This investigation presents an oval slot edge (OSE) antipodal Vivaldi antenna (AVA), hereinafter referred to as Fern AVA (FAVA), with an optimized radiation pattern. The use of OSE provided improvements in the antenna characteristics, especially regarding a lower-frequency limit reduction, an increase of the main lobe (ML) gain, and sidelobe level (SLL) reduction. Those contrasting characteristics are simultaneously obtained through the class of the Palm Tree antennas. The proposed FAVA at 1.5 GHz shows an improved gain of 6.66 dB, -12.9 dB of SLL, and 0 degrees of main lobe squint (MLS), in contrast with 4.41 dB of gain, -4.5 dB of SLL, and 4 degrees of MLS in the conventional AVA. For the FAVA, the notches in an elliptical shape, in addition to mitigating the SLL, direct the E-fields distributions towards the main lobe, which categorizes it into the same class as the Palm Tree Vivaldi Antenna. To study the performance of the proposed antenna for medical applications of near-field microwave imaging, a conceptual proof was performed, thus obtaining the microwave image of a Child Head Phantom, homogeneous and semi-realistic, being possible to detect a brain tumor.

This paper reports mutual coupling reduction in UWB (Ultra wideband) Coplanar Vivaldi Array (CVA) by incorporating truncated and corrugated slot at the border between adjacent elements. An examination of coplanar Vivaldi arrays shows that mutual coupling in the E-plane is more significant than in the H-plane. Subsequently, arrays using exponential and rectangular corrugated slot are compared with those without slot structure through simulation of surface current distribution. A novel Exponential Corrugated Truncated (ECT) structure is implemented to improve mutual coupling performance, while maintaining or even improving co-polar field patterns. The results of simulation and measurement indicate that mutual coupling and return loss performance can be improved by controlling the length of corrugated structure and the distance of the slot structure from the center of Vivaldi's tapered slot. CVA achieves bandwidth ratio of 5:1, i.e., from 2-10 GHz. ECT-CVA structure reduces mutual coupling to below -20 dB in a large portion of the whole band, shows 3.9-10.2 dBi gain over the entire band, increases SLL performance at 4-9 GHz compared to CVA without slot structure.

A comprehensive review on recent developments and applications of circularly polarized (CP) dielectric resonator antennas (DRAs) is proposed in this paper. DRAs have received more considerations in various applications due to their advantages such as wide bandwidth, high gain, high efficiency, low losses, and low profile. A broad justification for circular polarization and DRAs is stated at the beginning of the review. Various techniques such as single feed, dual, or multiple feeds used by different researchers for generating circular polarization in DRAs are briefly studied in this paper. Multiple-input-multiple-output (MIMO) CP DRAs, which can increase channel capacity, link reliability, and data rate, have also been analyzed. Additionally, innovative design solutions for broadening the circular polarization bandwidth and reducing mutual coupling are studied. Several applications of DRA are also discussed comprehensively. This paper finishes with concluding remarks.

Antennas with high gain that can operate in Super Wide Band (SWB) frequencies can be employed for a variety of wireless applications that serve different telecommunications infrastructure and radar applications. However, wide-bandwidth antennas suffer from interference from other wireless technology networks, necessitating the deployment of strategies to block some undesired signal frequencies. A new method for increasing bandwidth by shortening the taper slot length of the Vivaldi antenna and increasing the antenna radiation pattern by using a wavy structure and adding a Square-Complimentary Split Ring Resonator (S-CSRR) structure that can notched-band several frequencies has been investigated on the Coplanar Vivaldi Antenna (CVA). In this study, we investigated seven different types of antennas: Conventional CVA (C-CVA), CVA-Short Slot and Long-Slot (CVA-SS and CVA-LS) with antenna lengths of 10 and 15 cm, wave CVA (WCVA), and WCVA with CSRR. In all frequency bands ranging from 2.3 to more than 30 GHz, the S ₁₁ of the CVA-SS antenna is less than -15 dB with minimum S ₁₁ of-62.21 dB. When compared to the CVA-LS without a corrugated construction, the WCVA-SS antenna has 5.77 dBi improvement of directivity at 15 GHz. By incorporating the S-CSRR structure into WCVA, four notched frequency bands are formed: 3.335 - 3.72 GHz (WiMAX spectrum), 4.72 - 5.354 GHz (WLAN), 6.07 - 6.743 GHz (Wifi 6E usage), and 7.408 - 8.293 GHz (X- satellite bands). S-CSRR also potentially result in circular polarization at 4.6 - 5.3 GHz with the minimum AR of 0.438 (at 5 GHz), at 7.8 -8.2 GHz with the minimum AR of 0.732 (at 8GHz) and at 27 GHz with AR of 2.1 by constructing a U shape with four SCRRs. There was also good agreement between simulation and measurement results. As a result, the WCVA-SS antenna with a Square-CSRR structure may be recommended for the usage of SWB antennas, where a single antenna can serve numerous telecommunications and radar system applications.

In this paper, 1 × 2 MIMO of Palm Tree Coplanar Vivaldi Antenna is presented that simulated at 0.5–4.5 GHz. Some GPR applications require wideband antennas starting from a frequency below 1 GHz to overcome high material loss and achieve deeper penetration. However, to boost the gain, antennas are set up in MIMO and this is costly due to the large size of the antenna. When configuring MIMO antenna in the E-plane, there is occasionally uncertainty over which antenna model may provide the optimum performance in terms of return loss, mutual coupling, directivity, beam squint, beam width, and surface current using a given substrate size. However, the configuration of E-plane antenna in MIMO has an issue of mutual coupling if the distance between elements is less than 0.5λ. Furthermore, it produces grating lobes at high frequencies.We implement several types of patch structures by incorporating the truncated, tilt shape, Hlbert and Koch Fractal, Exponential slot, Wave slot, the lens with elips, and metamaterial slot to the radiator by keeping the width of the substrate and the shape of the feeder. The return loss, mutual coupling, directivity, beam squint, beamwidth, and surface current of the antenna are compared for 1 × 2 MIMO CVA. A continuous patch MIMO has a spacing of 0.458λ at 0.5 GHz, which is equivalent to its element width. From the simulation, we found that Back Cut Palm Tree (BCPT) and Horizontale Wave Structure Palm Tree (HWSPT) got the best performance of return loss and mutual scattering at low-end frequency respectively. The improvement of directivity got for Metamaterial Lens Palm Tree (MLPT) of 4.453 dBi if compared with Regular Palm Tree-Coplanar Vivaldi Antena (RPT) at 4 GHz. Elips Lens Palm Tree (ELPT) has the best beam squint performance across all frequencies of 0°. It also gots the best beamwidth at 4.5 GHz of 3.320. In addition, we incorporate the MLPT into the radar application.