Provided among other things is a wearable microwave radiometer. For example, a wearable microwave radiometer apparatus for measuring relative temperature differences comprising: (a) a circumambient garment configured to fit snugly； (b) control flat, flexible radiometer antenna(s) fitted to, or configured to fit to, the garment； (c) active flat, flexible radiometer antenna(s) fitted to, or configured to fit to, the garment, which active antenna(s) are configured in the apparatus to be positioned in a spaced-apart manner relative to the control antenna(s)； and (d) a radiometer configured to monitor microwave signal from the control and active antennas and fitted to, or configured to fit to, the garment, wherein the antennas are operatively connected to, or configured to connect to, the radiometer.
