Millimeter-wave power detectors

Kamble, Harshwardhan Baban ORCID: 0000-0002-7000-4897 (2024). Millimeter-wave power detectors. University of Birmingham. Ph.D.

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Abstract

The power measurement traceability above 100 GHz has been challenging due to the unavailability of commercial power transfer standards above 100 GHz. As the frequency increases, the sensor mounting becomes difficult in the increasingly small waveguides, posing fabrication challenges and losses. The commercial transfer standards based on thermistor mount were only operating up to W-band (75-110 GHz), and production has stopped. The emerging applications above the W-band demand the establishment of new power metrology capabilities. This thesis aims to develop new power detectors to meet this urgent demand.
This thesis primarily focuses on the bolometric power detector as a transfer standard in the D-band (110-170 GHz). The bolometric detector consists of a thin film sensor element in the E-plane of the waveguide. The element is designed to be a dual-line thin film on a quartz substrate and has proven to improve the bandwidth. The equivalent circuit analysis is presented on single and dual-line structures inside the waveguide. The power detector body is designed in plastic PEEK (polyether ether ketone). It is enclosed in dual shielding layers; the inner is PEEK, and the outer is aluminium. All these measures have helped achieve a power detector with a competitive response time of fewer than 2.6 seconds (a limitation of the external measurement system/facility). The device can operate at ambient temperature, benefiting from additional dummy sensors within the inner shielding. It has shown a very good short-term time response with only ∼0.19% deviation in a given time interval, which is very close to a commercial PM5 sensor with ∼0.27% deviation. The long-term time response is also impressive, with a deviation of less than 0.6%, similar to a commercial PM5 sensor. The fast response time, good thermal isolation, and ambient compensation ability make it suitable for transfer/working standards, which can be used in ambient temperature environments.
This thesis also demonstrated a Schottky diode power detector. Schottky diodes are most suitable for applications such as imaging, communication and particle accelerators where fast response time (in picoseconds or ps) is vital over absolute power measurement. The device has been successfully designed, fabricated and tested. This is a square law power detector, where the output voltage is proportional to the square of the input voltage. The detector split blocks are fabricated in aluminium and plated with gold. The measurement shows an average responsivity of 5000 V/W over the D-band, and the minimum is 1900 V/W at 160 GHz for -20 dBm input power.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):