Radiation efficiency of electrically small microstrip antennas with width discontinuities

When patch segments of different widths are adjoined to form a microstrip antenna, the resonant frequency is significantly lower than that of a conventional rectangular microstrip antenna with the same overall length. It is shown, however, that the radiation efficiency is substantially reduced as the antenna becomes small at a given frequency. As the resonant frequency decreases, the radiated power is lowered at a faster rate than the conduction and dielectric losses.