Design and performance of TEM horn antenna with low-frequency compensation

By adding a loop to an exponentially flared TEM horn and properly adjusting the loop structure, a TEM horn antenna with low-frequency compensation is designed. The added loop structure, together with the horn arms, provide an equivalent magnetic-dipole moment at low frequency to combine with the electric-dipole moment formed between the two arms of the TEM horn. The low-frequency radiation can be enhanced effectively when the two moments meet the balance condition. The performance of the designed TEM horn antenna, including the radiated field strengths on and off the boresight direction, the front-to-back ratio, the reflection from inside of the horn, and the field distribution on the horn aperture, is studied and compared to an ordinary TEM horn by using FDTD simulation. The TEM horn with low-frequency compensation provides higher radiation efficiency and broader beamwidth if compared to an ordinary TEM horn antenna.