Investigation On Large Aperture Antenna Array For Spatial Power Combination

Promoted by scientific research and military needs, high-power microwave(HPM) develops rapidly towards higher frequency and higher peak output power. There are many applications that require extremely high power support. Spatial power combination is a promising approach to increase the effective radiation power. In this approach, antenna arrays should be used in order to achieve the HPM spatial power combination. The traditional phased array antenna can not be applied due to its constraint of power handling capacity. Only by combining the traditional phased array antenna technology and the current HPM technology, can a better antenna array scheme, which meets the requirement of power handling capacity, be proposed. This dissertation proposed a spatial power combination approach by using large diameter antennas as the radiating units. These antennas are fed by the phase-locked HPM sources by the transmission waveguide and the phase shifter. This method has the advantages of high power handling capacity, steerable of wave beam, few number of antenna elements, easy in layout, and so on. Detailed theoretical analysis, numerical optimization and exploration of this approach for spatial power combination are carried out. The main contents of this dissertation are summarized as follows:1. The choice of the layout of antenna arrayTo meet the requirement of high power handling capacity at Ku-band, it is proposed to use large diameter antennas as the radiating units. Under the large element spacing condition, it is found that concentric ring array can be applied to achieve the goal of spatial power combination. Theoretical analysis shows that the radiation pattern of ring array antenna is a single beam which can prevent the generation of grating lobes. The layout of ring array is more flexible than the rectangular gridding antenna array.2. Radiation characteristics of single ring arrayEffects of ring array parameters on its radiation characteristics are studied. These parameters include the placement of antenna element at the origin, the radius of ring array, the number of elements, sparse rate, angular location, and so on. It is shown that the level of sidelobe can be reduced with an element placed at origin. The larger the radius of ring, the narrower is the width of main lobe. The number of sporadic high sidelobes is equal to the number of element when the element number is even, while the number of sporadic high sidelobes is twice the number of element when the element number is odd. The larger the sparse rate, the higher is the sidelobe level. The angular position of array elements can be adjusted to reduce the sidelobe level. This, consequently, increases the flexibility of ring array.3. Design of the concentric ring arrayThe method for designing two concentric ring arrays is presented. The radius of outer ring can be set according to the actual situation, then the radius of inner ring can be adjusted to make the first null of inner ring array radiation pattern fall near the second null of outer ring array radiation pattern. Finally, the number of element and the angular position of each element should be adjusted to reduce the sporadic high sidelobes. Based on this work, the design method of rotating ring array has been further studied. The arrangement of the ring arrays is made more closely to each other. Fewer antenna elements are used. Furthermore, wide beamwidth of array radiation pattern can be realized in this design.4. Exploration of the applications of spatial power combinationA numerical procedure, based on the genetic algorithms, is established in order to design an optimized layout of the antenna array. The optimized results show that with working frequency of 15 GHz, antenna element aperture of 90λ, and element spacing of 104λ, the averaged sidelobe level of the radiation pattern of antenna array is about-18 dB. Effects of excitation phase perturbation, position error of antenna element on the radiation pattern of ring array are analyzed. It is found that by increasing the aperture of antenna element and decreasing the number of antenna element, the sidelobe level of the radiation pattern of antenna array can be decreased. In general, this preliminary research shows that the spatial power combination by using large diameter antennas as the radiating units is feasible.