When modelling a Yagi in NEC the radiation pattern is essentially identical whether a conductive boom is included or not, see pictures below. An explanation says this is a limitation of the method of moments method in NEC-2; "only currents in the axial direction on a segment are considered, and there is no allowance for variation of the current around the wire circumference".

However when I sweep VSWR over frequency I get quite different plots for the boom vs. no-boom case. Why does NEC give different impedance results, and is this a true effect or an artefact of my modelling?

Edit: Here are some more details about my NEC setup;

• Auto segmentation with 20 segments/wavelength.
• Boom radius 12.5 mm, element radius 5 mm.
• (Boom segment) connects (reflector left and right) connects (boom segment) connects (driven element left and right) connects (boom segment) connects ... (directors and boom segments)
• Source is attached to the left driven element, at the connection to the right boom element and boom (see picture).
• 

When modelling a Yagi in NEC the radiation pattern is essentially identical whether a conductive boom is included or not, see pictures below. An explanation says this is a limitation of the method of moments method in NEC-2; "only currents in the axial direction on a segment are considered, and there is no allowance for variation of the current around the wire circumference".

However when I sweep VSWR over frequency I get quite different plots for the boom vs. no-boom case. Why does NEC give different impedance results, and is this a true effect or an artefact of my modelling?

Edit: Here are some more details about my NEC setup;

• Auto segmentation with 20 segments/wavelength.
• Boom radius 12.5 mm, element radius 5 mm.
• (Boom wire) connects (reflector left and right) connects (boom wire) connects (driven element left and right) connects (boom wire) connects ... (directors and boom wires)
• Source is attached to the left driven element, at the connection to the right boom element and boom (see picture).
• 

When modelling a Yagi in NEC the radiation pattern is essentially identical whether a conductive boom is included or not, see pictures below. An explanation says this is a limitation of the method of moments method in NEC-2; "only currents in the axial direction on a segment are considered, and there is no allowance for variation of the current around the wire circumference".

However when I sweep VSWR over frequency I get quite different plots for the boom vs. no-boom case. Why does NEC give different impedance results, and is this a true effect or an artefact of my modelling?

When modelling a Yagi in NEC the radiation pattern is essentially identical whether a conductive boom is included or not, see pictures below. An explanation says this is a limitation of the method of moments method in NEC-2; "only currents in the axial direction on a segment are considered, and there is no allowance for variation of the current around the wire circumference".

However when I sweep VSWR over frequency I get quite different plots for the boom vs. no-boom case. Why does NEC give different impedance results, and is this a true effect or an artefact of my modelling?

Edit: Here are some more details about my NEC setup;

• Auto segmentation with 20 segments/wavelength.
• Boom radius 12.5 mm, element radius 5 mm.
• (Boom segment) connects (reflector left and right) connects (boom segment) connects (driven element left and right) connects (boom segment) connects ... (directors and boom segments)
• Source is attached to the left driven element, at the connection to the right boom element and boom (see picture).
•