Abstract: In this paper,a new type of circular-shaped microshield and conductor-backed coplanar waveguide (CPW) is proposed.Analytical closed form expressions for characteristic impedance and effective dielectric constant for the new line are obtained using conformal mapping method under the assumption of pure-TEM propagation and zero dispersion.The new waveguide proposed by this paper and reduce radiation to much less than the conventional CPW and microstrip,and reduce the current concentration at both the edges of the signal,and has no need for viaholes or air-bridges for ground equalization and a wide range of impedances.