tailieunhanh - Advanced Microwave Circuits and Systems Part 7

Tham khảo tài liệu 'advanced microwave circuits and systems part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 174 Advanced Microwave Circuits and Systems This example structure is designed to work in X-band. Assuming that the working bandwidth is defined by dB drop of transmission coefficient the obtained bandwidth is equal to about GHz. Within the working bandwidth all the measured characteristics fall within the range -9 dB - dB. Depending on the application the useful working bandwidth may be defined differently for example on the basis of 1dB-drop of the transmission. For purposes of power combining from microwave amplifiers the combining losses should be as low as possible. The test structure presented here does not have silver or gold plating inside the cavity therefore the insertion losses may be decreased further. The input reflection coefficient has an acceptable value lower than -10dB within the working band. An example of measurements results for the test structure of the splitter is shown in Fig. 15. 28 liar 2008 13 48 23 Fig. 15. Example of measurement results - transmission characteristics from centre coax input to one of coax output port 5. Conclusion Solid-state power sources based on spatial power combining may successfully replace TWT central transmitters. This method of power combining offers several advantages compared to the use of multi-level three-port based approach. In high power transmitters it is important to reduce the combining losses to as low as possible. Spatial combining does not suffer from additive accumulation of insertion losses and phase mismatches of individual devices as in the tree-structure of cascaded two-input combiners which is the reason why it is very promising. In case of failures of power transistors solid-state transmitter exhibits soft output power degradation. The radar coverage which may be calculated for a given number of working modules reduces softly while failures proceed. It therefore gives additional reliability to radar systems using power sources based on spatial combining. Spatial power .