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Microwave oscillators - RF Cafe Forums

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E-goe
Post subject: Microwave oscillators
Unread postPosted: Mon Apr 11, 2005 5:40 pm
Offline
Lieutenant

Joined: Mon Apr 11, 2005 5:29 pm
Posts: 2
Hi

I designed a Microwave oscillator with the "Negative resistance method" as described in Gonzalez.

But when I tested the oscillator it resonates at2.6GHz in stead of 4Ghz (my goal). Oke I know that with this method the fundamental freq. can deviate a little from the designed one. But so MUCH.......

Can anbody give an explanation for this.

Is it because I'm using small signal S-parameters (as mentioned in the datasheet) ? Maybe I need to use Large signal S parameters?

Output power of the osc. is 13dBm

Greetz E-goe


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Profile

Guest
Post subject: Re: Microwave oscillators
Unread postPosted: Tue Apr 12, 2005 12:40 am

E-goe wrote:
Hi

I designed a Microwave oscillator with the "Negative resistance method" as described in Gonzalez.

But when I tested the oscillator it resonates at2.6GHz in stead of 4Ghz (my goal). Oke I know that with this method the fundamental freq. can deviate a little from the designed one. But so MUCH.......

Can anbody give an explanation for this.

Is it because I'm using small signal S-parameters (as mentioned in the datasheet) ? Maybe I need to use Large signal S parameters?

Output power of the osc. is 13dBm

Greetz E-goe



Have you called your local radio shack yet? There's some very knowledgable people there that might be able to help!


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joe
Post subject: oscillator
Unread postPosted: Tue Apr 12, 2005 10:57 am

Did you check the analysis at 2.6 GHz? The frequency with the better oscillation conditions will be where the oscillation occurs.

Large signal S-parameters would be preferred for the analysis, but small signal will still provide the correct starting conditions. When the oscillation starts, the frequency may shift due to the change from small to large signal.

Large signal S-parameters or non-linear models are available for some devices, but not for all. Contact the manufacturer for availability.


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E-goe
Post subject: Microwave oscillator
Unread postPosted: Thu Apr 14, 2005 8:43 am
Offline
Lieutenant

Joined: Mon Apr 11, 2005 5:29 pm
Posts: 2
Maybe it is because I had to add an extra feedback capacitor from Gate to Drain to make the transistor unstable.

In doing this I had to add an extra transmission line to get from the gate to the drain to add the feedback capacitor.(this is because the gate and drain are on the opposite side of the transistor).

So maybe this extra transmission lines have a serious influence on the S-parameters and so the resonating frequency has changed that much.

Any comments, suggestion how to solve this problem????

Any "Microwave" thaughts are welcome

Greetz E-goe


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Profile

Guest
Post subject:
Unread postPosted: Thu Apr 14, 2005 10:09 am

Try re-designing the oscillator with the modified S-parameters. In other words you saind you had to apply feedback to make the device unstable. So, using the simulator generate a new set of S-parameters which take the feed back into account. The use these S-parameters and redesign the network to see where the new resonance occurs.


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Guest
Post subject:
Unread postPosted: Thu Apr 14, 2005 10:21 am

Did you?

1) Simulate every single component of your circuit interconnection?

2) Estimate the parasitic inductance of the leads of devices optimisticly?

This might explain this big deviation...


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Otman
Post subject: Re: Microwave oscillators
Unread postPosted: Sat Jun 11, 2005 4:55 pm

I am designing a microwave scillator using NE71038 at frequency 2.45 GHz. so I have some problems. I would like to get an oscillator example from anyone who has an example of oscillator using FET,


thanks
E-goe wrote:
Hi

I designed a Microwave oscillator with the "Negative resistance method" as described in Gonzalez.

But when I tested the oscillator it resonates at2.6GHz in stead of 4Ghz (my goal). Oke I know that with this method the fundamental freq. can deviate a little from the designed one. But so MUCH.......

Can anbody give an explanation for this.

Is it because I'm using small signal S-parameters (as mentioned in the datasheet) ? Maybe I need to use Large signal S parameters?

Output power of the osc. is 13dBm

Greetz E-goe


Top


Guest
Post subject: Re: Microwave oscillators
Unread postPosted: Sat Jun 11, 2005 5:07 pm

I am designing a microwave scillator using NE71038 at frequency 2.45 GHz. so I have some problems. I would like to get an oscillator example from anyone who has an example of oscillator using FET,
email: omrabet@hotmail.com


Posted  11/12/2012
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