Waveguide-hologram-based true-time delay modules for K-band phased-array antenna system demonstration
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Phased-array antennas are more and more important in present-day communications. Optical true-time delay techniques are promising for the squint-free beam steering of phased-array antennas with the features of wide bandwidth, compact size, reduced weight, and no electromagnetic interference. In this dissertation, a digital and an analog true-time delay module were designed, fabricated and characterized. Optical heterodyne technique and gain tunable mechanism of PIN photodetector were analyzed. A true-time delay controlled K-band phased-array antenna system was designed, integrated, and measured. Two kinds of two-dimensional true-time delay module were proposed. The digital true-time delay module employs holographic volume gratings and the substrate-guided wave structure, providing time delays ranging from 0 to 443.03 picoseconds. The total insertion loss, including the propagation loss and the 1-to-64 fanout loss is confirmed to be less than 20 dB. The crosstalk among channels is measured to be less than –40 dB. The polarization dependent loss among 64 fan-outs is within 0.37 dB. The bandwidth of the fully packaged module is determined to be as high as 539 GHz. The continuously variable truetime delay module is based on substrate-guided-wave and the dispersion effect of holographic optical elements. This module can provide time-delay intervals from hundreds of picoseconds down to the sub-picosecond range with subfemtosecond resolution. Two heterodyne systems were investigated with a conversion effeciency approaching the theoretical limit. The frequency response versus the bias voltage of the PIN photodetector was analyzed, and a gain tunable photodetector bank was designed and manufactured based on this analysis. The simulation and experimental main lobes of the far field patterns covering all K-band agree very well. Furthermore, the PAA scanning angle is independent of the microwave frequency over the entire K-band. After a random digital signal with a back-to-back Q factor of 50.42 passed though the true-time delay module, an eye with 10.2 Q factor was obtained. Two forms of two-dimensional true-time delay modules were proposed. One is the digital module, employing the WDM technique and digital delay lines, while the other is the analog module, utilizing wavelength conversion technique and analog delay lines.