Double-loop antennas for a circularly polarized tilted beam

An antenna consisting of two concentric loops is analyzed using the method of moments. The antenna radiates a circularly polarized (CP) beam tilted from the direction normal to the antenna plane (the axial direction). First, an antenna with two feeds is analyzed. The configuration parameters are optimized in such a way that the inner and outer loops radiate CP axial and conical beams, respectively. These two radiation beams are then combined to form a CP tilted beam. It is found that the tilt angle is 25°, where the axial ratio and gain are 0.6 and 10 dB, respectively. Next, the phase between the two feeds is varied. Calculations show that the beam azimuth direction varies in a range of 360°. Finally, an antenna with a single feed is analyzed. The antenna shows radiation characteristics comparable to those for the two feeds. Further calculation reveals that a VSWR of 1.0 is obtained for another single feed using electromagnetic coupling. The VSWR remains less than 2 in the frequency bandwidth (of 2.5%) for a 1-dB gain-drop criterion. Within this bandwidth, the axial ratio is less than 3 dB.