A Compact Single Radiator CRLH-Inspired Circularly Polarized Leaky-Wave Antenna Based on Substrate-Integrated Waveguide

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Abstract
A circularly polarized (CP) CRLH-inspired leaky-wave antenna (LWA) based on substrate-integrated waveguide (SIW) and microstrip delay line is presented. The unit-cell of the proposed periodic antenna consists of two conventional CRLH SIW cells and two quarterwavelength microstrip lines. The interdigital slots on the CRLH SIW are rotated at +45° and -45° with respect to the wave propagation direction and separated by 90° to create circular polarization. Utilizing the microstrip line instead of the SIW delay section, the total size of the live unit-cell antenna is reduced by 24.4% in comparison to the previous single radiator CP LWA. Furthermore, microstrip lines provide improved matching for broadside radiation as well as better CP purity. The unitcell characteristics are investigated in detail through dispersion and Bloch impedance analysis. In addition, space harmonic analysis is carried out to explain the radiation mechanism of the proposed antenna. The proposed CRLH-inspired SIW CP antenna operates from 4.2 to 4.85 GHz and frequency scans from -25° to 26° along the elevation angle. Axial ratio is maintained below 3 dB throughout the operating frequency. The measured results show good agreement with the simulated results.

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