This paper presents the design and radiation properties of a linearly polarized radial line microstrip antenna array (RL-MSAA) with U-slot circular microstrip antennas. A circular microstrip antenna (C-MSA) with U-shaped slot is used as a radiation element of the RL-MSAA. Radiation phase of the U-slot C-MSA is controlled by tuning the radius of the C-MSA and dimensions of the U-slot on the C-MSA; therefore, the desired phase distribution of the RL-MSAA can be realized. In this paper, a linearly polarized RL-MSAA with three concentric rows of C-MSAs at a spacing of 0.65 wavelengths is designed for 12GHz operation. In order to realize uniform phase distribution, the U-slot C-MSAs are arranged for inner two rows and normal C-MSAs are arranged for the termination row. Validity of the linearly polarized RL-MSAA with the U-slot C-MSAs for radiation phase control is demonstrated by simulation and measurement.

This paper presents design and radiation properties of a radial line microstrip antenna array (RL-MSAA) for linear polarization. A stacked circular microstrip antenna (C-MSA) is used as a radiation element for the RL-MSAA. Radiation phase of the stacked C-MSA is controlled by tuning radii of the lower and upper patches, therefore, the desired phase distribution of the RL-MSAA can be designed. In this paper, a linearly polarized RL-MSAA with three concentric rows of the stacked C-MSAs at a spacing of 0.65 wavelengths for uniform aperture distribution is designed and tested in 12GHz. The experimental results reveal that validity of the linearly polarized RL-MSAA with the stacked C-MSAs for radiation phase control is demonstrated.