I don't know how it is fed, but it may be slots in the outer conductor of a coaxial feed up the centre, or perhaps 2 coaxial feeds both fed from half-way up. If fed with one line it would squint vertically too much across the band, I think. I think that fed from halfway up, the phase change across each half, across the band, would be acceptable. I'm assuming a bandwidth of less than 100 MHz.