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A multilayer reflectarray composed of two stacked arrays with rectangular patches of variable size is demonstrated. A progressive phase distribution on the reflector surface is achieved by adjusting the dimensions of the patches. The phase of the reflection coefficient at each element is computed by the method of moments in the spectral domain, assuming local periodicity. A technique is presented for the design of dual polarization reflectarrays that yields all the dimensions for the photo-etching mask. A prototype has been design, built and measured, and a superior bandwidth performance has been verified, compared to conventional single layer reflectarrays.

A method is proposed to design three-layer printed reflectarrays with patches of variable size for broadband operation. The patch dimensions are adjusted by an optimization routine to achieve the required phase distribution in a given frequency band. A 1-meter reflectarray was designed, and significant bandwidth and gain stability improvements were obtained.

An electronically switching-beam reflectarray antenna to be used in X-band has been designed, manufactured and tested, using PIN diodes as switching device. The antenna has 244 elements arranged in a circular aperture. With the aim of saving electronic devices and reducing both manufacturing complexity and cost, the phase control has been implemented at sub-array level, using aperture-coupled patches gathered by pairs to a common delay line. The antenna was designed to switch the beam between ±5 ^° , in a scanning plane tilted 18.3 ^° with respect to the YZ plane. Each state was obtained by forward biasing one half of the diodes, while the other half remains in reverse biasing. A third state with the beam pointing to 0 ^° was obtained when all the diodes are in reverse biasing. The concept has been demonstrated by manufacturing and testing a breadboard. The measured radiation patterns fulfill the design requirements.

A significant improvement in the bandwidth of large reflectarrays is demonstrated using elements which allow true-time delay. Two identical, large reflectarrays have been designed using different phase distributions to generate a collimated beam. In the former, the phase distribution is truncated to 360deg as is usual in reflectarray antennas, while in the second, the true phase delay is maintained (three cycles of 360deg). The chosen phase-shifter elements are based on previously measured and validated patches aperture-coupled to delay lines. The radiation patterns for both reflectarrays have been computed at several frequencies and the gain is represented as a function of frequency for both cases. Bandwidth curves are presented as a function of the reflectarray size.

The design, fabrication, and measured results are presented for a reconligurable reflectarray antenna based on liquid crystals (LCs) which operates above 100 GHz. The antenna has been designed to provide beam scanning capabilities over a wide angular range, a large bandwidth, and reduced side-lobe level (SLL). Measured radiation patterns are in good agreement with simulations, and show that the antenna generates an electronically steerable beam in one plane over an angular range of 55° in the frequency band from 96 to 104 GHz. The SLL is lower than -13 dB for all the scan angles and -18 dB is obtained over 16% of the scan range. The measured performance is significantly better than previously published results for this class of electronically tunable antenna, and moreover, verifies the accuracy of the proposed procedure for LC modeling and antenna design.