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vor 5 Jahren

EF 2018/2019

  • Text
  • Komponenten
  • Technik
  • Radio
  • Filter
  • Oszillatoren
  • Quarze
  • Emv
  • Wireless
  • Messtechnik
  • Bauelemente
  • Components
Einkaufsführer HF-Technik 2018/2019

RF & Wireless Figure 3:

RF & Wireless Figure 3: Simulation of 2.4 GHz harmonic filter, including device L-C parasitics ters or models for passives and compact nonlinear models and load-pull power device data for active devices, as provided by many component manufacturers. More recently X-parameter models are also provided by some manufacturers and model providers. At application frequencies above 1 GHz, the component parasitics such as series inductance in capacitors and shunt capacitance in inductors, as well as substrate-dependent component parasitics, significantly impact the actual circuit performance. If these component parasitics are not included in the simulation, the accuracy of the simulation results will be significantly degraded. Circuit simulations with accurate component models that include the component parasitics can produce very accurate results. For example, an accurate low-pass filter simulation might show steeper rolloff due to the parasitic series inductance in the shunt capacitors and will certainly show the “flybacks” (frequencies where the filter has degraded rejection in the stop band) where the series inductors are resonant. Many circuit designers recognize the importance of including component parasitics in their simulations and create their own models Figure 4: Redesigned 2.4 GHz harmonic filter schematic 36 HF-Einkaufsführer 2018/2019

RF & Wireless Figure 5: Complete harmonic filter PCB with pigtails; layout (left) and fabricated circuit (right) for the desired components by measuring S-parameters using a network analyzer and then deembedding the results. Models created using this approach are typically accurate only for a specific pad size, PCB thickness, and dielectric constant and this effort is time consuming and requires specialized test fixtures and measurement expertise. These models provide for pad scaling that account for substrate/ground-plane effects and are measurement validated on numerous substrates over a wide frequency range. Obviously, there is a cost required to develop component models, even if it is done in-house. Harmonic Filter Design Example In this design of a harmonic filter for a transmitter application, the cutoff frequency and level and frequency of the flybacks was crucial to ensure that the level of the transmit harmonics would be below the required limit. Using NI AWR Design Environment, the design of a low-pass harmonic filter appeared to be a straightforward effort. For this 1-W transmitter application, a filter was required to reduce the level of the second and third harmonics at the output (below -20 dBm), as well as the level of the higher order harmonics (below -80 dBc). Starting with ideal lumped-element capacitors and inductors and including the interconnecting microstrip lines, the 2.2-2.4 GHz harmonic filter shown in Figure 1 was designed for low S11 in the passband and high rejection at the second harmonic and above. The schematic shows the circuit using Modelithics model symbols but the parasitics were set to “ideal,” so are not included in the simulation results. Figure 6: Microwave Office with Modelithics results for the 2.4 GHz discrete harmonic filter (simulation vs. measured data) HF-Einkaufsführer 2018/2019 37

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