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Abstract-Analysis of U-slot loaded patch stacked with H-shaped parasitic elements is given in this paper. It is found that the antenna exhibits dual resonance and both the resonance frequency (upper and lower) depends directly on slot width and inversely on slot length. Both upper and lower resonance frequency increase with increasing the value of h 2 . Typically the bandwidth at lower and upper resonance is found 3.66% and 10.25% respectively. The radiated power at higher frequency (beamwidth 64 • ) is 0.73 dB as compared to lower resonance frequency (beamwidth 71 • ). The theoretical results are compared with the simulated data obtained from IE3D.

A novel design of 2 × 2 multiple-input-multiple-output (MIMO) antenna is reported for ultra-wideband applications. The neutralization line is implemented to minimize the mutual coupling between the radiating patches. The overall dimension of the designed antenna is 21 × 34 × 1.6 mm 3 . This antenna covers the measured bandwidth of 95.0% (3.52-9.89 GHz) with better isolation (≤−22 dB) over the entire operating frequency band. The measured gain varies from 3.08 to 5.12 dBi over the entire band. The various antenna parameters such as S-parameters, gain, efficiency, envelope correlation coefficient, mean effective gain, channel capacity loss, total active reflection coefficient, and radiation patterns are calculated and corresponding results are validated with the measured results. K E Y W O R D S ECC, MIMO antenna, mutual coupling, neutralization line, TARC

Abstract-A theoretical analysis of a gap-coupled stacked annular ring microstrip antenna with superstrate is performed in order to obtain wider bandwidth operation. The effects of air gap, superstrate thickness and feeding point location on the antenna performance are analyzed in TM 11 mode using equivalent circuit concept. It is noted that the proposed antenna is very sensitive to the feeding point location in TM 11 mode while annular ring microstrip patch antenna is independent of feed point in that mode. The optimized proposed antenna shows an impedance bandwidth of 13.96% whereas the antenna without air-gap has 8.75% bandwidth and without superstrate it has bandwidth of 10.89%. The theoretical results are compared with simulated and experimental results.

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Abstract-In this article, a novel design of butterfly-shaped compact and small size microstrip antenna is proposed. The radiating structure consists of four circular discs in coalesced form and fed with coaxial probe. The initial antenna resonates at 9.64 GHz with impedance bandwidth of 11.41%. The resonance frequency is further reduced to 8.12 GHz with bandwidth 10.10%, when a rectangular slot is incorporated in the initial patch. Finally, two parallel slots are embedded in the initial patch which improves the antenna bandwidth up to 21.50% (6.02-7.47 GHz). The gain and efficiency of this antenna are above 8.80 dBi and 90% respectively across the entire operating band. Radiation pattern is calculated at lower end (6.02 GHz), upper end (7.47 GHz) and centre frequency (6.75 GHz) of operating band. The proposed antenna is fabricated, and measured results are validated with the simulated ones.

The excessive use of digital platforms with rapidly increasing users in the wireless domain enforces communication systems to provide information with high data rates, high reliability and strong transmission connection quality. Wireless systems with single antenna elements are not able to accomplish the desired needs. Therefore, multiple-input multiple-output (MIMO) antennas are getting more attention in modern high-speed communication systems and play an essential part in the current generation of wireless technology. However, along with their ability to significantly increase channel capacity, it is a challenge to achieve an optimal isolation in a compact size for fifth-generation (5G) terminals. Portable devices, automobiles, handheld gadgets, smart phones, wireless sensors, radio frequency identification and other applications use MIMO antenna systems. In this review paper, the fundamentals of MIMO antennas, the performance parameters of MIMO antennas, and different design approaches and methodologies are discussed to realize the three most commonly used MIMO antennas, i.e., ultra-wideband (UWB), dual-band and circularly polarized antennas. The recent MIMO antenna design approaches with UWB, dual band and circularly polarized characteristics are compared in terms of their isolation techniques, gain, efficiency, envelope correlation coefficient (ECC) and channel capacity loss (CCL). This paper is very helpful to design suitable MIMO antennas applicable in UWB systems, satellite communication systems, GSM, Bluetooth, WiMAX, WLAN and many more. The issues with MIMO antenna systems in the indoor environment along with possible solutions to improve their performance are discussed. The paper also focuses on the applications of MIMO characteristics for future sixth-generation (6G) technology.

In the present paper the analysis of notch loaded shorted half disk patch is given. It is found that the bandwidth of the antenna depends inversely on the notch width whereas it is invariant with the notch length. Further, the antenna shows dual band behavior for a gap spacing below 7.5 mm in the gap coupled half disk shorted patch whereas it behaves as a wideband antenna for gap spacing more than 7.5 mm. Theoretical results are compared with simulated and experimental results.