A method to perform spectrum analysis on low power signals having frequency between 0.1 and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of the driving DC current. It is shown that the ATJ output voltage is strongly dependent on the thickness of the dielectric tunneling barrier. Spectrum analysis can be performed using an ATJ, whose frequency is linearly swept with time, and a low-pass filter, and a matched filter are used for signal processing. It is also found by simulation and analytical calculations that for an ATJ with a 0.1 μm² footprint, the spectrum analysis can be performed over a 0.25 THz bandwidth in just 25 ns on signals that are just above the Johnson–Nyquist thermal noise floor. This work has been published in Journal of Applied Physics and can be accessed here.