Easiest way to generate quadrature signal on PCB
Fast flip flops make light work of 0 to 90

Since the target system can accept a non-sine-wave signal, the solution to this problem is actually rather simple -- generate a 3.4 to 5GHz differential clock signal (by hook or by crook, I don't care how you get it), and then use 2 DFFs in the classical quadrature generator configuration, as depicted below (image from this article):



Considering that fast flip flops, such as the 10GHz NB7V52M have differential I/Os, we can elide the inverter (it becomes a differential transposition), yielding the resulting circuit (termination components not shown for clarity's sake):







simulate this circuit &ndash; Schematic created using CircuitLab

Parts cost is a non-issue -- I seriously doubt you can get a 5GHz generator for less than the cost of the two flip-flop ICs in the solution.