A planar loop antenna was designed using the finite difference time domain (FDTD) method. The antenna consists of a loop fed with twin lead transmission line. The twin lead is balanced and to feed it using a microstrip transmission line which is unbalanced one must use a balun. In this case a ladder type of balun is utilized. A thermal plot of the electric field magnitude as computed by FDTD at 2.45 GHz is shown to the right.
The antenna is designed to operate in the 2.1-2.5 GHz range. At 2.45 GHz FDTD predicts the radiation patterns (5.11 dB directivity) as shown below:
FDTD may be used to evaluate the operation of the balun feeding the planar twin lead transmission line at 2.45 GHz. The red values indicate an upward directed electric field and the blue values indicate a downward directed electric field. The balun is clearly producing a 180 degree phase difference at the two ports.
