Microstrip Ring Circuits

Hi, I am a newbie in microstrip filter design. Need some help to understand some basic fundamentals. As we know ring resonator supports 2 degenerate modes which are orthogonal and be interpreted as waves travelling in opposite direction in the ring.

1) from this formula nλ=2πr .. n is also known as mode number... what does this n stands for ?

2) normal filter designs we talk about n order.. but for ring circuit type of filter design do we need to look into the order?

3) What is the proper step by step approach to design a ring resonator type of bandpass filter? Any tips? thanks..