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requird help for designing 5.8GHz oscillator

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Abhishekabs

Abhishekabs

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build 5.8 ghz oscillator

hi friends
I am designing oscillator at frequencey 5.8GHz
I am using GaAsFET transistor as an active device.
I want do design oscillator with microstrip components(distibuted components).
I am using Rt-Duroid 5870 substrate.
Can any one tell me how oscillator is designed at this frequency??
I dont have any references
thanks
 

oscillator q 5.8ghz

I am a bit late here, but i may help first though i need to ask few things. what kind of oscillator you want to make ? what type of topology ? feedback or reflection ? your Resonator will be from microstrip lines ? dielectric, LC ? any output power requirements ? any phase noise specifications ?
 

1,3 ghz-oscillator

Oscillator is Feedvack type
Resonator is microstrip lines
power requirement is 7dbm
oscillator is with low Q
 

5.8ghz wilkinson splitter

Abhishekabs said:
Oscillator is Feedvack type
Resonator is microstrip lines
power requirement is 7dbm
oscillator is with low Q
Click to expand...

Resonator

well a simple microstrip resonator is a λ/2 line with inductive (shot circuit stubs) or capacitive coupling (open circuit stubs) details you can find in many books and in the web as well. The coupling coeficient of your resonator to a 50 Ω system should ½, that means the insertion loss of your resonator,S21, should be about -6dB at the operating frequency.

Coupler
to get the power out u need a coupler, well for couplers using microstips u can chose, either an unequal split wilkinson divider ( that can give u about 6dB coupling, losing a lots of power) but then again u will need about 13dB circulating power in the oscillator. Another solution is the simple coupled line couplers, u can get about 13-15dB coupling coeficient with them increasing your circulating power to 20-23 dBm. Ofcourse the higher the power the more stable your oscillator will be ( usually). The best solution is Lange coupler but difficult to make on shoft substrates so we take it out of the equation.

Amplifier
well u said u want to use a GaAs. I dont think is the best choise (I will prefer a SiGe BJT for that frequency) for an oscillator due to their high flicker noise characteristics but they will work anyway. Pick a device with a low noise figure as possible that can give enough gain for your oscillator to work ( u will need about 8-10dB of open loop gain to have oscillation going, depenting your total loses). Also make sure the device has P1dBm in the region u want to operate it. The amplifier should be a simple CS , and If u have enough excess gain I suggest a low frequency feedback to flaten its responce, that may also improve its flicker characteristics.

Simulation

U can build seperately all these blocks, then put them in a feedback topology conecting them with micrstip 50 Ohm lines.and simulate them, your simulation should always be large signal one, ( small signal S-Parameters will never work for an oscillator). First u will measure your open loop responce and see what is your phase at the frequency of operation (needs to N*360) and if u have 1dB-2dB excess gain, adjust the leanth of the lines till u get the correct phase and change the amplifier gain to get enough excess gain, then u can simulate the close responce of the oscillator. ADS can do all these kinds of simulations very nicely and quite aquarate as long u have a good model for your trasnistor and all the information for your substrate.


If u want to be more accurate u may need also to include a phase shifter in the loop to adjust it so u get the best result. Varactor is the best solution there.
**broken link removed** that article gives a imple example.

Ps-I suggest u transfer that discussion to the RF and Microwave Section, there will be more people to give u a hand :)

I hope I helped somehow
 

    Abhishekabs

    Abhishekabs

    Points: 2
    Helpful Answer Positive Rating
5.8ghz wilkinson ring

check this link
**broken link removed**

it is a good tutorial , and u can replace the BJT used with the HEMT , have done this but for 3 GHz oscillator , but used FR4 lossy substrate

if u use roger's u will get a good performance

khouly
 

12 ghz oscillator

Hi Soben
Thank you very much for your suggestions.
I am trying my simulation in ADS.
Still am not getting success
I also refered the reflection oscilation tutorial refered by Khouly.
I am struggling to get loop gain greater than one.
What do u think is Negative resistance oscillator method described in tutorial given in rfic.co.uk will work?
Please reply
Thanks again
ABhishekabs


Soben said:
Abhishekabs said:
Oscillator is Feedvack type
Resonator is microstrip lines
power requirement is 7dbm
oscillator is with low Q
Click to expand...

Resonator

well a simple microstrip resonator is a λ/2 line with inductive (shot circuit stubs) or capacitive coupling (open circuit stubs) details you can find in many books and in the web as well. The coupling coeficient of your resonator to a 50 Ω system should ½, that means the insertion loss of your resonator,S21, should be about -6dB at the operating frequency.

Coupler
to get the power out u need a coupler, well for couplers using microstips u can chose, either an unequal split wilkinson divider ( that can give u about 6dB coupling, losing a lots of power) but then again u will need about 13dB circulating power in the oscillator. Another solution is the simple coupled line couplers, u can get about 13-15dB coupling coeficient with them increasing your circulating power to 20-23 dBm. Ofcourse the higher the power the more stable your oscillator will be ( usually). The best solution is Lange coupler but difficult to make on shoft substrates so we take it out of the equation.

Amplifier
well u said u want to use a GaAs. I dont think is the best choise (I will prefer a SiGe BJT for that frequency) for an oscillator due to their high flicker noise characteristics but they will work anyway. Pick a device with a low noise figure as possible that can give enough gain for your oscillator to work ( u will need about 8-10dB of open loop gain to have oscillation going, depenting your total loses). Also make sure the device has P1dBm in the region u want to operate it. The amplifier should be a simple CS , and If u have enough excess gain I suggest a low frequency feedback to flaten its responce, that may also improve its flicker characteristics.

Simulation

U can build seperately all these blocks, then put them in a feedback topology conecting them with micrstip 50 Ohm lines.and simulate them, your simulation should always be large signal one, ( small signal S-Parameters will never work for an oscillator). First u will measure your open loop responce and see what is your phase at the frequency of operation (needs to N*360) and if u have 1dB-2dB excess gain, adjust the leanth of the lines till u get the correct phase and change the amplifier gain to get enough excess gain, then u can simulate the close responce of the oscillator. ADS can do all these kinds of simulations very nicely and quite aquarate as long u have a good model for your trasnistor and all the information for your substrate.


If u want to be more accurate u may need also to include a phase shifter in the loop to adjust it so u get the best result. Varactor is the best solution there.
**broken link removed** that article gives a imple example.

Ps-I suggest u transfer that discussion to the RF and Microwave Section, there will be more people to give u a hand :)

I hope I helped somehow
Click to expand...
 

micrstip line fr4

check this project , it is a microstrip resonator oscillator using HEMT GaAs

khouly
 

5.8ghz oscillator

Thanks Khouly again
Only one request ,I don't have new version of ADS & I cant download because I dont have broadband . I am using ADS2004.
Kindly send ADS2004 compatable file so that I can see.
Abhishekabs
 

simple oscillator ghz

Do we have to connect resonator like ring or hair pin in negative resistance oscillator.
I have terminated the drain with 50ohm & adjusted gamma of load network >1.
Still i did not get oscillation.
Can any one tell me the reason?
 

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