Equivalent circuit of a dielectric resonator coupled to a microstrip line

Hi! Everyone.

I am a student from Taiwan.

Please forgive me for my poor English.

I have some question as title.

I have already read some paper for DR these days.

There are some questions bother me.

Some paper says the equivalent circuit can be modelled by a transformer and a parallel RLC,but some says it can be modelled by a inverter and a series RLC.

Can anyone tell me why there have two different forms of them?

Another question is if a mutual inductance has a coupling coefficient "k" =1 ,we can model it as a ideal transformer,but if "k"<<1,we can model it as a inverter.

Is it ture or not?

DR coupled to a microstrip line should has a small "k" because it can only coupled a little energy to microstrip line , am i right?

Thankyou for answer me these questions.

Best regards,