"Current adds up in phase"

what do we mean when we say "current adds up in phase"? For a wire antenna, there's already a current arises from feed source and it causes antenna to radiate, then why we emphasize 'adds up in phase'. It sounds like we use a second source to increase the radiation. Doesn't it?

current adds like a phasor

if two (or more) current sources are in phase, the currents add
sort of like constructive interference for waves

if there are two current sources 180 degrees out of phase, they add to zero
sort of like destructive interference for waves

if you have 2 equal currents 180 deg out of phase in a wire - the net current is zero - if there are in phase then the current is 2x - this is why knowing the phase relationship is important to an engineer ...!

can you tell us the answer for 90 deg out of phase ...? if not learn vector addition ...

for real power to be radiated in an antenna the volts and current must be in phase - i.e. a purely resistive load - if they are out of phase you get a voltage standing wave ( hence VSWR - R = ratio ) and less radiated power ....

search for Standing Wave Ratio and VSWR in an RF system; how can a Standing wave can load the line.

A grasp of RF matters really needs an understanding of phasors and vector based mathematics. Starting there will make this more sensible or just think of it as magic.



With RF sometimes 1+1 is 2. Sometimes 1+1 is 0. That is what makes RF so interesting.