Volume 77, Issue 11-12

In recent years there has been a substantial growth in the usage of wireless gadgets in various fields like mobile communication, health monitoring, warfare communications, etc. However, the performance of the antenna is evaluated by the parameters like gain, directivity and bandwidth, VSWR and is enhanced as a continuous process. But on the other side, Specific Absorption Rate (SAR) is a parameter that is likely to be watched out for the safety concern which should be as low as possible for any antenna to ensure the minimum risk to human health. Many researchers have contributed an enormous amount of work to the SAR reduction. From this perspective, this work proposes a brief survey on low SAR antennas. An optimal low SAR antenna needs a perfect lossless impedance matching over a lossy medium (human body) for the eradication of spurious surface waves. The deployment of SAR reduction strategies, outcomes of the design, and open-end research challenges with the relative results are addressed as a part of the survey. The core impulse of this work is to induct the antenna designers to get indulged in designing low SAR antenna with enhanced performance for several WBAN applications like health monitoring and many more.

This article introduces two new compact ultra-wide band (UWB) rectangular dielectric resonator antennas (RDRAs) with enhanced bandwidth (BW), gain, and directivity. The RDRAs are designed at 10 GHz resonant frequency. The proposed RDRAs are compactly designed using resonating dielectric material (RDM) of Alumina_96 pct ( ε r  = 9.4, tan δ  = 0.006) with overall dimensions of 30 × 20 × 4.6 mm 3 . The RDMs are mounted on FR4 substrate ( ε r  = 4.4, tan δ  = 0.02) with defected ground structure (DGS). The DGS are comprised of rectangular and circular ring slots on it. These compact DGS-RDRAs provides enhanced BW. Prototypes of the two suggested RDRAs are fabricated. The fabricated RDRAs are validated by experimental set-ups. The RDRA with rectangular-ring slot DGS provides impedance BW ( S 11  < −10 dB) of 33.97 % (8.6658–12.071 GHz). The impedance BW of the other RDRA is 27.97 % (9.08–11.869 GHz). The rectangular-ring slotted RDRA offers radiation efficiency and peak realized gain of 86.4 % and 6.27 dBi, respectively within the band of operating frequencies. The radiation efficiency and realised gain of circular-ring slotted RDRA are 86.18 % and 5.9 dBi, respectively. Good agreements are achieved in between the simulated results and measured results. The results are compared with some recently developed antennas available in literature. The comparison shows that the proposed RDRAs can be suitable candidate for various X-band applications such as satellite downlinks, synthetic aperture radar, weather monitoring by military and some government organizations.

This article presents a conformal monopole antenna for wearable application in ISM band frequency of 2.45 GHz. The antenna has a return loss of 50.18 dB with good radiation performance. The gain of the antenna is 1.09 dBi which is improved to 3.28 dBi using a metasurface consisting of 3 × 3 array elements. The proposed metamaterial integrated antenna is fabricated on 1 mm thick flexible PDMS substrate. The metamaterial improves the gain while reducing the specific absorption rate (SAR) of the antenna. The geometry size of the metamaterial integrated antenna is 50 × 50 × 24 mm 3 . The loading effect of antenna by body is analyzed with a hand phantom model. Flexibility and conformability of antenna is analyzed by bending the antenna with various radii in x and y direction. Measured results of the fabricated prototype demonstrate the safety of the suggested wearable antenna for biomedical applications.

A novel strip line fed, circularly polarized (CP), annular slotted dual band antenna using hybrid electromagnetic band gap (EBG) structure for Global Positioning System (GPS) has been herein designed, analyzed, and investigated for wearable applications. Adjusting the radii of the annular slots on the radiating patch excellent circular polarized (CP) radiation and impedance matching is achieved. The design demonstrates Kapton based flexible, robust, and low-profile solution with permittivity of 3.4 to meet the requirements of wearable applications. Due to the high losses of the animal body, the electromagnetic band gap (EBG) structure is used to reduce back radiation and the effect of frequency detuning. The proposed antenna structure also enhances the front-to-back ratio (FBR) by 10 dB. This antenna with dimensions 0.56 λ 0  × 0.4913 λ 0  × 0.002 λ 0 analyzed using a flexible Kapton substrate. Optimized hybrid EBG structure provides an excellent Specific Absorption Rate (SAR) along with all other antenna parameters, within acceptable for GPS-based wearable applications at 1.13 GHz and 1.157 GHz frequency band. Therefore the proposed antenna is a suitable candidate for GPS-based tracking and wireless body area network (WBAN) applications. The proposed antenna was also tested upon fabrication and the measured results agree with simulated results.

The design and analysis of the electrically small eight-shaped wearable antenna for both on- and off-body communication is proposed in this paper. An eight-shaped radiating structure is placed over the jeans substrate and an I-shaped slot is introduced in the ground plane which makes the antenna resonates at the ISM-I band (2.4 GHz). The antenna has a compact size of 0.30 λ 0  × 0.20 λ 0  × 0.001 λ 0 , where λ 0 is the free space wavelength at the resonance frequency. The impedance bandwidth (≤−10 dB) of the antenna is 6.1 % and 5.8 % in free space and presence of a human body phantom respectively. The antenna design exhibits good gain along with an improved omnidirectional radiation pattern. The specific absorption rate (SAR) of the antenna averaged over 1 g of tissue is 0.21 W/kg at 2.45 GHz which is far below the FCC standard. The paper also discusses the bending analysis and the fundamental size limitations of the small antenna, concluding that it is suitable for practical use. The simulated results of the prototype are validated by the measured results.

In this paper, a high-gain dual-beam folded transmit-reflect-array antenna is designed based on the shared aperture method. It consists of the top transmit-reflect-array, the bottom transmitarray, and the feed horn located at the center of the bottom transmitarray. A phase-shifting surface is proposed as the transmission unit cell capable of transmitting incident waves while providing adequate transmission phase shift. The designed transmission unit cell is improved into the transmit-reflect unit cell by adding polarization grids to realize the reflection function. The bottom transmitarray is constructed by transmission unit cells. The top transmit-reflect-array is composed of transmit-reflect unit cells and polarization grids vertical to the unit cell. The x -polarized wave transmits through the top transmit-reflect-array and forms a pencil beam in the forward direction. In addition, the y -polarized wave is reflected by the top transmit-reflect-array and transmits through the bottom transmitarray to form a pencil beam in the backward direction. The tested realized gains of the transmitted beam and reflected beam at 10 GHz are 19.87 dBi with an aperture efficiency of 48.27 % and 23.95 dBi with an aperture efficiency of 30.88 %, respectively. With its low profile and ease of manufacture, it has great prospects for navigation and radar communication.

In this article, a planar dual-element frequency reconfigurable multiple-input multiple-output (MIMO) antenna for ultra-wideband (UWB) applications is studied. The frequency band can be switched between UWB operation and single band rejected UWB performance using a pair of PIN diodes in the MIMO configuration. The presented antenna is comprised of two similar slotted circular radiators, having tapered microstrip feedlines and separate partial ground planes. An RT/Duroid 5880 substrate with size 54 × 54 mm 2 is used for the design purpose. Rotational symmetry between the radiators and diagonally oriented t-shaped decoupling structure behind the substrate have been utilized for high isolation purpose. The designed MIMO antenna exhibits UWB performance in mode 1. In other mode, the antenna operates in the frequency range 2.46–10.44 GHz with Worldwide Interoperability for Microwave Access (WiMAX) band rejection. Thus, the MIMO antenna exhibits on-demand single band rejection behavior depending on the switching conditions of the diodes. The measured isolation is greater than −20 dB in both the modes. The presented MIMO configuration possesses compact and planar geometry with high gain, good isolation, ultrawideband performance with reconfigurable band elimination, high efficiency and efficient diversity performance parameters. The suggested antenna is a good choice to be utilized for portable UWB MIMO applications.

Millimeter (mmWave) and sub-terahertz communication is a key technology to support high data rate requirements of 5G and B5G mobile networks. However this field is still in its initial development stage because of the various technical difficulties in its practical implementation due to inherently distinct propagation properties of mmWave/sub-terahertz frequencies. A thorough investigation of mmWave/sub-terahertz communication link is required in order to successfully deploy these frequency bands in 5G and B5G mobile networks. This paper investigates the effect of atmospheric conditions like dry air, humidity, rain, snow, fog and foliage on the performance of the mmWave/sub-terahertz link. The work also presents a mathematical analysis of the coverage of mmWave/sub-terahertz communication link and investigates the effect of various parameters like frequency, bandwidth, transceiver antenna gain, path loss coefficient (LOS, NLOS case) and system noise on its performance.