Why microstrip oscillator frequency rises with temperature? i thought it must fall

[Terminator3]

Heating up microstrip oscillator results in higher frequency. But i thought as temperature become higher, PCB trace must become a little longer (bigger wavelenght), so frequency must become smaller. Instead i see frequency rise.

And also on this page the same with DR resonator: https://www.gedlm.com/DRO/ Fig.6 at the bottom. When temperature rises, frequency does too. But why? Resonator must become little bigger in size after thermal heatup, so wavelength longer -> frequecny lower. But what we see here is rise of frequency...

 

[davenn]

Heating up microstrip oscillator results in higher frequency. But i thought as temperature become higher, PCB trace must become a little longer (bigger wavelenght), so frequency must become smaller. Instead i see frequency rise.

you are looking at it the wrong way. .... consider the value of say the capacitors in the circuit ... one of the components, when its value changes will have the biggest effect on the osc. freq. ... as the capacitor warms it it may decrease in value giving rise to an increa in freq.

And also on this page the same with DR resonator: https://www.gedlm.com/DRO/ Fig.6 at the bottom. When temperature rises, frequency does too. But why? Resonator must become little bigger in size after thermal heatup, so wavelength longer -> frequecny lower. But what we see here is rise of frequency...

Did you notice that the DRO puck isnt directly connected to the circuit stripline ? DRO pucks are usually ceramic and will have very little variation with temperature

once again, as above, it will be any capacitors in the circuit or even variations in capacitance across the internal junctions of the transistor(s) or FET(s) in the circuit

Dave

 

[jiripolivka]

MIcrostrip alone is rarely used as a resonator in an oscillAtor as its Q is low. Use a coaxial resonator or a dielectric one.
You may be right that thermal dilatation causes the length to increase, so frequency should decrease. BUt coaxial resonators can be made of invar or use a capacitor with a desired thermal constant to compensate. Dielectric resonators are intentionally made to keep the frequency stable, either by material composition or by making a double-layer resonator.

 

[vfone]

Capacitance, Thickness, and Dielectric Constant, all are affected by temperature.
As an example, here you can see the variation vs temperature of these parameters for a thin film epoxy substrate, and you can estimate what is the influence to the resonant frequency of a microstrip oscillator

https://obrazki.elektroda.pl/5128411900_1375606603.gif

 

[biff44]

the reality is that I could go either direction with temperature. u have a device whose reactance changes with temperature (Angle S11 and Angle S21 vary with temp), a resonator that could be purchased with a positive OR negative temperature coefficient, maybe a tuning diode that is strongly temperature dependent for its capacitance, a housing that expands and shrinks with temp (especially the cover), and chip componenents that might also drift. Which ever one of those multiple effects dominates--that is going to determine the direction the VCO drifts with temperature

 

[BigBoss]

Microstrip temperature dependency is much less efficient on the freuency of an oscillator.The other more sensitive components such as transistor parameters,cap. and ind. drifts etc. are much more effective on the frequency.If there isn't any frequency defining elements, transistor parameters are much impacting on the frequency drifting.