Measuring antenna parameters in a GHz transverse electromagnetic (GTEM) cell

Using a GTEM cell allows accurate far-field calibration of any antenna that can be placed in the test volume of the GTEM, from a few hertz up to approximately 26 GHz, the highest frequency that can be used to excite current GTEMs. Since the GTEM exhibits a high degree of reciprocity, passive antennas can be used to transmit as well as receive during their calibration and active antennas can be calibrated in a known field. The method of calibrating an antenna in a GTEM is to place the antenna in the center of the test volume, aligned such that the linearly polarized antenna is oriented vertically between the septum and the floor of the GTEM. The GTEM is then excited at its input port with a known RF voltage. The output voltage is measured at the connector port of the antenna. Testing has been conducted with a small log periodic antenna covering the frequency range of 300 MHz to 1.0 GHz. A spectrum analyzer with a tracking generator was used for the measurements. The test results are tabulated. As can be seen from the numerical data, good agreement is shown between antenna factors for the same antenna calibrated in the GTEM and over a ground plane in accordance with ANSI C63.5.<>