Abstract
•A tunable dual band circularly polarized antenna is proposed and fabricated. Resonance frequencies can be tuned around 10 percent by changing the applied magnetic bias.•Two types of unidirectional modes of ferrites are used to achieve dual band circularly polarized antenna.•A simple theoretical model is proposed to model the antenna behavior.•Antenna has a large axial ratio beam width (circular polarization is achieved at all of the half power beam-width of antenna) over its impedance bandwidth.
We have designed and fabricated a dual-band circularly polarized antenna using a normally magnetized ferrite disk. The disk is metallized on top and is mounted on a grounded dielectric substrate. A hole is then punched at the center of the top metallization. The dual band operation of the antenna is due to two separate unidirectional resonances. The field intensity at the lower resonance is largest close to the outer periphery of the disk whereas at the higher resonance the electromagnetic field is concentrates near the punched hole. A two-section feeding network is used to feed the antenna. Central frequencies of the upper and lower bands are 4.62 GHz and 5.97 GHz, respectively. Experimental impedance bandwidths are 1.5% for the upper band and 3.5% for the lower band with respective axial ratio bandwidths of 17% and 3.3%. Axial ratio beam-width of the antenna is 90–125 degrees in the lower band and 80–130 degrees for the upper band with respect to the bore-sight. Antenna gain at upper and lower frequencies are 5.5 dB and 7.1 dB. Cross polarization of the antenna is 25 dB at both frequency bands.