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This article presents the experimental proof of concept of high–frequency microwave breast imaging system operating from 16 to 20 GHz. At those frequencies the wavelengths are in the order of millimeter range which support better resolution in localizing cancerous tumors compared to the conventional microwave imaging systems. A new antenna is developed with a compact size of 7 $\times $ 7 mm 2, which relies on an ultra-wideband, planar bowtie-like antenna structure. Practical results show that a bandwidth of 23.45 GHz is achieved (16 – 40 GHz) for a reflection loss higher than 10 dB. Furthermore, artificial breast tissue models based on glycerol–oil mixture with agar powder are developed. Dielectric properties of the tissue are stable over a wide frequency range up to 20 GHz at room temperature. The typical high microwave power losses within biological tissue at the operating frequency range are addressed by contacting the antennas directly to the tissue and slightly compressing the phantom without any coupling medium. Hence, the compressed breast geometry has a flat surface with well–defined boundaries, which simplifies tumor localization algorithms. For the purpose of demonstrating the current stage of research, a one–dimensional scanning system is used to localize the tumor’s positions inside the simulated, heterogeneous breast model of 36 mm thickness. Using the root mean square deviation algorithm, we can accurately detect positions of the tumors, which have a cross-sectional area down to 4 $\times $ 4 mm 2. The preliminary results show the feasibility of achieving a high resolution with a compact microwave system for early-stage breast cancer detection.

High accuracy and low noise measurement of the phase of a microwave signal requires that spurious contributions are adequately dealt with. In this paper we investigate the power-to-phase coupling in two commercial high bandwidth P-I-N, near-IR photodetectors. We observe that a sudden change of the optical power induces a transient of the phase of the 20 GHz signal, at different time scales. The temperature rise of the photodetector junction is likely to be involved in this dynamical behaviour. The value of the bias voltage applied to the photodetector appears to control the size of the phase transients, as well as the optical power for which the slope of the amplitude-to-phase coupling cancels. The most efficient way to reduce amplitude to phase couplings consists in implementing optical demodulation, instead of electrical demodulation, of the microwave signal. [ABSTRACT FROM PUBLISHER]

Nanocrystalline CoFeAIO thin films have been fabricated for the application of ultrahigh frequency devices. A Co69.9Fe20.5Al4.4O5.2 thin film is observed to exhibit good magnetic properties: magnetic coercivity (He) of 0.8 Oe; anisotropy field (Hk) of 23.9 Oe; saturation magnetization (4πM8) of 18.1 kG, and electrical resistivity (ρ) of 560.67 μΩcm. The frequency response of permeability of these films is excellent. The effective permeability (μeff) of 1024 is stable up to 1 GHz. [ABSTRACT FROM AUTHOR]

It is shown that the results presented in the above letter, and attributed by the authors to amplitude-to-phase conversion in the photodetector, do not originate in the photodetector under test, due to the power dependence observed. More recent results show that conversion effects with the same size and frequency dependence are observed in passively mode-locked nonlinear polarization rotation mode-locked lasers. [ABSTRACT FROM PUBLISHER]