Measurement of Microwave Signal Frequency by a Pair of Spin-Torque Microwave Diodes

A single resonance-type spin-torque microwave diode (STMD) can be used as a quadratic detector to determine the frequency f of an external microwave signal when the power P _rf of this signal is known. However, unless the signal's frequency f exactly coincides with the detector's resonance frequency f _res , there exists a finite frequency determination error Δf. In this letter, we show theoretically and experimentally that if a pair of independent STMDs with different resonance frequencies connected in parallel is used for the signal frequency determination, knowledge of the signal power is not necessary, and the frequency determination error can be substantially reduced to Δf ≈ 30 MHz at the frequency of f ≈ 5.0 GHz.