Theory And Application Research For Time Modulated Array

Active antenna arrays are extensively used in the radar, the communication, the navigation and the radio astronomy systems. They have advantage in the flexible beam scanning, which can help to realize the multibeam and ultra-low sidelobe characteristic for the antenna arrays. The active antenna arrays implement the pattern synthesis and the beam agility by weighting the amplitudes and initial phases in all the RF channels. According to the different weighting methods, the traditional active antenna arrays can be divided as the analog antenna arrays and the digital antenna arrays. Among the analog antenna arrays, the phased arrays are well known. They weight the amplitudes and initial phases in all the RF channels by the variable gain amplifiers and phase shifters, respectively. The digital antenna arrays, also called the soft antenna arrays, add the complex weights to all the RF channels in the digital domain by the digital signal processing. In order to obtain the better performance, the active antenna arrays usually exploit thousands of elements. Thus, the system complexity and cost increase dramatically for the active antenna arrays. Therefore, it is of important significance to develop low complexity and low cost active antenna arrays. In this context, the time modulated array, as a novel kind of active antenna array with low complexity causes a lot of attention in recent years. The time modulated array, also called 4D array, has new structure compared to the traditional active antenna arrays, which adds the RF switches to the RF front. It synthesizes the array patterns by periodically modulating all the RF switches.Because of the periodical modulation, the fundamental and the harmonic components are generated simutaneouly. The fuandament component can be used in the pattern synthesis, and the harmonic components can be exploited in the beamforming. Though the time modulated array has simple structure and low complexity in control, its disadvantages cannot be ignored. After the periodical modulation to a single frequency sinusoidal signal, the fundamental and the harmonic components are generated simultaneously. While the fundamental component is exploited to synthesize the pattern, the harmonic components generate the undesired sideband radiation. On the basis of the existed methods, we have proposed a novel sideband radiation suppress method for the time modulated array with non-uniform period modulation, which has a low computational complexity. The harmonic components are useful for the beamforming of the time modulated array. However, the basic time modulated array has a low power efficiency in harmonic components’ beamforming. We have improved the basic time modulated array with quasi single sideband modulators, which increases the power of the desired harmonic component by 9d B, and the ideal loss caused by the time modulation drops to about 1d B.The direction finding characteristic of the time modulated array attracts broad attention in recent years. In the public literatures, the researchers realize that the incident direction is related to the harmonic components’ patterns. However, the mathematical relation has not been analyzed yet. We have deduced the relation formula during the incident direction, the fundamental components and the positive first harmonic component. Numeric simulations and the experiment are provided to verify the proposed direction finding method. On the basis of the time modulated array, we have developed a novel fast calibration method for the active phased arrays, which can calculate the amplitude and phase mismatches among the RF channels in parallel by the time modulation.The research to the time modulated array is growing, and its application in the future wireless communication arouses many researchers’ interest. The space division multiple access(SDMA) technique can improve the spectrum efficiency exponentially, and this thesis has discussed to implement the SDMA with the time modulated array. In addition, the thesis has discussed the application of the time modulated array in the compensation of the Doppler shift in high speed mobile communication. Because the time modulated array system can compensate the Doppler shift in the RF front, the complexity of the signal processing in the baseband can drops correspondingly.In conclusion, this thesis has researched the sideband radiation suppression method first, then improved the basic time modulated array to increase the power efficiency in the harmonic beamforming of the time modulated array. Based on the ideal of the time modulation, this thesis has discussed the direction finding method.