Designing Comb Generator using SRD

Have anyone ever design Comb Generator using SRD (high frequency up to 20GHz, 20th order)? Any useful advise? Thanks..

Interested is this area too! Anyone has experience with this? Or at K-band, there are other more efficient way of generating these signals?

Thanks!

Hello;
JOhn wrote:

Please explain about comb and SRD for me.

I am not sure whether i can explain well.. Comb generator... Let assume that the Comb generator is a box... If i input a signal with frequency, of F1 Hz into the box, the output of the box should give me, a signal at 1 x F1 Hz, a signal at 2 x F1 Hz, a signal at 3 x F1 Hz, a signal at 4 x F1 Hz, ....... all the way until N x F1 Hz. Of course, as it goes higher harmonic, the signal will become weaker. Hence if you can imagine, at every harmonic, there will be an impulse, that's where you can see the "comb" shape at frequency domain. My objective is to design the comb generator with minimum conversion loss.

SRD, step impedance diode, are use to generate pulses rich in harmonics. Since we are input an AC signal. During "+" cycle, the diode will store charge. During "-" cycle, charge is extract. Due to this effect, current pulse (with rise time = snap time of the diode) is generated when an inductor is connected in serie with diode. In frequency domain, it will appear like a "comb" signal.

Pardon me if my explaination is poor and correct me if i am wrong, i'm still learning.

But how to get SRD at a cheaper price is the problem?

Hmm, my problem is designing a comb generator with minimum power conversion loss, so i don't have to input high power.

A comb generator generates just that, a large number (comb) of output frequencies. By conservation of energy, if you put 1 watt in, have a 10 dB converson loss, and then spread the remaining 100 mW of output power over 30 comb teeth, then at best you will have 100 mw/30 or 2 mW per comb tooth. There is no way to change this. The best you can do is to have the input and output impdance matches optimized, and have no input power leaking out of the output port. You also have to select a SRD diode that is capable of a very small transition time needed to be able to generate the 20th harmonic energy without rolling off (hence, unfortunately, dooming you to lose power at even higher output harmonics).

If, instead, you only want one of the comb teeth outputs, like in only wanting the 20th comb tooth and not all the others, then one could simply design a 20X frequency multiplier circuit, which CAN be optimized for better conversion efficiency.