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Microwave imaging has become a popular research issue in recent decades as a result of its several benefits over traditional imaging technologies. To analyse biological tissues in depth, a microwave imaging instrument is employed.The test determines the presence and location of morphological alterations in specific biological tissues. Ultrawideband (UWB) microwave imaging is a new technique that produces improved results while avoiding the use of ionizing radiation. Antennas play a critical part in these systems, and as a result, antenna optimization has become a hot topic due to the device's proximity to the human body. Recent research has revealed a number of initiatives to improve the electromagnetic sensors employed in these systems, whether as single or array components. In this article, the development of a compact ultrawideband (UWB) antenna functioning in the frequency range of 3.25-14.63GHz is proposed. The reported antenna comprises of a rectangular patch and a modified ground plane “etched on a FR4” substrate excited by a 50Ω feed line. The overall dimension of antenna is \(0.44 {\lambda }_{0}\times 0.38 {\lambda }_{0}\times 0.02{\lambda }_{0}\). The proposed antenna has been fabricated on FR-4 substrate. Measused and simulated results are in good agreement. The proposed antenna is compact and displays good radiation characteristics along with good gain. 1. INTRODUCTION In recent years, UWB technology has gained significant interest from researchers throughout the globe. In February 2002, the Federal Communication Commission (FCC) released the frequencies of 3.1GHz to 10.6GHz for commercial applications [1]. The design of a UWB antenna requires the antenna to be small and compact, it should have wide bandwidth performance, the radiation pattern has to be Omni-directional and the antenna should be easy to fabricate [2–3]. The benefits of an ultra-wideband antenna are its low complexity and it is inexpensive to manufacture. UWB patch antenna can be designed with various geometries such as circular, triangular, square, or rectangular. UWB technology is applied in several fields such as microwave imaging and radar systems. Microwave imaging utilizes EM waves to see through the inner structure of a tissue. It recognizes tumors based on dielectric properties, which are different compared to normal tissue [4–5]. X-rays, ultrasound, and MRI scans are used in the early detection of cancerous cells [6]. However, these methods pose some disadvantages. X-ray mammography is agonizing for patients, and long exposure to X-ray may cause healthy cells to become cancerous [7]. Another technique used to detect cancerous cells is ultrasound, but this technology is unable to detect deeply buried tumors and it is comparatively expensive [8]. To overcome these limitations, microwave imaging employs low ionizing radiation and is cost-effective compared to other methods [9]. Microwave imaging incorporates the use of UWB pulses which range from “low to high” frequencies in order to generate images of human tissues [10]. The higher frequency band is used to create high-resolution images of the tissue, whereas the lower frequency band is used to detect deeply buried tumors [11]. A microwave imaging system has two parts, a “front end,” which requires the antenna to be inexpensive, compact and it should operate efficiently, whereas the second part requires analyzing the performance of the antenna to detect the tumor and generate the image using the various processing techniques. The need for the antenna to be is compact is because it is to be incorporated into portable microwave imaging systems. This paper overviews the design and optimization of a novel microwave antenna which must serve as an element in a sensor array for early detection. The proposed microstrip patch antenna in this work displays good UWB characteristics and also displays good gain characteristics. The antenna consists of a modified square patch and a ground plane built on a FR4 substrate. Parametric analysis is done on the proposed antenna to observe the effect of various design parameters on the antenna performance, further, the simulations of the current density, gain and radiation pattern are also reported in this paper.

A compact triple band antenna with stacked T-shaped strips inside a rectangular ring monopole has been proposed. This novel structure with a slot in the defected ground achieves triple band opration i.e. 2.47–2.77 GHz, 3.3–3.7 GHz and 5.10–6.62 GHz. These bands find application in important wireless communication standards like WiMAX (3.3–3.8 GHz, and 5.25–5.85 GHz, WLAN (2.4 G-2.5 GHz, 5.1–5.3 GHz, and 5.72–5.85 GHz). The antenna is printed on a FR-4 substrate with an overall dimension of $$33 \times 17 \times 1.6 \;{\text{mm}}^{3}$$ 33 × 17 × 1.6 mm 3 . An impedance bandwidth of 11% (2.47–2.77 GHz), 11% (3.3–3.7 GHz) and 25% (5.10–6.62 GHz) is obtained. A good conjunction between the simulated and measured results is inferred from the antenna design analysis.

A planar microstrip transmission line with dual semicircle complementary split-ring resonator (CSRR) is proposed as a high sensitivity RF sensor for detecting non-uniformity of the surface of the thin metal plate. In automotive industries, a surface deformity on lightweight aluminum sheet components is a serious problem. Due to the uneven surfaces of the parts, typical flaws such as dents, dings, and waviness are not visible in the early stages of production. The defects, if ignored at an early stage, may lead to more production cost. So in this paper, we investigated the detection of flaws on the thin aluminum sheet under variable load conditions. The dual ring semicircle CSRR loaded microstrip transmission line implemented on Teflon (thickness = 0.08 mm) coated aluminum sheet (thickness = 3 mm) which behave as an RF sensor. By varying the depth of the dent from 1 to 2.05 mm on the aluminum sheet, the sensor was able to find the maximum frequency shift (nearly 800 MHz frequency) as compared to faultless (without a dent) aluminum sheet, in both simulations as well as in measurement conditions. As compared to circular shape CSRR, the dual ring semicircle CSRR has a high bonding effect between the electric field and metal sheet, which gives a more accurate prediction of dent portion on a thin metal sheet. This proposed compact RF sensor can be effectively utilized for crack avoidance in fiber optic glasses, crack avoidance in the gas pipeline, aircraft plate etc. By comparing frequency shift of the proposed CSRR sensor is more accurate, even invisible non-uniformities can be easily detected and thus can be prevented at an early stage to avoid any damage.

The exponential rise in wireless communication demands and allied applications have revitalized academia-industries to develop an efficient and potential solution. Furthermore, the high-pace increasing scarcity of radio spectrum has also alarmed researchers to achieve better Quality of Service (QoS) centric solution. To meet such demands Visible Light Communication (VLC) systems have gained global attention; however, up surging high rate, range and reliability (3R) needs demand better performance. Towards these goals, Multiple Input Multiple Output (MIMO) based VLC systems is an efficient approach; though its efficacy under Multiple Users (MU) conditions remains least explored. Enabling MIMO-MU based VLC can achieve 3R objectives effectively; however, factors like multipath attenuation, interferences and varied impairment-affects makes classical approached confined. The MIMO-MU VLC systems require robust error, noise or interference resilient transmission even under adverse conditions such as non-linear LED, multipath attenuation and interference. Towards these objectives, in this paper a highly robust MIMO-MU VLC system is developed that incorporates an augmented MIMO channel design and combined pre-coding and post equalization schemes. To alleviate major interference probability in MIMO-MU environment, proposed model incorporates time (delay)-multiplexing based data transmission followed by signal adaptive precoding and Volterra Kernel based Hybrid-equalizer. This approach enables interference and noise removal as well as LED non-linearity handling under MIMO-MU VLC communication. The use of a Volterra Kernel based Decision Feedback Equalization with both linear as well as non-linear equalization enables proposed VLC system to exhibit low Bit Error Rate with low modulation index and taps, that optimizes trade-off between performance as well as complexity.

Mutual coupling between the multiple antenna designs is a critical problem which deteriorates the performance of multiple input multiple output (MIMO) system. It affects the antenna efficiency and influences the correlation. In this paper, a study on the isolation between the multiple antenna elements is presented. The antennas are placed on a cost-effective compact dielectric substrate with different orientations to minimize the correlation. A CPW fed antenna is designed using FR4 substrate, using which two and four element antenna structures are developed. The performance parameters are analysed, wherein the envelope correlation coefficient (ECC) has to be less than 0.5, diversity gain nearer to 10 dB in the operating bandwidth, mean effective gain (MEG) less than 3 dB, channel capacity loss (CCL) less than 0.4 bits/s/Hz and the isolation between the antenna elements well above 20 dB. Acceptable gain, high radiation efficiency, and stable radiation pattern of the proposed design are analysed and the fabricated prototype of two and four element is measured for its performance parameters. All the necessary simulations are carried out in the EM simulator Ansys HFSS v.14.0 and a detailed comparison study is done based on the existing antennas.

A novel miniaturized slotted multiband antenna is presented in this article. The antenna consists of a kite-shaped slot in the radiating patch to obtain miniaturization, C- and G-shaped slots in the ground plane to incorporate multiband operation and a microstrip feedline to obtain an impedance matching. The aforementioned miniaturization method results in about 50% reduction in active patch area and about 36% reduction in volume of the proposed design, as compared to the conventional antenna. G-shaped slot is used to obtain operations at 3.6 and 5.8 GHz, while C-Shaped slot is used to obtain operations at 6.9 and 9.5 GHz. The antenna has an active patch area of only 384 $$\hbox {mm}^{2} (24\times 16\,\hbox {mm}^{2})$$ , and the entire performance analysis of the antenna are carried out using HFSS v.13.0 simulation software. The proposed design operates at about 3.58 (WiMAX), 5.9 (WLAN), 6.72 (Satellite TV), 8.51 and 9.76 GHz (X-band) with $${S}_{11}