Photonic Balun for Antenna Measurements Free of Coaxial Cables

We have developed a new type of balun, called "photonic balun", to receive the balanced component of a RX antenna. Because the photonic balun is connected to a receiver through an optical fiber, we can realize an ideal antenna measurement free of unwanted effects of a coaxial cable. To demonstrate the superiority of the photonic balun in antenna measurements, we compare the vertical polarization patterns of a dipole antenna using the photonic balun and a conventional balun and show that the maximum deviation of the pattern using the photonic balun is 0.4 dB whereas that using the conventional balun is 2 dB. The conventional coaxial cable influences antenna measurements because the cable is made of metal. Therefore, it is necessary to devise the arrangement of the cable as much as possible to remove unwanted effects of the coaxial cable on antenna measurements.