A novel broadband unit-cell is proposed in this paper. 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 o 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 a moderate size reflectarray, 27×27 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.Index Terms-Quasi-spiral phase delay line, phase shift mechanism, reflectarray antenna, delay line.

In this letter, the effect of moving the feed on the operation bandwidth of a broadband reflectarray is investigated through simulation and measurement. A new broadband cell element with optimized dimensions to achieve linear phase shift is proposed in this investigation. A square reflectarray of 40 40 cm comprising this particular unit cell was designed and fabricated to demonstrate wideband operation at X-Ku band. The effect of feed movement on the operating band was studied by exciting the reflectarray with a plane wave and monitoring the near field on the line passing through the assumed feed locations over a wide frequency band. Considering three different feed positions, the reflectarray was simulated, and good agreement between simulated and measured results was observed. It is shown that changing the feed location leads to a considerable shift in operating frequency window of the reflectarray and also its maximum gain, which gives rise to the possibility of changing the operating band without redesigning the reflectarray by only moving the feed. Moreover, a remarkable value of 36% of 1.5 dB gain-bandwidth was measured, which is higher compared to previously reported designs in the literature.Index Terms-Broadband reflectarray, cell element, focal shift, gain-bandwidth.

No abstract

No abstract

No abstract