Investigations On Microstrip Antennas

In recent years, the microstrip antennas have attracted numerous attentions. In this thesis, based on the engineering background we have done some researches on the microstrip antenna elements and arrays. The main contents and contributions of the thesis are listed below:The full wave based network method has been proposed to solve the full wave analysis problem of electrically large microstrip antenna arrays. In this method, the radiation element array and the feed network are divided into two parts. For each part, the full wave analysis is carried out. This two parts are then cascaded by using the network method. In using this method, the frequency dependent closed mutual coupling impedance formula is developed in order to accommodate the wide-band analysis. In addition, the limitation of this formula is removed through introducing the general expansion functions.To improve the performance of the adaptive array, we have done a series works. They include: propose the new structure to reduce the mutual coupling between the microstrip elements through using the parasitic metal strip, this new structure can be used to avoid the blind scan angle in one dimensional phased array; propose the new method to reduce the mutual coupling between the sub-arrays through optimizing the distances between the elements in the sub-arrays; propose the new method to reduce the grating lobes at the limited scan phased array through adopting the optimized amplitude distribution, random sub-arrays and random staggering the rows of the array.A single layer monopulse microstrip antenna array has been proposed. In this array, the array, the comparator and the feed network are placed at the same layer which results in the compact structure. The limitation of this array has been discussed and the design guideline of this array has also been introduced. A single channel electrical tracking microstrip antenna array has been proposed in the same chapter. This antenna array is formed by 2×2 microstrip subarrays. Through time sequence phase weighting on each subarray, the amplitude and the phase on each sub-array can be recoved from the output of the resultant single channel. The amplitude and the phase on each array may be used to produce the sum and difference radiation pattern by digital signal processing. As such, compared with the monopulse system, to obtain the tracking signal, the RF comparator is eliminated and the number of the receiver channels is reduced from 3 to 1.A new scheme of two-dimensional microstrip antenna array with frequency scan capability in one dimension is proposed. Through many novel measures, the contradictions among many factors such as frequency bandwidth, scan angle, loss, complexity and cost are properly solved. This array is compact, low loss and low cost with limited frequency bandwidth and very large scan angle.According to the requirements of the engineering application, some kinds of microstrip elements and arrays have been developed. They are: wideband tooth-like-slot microstrip antenna array, single layer wideband U-slot micriostrip antenna array, shorten SIW H-plane horn antenna, polarization agile microstrip antenna array, low cross-polarization corner-fed microstrip antenna array,modified T-probe wideband linear polarization and circular polarization microstrip antenna element and new feeding correction method to design the circular polarizaton microsrip antenna element.