Design and Development of Thermistor based Power Meter at 140 GHz Frequency Band

Abstract

Design and development of thermistor based power meter at 140 gigahertz (GHz) frequency band have been presented. Power meter comprises power sensor, amplifier circuit and dialog based graphical user interface in visual C++ for the average power measurement. The output power level of a component or system is very critical design factor. Thus there was a need of a power meter for the development of millimeter wave components at 140 GHz frequency band. Power sensor has been designed and developed using NTC (Negative Temperature Coefficient) thermistors. The design aims at developing a direct, simple and inexpensive power meter that can be used to measure absolute power at 140 GHz frequency band. Due to absorption of 140 GHz frequencies, resistance of thermistor changes to a new value. This change in resistance of thermistor can be converted to a dc voltage change and amplified voltage change can be fed to computer through data acquisition card. Dialog based graphical user interface (GUI) has been developed in visual C++ language for average power measurement in dBm. WR6 standard rectangular waveguide is the input port for the sensor of power meter. Temperature compensation has been achieved. Moderate sensor return loss greater than 20 dB has been found over the frequency range 110 to 170 GHz. The response time of the power sensor is 10 second. Average power accuracy is better than ±0.25 dB within the power range from −10 to 10 dBm at 140 GHz frequency band.

Investigation of detection properties of planar microwave diodes based on A3B5 semiconductor compounds in millimeter–wavelength range

“…A thermistor detector (a bolometer detector type) is among the first power sensors. These power meters are used as primary standard transmission power meters for RF measurements due to satisfactory accuracy, long-term stability, and power substitution capability ("Fundamentals of RF and Microwave Power Measurements," 1977;Lindsay, 2016;Roy, Kush, & Dixit, 2011;Collier & Skinner, 2007). Still, the dynamical range of a thermistor is very limited (sometimes only -20 dBm to +10 dBm), it is easily damaged and has a slow response time, with a continuous wave CW burnout of only around +20 dBm (Lindsay, 2016;Collier & Skinner, 2007).…”