We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25--3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (<5 mm×5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure. Numerical simulations were performed to test the design conceptsbefore building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed a superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.
2. Bardati, F. and S. Iudicello, "Modeling the visibility of breast malignancy by a microwave radiometer," IEEE Transactions on Biomedical Engineering, Vol. 55, No. 1, 214-221, Jan. 2008.
3. Arunachalam, K., P. R. Stauffer, P. F. Maccarini, S. Jacobsen, and F. Sterzer, "Characterization of a digital microwave radiometry system for noninvasive thermometry using a temperaturecontrolled homogeneous test load," Physics in Medicine and Biology, Vol. 53, No. 14, 2008.
4. Arunachalam, K., P. F. Maccarini, V. D. Luca, F. Bardati, B. W. Snow, and P. R. Stauffer, "Modeling the detectability of vesicoureteral reflux using microwave radiometry," Physics in Medicine and Biology, Vol. 55, No. 18, 5417, 2010.
5. Aitken, G. J. M., "A new correlation radiometer," IEEE Transactions on Antennas and Propagation, Vol. 16, No. 2, Mar. 1968.
6. Ulaby, F., R. Moore, and A. Fung, Microwave Remote Sensing Fundamentals and Radiometry, 1 Ed., Vol. 1, Artech House, 685 Canton Street, Norwood, MA 02062, USA, 1981.
7. Jacobsen, S. and O. Klemetsen, "Improved detectability in medical microwave radio-thermometers as obtained by active antennas," IEEE Transactions on Biomedical Engineering, Vol. 55, No. 12, 2778-2785, Dec. 2008.
8. Edwards, M. and J. Sinsky, "A new criterion for linear 2-port stability using a single geometrically derived parameter," IEEE Trans. Microw. Theory Tech., Vol. 40, No. 12, 2303-2311, Dec. 1992.
9. Allan, D. W., "Should classical variance be used as a basic measure in standards metrology?," IEEE Trans. Instrum. Measurements, Vol. 36, No. 2, 646-654, 1987.
10. Land, D. V., A. P. Levick, and J. W. Hand, "The use of the allan deviation for the measurement of the noise and drift performance of microwave radioemters," Measurement Science Technology, Vol. 18, No. 7, 1917-1928, 2007.
11. Barnes, J. A., A. R. Chi, L. S. Cutler, D. J. Healey, D. B. Leeson, T. E. McGunical, J. A. Mullen, W. L. Smith, R. L. Sydnor, R. F. C. Vessot, and G. M. R. Winkler, "Characterization of frequency stability," IEEE Trans. Instrum. Measurements, Vol. 20, No. 2, 105-120, 1971.
12. Bocquet, B., J. C. van de Velde, A. Mamouni, Y. Leroy, G. Giaux, J. Delannoy, and D. Delvalee, "Microwave radiometric imaging at 3 GHz for the exploration of breast tumors," IEEE Trans. Microw. Theory Tech., Vol. 38, No. 6, 791-793, Jun. 1990.
13. Stauffer, P., F. Rossetto, M. Leencini, and G. Gentilli, "Radiation patterns of dual concentric conductor microstrip antennas for superficial hyperthermia," IEEE Transactions on Biomedical Engineering, Vol. 45, No. 5, 605-613, May 1998.
14. Maccarini, P., K. Arunachalam, T. Juang, V. De Luca, S. Rangarao, D. Neumann, C. Martins, O. Craciunescu, and P. Stauffer, "Shaping and resizing of multifed slot radiators used in conformal microwave antenna arrays for hyperthermia treatment of large superficial diseases,", 746-749, Sep. 2009.
15. Brelum, S. H., "A numerical study of planar elliptical antennas applied to ultrawideband (UWB) imaging of breast tissue,", LAP LAMBERT Academic Publishing， 2010.
16. Jacobsen, S. and P. Stauffer, "Nonparametric 1-D temperature restoration in lossy media using tikonov regularization in sparse radiometry data," IEEE Transactions on Biomedical Engineering, Vol. 50, No. 2, 178-188, Feb. 2003.