Frequency-selective polarisation antenna based on simple rotational symmetric printed bow-tie dipole structure

In this study, a simple antenna with rotational symmetric bow-tie dipole structure is proposed. The polarization of this antenna varied with the frequency, and is named frequency-selective polarization antenna (FSPA). It is evolved from a basic bow-tie dipole structure. After symmetrically cutting off two ellipses and rotational symmetrically incising two wide slits on the two arms of the bow-tie dipole, FSPA is achieved. The lower linearly polarized (LP) and circularly polarized (CP) waves are produced by the larger tip. In the same way, the upper LP and CP waves are generated by the smaller tip. It can not only generate right-hand circular polarization and left-hand circular polarization with center frequencies of 2.40 and 5.30 GHz, but also radiate different LP waves as a dipole at two different bands. This antenna can get an impedance bandwidth (S11 < -10 dB) of 98.7% from 1.9 to 5.65 GHz, the 3 dB axial ratio bandwidths can reach 8.3% (2.3-2.5 GHz) and 13.3% (4.9-5.6 GHz). The antenna peak gains at CP bands are 2.1 and 4.4 dBic, respectively. The peak gains at LP bands are 2.4 and 3.0 dBi, respectively. Furthermore, the radiation patterns perform well within these frequency bands.