AN369: Si4010 Antenna Interface and Matching Network ... - wless.ru

AN369Unfortunately, around the 5th harmonic frequency the 50 balun core output (at the C1 capacitor, before the filter)has a very low impedance and thus the filter could not attenuate properly. To avoid this, a 8.5 mm long50 coplanar transmission line is introduced between the C1 capacitor and the filter. This line transforms theimpedance at the 5th harmonic to higher values. In this way, significant reduction of the 5th harmonic level isachieved.Figure 14. Top Layout of the SI Testcard with SOIC Packaged Si4010The measured spectrum by a 50 spectrum analyzer up to 3.6 GHz is shown in Figure 15. The realized matchinghas ETSI compliance in this conductive measurement. Assuming 0 dB gain antenna, the compliance will beobserved in radiated measurements as well.The fundamental power is ~+9.6 dBm. Assuming 1.0 dB loss for the balun and 0.1 dB loss for the filter, the powerdelivered to the differential port of the balun is ~+10.7 dBm. That is, the power goes into a properly designeddifferential antenna input without external matching elements.Figure 15. Measure Output Spectrum Up to 3.6 GHz16 Rev. 0.1