Circular Polarization Leaky-wave Antenna Based on Substrate Integrated Waveguide with Wide Axial Ratio Bandwidth for Millimeter-Wave Applications

A wide axial ratio bandwidth circular polarization (CP) leaky wave antenna (LWA) based on substrate integrated waveguide (SIW) is proposed in this paper for millimeter-wave (MMW) applications. Each element is composed of a slot on top side of the SIW, and two pairs of dipoles placed orthogonally. The slots couple out energy from the SIW and excite the cross dipoles through two vertical vias. Phase delay lines are used to connect the two pair of dipoles to produce the required 90 degrees phase difference for circular polarization. The proposed CP-LWA can achieve a broad impedance matching bandwidth about 29% (from 24.2 GHz to 32.4 GHz) with a peak gain of 17 dBi. The axial ratio (AR) is 0.9 dB at the main beam direction at 28 GHz. The antenna can keep a wide 3-dB axial ratio (AR) bandwidth about 13.79% when frequency changes from 27 GHz to 31 GHz.