A sub-array of slot-coupled microstrip antennas fed using microstrip lines on an opposing substrate. Also provided is an omni-directional antenna comprised of six of the sub-arrays arranged in a hexagonal fashion. The gain of the antenna is ˜6 dB with a 3 dB elevation beam width of ˜30 degrees. The design provides constant beam angle over frequency, which is important for frequency-hopping applications, and the potential to add beam control to mitigate jamming in different sectors.