Designing for high peak power

Updated August 28, 2011

New for September 2011!

High peak power is something that most designers can ignore, it is a specialty field. Then someone throws a limiter design your way and you have to learn about it!

We will deal with this a little at a time.

How high is high? In vacuum electronics and waveguide, it is possible that you might be dealing with megawatts. No one at Microwaves101 has much experience with that, so until someone throw some content our way we will likely not dive into that. But in microelectronics, high peak power can be tens or hundreds of watts. This is what we will concern ourselves with on this page.

Places where high-peak power is present are high-power limiters.

Voltage standing waves... Most engineers thing "VSWR" is an anachronism from their forefather's use of the standing wave meter to measure reflection coefficient. Yet they are ignorant to the problems (and analysis of) standing waves in a high-power system. Standing waves matter, you need to visual them. If you know where the peaks are, you know where the circuit is likely to start arcing.

Standing waves are not like these guys...

So what can you do?

Avoid open circuit stubs

Avoid open circuit stubs uses as tuning elements. The voltage along an open stub grows, much like the excursion of a wave going down a bullwhip. While we're on that subject, did you know that the bullwhip was the first man-made object to exceed the speed of sound? What did you think that cracking noise was? If you need capacitive tuning, consider using an actual capacitor.

Think about where that wirebond is located

Wirebonds typically make jumps from chip to a substrate. In between the wire is suspended in air, and the breakdown voltage in air is much less than it is in a dielectric. In a limiter design, the PIN diode forms a short circuit, and the voltage is minimum there. A quarter-wave away it is maximum. This is not the best place to leap off the chip!

More to come!