Multi-scale rectangular mushroom structure, high impedance ground plane (HIGP), is designed to achieve large band gap. By suppressing surface waves, the structure becomes eligible for antenna applications. The HIGP's are composed of three different sized rectangular patch mushroom elements for different resonance frequencies. The characterizations of the three scaled HIGP with varying all dimensions are observed for GHz frequency range. Some antenna designs for free space application and the effect of the multi-scale HIGP on these antennas are also presented.