Isothermal port for microwave network analyzer and method

The present invention relates to an isothermal port and method for a microwave network analyzer. The present invention provides an isothermal port and method for a microwave network analyzer and more particularly an isothermal port and method to control the temperature of microwave standards to 23″ 0.050° C. A test port adapter is used to adapt the test port connector to a DUT (device under test, which might be a standard connector). A thermoelectric cooler surrounds the test port adapter in order to precisely control its temperature. By controlling the temperature of the adapter, the temperature of the DUT is controlled since there is good heat conduction between the DUT and the test port adapter. The standards quickly attain the temperature of the test port adapter (less than 2 minutes, 1 minute typical). The system includes a computer, one or more thermoelectric coolers, a heatsink, a split thermal mass that has a through hole for the test port adapter, a power supply, a PRTD (Platinum Resistance Thermal Detector), and an ohmmeter capable of measuring using 4 wire Ohms. The resistance of the PRTD is sensed by the ohmmeter, and a PID (Proportional Integral Derivative) algorithm calculates the correct supply current for the current time interval. The desired power supply current is signaled to the power supply, which sends the current to the thermoelectric coolers. The coolers can remove heat from the test port adapter which tends to lower its temperature. In one embodiment, the control process is repeated every five seconds, and a graph is generated showing the history of the temperature versus time on a computer screen.