  Arrays of spin-torque nano-oscillators are promising for broadband microwave
signal detection and processing, as well as for neuromorphic computing. In many
of these applications, the oscillators should be engineered to have
equally-spaced frequencies and equal sensitivity to microwave inputs. Here we
design spin-torque nano-oscillator arrays with these rules and estimate their
optimum size for a given sensitivity, as well as the frequency range that they
cover. For this purpose, we explore analytically and numerically conditions to
obtain vortex spin-torque nano-oscillators with equally-spaced gyrotropic
oscillation frequencies and having all similar synchronization bandwidths to
input microwave signals. We show that arrays of hundreds of oscillators
covering ranges of several hundred MHz can be built taking into account
nanofabrication constraints.
