Recommended reading for designing a cascaded coupler

Hello,

I need to design a cascaded coupler (3 or 5 sections) on microstrip, to get a flat response in the useful bandwidth. Please recommend a book/paper/tutorial useful for designing cascaded couplers.

Edit:
I optimized a 5 section coupler, for flat response and I got a very tight coupling for the central coupler, Z0E=191 Ohm , Z0o=13 Ohm . This values are extreme for implementing in microstrip, resulting in a very tight coupling, very narrow spacing.
Can I implement the central coupler as a Lange or cascaded Lange coupler? This will affect the phase response of the central coupler, and the overall coupler frequency response?

Thanks

These impermanence are reliasable with CPW. Have you tried it?

As you can see I don't have enough experience with MW, just starting.
I will try it, though I read CPW is quite difficult to design and simulate, with no equations available...
I was told it is easier to do it in stripline.

Anyway it's just a school project and not an actual design, but I was curious how this could be done.

A cascaded Lange is difficult to build but works. A great deal depends on what you want to accomplish (frequency, bandwidth, producability, cost). Cascaded Wilkinson is cheaper & easier to build,
(###.microwaves101.com/encyclopedia/couplers.cfm).
Somewhere I've got a book with good information on cascaded Lange couplers.