7/28/2019 ASA07 Paper 048 Final

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10th Australian Symposium on Antennas, Sydney, Australia, 14-15 Feb. 2007

UWB REFLECTOMETER FOR MICROWAVE BREAST CANCER DETECTIONNorhudah Seman and Marek E. Bialkowski

School of Information Technology and Electrical Engineering,

The University of Queensland, St Lucia, Queensland 4072, Australia

The design of a compact reflectometer operating in the 3-10GHz band for the purpose of breast

cancer detection is presented. The device measures a reflection coefficient in the frequency domain and the

time/space domain results are obtained using Inverse Fast Fourier Transform (IFFT).

Fig. 1 shows the reflectometer formed by quadrature hybrids (Q) and two-way power dividers (D).

DUT represents an antenna in a cancer detection system. In order to obtain a compact device, a 3dB

microstrip-slot coupler is selected as Q hybrid and a two-stage Wilkinson power divider is used as D hybrid.

The Q hybrid uses 3 conductor layers with 2 substrates between each layer. Upper and lower layer consist of

elliptical microstrip patches with Port 1-2 and Port 3-4, respectively. The patches are coupled by an elliptical

slot in the common ground plane.

Fig. 1. Configuration of a reflectometer.

Corn4

Corn3

TL15

Tee1 Curve1TL9

TL13

Curve2

TL10

TL14

TL16

TL17

Curve3

Curve4

Tee4

Tee5

Corn1Tee2

Tee3

Corn2

Bottomlayer

Mid layer

Top layer

Port 1

Port 3 Port 2

Port 4

(a) (b)

Fig. 2. Configurations of (a) Wilkinson power divider and (b) 3dB

slot-coupled microstrip coupler.

113 4 5 6 7 8 9 10

0

0.1

0.2

0.3

0.4

0.5

0.6

0.70.8

0.9

1

Frequency, GHz

ReflectionCoefficient(magnitude)

5 ohm

100 ohm

40 ohm

45 ohm

with 3 transmission line

without transmission line

Fig.3. Reflection coefficient responses of reflectometer for 4 loads.

0 0.5 1 1.5 2

x 10-9

0

0.1

0.2

0.3

0.4

0.5

Time (second)

Magnitude

5ohm

40ohm

45ohm

100ohm

Fig.4. IFFT results of the measured reflection coefficient.

By assuming square-law detectors at Ports 3-7 and ideal performance of Q and D hybrids, the

reflection coefficient can be obtained using simple formulas involving the detectors output voltages. To

assess the reflectometers performance via simulations, the following Eq. (1) employing S-parameters is used

followed by the calibration procedure using open, short and match load standards:

2

31

2

51

2

41

2

31

2

71

2

61

21

S

SSj

S

SSj

b

a +

=+== (1)

Fig. 3 shows results obtained with the calibrated system for the loads formed by a 50 ohm

transmission line of length 3 (at 6.5GHz) terminated at 5, 40, 45 and 100 ohm. The results are generated

using ADS and MATLAB based on Eq. (1) and the 3-standards calibration. Ideal magnitudes of reflection

coefficient of 0.819, 0.111, 0.053 and 0.333 are well approximated in the case of small reflections. IFFTresults shown in Fig. 4 well indicate the location of the termination.