AWR eBooks

RF Electronics Chapter 7: RF Filters Page 224 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. measured performance has a significant amount of coupling between the input and output, which is due to electromagnetic coupling between the input and output tracks and leads connecting the filter. The stopband performance was improved by enclosing the filter and placing microwave absorber on the ground-plane on the back of the filter and on the inside lid of the enclosure. The EM simulation in the stopband is sensitive to cell size. Figure 7.26 uses a cell size of 0.1 mm, using a cell size of 0.25 mm does not show a peak of -44 dB at 5.5 GHz and shows a larger peak at 6.5 GHz. Figure 7.26. Simulated and measured performance of 2 GHz lowpass filter with stubs. Bandpass Filter Design LC Bandpass Filters To illustrate the design principles, a filter with a centre frequency of 18.48 MHz and a bandwidth of 2 MHz is designed, using different techniques. This particular filter was required for a weather satellite data receiver, designed at JCU, to filter the IF data signal prior to demodulation. Since the transmitted signal is a Binary Phase Shift Keyed (BPSK) modulated RF signal containing digital data, a Bessel filter results in the lowest BER after demodulation. Low-Pass to Band-Pass Transformation A simple way of designing bandpass LC filters is to use the low-pass to band-pass transformation, described in most filter books. The low-pass to band-pass transformation will often give impractical component values for the bandwidths required for most RF filters. As a result, the low-pass to band-pass transformation is not suitable for most bandpass filter designs. More practical component values are obtained using coupled resonator designs. The filter resulting from the low-pass to band-pass transformation is shown in figure 7.27. A RF Electronics: Design and Simulation 224 www.cadence.com/go/awr

• Cover