does anyone know how to design an oscilator

[andrew_luo]

the oscliator is working at 315MHz and designed by microwave transister with ft=7Ghz and SAW devise. The critical problem is the whole board including the antenna is limitted in the 18*20mm area. i want to know: 1.how to desing an high gain microstrip antenna in this situaton. 2.how to match the antenna with the oscilator. 3. if the oscilator did not work at all ,how can i debug it ,does the VNA can be used for designing an osc.
as we know,osc is a loop, to test the S22 is impossible since the osc will output signal while the VNA may consider it as an reflected signal.

 

[Puppet1]

get the book called microwave circuit design using linear and nonlinear techniques by vendelin.

it's not here though.

 

[andrew_luo]

thanks, but i cant find that book.

can somebody give me some hint or experience on designing an oscillator . i really appreciate for that.

 

[gecky]

Hi Andrew,

what sort of training you had relating to RF?

I'm an undergrad doing a final year project on self-oscillating mixer. Am currently designing a DR stabilised oscillator. You may refer to some of the threads i started. Several members gave some very useful replies.

I find the book "Microwave Transistor Ampesign and Analysis" by Guillermo Gonzalaz particularly useful. Ypu may like to check that out.

Good Luck!

 

[gecky]

Oh,

frequency is so low....... 315MHz.......Lamda~1m

Can the antenna be that tiny for efficient transmission???

 

[radiohead]

Indeed, you will need to use antenna that is much shorten than the wavelength. This look dominantly capacitive, so put an inductor in parallel to resonate this out. The result is a low resistive input impedance.

 

[andrew_luo]

lots of compact antenna employ some load (resistance.inductance,capacitance)to achieve high gain.
somebody know that? plz tell me, thanks a lot.

 

[DJ]

Use a spiral indactor in series with a capacitor. or SMD indator and resonant it with a cap. If you resonant it parallel the resistance (load) at resonance is high, and series resonant show low resistance at resonance.
A parallel resonance could be at the Emitter when the Collector has low impedance load. You can have also a parallel resonance at the collector but then match it to a low impedance at the Collector port.
Series resonance can load directly the Collector or maybe the base as the oscillator resonance (I'm not sure, you have to check it becouse the equivalent resistance at resonance).

 

[djalli]

Why you do not make an amplifier in these ranges, add positive feedbacks to move in stability circle of smith chart and make the oscillator?

I know this way you can make the oscillator which will have frequency stability pretty nice.

 

[djalli]

and here is a paper:

 

[andrew_luo]

Why you do not make an amplifier in these ranges, add positive feedbacks to move in stability circle of smith chart and make the oscillator?

I know this way you can make the oscillator which will have frequency stability pretty nice.

i dont know your meaning?