Conventional breast cancer detection techniques including X-ray mammography, magnetic resonance imaging, and ultrasound scanning suffer from shortcomings such as excessive cost, harmful radiation, and inconveniences to the patients. These challenges motivated researchers to investigate alternative methods including the use of microwaves. This article focuses on reviewing the background of microwave techniques for breast tumour detection. In particular, this study reviews the recent advancements in active microwave imaging, namely microwave tomography and radar-based techniques. The main objective of this paper is to provide researchers and physicians with an overview of the principles, techniques, and fundamental challenges associated with microwave imaging for breast cancer detection. Furthermore, this study aims to shed light on the fact that until today, there are very few commercially available and cost-effective microwave-based systems for breast cancer imaging or detection. This conclusion is not intended to imply the inefficacy of microwaves for breast cancer detection, but rather to encourage a healthy debate on why a commercially available system has yet to be made available despite almost 30 years of intensive research.

A novel wideband and high-gain millimeter-wave antenna is presented. The wide 3 dB gain bandwidth is achieved by using Fabry-Perot cavity (FPC) and printed ridge-gap waveguide technologies. The FPC is formed by placing a dual-layer partially reflective surface (PRS) above a slot antenna operating at 60 GHz and fed by a printed ridge-gap waveguide for surface-wave suppression. The PRS is based on a 2-D printed unit cell, the unit cell composed of two different frequency-selective surfaces (FSS) provides a positive phase gradient over the desired frequency range. The impedance bandwidth of the proposed antenna is 18.4%, from 55.4 to 66.6 GHz. Moreover, the 3 dB gain bandwidth is 12.5%, from 58.6 to 66.4 GHz. A maximum gain of 16.8 dB is achieved; this is about 12.2 dB over the gain of the slot antenna only. Consistent radiation patterns are achieved over the operating bandwidth. Experimental and numerical results are presented to justify the improved antenna performance. This communication, to the best of our knowledge, is the first one to utilize a dual-layer printed FSS-based superstrate at 60 GHz to enhance the radiation characteristics of a printed ridge-gap waveguide-fed slot antenna.

This letter presents a novel engineered magnetic superstrate designed to enhance the gain and efficiency of a microstrip patch antenna without any substantial increase in the profile of the whole structure (the antenna with the superstrate). The modified split ring resonator (MSRR) inclusions are used in the design of the engineered magnetic superstrate. Numerical full-wave simulations as well as analytical models are used to analyze the entire radiating system. Considering as an example a microstrip antenna operating within the UMTS band, the broadside gain of the antenna was improved by 3.4 dB and the efficiency was improved by 17% when using the engineered superstrate. The total height of the proposed structure, antenna with superstrate, is lambda₀/7, where lambda₀ is the free-space wavelength at the resonance frequency of the antenna.

This work presents a new technique to reduce the correlation coefficient value between adjacent antenna elements in multiple-input-multiple-output (MIMO) configurations. Unlike the conventional works which utilize port isolation enhancement methods for this purpose, the proposed approach adopts decorrelation of the radiation patterns of individual elements. To achieve this, a phase-gradient frequency selective surface (FSS) is used as a superstrate above the antenna elements in a low profile Fabry- Perot (FP) cavity configuration. The effectiveness of the method is demonstrated by designing the system for a two-element MIMO antenna at 5.25 GHz. The proposed technique results in more than 95% reduction in the correlation coefficient value, thus projecting better MIMO performance.

This paper proposes a simple novel technique for self-isolating a MIMO antenna for mm-wave applications. MIMO antenna elements with inter-element separation of 0.2 mm (0.023λ at 35 GHz) and measured high isolation (> 50 dB) are presented. By observing the concentration of surface waves on the radiating patch, several rigorously optimized slots of different shapes, positions, and dimensions are etched on the patch to enhance the inter-element isolation and increase the bandwidth within 28-37.5 GHz. The circuit models of the reference and proposed antennas have been presented. The coupling is measured by the level of the differences in the output voltage in both antennas. The novel mm-wave antenna exhibits high impedance bandwidth (> 29%), high isolation (> 50 dB), high efficiency (> 90%), and low envelope correlation coefficient (<0.005). Two configurations of MIMO antenna (i.e, 1×2 and 1×4) are fabricated and measured to validate the simulation outcomes. The single reference antenna has dimensions of 10x12 mm2 while the 1x2 array has dimensions of 19x12 mm2. The presented design is the first to exhibit such wideband isolation improvement without any external decoupling structure at the mm-wave frequency range, to the best of the authors’ knowledge.

A new wideband and enhanced gain Fabry-Perot cavity antenna is presented in this paper. The Fabry-Perot cavity is established between a single-layer metamaterial-based partially reflective surface (PRS) and a simple feeding slot antenna. The unit cell of the PRS consists of printed and etched square rings on both sides of the superstrate. A 6x6 array of the unit cells are optimized to produce a positive reflection phase gradient required for the gain enhancement. Simulated results of the designed Ku-band antenna demonstrate an impedance bandwidth of 13.1-15.3 GHz (15.5 %) with a gain enhancement up to 8.2 dB (i.e., 150% gain increase above the feeding antenna) and a 3-dB radiation bandwidth of 18.7%. Experimentally observed reflection and radiation responses of the fabricated prototype validate the simulated results.