Adding some words of my own to Mike words. First of all I appreciate A75GR 's efforts to simulate the feed. However, we do not live in a simulated world. This implies compromises. Like Mike said, during Christmas last year we had to take some decisions concerning 'what is good enough'? The result is a feed which performs well enough, even better than (most criticists) expected (!)
One simulates 3 dB AR, somebody else simulates 0.1 dB AR ...
Concerning the double dip, this was simulated and also measured in practice.
The trick is to get Z=1 (50 + j0) in the centre of the 'balloon' and that took some (trail and error) efforts to find the right feedpoint (several attempts/prototypes have been constructed).
Not preaching to my own parish, the result is an ultra simple solution to dual feed a single dish with relative good efficiency, easy to construct with simple metal working tools.
Two sheets of brass, a piece of copper pipe (with some nylon) compared to a solid piece of aluminum with four ports, (phase) couplers etc ...
So, I also challenge people to come with a better solution given the simplicity and ease of the design: two plates, a piece of copper pipe (and maybe some nylon (or other dielectric)).