Microwave properties of superconducting $MgB_{2}$

Measurements of the $10GHz$ microwave surface resistance of dense $MgB_{2}$ wire and pellet are reported. Significant improvements are observed in the wire with reduction of porosity. The data lie substantially above the theoretical estimates for a pure BCS s-wave superconductor . However the $R_{s}(20K)$ of the wire is an order of magnitude lower than that of polycrystal $YBa_{2}Cu_{3}O_{6.95}$ and matches with single crystal $YBa_{2}Cu_{3}O_{6.95}.$The results show promise for the use of $MgB_{2}$ in microwave applications.