New-Tech Europe Magazine | Oct 2017 | Digital Edition

Figure 2: Test board for XHF- 292M+ and XLF-73+

Figure 3: Measurement plots of S21 (black), S11 (red), and S22 (blue) for combined XHF-292M+ and XLF-73+, exhibiting a bandpass response with roughly 121% bandwidth.

because this filter incorporates two and three section designs, we also expect to see very high rejection in the upper and lower stopbands. A simulation combining these two models in series is shown in figure 4, exhibiting a 3 dB passband from 450 MHz to 5.7 GHz (12.7:1 or 171% bandwidth). Note that a logarithmic frequency scale is used to better show the shape of the response. Also note the lower stopband rejection greater than 30 dB and upper stopband rejection reaching the 50 to 60 dB range, again a function of the two- and three-section designs used in this case. The filters were mounted on the test board shown in figure 5, and again insertion loss, input and output return loss were swept from 0.1 to 40 GHz and from 450 MHz to 2 GHz at fine resolution to capture more detail at low frequency. The measurements were corrected for the fixture by subtracting the loss of a straight thru-line. The measurement plots are shown in figure 6. Again, note the logarithmic frequency scale to better represent the filter behavior.

Figure 4: Simulation of band pass response combining XHF-581M+ and XLF-312H+

the high-pass filter used in this case. Input and output return loss are also plotted in red and blue, respectively, simply to highlight the good matching in the passband and the stopband, which is a differentiating feature of these filter designs. Case 2: Maximizing Bandwidth Case 1 establishes the viability of the technique by combining high pass

and low pass reflectionless filters to create an ultra-wideband bandpass response. By employing the same technique, we can now experiment with different models to shape the response and achieve desirable characteristics. In this case, we seek to create the widest passband possible with models available, combining two-section, high pass model XHF-581M+ and low pass, three-section model XLF-312H+. In addition to the wide bandwidth,

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