How to calculate impedance of a PCB trace Antenna in Altium w.r.t. a given frequency?
1. how is that the impedance is not dependent on trace length and only on trace widths ?
There are two kinds of impedance: The (usual) resistive impedance is only dependent on trace length. The travelling wave impedance is only dependent on trace widths (The wave only &quot;sees&quot; what is beside its propagation direction, not what's ahead).
2. how can Altium suggest a trace width without me specifying the frequency?...
The wave impedance is almost not dependent on frequency. Think of light rays of different colors (frequency) which propagate the same way in air. Wave impedance is only dependent on geometry.
3. Is there a way I can calculate Impedance between any two given points on a trace for a given frequency ? I want both the resistance and reactance to design matching .
Impedances between any two points in the world can be calculated. When dealing with (high frequency) waves, you may want to calculate scattering parameters and reflection coefficients instead of resistances and reactances.
4. If there is no such way in Altium(which I suspect), then how do people design Antennas these days?
Altium Designer does not provide antenna design tools. But it can calculate the wave impedance of a trace that feeds an antenna structure.