Some time ago YU1AW published some documentation about his experiments and simulations with stacked quad elements for 13cm. He optimized the stacked quad design by changing the distances of the quad elements by using parallel wires in between. He showed that these antennas show some improvements against traditionally stacked bi-quad elements were the distance is too low. He published data for 4 quad element antennas (Quados4), such with 6 quad elements and with 8 elements.
DF9IC published some results with the 8 quad element version recalculated for 23cm. This year DH1FM built two of these Quados 8 antennas for 23cm and used it successfully in contest operation.
To get a feeling of this antenna type i built the Quados4 antenna for 23cm. A big problem for me was to get it somehow mechanically stable. The accuracy of the quarter lambda transformer and the big distance between the wires at the feedpoint showed some difficulties as well. In the end the antenna seems to work and brings close to 6dB better results than my biquad antenna. But in fact it seems that the distance between the reflector and the antenna element is still too large because it improves if the end elements are bent towards the reflector.
Find some pictures below.
For the future i will try to build a 2x Quados4, means two of the elements above side by side.