Single-Layer Broadband Reflectarray Antenna by Using Quasi-spiral Phase Delay Line

A novel broadband unit cell is proposed in this letter. This new cell element consists of three coupled circular rings where four quasi-spiral delay lines are connected to the outer ring to provide the required phase shift. The spiral shape of the delay lines exhibits more than 1000 degrees of phase swing. The cross-polarization level of the presented element is considerably improved compared to previous designs with a similar phasing mechanism. The capability of operating in linearly or circularly polarized incident wave is an important advantage of the proposed cell. In other words, depending on polarization of the feed antenna, the present reflectarray can operate in vertical, horizontal, or circular polarization. Finally, amoderate-size reflectarray, 27 x 27 cm(2), is designed and fabricated based on the mentioned element. The measured results showed about 16.5% of 1-dB gain bandwidth. The antenna gain at 8.5 GHz is 26.4 dB, which is equivalent to 59.2% efficiency. Also, the measured sidelobe level and cross polarization of this antenna are about -20 dB and -25 dB, respectively.