I had an idea for a wideband antenna design that I think is new, or at least I haven't encountered it in my travels on Google and other sources researching antenna theory.
The basic idea is to take a folded 1/4-wave ground plane antenna whose overall length is set to be resonant at the lowest frequency you're trying to receive, and starting a short distance above the feedpoint, periodically shunt the parallel vertical conductors with capacitors, starting with small value capacitors and small intervals, and gradually increasing the capacitor values and the intervals at which they are spaced.
So if you wanted to operate 100-800MHz, the overall length of the verticals would be selected to resonate at 100MHz. But to allow the antenna to perform at 800MHz, the first shunt capacitor would be placed approximately 1/8 of the way up the verticals, and its value chosen so that a 800MHz signal goes primarily up one vertical from the feedpoint, through the capacitor, and down the other vertical to ground. Other frequencies between 100 and 800MHz would be tuned by proportionately larger shunt capacitors placed proportionately farther up the antenna verticals. The idea is to make a more elegant fan dipole (or rather the top half of one) that can be designed to be resonant at more frequencies without having a Christmas tree of vertical elements interacting with each other.
I'm trying to model the concept, but I don't see in 4NEC how to model the shunt capacitors as part of the active antenna structure.
The basic idea is to take a folded 1/4-wave ground plane antenna whose overall length is set to be resonant at the lowest frequency you're trying to receive, and starting a short distance above the feedpoint, periodically shunt the parallel vertical conductors with capacitors, starting with small value capacitors and small intervals, and gradually increasing the capacitor values and the intervals at which they are spaced.
So if you wanted to operate 100-800MHz, the overall length of the verticals would be selected to resonate at 100MHz. But to allow the antenna to perform at 800MHz, the first shunt capacitor would be placed approximately 1/8 of the way up the verticals, and its value chosen so that a 800MHz signal goes primarily up one vertical from the feedpoint, through the capacitor, and down the other vertical to ground. Other frequencies between 100 and 800MHz would be tuned by proportionately larger shunt capacitors placed proportionately farther up the antenna verticals. The idea is to make a more elegant fan dipole (or rather the top half of one) that can be designed to be resonant at more frequencies without having a Christmas tree of vertical elements interacting with each other.
I'm trying to model the concept, but I don't see in 4NEC how to model the shunt capacitors as part of the active antenna structure.