tailieunhanh - Microwave Ring Circuits and Related Structures phần 9

Sự mất cân bằng biên độ tối đa của cánh tay-E là 0,5 dB trong dải tần 2-4 GHz. Sự mất cân bằng biên độ tối đa của cánh tay-H là 0,4 dB trên cùng một dải tần số. Hình 9,30 cho thấy sự cân bằng pha 180 ° out-of-pha và khớp nối chế độ trong giai đoạn. Các lỗi giai đoạn của cánh tay-E là 3 ° tại tần số trung tâm của 3 GHz. Giai đoạn mất cân bằng tối đa của E-cánh tay là 5 ° trong dải tần số từ 2-4. | CHAPTER ELEVEN Ring Antennas and Frequency-Selective Surfaces INTRODUCTION The ring antenna has been used in many wireless systems. The ring resonator is constructed as a resonant antenna by increasing the width of the microstrip 1-4 . As shown in Figure a coaxial feed with the center conductor extended to the ring can be used to feed the antenna. The ring antenna has been rigorously analyzed using Galerkin s method 5 6 . It was concluded that the TM12 mode is the best mode for antenna applications whereas TM11 mode is best for resonator applications. Another rigorous analysis of probe-feed ring antenna was introduced in 7 . In 7 a numerical model based on a full-wave spectral-domain method of moment is used to model the connection between the probe feed and ring antenna. The slot ring antenna is a dual microstrip ring antenna. It has a wider impedance bandwidth than the microstrip antenna. Therefore the bandwidth of the slot antenna is greater than that of the microstrip antenna 8-10 . By introducing some asymmetry to the slot antenna a circular polarization CP radiation can be obtained. The slot ring antenna in the ground plane of a microstrip transmission line can be readily made into a corporate-fed array by implementing microstrip dividers. Active antennas have received great attention because they offer savings in size weight and cost over conventional designs. These advantages make them desirable for possible application in microwave systems such as wireless communications collision warning radars vehicle identification transceiver self-mixing Doppler radar for speed measurement and microwave identification systems 11 12 . Microwave Ring Circuits and Related Structures Second Edition by Kai Chang and Lung-Hwa Hsieh ISBN 0-471-44474-X Copyright 2004 John Wiley Sons Inc. 297 298 RING ANTENNAS AND FREQUENCY-SELECTIVE SURFACES FIGURE The annular ring antenna configuration. Frequency-selective surfaces FSSs using circular or rectangular rings have