A simple analytical representation supported with equivalent circuit modeling is presented for a nonradiative dielectric coupler. A matrix form for the dispersion relation and the field coefficients is introduced for simplicity. The design methodology and miniaturization of such couplers using two vertical mirror conducting planes is studied. The new image-nonradiative dielectric coupler is 50% smaller in the cross sectional size and has a relatively good reduction in the required coupling length, as compared to conventional coupler without the conducting walls. Those image conducting planes suppressed the unwanted modes and guaranteed a single mode operation when exciting the structure with a horizontally polarized field.