Complex sentence: However, the early development of radio was limited to lower frequencies at which parabolic antennas were unsuitable, and they were not widely used until after World War 2, when microwave frequencies began to be exploited.
Split into simpler sentences: However, the early development of radio was limited to lower frequencies at which parabolic antennas were unsuitable. Parabolic antennas were not widely used until after World War 2, when microwave frequencies began to be exploited.