A SIW-Fed Double-Helix Antenna With Broadband Circular Polarization for MMW Applications

In this letter, a planar double-helix antenna with circular polarization is proposed for millimeter-wave (MMW) applications. The double helical strips are printed on the two opposite surfaces of the substrate in a 180
^o
rotational symmetry and connected by metalized via-holes. The circularly polarized wave is achieved by the currents along strips and via-holes, which generate the horizontal and vertical polarization, respectively. In addition, currents along the ground edges near helixes are implemented to balance the amplitudes of electric fields along strips and via-holes for good circular polarization. To improve bandwidths and circular polarization performance, moderate tapered helixes are applied. With the advantages of low transmission loss, planar and fully enclosed structure, the substrate integrated waveguide is applied as the feeding line for easy integration with MMW circuitry. Experimental results show that the antenna obtains an operating bandwidth of 28.6% from 24 to 32 GHz, a peak gain of 7.8 dBic and a low profile of 0.14 λ
₀
(λ
₀
is free-space wavelength at the center frequency of 28 GHz).