An Ultra-wide-band Tightly Coupled Dipole Reflectarray Antenna

A novel ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is presented in this paper. This reflectarray antenna consists of a wide-band feed and a wide-band reflecting surface. The feed is a log-periodic dipole array antenna. The reflecting surface consists of 26×11 unit cells. Each cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is 8mm, which is about 1/10 wavelength at the lowest operating frequency. By combining the advantages of reflectarray antennas and those of tightly coupled array antennas, the proposed TCDR antenna achieves ultra-wide bandwidth with reduced complexity and fabrication cost. A method to minimize the phase errors of the wideband reflectarray is also developed and a concept of “equivalent distance delay” is introduced to design the unit cell elements. To verify the simulations, a prototype operating from 3.4 to 10.6 GHz is simulated and fabricated. Good agreement between simulated and measured results is observed. Within the designed frequency band, the radiation pattern of the TCDR antenna is stable and the main beam of the antenna is not distorted or split. The side lobe levels of the radiation patterns are below -11.7 dB and the cross-polarization levels are below -20 dB in the entire operating band. This TCDR antenna combines the reflectarray and tightly coupled arrays for the 1st time and achieves the widest bandwidth (in terms of stable radiation patterns and low sidelobes) reported so far. This work is expected to have significant impact on antenna development for broadband satellite communications and the base stations in 5G mobile communications.