I am a beginner. I have designed a printed monopole antenna in CST. Multiple resonant peaks are coming but not broadband. It's most probably that the antenna is not matched. I need the relation between feed width and reflection coefficient or vswr.
I think monopole antennas usually have narrowband resonances and the skill is in changing their shape of the shape of the feed or ground so that the resonances become more broadband or merge into each other.
The feed will usually have a defined impedance. If it is microstrip then the wider the strip, and the closer to the ground, and the higher the dielectric constant of the insulator, the lower the impedance. The antenna is matched when the line impedance is the same as the antenna impedance (they are matched). The line impedance is real. The antenna impedance will be complex (resistance and inductance or 1/capacitance) and vary with frequency. When the imaginary part is small and the real part is close to the feed impedance, the antenna is matched. The monopole shape can be changed to change the imaginary part, and matching circuits can be added to the feed or antenna to change the imaginary part to make the total imaginary part as small as possible, and the real parts as close to each other as possible over a large frequency range.
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