Design and measurement of a wideband aperture-coupled and polarization-agile stacked-patch antenna-array for monopulse radar applications

A wideband, circularly-polarized antenna array covering the frequency range 1.7 GHz to 2.5 GHz for telemetric monitoring and monopulse application is presented. Using a subarray design, monopulse functionality can be achieved with an external comparator network. The high bandwidth of 38% is realized by using the principle of the aperture-coupled stacked-patch microstrip antenna. By integrating a quadrature coupler, the polarization sense can be selected. Sequential rotation technique is used for enhancing polarization purity. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. A stacked-patch antenna element, a 2times2 antenna quadrant and a 4x4 antenna array have been designed, fabricated and measured. The measured return loss of one quadrant is better than 11 dB in the desired bandwidth for both circular polarization senses. Maximum antenna gain ranges between 7 dB and 18 dB for the sum pattern while the null depth of the difference pattern is always better than 30 dB. Theoretical and measured results of S parameters and radiation patterns are presented and discussed.