Abstract
An increasing number of operational microwave imaging systems have been presented
in recent years, especially for medical imaging. This has increased the focus
on the practical aspects of microwave imaging, such as the need for calibration, how
to decrease measurement time, and how to minimize the effect of noise.
At the Technical University of Denmark, a 32-channel microwave imaging system for
breast cancer screening has been under development for some time. In this system,
each antenna is equipped with its own transceiver module, containing amplifiers,
switches, and a mixer. This design ensures that the low-amplitude RF signals,
available at the terminals of the antennas, only need to travel a very short distance
to get to the low-noise amplifier, while the RF as well as the IF signals running to
and from the transceiver modules all have significant amplitudes.
However, some leakage between the transmission and receiving channels inside of
the transceiver modules has been detected. This is most likely caused by the lessthan-
perfect isolation of the switches in the modules as well as leakage through the
PCB itself. Since the presence of such a leakage signal in the measurements seriously
influence the imaging capability of the system, it is of interest to remove it.
In this work, a calibration procedure capable of removing a constant offset, i.e., the
leakage, from the measured signals is presented. The calibration procedure is based
on a comparison between the relative change observed between a measurement with
an empty imaging system and a measurement with a simple known object in the
system, i.e., a metal cylinder, and the relative change observed between simulations
of the same two situations. Assuming that the simulation software is capable of
accurately modeling the imaging system, some relatively simple considerations on
the difference between the measured and simulated results lead to an expression for
the offset. Once the offset is known, this can be subtracted from the measurement
of the unknown object to be investigated (the breast).
The main advantage of the calibration procedure presented here is that the time
needed for doing the calibration is very low compared to a more rigorous and classic
type of calibration in which measurements should be made for all combinations
of transmitters and receivers with and without the antennas connected to the
transceiver modules to allow for determining the leakage signal. Apart from being a
time consuming task, the bending of the cables caused by removing the transceiver
modules from the antennas would change the phase of the measured signal, thereby
introducing a source of error in the calibration procedure. In the procedure presented
here, one can simply remove the object to be imaged (the breast) after the
measurement is complete, insert the known scatterer, and do a single standard measurement,
thereby allowing for running the calibration after each measurement.
| Original language | English |
|---|---|
| Title of host publication | Proceedings of the IEEE AP-S International Symposium on Antennas and Propagation |
| Number of pages | 1 |
| Publication date | 2010 |
| ISBN (Print) | 978-1-4244-4968-2 |
| Publication status | Published - 2010 |
| Event | 2010 IEEE Antennas and Propagation Society International Symposium - Toronto, Canada Duration: 11 Jul 2010 → 17 Jul 2010 https://ieeexplore.ieee.org/xpl/conhome/5548930/proceeding |
Conference
| Conference | 2010 IEEE Antennas and Propagation Society International Symposium |
|---|---|
| Country/Territory | Canada |
| City | Toronto |
| Period | 11/07/2010 → 17/07/2010 |
| Internet address |
