such rectennae are basically Rf diodes and when you operate them in a simple manner in series you are likely to chance the working point via the current from the other elements.And keep in mind that microwave diodes dont work like normal diodes for AC voltages of say 30 Volt but essentially via the second derivative of their V/I characteristic..since the Rf voltage to be rectified is often below say 0.3 Volt peak.

I agree with Mr Fritz caspers .