Can you give me some idea about this coupler design?

Design an edge-coupled 10-dB microstrip coupler on 0.25 mm alumina substrate for operation over 30 to 40GHz band. The required return loss and the directivity are 30 and 45dB respectively. Use suitable capacitances for phase velocity compensation.

I think it should be a multisection microstrip. But I have no idea how to start. BTW i use ADS for simulation.

I would say the first thing to get is a good book on
coupled transmission lines, example:
RF and Microwave Couple-Line circuits
R. Mongia, I.Bahl and P. Bhartia.
Artech House ISBN: 0890068305

Specially take a look to Chapters
Ch.5: Broadband Forward Wave Directional Couplers
Ch.7: Nonuniform Broadband TEM Directional Couplers

For 30 to 40 GHz the only structure that comes to my mind is the
Lange configuration.

may i ask one question?
0.25 mm alumina substrate for operation over 30 to 40GHz band
is it possible?

Also a useful book will be The Rf And Microwave Handbook of CRC ISBN 0-8493-8592-X

30 dB return loss at 30 Ghz? I'll have whatever you are smoking!

Hi,

I also think alumina has too high dielectric constant to be used at those frequencies with such a stringent specifications. Soft substrates (teflon based) are generally workning much better at those frequencies. If you really intend to make this circuit and measure it change the substrate. For the design exercise it is OK.

flyhigh