High-Gain and Broadband Transmitarray Antenna Using Triple-Layer Spiral Dipole Elements

A triple-layer transmitarray antenna has been designed, fabricated, and tested at X-band. Using a spiral-dipole element, a full transmission phase range of 360
^°
is achieved for a transmission magnitude equal to or better than -4.2 dB. The transmission phase distribution of the transmitarray elements has been optimized to reduce the effects of the lossy elements with low transmission magnitudes on the antenna gain, leading to an average element loss as low as 0.49 dB. The measured gain of the transmitarray prototype is 28.9 dB at 11.3 GHz, resulting in a 30% aperture efficiency. Antenna bandwidths of 9% for 1-dB gain and 19.4% for 3-dB gain are achieved in this design.