Power dividers in microstrip transmission line

Hi All,
I'm interested in designing an edge-fed micostrip antenna array, where I would have to use power-dividers to split the input power equally to both the arms/patches. Now the question is can anyone suggest what type of power divider I must use. Is it basic t-junction, quarter-wave matched t-junction or wilkinson power divider, or if you have any other better ones to let me know, please feel free to suggest some good options. And also could you send me a detailed calculation/schematic of the power divider layout, that would help me to make my antenna impedance matched.
I would really appreciate if someone could help me with this.
Many Thanks in advance
Henry797

Hi Henry797,

I believe in most commercial arrays, T-juntions are used for their simplicity. You would need to take care to make sure that everything is impedance matched, however. See for example this thread.

Hi PlanarMetamaterials,
Thanks alot for the link to that forum. However I would like to share my experience, as I have designed a quater-wave matched T-junction and noted the S11,S21,S31 & S23 on CST and found un-realistic. Hence was wondering if someone could help me with the dimensions of a proper T-junction power splitter used in antenna arrays?
I've used wilkinson power divider before, but it requires an active lumped component in the design (100ohm resistor) for the isolation. I want to use a t-junction power divider this time, be it quater-wave or not, which would be matched using rampart lines and a 90 degree V. Is there anyone who could help me with this?
Many Thanks

Henry797 said:

Hi PlanarMetamaterials,
Thanks alot for the link to that forum. However I would like to share my experience, as I have designed a quater-wave matched T-junction and noted the S11,S21,S31 & S23 on CST and found un-realistic. Hence was wondering if someone could help me with the dimensions of a proper T-junction power splitter used in antenna arrays?
I've used wilkinson power divider before, but it requires an active lumped component in the design (100ohm resistor) for the isolation. I want to use a t-junction power divider this time, be it quater-wave or not, which would be matched using rampart lines and a 90 degree V. Is there anyone who could help me with this?
Many Thanks

Click to expand...

But isolation is the key parameter to connect two antennas to a single source. Isn't it ??
In this case, you'd better to use Wilkinson Power Divider to obtain a relatively good isolation.

I am building something similar. As a newbie to this stuff there is a chance I am doing something silly, but you learn best by doing, so onward i go.

I need a very broadband split and considered the multistage Wilkinson divider to be too complex to design and build reliably. Also it would take up a lot of pcb space. My plan is to build a simple T junction from 50ohm into two 100ohm tracks, with an appropriate sized v cut out the top of the T to maintain the correct impedence. I have plenty of width between the antennas so I'm planning to use a simple taper to bring the impedence back to 50ohm on the output ports. The antenna has a very good S11 so I'm hoping that the lack of isolation between the ports won't hurt too much.

Fingers crossed it will work.

BigBoss said:

But isolation is the key parameter to connect two antennas to a single source. Isn't it ??

Click to expand...

No it isn't.

Feed networks in arrays usually have no isolation resistors because antennas are driven in phase and then we don't need the resistor anyway (zero voltage across the resistor for in-phase signals).

volker@muehlhaus said:

No it isn't.

Feed networks in arrays usually have no isolation resistors because antennas are driven in phase and then we don't need the resistor anyway (zero voltage across the resistor for in-phase signals).

Click to expand...

If it's so, will radiations create an interference in the air since the phases can not made exactly 0 degree in practice ?? Or fading ??

Hi All,
I've designed another Wilkinson power divider, and have checked that the isolation between ports 2 & 3 are pretty bad without the 100ohm lumped component. Hence could anyone suggest a way of getting rid of the lumped component. And another question is I have never seen an active resister in an N-array microstrip patch, and was wondering how the isolation between two output ports is maintained.
Many Thanks
Henry797

Henry797 said:

I've designed another Wilkinson power divider, and have checked that the isolation between ports 2 & 3 are pretty bad without the 100ohm lumped component.

Click to expand...

Sure, but isolation only that matters for out-of-phase signals. For signals that are in phase, the voltage across the resistor is zero and the resistor can be omitted. And in the main lobe, signals from the antennas are in phase with equal amplitudes, unless you have made a mistake in line feedline length. That's why we never have resistors in array feed networks.

Hi volker,
Many Thanks for the reply. Your answer was somehow of help. However, I didn't understand some bits. The voltage across the resistor is zero for signals that are in phase? So what about the signals that are not in phase?
The reason I'm worried about this design is that when I remove the resistor, the S23 becomes almost close to -3dB, which means there is absolutely no isolation between outputs. But with the lumped resistor, there is a high isolation and the S23 goes below -16dB. And I am using a Wilkinson power divider, whose basic principle is to have a 100ohm resistor at the output for isolation.
And if I understood well, you were saying that a Wilkinson power divider can be used without a 100ohm lumped element. If so how? because although the power divider is matched (S11 brilliant), there is still no isolation between the outputs?
However, I heard that instead of using resistors, the outputs can be isolated using passive elements such as stubs. Do you happen to know anything about stubs and isolation?
Many Thanks
Henry797

Henry797,

You seem to think that for such an antenna array, you need isolation between then elements. Why?

As pointed out above, the load seen by each branch of the power dividers should be equal, hence there is no need for isolation.

In my opinion an Wilkinson divider without a resistor cannot be named Wilkinson, but whatever else.
Planar antenna arrays can use various dividers without lumped elements, and using on board phase shifters to get the desire phase change.

https://www.radartutorial.eu/06.antennas/Phased Array Antenna.en.html

Henry797 said:

So what about the signals that are not in phase?

Click to expand...

In beam direction, signals from the antennas are equal in phase and magnitude. There is no need for isolation. You can leave out the resistor, so that your Wilkinson becomes a simple power splitter. Same for transmission case, the resistor does nothing at all.

Henry797 said:

However, I heard that instead of using resistors, the outputs can be isolated using passive elements such as stubs. Do you happen to know anything about stubs and isolation?

Click to expand...

I am not aware of that. You will need some place where the energy can go, some kind of load (resistor or additional port). But as said ... no need for isolation in this antenna array application.