Tham khảo tài liệu 'antennas with non-foster matching networks phần 3', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 16 ANTENNAS WITH NON-FOSTER MATCHING NETWORKS Active matching network Two-port model of antenna Z 0 FIGURE 12 Antenna with active matching network using non-Foster reactances PERFORMANCE OF ESA WITH IDEAL NON-FOSTER MATCHING NETWORK A conceptual representation of the simplified ideal active matching network together with the two-port antenna model is shown conceptually in Fig. 12. The design equations for the components of the active matching network can be readily extracted from 3 4 as follows. To design the active matching network we first fit the antenna impedance to a simple model. Since the antenna is an electrically small monopole the real part of the antenna impedance is assumed to vary as the square of frequency and the imaginary part is modeled as a series LC. This simple model predicts an impedance that is denoted as Za and given by __ Za R ì ứ La 1 ứCa 22 The parameters of the model may be obtained from the actual antenna impedance Za obtained from simulation or measurement as Ro Re Za ứo -1 La ứ1 ứ1 -1 1 ứ2 ứ2 Ca Im Za ứi Im Za ứ2 23 where ứo is the design frequency in radians per second ứi and ứ2 define the band of frequencies over which the model is being applied and Re Za and Im Za are the real and imaginary ANTENNAS WITH NON-FOSTER MATCHING NETWORKS 17 parts of the antenna impedance respectively. The last of the necessary design equations is Lm R0Zĩ. 24 0 Basically the active matching network works by canceling the antenna s reactance over a broadband using negative impedance elements and then using a transformer section consisting of Lm in series and Lm in shunt to match the real part of the antenna impedance with its frequency-squared dependence to the desired impedance level Z0 over a broadband. Using the above design equations with 1 2n X 50 MHz and 2 2n X 70 MHz we obtain the following component values for the active matching network Ca pF La nH Lm nH. 25 Fig. 13 shows the schematic captured from Agilent ADS of the two-port
