There are currently two detectors focused on the higher end of the gravitational wave spectrum (10 to 10 Hz): one at University of Birmingham, England, and the other at INFN Genoa, Italy. A third is under development at Chongqing University, China. The Birmingham detector measures changes in the polarization state of a microwave beam circulating in a closed loop about one meter across. Both detectors are expected to be sensitive to periodic spacetime strains of h ~ 2 × 10 / √ Hz, given as an amplitude spectral density. The INFN Genoa detector is a resonant antenna consisting of two coupled spherical superconducting harmonic oscillators a few centimeters in diameter. The oscillators are designed to have (when uncoupled) almost equal resonant frequencies. The system is currently expected to have a sensitivity to periodic spacetime strains of h ~ 2 × 10 / √ Hz, with an expectation to reach a sensitivity of h ~ 2 × 10 / √ Hz. The Chongqing University detector is planned to detect relic high-frequency gravitational waves with the predicted typical parameters ≈10 Hz (100 GHz) and h ≈10 to 10.