Ham Radio Forum

Hello friends,
I am building a 10 element Yagi for 916 MHz with folded dipole.

I want to know how does element diameter affect the overall antenna performance..at present i am using hollow aluminium tubes with 9mm diameter.

Also i would like to know what difference will it make if i use hollow conductors for elements or solid conductors.

I also want to know the effect of the radius of the folded curve in an folded element. What will happen if radius is large and the distance between the two parallel parts of the folded dipole is comparable to that of a half-wavelength

Thanks

trupti

Increasing folded dipole element diameter has the following effects:

1) Antenna bandwidth increases (the VSWR changes less with frequency changes). However, the bandwidth of a folded dipole already is significantly wider than the bandwidth of an unfolded dipole, so the percentage of bandwidth increase is less than the percentage increase would be if an unfolded dipole diameter was increased the same amount.

2) Yagi antenna forward gain at resonance decreases slightly. The amount of gain reduction depends on the number of parasitic elements and whether their diameters also are increased. With no parasitic elements the gain reduction is minuscule. The gain reduction is greater with an increasing number of elements and if their diameters are also increased.

There is no difference in antenna RF performance between solid and tubular antenna elements at such a high frequency, because nearly all the RF current flows very near the surfaces of the conductors.

The radius of the bends at the ends of a folded dipole has very little effect on antenna performance with the relatively narrow spacings normally used between folded dipole elements. However, if the spacing between dipole elements is an appreciable fraction of a wavelength a radiator will have the characteristics of a loop antenna, rather than a dipole. Loop antenna characteristics cannot be summarized simply without specifying all the dimensions.

Thanks a lot for the reply.

I have kept the spacing between the folded dipole elements at 6.5cm while the wavelength is around 33cm and length of folded dipole is 15cm, while diameter of the element is around 9mm. Will this act as a folded dipole or loop antenna?

Thanks

trupti