Globally, breast cancer is a major reason for female mortality. Due to the limitations of current clinical imaging, the researchers are encouraged to explore alternative and complementary tools to available techniques to detect the breast tumor in an earlier stage. This article outlines a new, portable, and low-cost microwave imaging (MWI) system using an iterative enhancing technique for breast imaging. A compact side slotted tapered slot antenna is designed for microwave imaging. The radiating fins of tapered slot antenna are modified by etching nine rectangular side slots. The irregular slots on the radiating fins enhance the electrical length as well as produce strong directive radiation due to the suppression of induced surface currents that radiate vertically at the outer edges of the radiating arms with end-fire direction. It has remarkable effects on efficiency and gain. With the addition of slots, the side-lobe levels are reduced, the gain of the main-lobe is increased and corrects the squint effects simultaneously, thus improving the characteristics of the radiation. For experimental validation, a heterogeneous breast phantom was developed that contains dielectric properties identical to real breast tissues with the inclusion of tumors. An alternative PC controlled and microcontroller-based mechanical MWI system is designed and developed to collect the antenna scattering signal. The radiated backscattered signals from the targeted area of the human body are analyzed to reveal the changes in dielectric properties in tissues. The dielectric constants of tumorous cells are higher than that of normal tissues due to their higher water content. The remarkable deviation of the scattered field is processed by using newly proposed Iteratively Corrected Delay and Sum (IC-DAS) algorithm and the reconstruction of the image of the phantom interior is done. The developed UWB (Ultra-Wideband) antenna based MWI has been able to perform the detection of tumorous cells in breast phantom that can pave the way to saving lives.

/pdf/a-low-cost-and-portable-microwave-imaging-system-for-breast-4tdguxwfma.pdf

A Low Cost and Portable Microwave Imaging System for Breast Tumor Detection Using UWB Directional Antenna array

In this paper, a multifunctional active frequency selective surface (MAFSS) is presented based on the switching responses of active components. The proposed structure comprises periodic arrays of metallic patterns imprinted on both sides of an FR4 substrate on which p-i-n diodes are embedded with parallel feed networks. The novelty of the design lies in its multifunctional characteristics with independent control of the biasing states (ON/OFF) of the diodes mounted on opposite layers. This leads to four different working states (dual bandpass for OFF–OFF state, single-band absorber for OFF–ON state, single-bandpass for ON–OFF state, and reflector for ON–ON state) being facilitated by the proposed reconfigurable AFSS. Furthermore, the effects of the design parameters and active components on multifunctional responses are extensively analyzed by deriving equivalent circuit models. Even though the topology is polarization sensitive, multiple dividable working functions (transmission, absorption, and reflection) have been realized in single geometry, unlike the earlier reported designs. The proposed structure has also been fabricated, and the measured responses show reasonable agreement with the simulated results under normal incidence. An MAFSS with such diverse characteristics is an essential element for regulating electromagnetic wave propagation in manifold applications.

Novel Multifunctional Reconfigurable Active Frequency Selective Surface

This letter presents an eight-port, multiple-polarization, ultrawideband (UWB) diversity antenna array. The unit-cell antenna is constructed from a basic square monopole antenna. With suitable modifications in the radiating plane and the ground plane, the unit-cell antenna is designed to operate between 2.9–12 GHz to cover the entire UWB range. The designed UWB radiator is then replicated within a small space to generate triple polarization. The proposed diversity antenna array consists of eight uncorrelated antennas, of which four are horizontally oriented and the remaining four are vertically oriented to achieve polarization diversity. Diversity performance metrics such as envelope correlation coefficient, apparent diversity gain, and effective diversity gain are evaluated and presented. The prototype diversity antenna is fabricated, and experimental results are presented.

3-D Eight-Port Ultrawideband Antenna Array for Diversity Applications

A single-substrate-layer frequency selective surface (FSS) with a 1.6 mm thick FR4 substrate is proposed for triple-band-stop filtering applications. The proposed design includes simple conductive elements on both sides of the substrate. A square loop is located on the top side, while on the backside, another square loop being combined with two folded arms is embedded. Wise inclusion of the conductive elements with proper dimensions stimulated a three-band operation in 3.2-3.7, 4.1-6, and 8-12.1 GHz. WiMAX, WLAN, and X-band are covered within the mentioned frequency bands, respectively. As a figure of merit, for the presented band-stop FSS structure, stable frequency response is obtained against different angles of TE and TM polarizations. Moreover, experimental results obtained from the fabricated prototype are in close agreement with simulation studies confirming the FSS outperformance in real-world applications. Single substrate layer structure, small size, simple conductive elements, and coverage of in-service frequency bands are some of the advantages of the proposed FSS.

WiMAX, WLAN, and X-Band Filtering Mechanism: Simple-Structured Triple-Band Frequency Selective Surface

This paper presents a multifunctional reconfigurable frequency-selective surface (FSS) based on liquid-metal-filled microchannels engraved in an elastomeric substrate. The proposed FSS comprises two layers of periodic meandered patterns encased within the opposite sides of a dielectric, where the layers are arranged in orthogonal polarization with independent control of reconfigurability. The novelty of the design lies in its switching characteristic between four different working states (dual-polarized all pass, single-polarized low pass, single-polarized bandpass, and dual-polarized bandpass) with the injection of a liquid metal in the top and bottom microchannels. Moreover, the design exhibits miniaturization performance during one of the states (exhibiting dual-polarized bandpass response at 1.58 GHz) corresponding to the unit cell dimensions of $0.052\lambda _{0} \times 0.052\lambda _{0}$ . The equivalent circuit models and parametric variations are extensively analyzed for understanding the design principles. Because any liquid-metal-based reconfigurable FSS structure has not been reported earlier, a detailed description of the fabrication and measurement procedure are presented in this paper. The experimental validation of the fabricated prototype also confirms the potential use of microfluidic technology-based reconfigurable structures in future.

Fluidically Reconfigurable Multifunctional Frequency-Selective Surface With Miniaturization Characteristic

A reconfigurable frequency-selective surface (RFSS) for electromagnetic shielding applications is presented in this letter The unit cell of the proposed RFSS contains a pair of shorted square loops separated by a uniform distance Wideband RFSS with the frequency tuning ratio of 1:234 achieved by varying the horizontal spacing is proposed The RFSS covers the frequencies 35, 5, and 58 GHz shielding the WiMAX, WLAN, and ISM/WiMAX bands, respectively The prototype of the proposed RFSS is fabricated and loaded on to the mechanical tuning setup The tuning setup has a box frame with rotating shafts attached to the bevel gears to control the horizontal spacing The use of collapsible linkage mechanism ensures uniform spacing during reconfigurable operation The simulated results are validated with measurements The proposed FSS offers wideband frequency tuning for electromagnetic shielding applications

A Wideband Frequency Tunable FSS for Electromagnetic Shielding Applications

In this study, a modified antipodal Vivaldi antenna (AVA) with low cross-polarisation is proposed for ultra-wideband communications. The bandwidth offered by conventional single petal AVA is enhanced by adding another petal. This dual petal antenna occupies a small volume of 60 × 60 × 0.8 mm
 3
 and provides operating bandwidth from 2.4 GHz to frequencies >14 GHz. The proposed antenna configuration provides low cross-polarisation level which is 5 dB and an average group delay variation of 0.5 ns. The prototype antenna is fabricated and tested to validate the simulation results.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-map.2015.0089

Modified antipodal Vivaldi antenna for ultra-wideband communications

An ultra-wideband (UWB) frequency-selective surface (FSS) exhibiting band rejection characteristic is presented in this paper. The proposed unit cell has the size of 14 × 14 mm2 which is approximately 0.18 × 0.18 λo, where λo corresponds to free space wavelength at the lower cut-off frequency. The proposed UWB FSS consists of a single-layer substrate and provides 20 dB attenuation level for a wide bandwidth of 7.53 GHz at the normal incidence. The proposed FSS is polarization independent and also provides angular-independent operation for the EM wave incidences of 15°, 30° and 45° with 11.5 dB attenuation over a wide range from 4 to 14 GHz.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1759078715001439

Polarization-independent single-layer ultra-wideband frequency-selective surface

A compact, unilateral grounded Coplanar Strip (CS) antenna for automotive communications is presented in this letter. The antenna is designed for quad band operation covering DCS1800, IEEE 802.11b/g/n standards, Wi-MAX, Vehicle-to-Vehicle (V2V), and Vehicle-to-Infrastructure (V2I) Communications. A simple folded microstrip line radiator along with unilateral ground plane of CS is attempted to generate the required frequency bands. To achieve polarization and pattern diversity functionality, a 4 port diversity antenna array is developed. The antenna unit cells are spaced $0.125{\lambda _{{\rm g}1}}$ calculated at the lowest resonant frequency and are oriented orthogonal to adjacent unit cells to achieve high isolation greater than 20 dB, correlation coefficient less than 0.25 and diversity gain greater than 9.5 dB. The proposed antenna is suitable for automotive communications as it can be conveniently placed anywhere inside the vehicle more specifically in the wind screen, side mirrors and fenders.

Quad-Band Diversity Antenna for Automotive Environment

Phase shifters are indispensable microwave components. In this paper, a dual-frequency, passive, analog, and reciprocal phase shifter is proposed, deploying the phase-delay characteristics of complementary split-ring resonator (CSRR). A transmission line is loaded with a pair of CSRR in the ground plane and the phase variations are compared with an ideal transmission line. The proposed phase shifter operates in the industrial, scientific and medical (ISM) and wireless local area network (WLAN) bands, providing a phase of 180° at 2.4 GHz and 90° at 5.4 GHz for beam steering applications.

Balaji Moorthy

Papers

A Wideband Frequency Tunable FSS for Electromagnetic Shielding Applications

Modified antipodal Vivaldi antenna for ultra-wideband communications

Polarization-independent single-layer ultra-wideband frequency-selective surface

Quad-Band Diversity Antenna for Automotive Environment

Dual-frequency phase shifter deploying complementary split-ring resonator