# RF Power splitter design

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Dear all,

Hope everyone is fine and doing well with good health. Here, i need a little help from all you, I need to design a RF Power splitter circuit ( The output power is 30W and signal voltages are 40V) which splits one input into four channels. i found some examples but still unable to design it. if someone can help me in this regard then i shall be highly grateful to him/her for this act of kindness.

Looking forward for kind response.

Regards

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Hello,

What frequency range should be splitted?
This page gives you a design of a 2 way splitter:
https://www.minicircuits.com/appdoc/PWR2-4.html

Bertus
Dear Respected bertus,

Thank you very much for your kind concern and help. Secondly i wanna inform you that my frequency range is 7MHz ~ 9MHz .
between this frequency range i wanna design a signal splitter (Signal contains 40Vp-p) into four way splitter.

Regards

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Dear All,

Hope you are doing well with good health. Here, i would like to ask that i am interested to design a power splitter for the freuency range of 7.7MHz ~ 8.7MHz. i already designed the splitter ckt with the help of RL and LC lumped components, but in this case my power level decreases to 5W from 12W. (screen shot is attached for your reference please)

Now, i am interested to design this ckt by using op-amp. In this regard i need your suggestions and help, for the reference a sample ckt is attached.

Anxiously waiting for your kind and prompt response.

With kind Regard

#### Papabravo

Joined Feb 24, 2006
16,118
What is the open loop gain of a TL084 in the 7.7 to 8.7 MHz range?

#### Delta Prime

Joined Nov 15, 2019
998
Hello there sir.

What is the open loop gain of a TL084 in the 7.7 to 8.7 MHz range?

Note to Delta prime: Your graph contained a grid but no plot, so, hoping you would approve, I substituted the above chart from a TI datasheet -moderator.

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#### Papabravo

Joined Feb 24, 2006
16,118
Ohhhh.... That's impressive!
EDIT: I thought the blank plot was real in the sense of "no measurable gain" in the desired frequency band and that @Delta prime was making a humorous if somewhat oblique statement. It would seem that the unity gain bandwidth is on the order of 3MHz, which corresponds to my recollection..
Suggestion: The OPA847 may be more to your liking.

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#### andrewmm

Joined Feb 25, 2011
1,467
Silly question
and RF is not my top skill

But
How about
a transformer splitter.
resistor splitter

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Silly question
and RF is not my top skill
Dear Respected andrewmm, Papabravo & Delta prime,

First of all thank you very much for your kind help and concern. Secondly, i wanna inform you that i need a splitter ckt after the RF Power Amplifier's output & before antennas. The main purpose of this splitter ckt is to split one signal into three parallel signals with equal power and voltage level. These splitter ckts may be Resistive, OP-amp, or Transformer splitter, more preferable is transformer splitter. But remember the load (antenna) input impedance is 0.1ohm + 0.1uH. I am trying to design for these requirements but frankly speaking i am failed , didn't designed in the right way.

I shall be highly grateful to for this act of kindness if you help me in this regard.

Kind Regards

#### andrewmm

Joined Feb 25, 2011
1,467
What sort of power do you have ?
is your antenna not 50 / 75 Ohms ? 0.1 ohm is incredibly low,
Also your frequency is very low for typical RF circuits, but high for typical "audio" circuits

Your at the bottom of the LF , upper VLF band

which is a bit specialised

something like these

https://www.herostechnology.co.uk/pages/RF_Splitter-Combiner.html

A wilkinson might work
https://www.microwaves101.com/encyclopedias/wilkinson-power-splitters

that site has a world of very useful information that I keep reffering back to

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
What sort of power do you have ?
is your antenna not 50 / 75 Ohms ? 0.1 ohm is incredibly low,
Also your frequency is very low for typical RF circuits, but high for typical "audio" circuits

Your at the bottom of the LF , upper VLF band

which is a bit specialised

something like these

https://www.herostechnology.co.uk/pages/RF_Splitter-Combiner.html

A wilkinson might work
https://www.microwaves101.com/encyclopedias/wilkinson-power-splitters

that site has a world of very useful information that I keep reffering back to
Dear Respected andrewmm,

You are right it's lower bottom of RF frequencies. The freq range is 7.7MHz ~ 8.7MHz and the obtained power is about 30W, used in Electronic Article Surveillance (EAS) system, RFID application. The antenna used in tag containing low input impedance about 0.1 ohm (Actually my senior told me) i am afraid how can we couple and split our signal & further fed to antenna's ports. so he said transformer splitter is best option. i tried to find some related info and design a ckt as desired, but failed.

I shall be highly grateful to you if you help me in this regard. Anxiously waiting for your kind and prompt reply please.

Regards

#### Papabravo

Joined Feb 24, 2006
16,118
Doesn't a Wilkinson Power Divider require trace lengths on the order of a quarter wavelength? The geometric mean frequency of the 7.7 to 8.7 MHz band is 8.18 MHz which means a quarter wavelength is just over 9 meters. That is an impractical dimension for a Wilkinson Divider. They are useful at microwave frequencies and tend to be very narrow bandwidth.

#### andrewmm

Joined Feb 25, 2011
1,467
Doesn't a Wilkinson Power Divider require trace lengths on the order of a quarter wavelength? The geometric mean frequency of the 7.7 to 8.7 MHz band is 8.18 MHz which means a quarter wavelength is just over 9 meters. That is an impractical dimension for a Wilkinson Divider. They are useful at microwave frequencies and tend to be very narrow bandwidth.
@papabrave

Totaly true

the other parameter in a Wilkinson is the impedance of the source and destinations,

which is reported as 0.1 Ohms , which is Very low.

I have impression OP and there supervisors are not "on the same page",

I hope by sharing the site,
is that the OP can read up , there are hundreds of pages of very good IMHO information
I hope they might then be able to ask there supervisor more detailed questions given what they have found.

As it is I'd say ,a power splitter into a 0.1 ohm load is going to be "impossible" .

I'm also wondering what an antenna at around 8 Mhz , of 0.1 Ohms looks like.

#### Papabravo

Joined Feb 24, 2006
16,118
@papabravo

Totaly true

the other parameter in a Wilkinson is the impedance of the source and destinations,

which is reported as 0.1 Ohms , which is Very low.

I have impression OP and there supervisors are not "on the same page",

I hope by sharing the site,
is that the OP can read up , there are hundreds of pages of very good IMHO information
I hope they might then be able to ask there supervisor more detailed questions given what they have found.

As it is I'd say ,a power splitter into a 0.1 ohm load is going to be "impossible" .

I'm also wondering what an antenna at around 8 Mhz , of 0.1 Ohms looks like.
The impedance of the antenna at 8.18 MHz. is about 5.1 Ω. The real part contributes a negligible amount to the total. Still a 5Ω impedance is a pretty difficult thing to work with. There is a reason why higher impedances are normally used. The TS and his supervisor don't appear to have a clue why that should be the case.

https://www.microwaves101.com/encyclopedias/why-fifty-ohms

#### andrewmm

Joined Feb 25, 2011
1,467
The impedance of the antenna at 8.18 MHz. is about 5.1 Ω. The real part contributes a negligible amount to the total. Still a 5Ω impedance is a pretty difficult thing to work with. There is a reason why higher impedances are normally used. The TS and his supervisor don't appear to have a clue why that should be the case.

https://www.microwaves101.com/encyclopedias/why-fifty-ohms
My only thought is they might be using a short antenna, due to the low frequency
certainly not a 1/2 or 1/4 wavelength aerial,
so it appears as a "short"

But we await more information.

My thought is,
an amp at such a low frequency is relatively standard,
so how about using two amplifiers, and splitting at the low power end ?

#### Papabravo

Joined Feb 24, 2006
16,118
My only thought is they might be using a short antenna, due to the low frequency
certainly not a 1/2 or 1/4 wavelength aerial,
so it appears as a "short"

But we await more information.

My thought is,
an amp at such a low frequency is relatively standard,
so how about using two amplifiers, and splitting at the low power end ?
Using a short antenna at that frequency can be done but the reason for doing so needs to be more than ordinarily compelling.

Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Using a short antenna at that frequency can be done but the reason for doing so needs to be more than ordinarily compelling.
Dear Respected @Papabravo and @ andrewmm,

First of all thank you very much for your kind concern. Secondly, accordingly sir Papabravo, the impedance of antenna at 8.18MHz is about 5.1ohm. As i mentioned in previous posts that i need a splitter ckt for 0.1ohm + 0.1uH (which seems very hard and difficult, agreed with both of you, but i need). The type of antenna we used is mentioned below for your kind perusal pls (No BNC connector is attached in real);

Sir, I have designed a splitter ckt for two ports, but i am not sure weather it's fine or not. please review the attached splitter circuit and suggest me how can i create a third connection for output from the same ckt ( by using the same transformer configuration). Sir, better if you draw on the paper and upload here, then i shall be highly grateful to you for this kind act of kindness.

Looking forward for your kind reply please.

Regards

#### Papabravo

Joined Feb 24, 2006
16,118
Dear Respected @Papabravo and @ andrewmm,

First of all thank you very much for your kind concern. Secondly, accordingly sir Papabravo, the impedance of antenna at 8.18MHz is about 5.1ohm. As i mentioned in previous posts that i need a splitter ckt for 0.1ohm + 0.1uH (which seems very hard and difficult, agreed with both of you, but i need). The type of antenna we used is mentioned below for your kind perusal pls (No BNC connector is attached in real);
View attachment 229825

Sir, I have designed a splitter ckt for two ports, but i am not sure weather it's fine or not. please review the attached splitter circuit and suggest me how can i create a third connection for output from the same ckt ( by using the same transformer configuration). Sir, better if you draw on the paper and upload here, then i shall be highly grateful to you for this kind act of kindness.

View attachment 229831

Looking forward for your kind reply please.

Regards
Without component values for RX4 & RX5, and construction details for T6 & T7 it is a bit hard to evaluate. I recommend that you simulate the design for confirmation.
The simulation will also reveal the minimal power transfer from the source to the antenna.

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Thread Starter

#### Mike2526

Joined Nov 10, 2020
30
Without component values for RX4 & RX5, and construction details for T6 & T7 it is a bit hard to evaluate. I recommend that you simulate the design for confirmation.
The simulation will also reveal the minimal power transfer from the source to the antenna.

Dear Respected Papabravo,

Thank you very much for your kind reply. What you said in post #18 that is true, without components value it's hard to determine ckt performance. Here, i have two questions, please tell me the answer;

Q1: Is RX4 & RX5 are mandatory to add in the ckt or we can exempt, If necessary then what should be values for these two resistors. While the load is 0.1 ohm + 0.1 uH. please suggest with your expertise.

Q2: If we add and other transformer (T8) for third output port, then what should be the configuration, it will same as T7 or different ?

Dear Papabravo, Thanks in advance for your kind help.

With kind Regards

#### Janis59

Joined Aug 21, 2017
1,332
Just few days ago realized how damn expensive may be the active 2-way splitter. At marine equipment that is common problem how to put the antennas for VHF (155-176 MHz) and antenna for AIS (162 MHz). The distance betw antennas is demanded no any case less than 3 meters thus the only sound choice on sailboat mast is to use a common antenna and active splitter commanded by nmea when to switch one or other transceiver to common antenna. As known, one is 25W transmitter with 0,15 uV SNR receiver and other is 2W transmitter with 0,4 uV receiver. Price is over 600 USD.