Penang wrote:

...
Specifically, my interest is in the "broadcast" type of antenna ...
trying to find a way to "extend" the range of a typical wifi
basestation using antennas alone (maybe with the help of MIMO
antennas), without "range repeaters" or whatnots.
...
Thank you all !

Much research is going on and designs/parameters advanced. These two
papers represent the direction this is taking:

http://ceta.mit.edu/pierl/pierl01/10.07111810.pdf
http://www.ece.uci.edu/~ayanoglu/MIMO_MRAA_IEEEAWPL.pdf

However, the DLM (Distributed Load Monopole) antenna by Robert Vincent
is an excellent design for such applications.

However, since size is not a major consideration in my external wifi
antennas, a conventional 1/2 or 5/8 wave end fed design is what I have
implemented, with a gamma feed ...

I use a biquad with a parabolic reflector (from a direct TV sat.
antenna) for directional antenna implementations ...

I am following the KISS method (or, Keep It Simple Stupid! -- NO insult
intended ...)

Regards,
JS