This paper describes a concept of air miniature SIR coaxial resonator built from coaxial sections fitted inside one another. This topology leads to an important size reduction. This solution is also based on the well-known Stepped Impedance Resonator (SIR) principle. An advantageous property of SIR resonators is that they allow an extra substantial reduction in size, while maintaining an acceptable quality factor and a significant distance from the first harmonic. We present the concept which can be applied to n coaxial sections. However, we will describe here the behavior only with two sections.