1/4 wavelength or 1/2 wavelength

1/4 wavelength

As for these two kinds of transmission line .
Which one should I take ?
The main difference is only angle.
Any else different ???

In a narrow band system, I think 1/2wavelength is useless.
the voltages and currents in transmmision lines are periodical of T=1/2 wavelength.

What u gonna use it for?

The input impedance differs between those 2 of coarse ... if u connect a 1/2 wavelength to a load .. the generator "see's" the same load impedance unchanged.

while if u put a 1/4 wavelength line .. the input impedance the generator can see is = (( characteristic impedance of line)^2)/(load impedance)

as was told to u previously what purpose do u need them for ?

i want to creat two feedline,either 1/2 wavelenght or 1/4 wavelength.
In order to make SMD component mounted on terminal.
Let me show a simple representation.

_____[SMD]_____

Both of the sides are my feedlines.
The middle is SMD component.
I just want to know which one should I use.

I don't really understand you. For feedlines, just keep them short. If you want to connect your SMD component to external connectors such as standard SMA connectors, just use the shortest, physically realizable 50 ohm lines (for 50 ohm components).

The longer the line, the more ripple you will generate. See file below.

dear sir:
Thanks for your feedback.
When I am simulating 50-ohm transmission line by ADS.
The S11 of 1/2 and 1/4 wavelength are different.
S11 of 1/2 is better than 1/4 .

However,as what you said, the longer line, the more ripple.
Could you explain it for me ?

Hi. I don't want to dig too much into theoretical derivation. There is a paper " Long line effect in pulse compression radar" by Reed, J , published in Microwave Journal Sept 1961.

Alternatively, get the Artech House book " High Resolution Radar" by Donald R Wehner. There is a discussion under section 3.4 of the book on the long line effect.

Well, the basic idea is that multiple reflection along a transmission line could induce phase and amplitude ripple in the otherwise ideal radar waveform, generating what the radar people call sidelobes.

I think some practical pointers are more important, rather than the theory:

[1] Keep the VSWR at all transition / interface small (use matching, ensure ground continuity etc)
[2] Keep interconnecting trace small.

8)

if your device ia 50 ohm, i dont think the length of the trasmission line matter. however, if your device is not 50 ohm, you just need to use the smith chart to see where your impedane end up for various length of the TL.