Its called an SLx aerial mast in the Tv section. It has two reduced 35 degree angles compared to the normal 45 degree is about £9 you could use the double bend or I cut it in half and only used one bend. Because it comes with a long straight bit you can make it any length to reach over deep cills. Simply fit say a 8" section broom handle inside it till it hits the bend and use some pvc tape near the tip to jamb it in.Then fit it onto your pole if the diameter is right. I use it on the no4 Zensorflex-just pushes on. Then fit that to any modular.
Or you could use an internal joining piece of broom hndlw say about 8" and put 4" into the aerial and 4" into the Harris pole.
Cannot put a link to the diy forum as its closed til the end of the month. But the way this forums going it will turn into the biggest diy forum anyway :
Could put a pic but its only a double bend g neck similar to Gardiners.