# Transmission line length

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#### Yash_05

##### Newbie level 3
Hello everyone,
I was working on a spiral antenna in hfss. As for microstrip transmission line calculation I know the length should be lambda/4 for Z0=Zin.
But when I am changing the length to some other value higher then lambda/4 my results are a little better.
Is it okay to take random value of the transmission line?

#### PlanarMetamaterials

But when I am changing the length to some other value higher then lambda/4 my results are a little better.

Which results are better?

For any load fed by a transmission line, you want Zin = Zo if at all possible. Any deviation just ends up in wasted energy, which in your case will lead to lower (realized) gain.

I know the length should be lambda/4 for Z0=Zin

I assume you mean for your antenna. This is obviously not true for any load.

#### Yash_05

##### Newbie level 3
Hey!!
Rather than taking lamda/4 as a length for my transmission line, I have increased and hence, the results S11 vs Frequency have improved.

#### PlanarMetamaterials

S11 will be optimum where your input waveguide is matched to the input impedance of the transmission line segment and antenna (together, I call these the "load").

If it improves while adjusting your load, then the load was obviously not matched to the waveguide in the first place, which is what you stated.

Therefore, as I suspected, Z_0 = Z_in must not be true in your 1/4 wavelength case.

Okay sir!

#### Yash_05

##### Newbie level 3
[Moved]Rectangular sipral slot antenna

hello everyone!!
I am designing a rectangular slot spiral antenna in hfss.
I want to utilize this antenna in high frequencies regions for energy harvesting purposes.
I read a lot of material and research papers but I cant find the designing equations for my antenna.
Can anyone guide me for this purpose.

#### electrify_me

##### Newbie level 2
As for microstrip transmission line calculation I know the length should be lambda/4 for Z0=Zin.

What TL? What calculation? If you are saying that all TL's should be lambda /4 long, then you need to review your basic Tl theory in a text.

Is it okay to take random value of the transmission line?

Nothing in microwave design is ever random. The length of a TL affects both the magnitude and phase of your reflection coefficient.

Judging from your questions it seems that you are trying to use a tool that's way beyond your knowledge of EM / MW design. I would recommend that you study some of the basic theory first - try Microwave Engineering by Pozar for TL theory, and then maybe a book on antennas by Balanis or Stutzman.

#### electrify_me

##### Newbie level 2
Re: [Moved]Rectangular sipral slot antenna

I read a lot of material and research papers but I cant find the designing equations for my antenna.
Can anyone guide me for this purpose.

Balanis has a few sections on spiral antennas with some design equations, and he also references some IEEE papers.

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