Các chuyên ngành cơ bản của cơ khí bao gồm: động học, tĩnh học, sức bền vật liệu, truyền nhiệt, động lực dòng chảy, cơ học vật rắn, điều khiển học, khí động học, thủy lực, chuyển động học và các ứng dụng nhiệt động lực học. Các kỹ sư cơ khí cũng đòi hỏi phải có kiến thức và năng lực áp dụng những khái niệm trong môi trường kỹ thuật điện và hóa học. Với một mức độ nhỏ, cơ khí còn trở thành kỹ thuật phân tử - một mục tiêu viễn cảnh của nó là tạo. | 354 Advanced Microwave Circuits and Systems The simulated magnitudes of q4 q5 q6 and q7 are and while the measured ones are 2 1 and in the frequency band between 3 and 11 GHz. Therefore there is a reasonable agreement between the two sets. As observed from the polar plot in Fig. 12 the circle centres of qi for this reflectometer deviate from the ideal separations of 90 0 90 180 and 270 . The actual phase separation is given by n 2 0o kAf where k and 0o are constants and Af is the shift from the midfrequency Yao Yeo 2008 . The measured phases of q4 q5 q6 and q7 are 180 10 0 20 -90 18 and 89 19 respectively from 3 to GHz. The measured phase characteristics qi i 5 6 7 can be referenced against q4 by the following equation of 30 phase qAi phase qi - phase q4 i 5 6 7 30 The measured phase qAi deviation compared to the ideal case is 20 for frequencies from 3 to GHz. Although Fig. 12 shows a good behaviour of q-point characteristics better results could be obtained if the factors k 0o and Af were included in the design specifications. In the present case the design of seven-port reflectometer was accomplished by just integrating individually designed Q and D components. There is one remaining criterion of performance of the designed seven-port reflectometer and it concerns the magnitude of reference point q3. The simulated and measured results for q3 are shown in Fig. 13. They are dissimilar. However in the both cases the q3 values are greater than . These results indicate that the reflectometer fulfils the optimum design specification of I qi I I q3 I. Fig. 13. Simulated and measured magnitude of q3. 5. Calibration Procedure Following its successful design and development the reflectometer is calibrated prior to performing measurements. A suitable calibration procedure to the reflectometer offers high measurement accuracy that can be obtained with the error correction techniques. There are various .
