (+/-0.5, tand=0.02

Pay attention working PE: It's easy destroy it with heat and/or using aromatic solvents (Acetone, alcool etc.)

 

[dienal]

Re: Microstrip Discontinuity

Thanks for your comments Sergio.

My problem, now is this, your comment about PE is very problematic with products that i used to paste the copper.
For this reason I would like to use the FR4.

You know what are the problem with this PE and for the time?

Dienal

 

[sergio mariotti]

Microstrip Discontinuity

when you say: "You know what are the problem with this PE and for the time?", Do you mean the "life"?
If you ask for the life, some years are the typical life. It depends if the dielectrics are exposes to the sunlight. If exposed, the life decrease.

 

[zubair]

Re: Microstrip Discontinuity

My advice is to to use a quarter wave transformer at the middle of T and match 50 ohm to 100 ohm.