designing Microstrip line Combiners/Splitters in FM band

[pnnavigator0915]

Hello guys!

I have joined this forum just now. I am an Electronics and communication engineer, from Gujarat University. I am in 8th sem. I have got a project to design the RF combiners and splitters of the Power amplifier module (1 to 3 Kw), with micro stip lines.

I needed some help on this subject. Where could I find the basics and design issues of microstrip line designing? If any body has the guidelines to this project please help me out.

Thank you for your kind Attention..[/b]

 

[g86]

High power and low frequency. FM band means 88-108 MHz in India. For 100 MHz freespace λ = 3m. And λ/4=3/4m. You do one thing..design with air substrate. Take substrate height = 1 cm. Use a 2mm thick aluminium sheet of 1.5-2 m square as a ground plane. For microstrip line use 2mm aluminium strip. you will face a major problem while finding 100 Ohm resistor with such a high power rate. will be very costly in fact. I have only seen some old 100 watt RF resistor so far and they are quite a big and of weight approximately 20 kgs.

You may PM me for more..

Hello guys!

I have joined this forum just now. I am an Electronics and communication engineer, from Gujarat University. I am in 8th sem. I have got a project to design the RF combiners and splitters of the Power amplifier module (1 to 3 Kw), with micro stip lines.

I needed some help on this subject. Where could I find the basics and design issues of microstrip line designing? If any body has the guidelines to this project please help me out.

Thank you for your kind Attention..[/b]

:!::?::idea:

 

[pnnavigator0915]

Thankyou! These are my specifications:

Thank you very much for that help. It indeed helped me.

I have got the specifications for designing now.
The specifications are as follows:

Frequency : 88 to 108 MHz

Division : 2 way (0°)

Insertion loss: 0.1 dB

Isolation port to port : 25 dB

Return loss (i/p - o/p) : ≥ 25 dB

Impedance (i/p and o/p) : 50Ω

Divider : 100 W capacity.

Combiner : 1kW capacity

Glass epoxy material to be used : 1.6 mm for Divider section.
2.4mm for Combiner section.

Moreover the Z0 = √(100 + 50) = 70.71Ω
Here Absorber resistance, R = 100Ω
And I/P or O/P impedance = 50Ω

For center frequency of 97 MHz : λ/2 = 644 mm



Please Tell me how do i approach with this designing what should be my first step?

Thank you for your kind attention.

 

[g86]

Re: Thankyou! These are my specifications:

Nornally Glass-epoxy subtrate for PCB will be very lossy and during 100watt power division it will be heated.

Thank you very much for that help. It indeed helped me.

I have got the specifications for designing now.
The specifications are as follows:

Frequency : 88 to 108 MHz

Division : 2 way (0°)

Insertion loss: 0.1 dB

Isolation port to port : 25 dB

Return loss (i/p - o/p) : ≥ 25 dB

Impedance (i/p and o/p) : 50Ω

Divider : 100 W capacity.

Combiner : 1kW capacity

Glass epoxy material to be used : 1.6 mm for Divider section.
2.4mm for Combiner section.

Moreover the Z0 = √(100 + 50) = 70.71Ω
Here Absorber resistance, R = 100Ω
And I/P or O/P impedance = 50Ω

For center frequency of 97 MHz : λ/2 = 644 mm



Please Tell me how do i approach with this designing what should be my first step?

Thank you for your kind attention.

:!::?::idea:

 

[pnnavigator0915]

So what do you suggest


Hey thanks once again for the prompt reply.
Ya, I checked out the glass epoxy substrate information on net. It's ofcourse lossy. But our company has a already got the material for glass epoxy PCB. Yet, i will try to convince them. So what should I use?

Which material do you suggest would not incur this much loss?

Do you have any idea of any simulation software which would help me design the Combiners and Dividers as shown in the specifications?

THANKS!..

 

[flyhigh]

Hi

Very serious design. Just to comment that with the quarterwavelength of ~650mm it is goin to be biiig combiner. It is bad that you have to use microstrips, coaxial transmission line is much more suitable to this designs (less lossy and better voltage brakedown performance). By the way, resistor must be able to handle 500W at least to fascilitate 1kW combiner. Connecting this to the rest of the combiner will be fun...

good luck

flyhigh

 

[pnnavigator0915]

Thanks Flyhigh!..

You are absolutely right!

I am going to use a 100Ω/25 W resistor at the input side that is on the divider side and a 100Ω/800W resistor at output side, that is combiner side.

I have already got all the specifications and calculated the required impedance and all other parameters.

I wanted to know, as to what other calculations and parameters are included in the microstrip line design technique.

Thank you for your kind attention..

Regards.

 

[Manjunatha_hv]

Hello,


Use the Txline -Calculator

http://www.appwave.com/src/products/TXLine.zip

TX-Line Transmission Line Calculator
TX-Line is a free, easy-to-use, Windows-based interactive transmission line calculator for the analysis and synthesis of transmission line structures. TX-Line enables users enter either physical characteristics or electrical characteristic for common transmission medium such as:

Microstrip
Stripline
Coplanar waveguide
Grounded coplanar WG
Slotline
TX-Line has an easy-to-use interactive graphical user interface and runs on Microsoft Windows 2000/XP.


---manju---

 

[pnnavigator0915]

Thanks Manju

That really helped!..

I would like to have some reading material or some reference material, theory sort of...

Would u suggest some e-book or any other books, which might consolidate my knowledge in designing a perfect microstrip divider/combiner?

Thankyou..

Regards

 

[Manjunatha_hv]

Hello,

Here are the couple of good books microstrips, but anyway you can search for microstrip books in this eda board...

Lumped Elements for RF and Microwave Circuits By Inder Bahl




Microstrip Lines and Slotlines By K.C Gupta, Ramesh Garg, Inder Bahl, & Prakash Bharatia





---manju---

 

[pnnavigator0915]

Will a Microwave design work for FM

I have searched on many sites, but the specifications for Microstrip designing of Combiners and dividers, include Microwave operation?

I have read many of these specifications and got certain schematics done..
But these are for Microwave frequency.. Are these calculations valid for FM band also?

And thanks for the help Manju!.. But i cant downlaod the books, not having a download capacity more than 0.38 MB..

Thankyou for kind attention

Regards...

 

[Manjunatha_hv]

Hello pnnavigator0915,


Provide me your email id, I will send you the books & some papers ...which are useful for you...


---manju---

 

[BigBoss]

If you may use ferrite cores, combiner can be smaller. For more information look for Philips RF Power Transistors Design Guide (it's a little bit old but quite instructive).

Otherwise if you follow the classical Wilkinson or other methods, you combiner can look like a elephant...

 

[pnnavigator0915]

Here's my Email address

gadkari.abhijeet@gmail.com
pnnavigator915@gmail.com

U can mail me the material on any of the above addresses..

Thanks manju, u have been a great help 2 me. Ur software for designing the microstrips worked great!..

Thank you very much to you too, Bigboss!

I am obliged by your sincere efforts to help me..
Thanks..

Regards.

 

[BigBoss]

Look at these and check the references in documents...

 

[pnnavigator0915]

Thanks guys.. Thanks Manju i got your message.. But the other 9 MB file is not being downloaded completely.. I dunno what to do.. It juz gets downloaded upto 1.6 MB and then the download stops!..

Ne how the other files were helpful

So when you say you are designing Microstrip lines, what are you exactly doing?

1. width height and length calculations
2. Material selection
etc.. do these points come under design process?

 

[biff44]

Interesting problem! That is a long length of microstrip line to hold to under 0.1 dB! A lot of FM components are made in big diameter coaxial line, because the coax is pretty lossless and it is hard to melt!

The first question I would be asking the amplifier designer is: "What would be the preferred output impedance that one of you amplifiers would like to drive?"

I am going to bet he will say something like "12 ohms"! So, assuming that, try to get him to design the amplifier output for that lower impedance, and you can use the combiner to combine and transform the total impedances in parallel to the 50 ohm output load. Designing the combiner for a lower input impedance than 50 ohms would have a number of benefits:

You can use wider (lower impedance lines) that will not vaporize as easily with the heat.

The lower impedance structure also lowers the RF voltage accordingly, and you will not have as much trouble with the voltage arcing over.

In the wider lines, you will be more able to get the heat out of them thru the substrate, since they have a bigger surface area, and the poor thermal characteristincs of the microstrip substrate will be less important.

The wider lines will have less resistive loss, and therefore a better chance at meeting the 0.1 dB loss goal.

If you are unable to get such a structure to work, I would abandon the microstrip approach and go with a suspended stripline structure of some sort. I would try to get the heat out of the edges of the board.

In any case, make sure you heatsink the isolation resistors very well straight to a metal case. If one of the amplifier modules ever blows, that isolaton resistor will be seeing a LOT of heat!

 

[pnnavigator0915]

Where can i see a sample of designed Microstrip?

Hey guys thanks for your sincere support.

But I wished to see a readymade microstrip combiner divider for any band, be it a microwave range, but i need to find it out. Try for FM band but any band would do, coz i just need to hav a good idea about how exactly a microstrip combiner/divider looks like.. let it be a two way, or three way ne thing..

Thank you for your kind attention


Regards

 

[biff44]

Dude, are you serious? If you have never seen a power divider before, how do you expect to make a 3 KW one?

Start off making a small signal one first and see if you have the ability to make that one work first.

 

[pnnavigator0915]

Well the fact is I have only seen a simple coaxial combiner/divider, never worked on Microstrip line designing. And now i'm supposed to make this divider/combiner, for 1KW first and then for 3KW. So you can say I am totally new to this concept. I know nothing about microstrip lines.

But I have to do it, because it's my project for the last semester, if not Fabrication part, but still i need to complete designing.

Please help me out yaar. I've read many fundamental notes related to this Microstrip design technique. So I am kinda familiar to few terminologies. I have to submit a design of 1Kw divider and combiner by three days.

I earnestly request you to send me some links wherein I would get to see as to how a Microstrip combiner/divider looks like, and help me out with some basics of designing.

Thank you for your kind attention..


Regards.