Q:Directional Coupler

in two articles ,i have seen two similar directional couplers.but their coupled output and isolated output are different.it puzzles me!and how can i design a directional coupler.thank u.
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In these parallel line couplers, the coupled power appears at the secondary coupled line in the end that is near the source of the power in the main line. The coupling depends upon the differential mode impedance and the common mode impedance. This is called odd and even modes in the RF world.

The confusion is decades old. Waveguide coupler's coupled output port is farthest away from the input port. Conversely, microstrip or stripline coupled line's coupled output port is closest to the input port.

Any system level schematic symbol should rely on no assumptions in the reader's mind, and should always show an arrow or words depicting coupling direction.

Figure 1 show roughly the layout of a ustip/stripline coupler
Figure 2 show rougly both the layout of a waveguide coupler and a generic coupler.

Both pictures may be used in a block schematic, it's important to draw the arrow that decribe the coupled port.

Then, the correct displacement of the coupler will be choosed during the assembly procedure.

Fig.2 shows the hybrid coupler, and Fig.1 shows the parallel coupled-lines or parallel coupled-waveguide coupler.

The first picture is only symbolic and second shows a kind of realization. Ports on both pictures are marked equal and correct.

Hi,

Good comments above, just to add mine

Yeah, there is a kind of (unwritten?) convention that

port 1 is an input
port 2 is trough output
port 3 is coupled output
port 4 is isolated

I think that both pictures are schematics only without any reference to the internal realizations of the couplers, and the port assigments are in that sence correct.

The internal structures could be waveguide or planar lines, but one can manipulate the locations of the ports on schematics to simplify the drawing.

flyhigh

I think sergio mariotti's comments on Fig 1 and Fig 2 are interchanged. Fig 2 shows the strip/ustrip realization.
g579

Hi g579,
Probably you didn't realize that fig. 1 is the bottom gifure in liberal's post, and fig. 2 is the top one.
Sergio's comment is ok, in agreement with bif44.
Regards
Z

Hi zorro,

You are absolutely right, I am sorry, I presumed that Fig 1 is the first and Fig 2 is the second fig.
I was mistaken. Sorry again. sergio marotti is right.
Regards
g

Hi~!.

The propagation of TEM mode and quasi-TEM mode is related to backward directional coupler and the progapation of TE mode and TM mode is related to forward directional coupler.

It's mean backward directional coupler has backward coupling and forward directional coupler has forward coupling.

Have a good time!