International Journal of Antennas and Propagation

International Journal of Antennas and Propagation / 2012 / Article
Special Issue

MIMO Antenna Design and Channel Modeling

View this Special Issue

Research Article | Open Access

Volume 2012 |Article ID 180158 | 7 pages |

Design of Ultra-Wideband MIMO Antenna for Breast Tumor Detection

Academic Editor: Yuan Yao
Received21 Jul 2011
Accepted24 Aug 2011
Published14 Nov 2011


A MIMO antenna composed by microstrip line-fed circular slot antenna is proposed. This antenna is used in ultra-wideband microwave imaging systems aimed for early breast cancer detection. The antenna is designed to operate across the ultra-wideband frequency band in the air. The mutual coupling between the antenna elements has been investigated to be low enough for MIMO medical imaging applications. Both the simulation and measurement results are shown to illustrate the performances of the proposed antenna.

1. Introduction

Breast cancer is one of the most common types of cancer and a major cause of death among women. However, a high percentage of the cases can be cured if they are detected in time. An important tool for detection is the mammogram, which exploits the differences between the scattering cross-section of normal and malignant tissues to X-rays. But this technique presents important limitations [1]. Recently, an alternative approach is to use microwave imaging, which has the potential advantages of low cost, improved safety, and greater availability [2, 3]. The working principle of microwave imaging techniques is based on the dielectric contrast between the malignant tumor tissues and the healthy ones [4]. In these techniques the tumor is identified from the processing of the scattered signals collected at the antennas. Several approaches can be found in the literatures. However techniques based on ultra-wideband signals have recently woken up a great deal of interest [57]. MIMO technique is also applied to this application [8]. In [9], an electrically switched array transmits and receives an ultra-wideband signal. Measurements are time aligned to estimate the return in a particular volumetric pixel. In [10], ultra-wideband MIMO concepts applied to tumor detection are explicitly addressed.

In this paper a novel ultra-wideband MIMO antenna is designed with this goal in mind. It can provide ultra-wideband characteristic, covering 2.3 GHz–12.2 GHz. This ultra-wideband characteristic is obtained by loading a rectangular patch to circular slot antenna. Two elements of such antennas are used for MIMO applications. The proposed structure obtains low mutual coupling and envelope correlation due to the orthogonal polarization.

2. Antenna Structure and Mechanism

As we know, wide slot antennas have received more attention due to their ultra-wideband characteristic. They are very popular for volume-limited and wideband applications. The structure of the proposed UWB MIMO antenna is shown in Figure 1. This antenna is printed on a FR-4 substrate with relative permittivity 4.4 and thickness of 1 mm. The two identical antenna elements have the same structure and dimensions. The antenna has two layers, the top layer and the bottom layer. On the bottom layer there are the grounds with length and width . There are the circular slots in the bottom ground with radius . And in the circular slots there are the rectangular patches with length of and width . On the top layer is the microstrip line with circular patch. The fed line with width to match 50  and the radius of the circular patch is . The two identical antenna elements are connected with no spacing between them. The detailed antenna dimensions are listed in Table 1.

Dimension W line

Size (mm)70351061652

According to Babinet’s theory, the slot antenna can be solved through analyzing its complementary antenna. So the circular slot in this paper can be seen as equivalent to a disk monopole antenna which is already studied [11, 12]. The circular slot antenna has wideband characteristic covering from 6 to 10 GHz. And the rectangular patch in the slot greatly impacts the impedance bandwidth characteristics of the antenna. Figure 2 shows the current distributions on the circular slot antenna with rectangular patch at 4 GHz. It can be seen that the rectangular patch resonates at 4 GHz and widens the frequency band. Figure 3 shows the return loss of the antenna with and without rectangular patch. Thus the proposed antenna has ultra-wideband characteristic.

Compared with the traditional antenna parameters, such as gain, radiation pattern, and reflection coefficients, new parameters and aspects have to be included in the design for MIMO systems. Mutual coupling between antenna elements is a key factor to achieve high antenna performance in the MIMO antenna configuration. For a low mutual coupling, antennas must be far away from each other. But the space for the internal antenna is not enough to obtain low correlation and mutual coupling. In this paper we present a structure for the MIMO antenna elements, in which the identical two antenna elements are orthogonally placed. Then the two antenna elements have orthogonal polarization which can reduce the mutual coupling between the two antennas. Figure 4 shows the simulated 3D radiation patterns of the two antenna elements. It can be seen that the two antenna elements have orthogonal polarizations.

3. Simulation and Measurement Results

Both the simulation and measurement are carried out to verify the above analysis. The proposed structure is simulated in HFSS and measured in an anechoic chamber. The fabricated proposed UWB MIMO antenna is shown in Figure 5. The detailed dimensions can be found in Table 1. Figure 6 shows the simulated and measured return loss, which agree well. The measured −10 dB return loss bandwidths are from 2.3 GHz to 12.2 GHz, which covers an ultra-wideband. The mutual coupling between the two ports is less than −15 dB across the common bandwidth, as shown in Figure 7.

Figures 8 and 9 show the radiation patterns of the antenna 1 and the antenna 2 at 3 GHz, 6 GHz, and 8 GHz at E-plane and H-plane, respectively. The antenna 1 has bidirectional vertically polarized patterns, and the antenna 2 generates horizontally polarized radiations. Thus the proposed antenna is more attractive for ultra-wideband MIMO application for breast tumor detection.

4. Parameter Study

For the purpose of optimized performance, parametric studies of the dimensions of the antenna structure are carried out. First, we analyze the length of the rectangular patch in the slot. As shown in Figure 10, when the length equals 8 mm, the lower frequency band is bad. And when the length is 10 mm, the impedance matching is good over the whole band. When the length is 12 mm, even though its lower frequency band is better than 10 mm, the middle frequency band is worse. Thus the 10 mm is the best length.

Second, we analyze the radius of the microstrip circular patch. The radius varied from 4 mm, 5 mm, to 6 mm while other parameters are fixed. As shown in Figure 11, when the radius is 4 mm, the return loss at 5 GHz-6 GHz and 9 GHz–11 GHz is bad. When the radius is 5 mm, the impedance matching is good. When the radius equals 6 mm, the return loss gets worse. Thus, the radius is 5 mm in the proposed antenna.

The isolation between two polarizations will be affected by the dimension of spacing. In principle, the larger of the spacing, the lower of the mutual coupling will be obtained. In this paper the spacing of the two antenna elements is zero which means that the grounds of the two antenna elements are connected without any gap and the mutual coupling is lower than −15 dB over the entire band so there is no need to increase the gap between the two antenna elements.

5. Conclusion

In this paper a design of ultra-wideband MIMO antenna for breast tumor detection has been proposed and implemented. Simulated and measured results showed that the antenna can cover from 2.3 GHz to 12.2 GHz and has high isolation. The proposed antenna will provide better performance to detect breast tumor.


  1. M. Klemm, I. J. Craddock, J. A. Leendertz, A. Preece, and R. Benjamin, “Radar-based breast cancer detection using a hemispherical antenna array - Experimental results,” IEEE Transactions on Antennas and Propagation, vol. 57, no. 6, pp. 1692–1704, 2009. View at: Publisher Site | Google Scholar
  2. A. Lazaro, R. Villarino, and D. Girbau, “Design of tapered slot Vivaldi antenna for UWB breast cancer detection,” Microwave and Optical Technology Letters, vol. 53, no. 3, pp. 639–643, 2011. View at: Publisher Site | Google Scholar
  3. Y. Xie, B. Guo, J. Li, and P. Stoica, “Novel multistatic adaptive microwave imaging methods for early breast cancer detection,” Eurasip Journal on Applied Signal Processing, vol. 2006, Article ID 91961, 13 pages, 2006. View at: Publisher Site | Google Scholar
  4. M. Lazebnik, D. Popovic, L. McCartney et al., “A large-scale study of the ultrawideband microwave dielectric properties of normal, benign and malignant breast tissues obtained from cancer surgeries,” Physics in Medicine and Biology, vol. 52, no. 20, pp. 6093–6115, 2007. View at: Publisher Site | Google Scholar
  5. Y. Chen, E. Gunawan, K. S. Low, S. C. Wang, Y. Kim, and C. B. Soh, “Pulse design for time reversal method as applied to ultrawideband microwave breast cancer detection: a two-dimensional analysis,” IEEE Transactions on Antennas and Propagation, vol. 55, no. 1, pp. 194–204, 2007. View at: Publisher Site | Google Scholar
  6. S. K. Davis, B. D. Van Veen, S. C. Hagness, and F. Kelcz, “Breast tumor characterization based on ultrawideband microwave backscatter,” IEEE Transactions on Biomedical Engineering, vol. 55, no. 1, pp. 237–246, 2008. View at: Publisher Site | Google Scholar
  7. I. Hilger, C. Geyer, G. Rimkus et al., “Could we use UWB sensing for breast cancer detection?” in Proceedings of the 4th European Conference on Antennas and Propagation (EuCAP '10), pp. 1–4, April 2010. View at: Google Scholar
  8. O. T. Z. Daniel, Z. Yuanjin, and L. Zhiping, “Design and experimental investigation of UWB microwave imaging via MIMO beamforming,” in Proceedings of the IEEE International Conference on Ultra-Wideband (ICUWB '10), pp. 851–854, September 2010. View at: Publisher Site | Google Scholar
  9. S. K. Davis, H. Tandradinata, S. C. Hagness, and B. D. Van Veen, “Ultrawideband microwave breast cancer detection: a detection-theoretic approach using the generalized likelihood ratio test,” IEEE Transactions on Biomedical Engineering, vol. 52, no. 7, pp. 1237–1250, 2005. View at: Publisher Site | Google Scholar
  10. D. W. Bliss and K. W. Forsythe, “MIMO radar medical imaging: self-interference mitigation for breast tumor detection,” in Proceedings of the 40th Asilomar Conference on Signals, Systems, and Computers (ACSSC '06), pp. 1558–1562, November 2006. View at: Publisher Site | Google Scholar
  11. J. Powell and A. Chandrakasan, “Spiral slot patch antenna and circular disc monopole antenna for 3.1–10.6 GHz,” IEEE Transactions on Antennas and Propagation, vol. 46, no. 2, pp. 44–49, 1998. View at: Google Scholar
  12. Z. H. Song, J. R. Qi, J. H. Qiu, and T. X. Zhou, “Study of properties of the circular monopole ultra-wideband antenna,” Journal of Harbin Engineering University, vol. 28, no. 1, pp. 26–30, 2007. View at: Google Scholar

Copyright © 2012 Liting Wang and Bin Huang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

More related articles

2739 Views | 1540 Downloads | 9 Citations
 PDF  Download Citation  Citation
 Download other formatsMore
 Order printed copiesOrder

Related articles

We are committed to sharing findings related to COVID-19 as quickly and safely as possible. Any author submitting a COVID-19 paper should notify us at to ensure their research is fast-tracked and made available on a preprint server as soon as possible. We will be providing unlimited waivers of publication charges for accepted articles related to COVID-19. Sign up here as a reviewer to help fast-track new submissions.