Correlation of Binary-Code-Modulated Microwave Signals by Parametric Pumping of Spin Waves

An analog microwave signal correlator, based on parametric pumping of a spin wave by a radio frequency (RF) magnetic field, is demonstrated. The binary codes to be correlated modulate the two microwave signals input to the device to, respectively, excite the spin wave and RF field at twice the carrier frequency of the spin wave. The magnetic field parametrically pumps the spin wave, generating a counterpropagating idler spin wave, the modulation of which is the cross-correlation of the binary codes. In the experimental device implemented, correlation of codes up to 16 chips in length at a spin-wave carrier frequency of 1.2 GHz is demonstrated. The code length is limited by the time available for the parametric interaction as well as the signal bandwidth of the device. Process gain, which quantifies the performance of the correlator in recognizing a given code and rejecting interfering codes, is determined for shorter codes and found to be close to the theoretical maximum for each length. The correlator efficiency, with a bilinearity coefficient of -79 dBm, is poor. However, there remains a significant scope for optimization of the experimental device so that correlation of longer codes with improved efficiency will be possible.