1. HFSS solution method
1) Drive mode: The S parameter is obtained from the reflected wave power of the incident wave, which is commonly used in the model of microstrip, waveguide and other transmission lines;
2) Terminal drive mode: Calculate S parameters according to terminal voltage and current, which is often used to solve signal integrity problems;
3) Eigenmode mode: The solution obtained is the resonant frequency of a given structural model and the field mode at that resonant frequency.
2. Three types of frequency sweep: fast frequency sweep, discrete frequency sweep and interpolation frequency sweep
1) Fast frequency sweep: Based on the Adaptive Lanczos-Pade Sweep (ALPS) method, the entire frequency field is extrapolated from the center frequency to scan, and the results of all field points in the entire frequency range are obtained. The calculation speed mainly depends on the complexity of the model and the complexity of the field, and the number of frequency points has little effect. Suitable for resonant structures and structures with small changes in S-parameters;
2) Discrete frequency sweep: only calculate the result of a given field point within the frequency sweep range;
3) Interpolation frequency sweep: between the above two. HFSS will automatically select the frequency points to be solved according to the convergence accuracy of the iteration. When the S parameter error between the two frequency points is less than the convergence accuracy, the sweep ends, and the field values of other frequency points are given by interpolation.
3. Return loss (RL, return loss)
1) A parameter indicating the performance of signal reflection. Part of the incident power is reflected back to the signal source. RL=10log(Pr/Pi) Pr--reflected power, Pi--incident power;
2) S parameter:
· S11: Input reflection coefficient, that is, input return loss; S11 can see the antenna resonance frequency bandwidth and other parameters;
· S22: Output reflection coefficient, that is, output return loss
· S12: Reverse transmission coefficient, that is, isolation
· S21: Forward transmission coefficient, that is, gain
· S11=20log(T), T is the reflection coefficient. T = reflected voltage/incident voltage.
4. Standing wave ratio (VSWR)
1) The reciprocal of the traveling wave coefficient. Its value is between 1 and infinity. VSWR=1 means perfect match; infinity means perfect reflection; mobile communication generally requires VSWR<1.5;
2) VSWR=antinode voltage/node voltage;
3) VSWR=(1+T)/(1-T); T - reflection coefficient
4) VSWR=The ratio of the maximum value to the minimum value of the voltage amplitude.
5. Smith chart
1) The Smith chart is still the basic tool to determine the impedance of the transmission line;
2) The Smith chart is a polar coordinate chart of the reflection coefficient (gamma, denoted by the symbol Γ). The reflection coefficient can also be mathematically defined as a single-port scattering parameter, namely s11;
3) When dealing with the practical application of the RF system, there will always be some very difficult tasks. Matching the different impedances of each part of the cascade circuit is one of them. Generally, the circuits that need to be matched include the matching between the antenna and the low noise amplifier (LNA), the matching between the power amplifier output (RFOUT) and the antenna, and the matching between the LNA/VCO output and the mixer input. The purpose of matching is to ensure that the signal or energy is effectively transmitted from the "signal source" to the "load".
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