This work reviews design aspects of liquid metal antennas and their corresponding applications. In the age of modern wireless communication technologies, adaptability and versatility have become highly attractive features of any communication device. Compared to traditional conductors like copper, the flow property and lack of elasticity limit of conductive fluids, makes them an ideal alternative for applications demanding mechanically flexible antennas. These fluidic properties also allow innovative antenna fabrication techniques like 3D printing, injecting, or spraying the conductive fluid on rigid/flexible substrates. Such fluids can also be easily manipulated to implement reconfigurability in liquid antennas using methods like micro pumping or electrochemically controlled capillary action as compared to traditional approaches like high-frequency switching. In this work, we discuss attributes of widely used conductive fluids, their novel patterning/fabrication techniques, and their corresponding state-of-the-art applications.

The Nigeria agriculture sector is receiving a lot of attention in recent years due to the need to diversify its economy. Two key gaps facing the agriculture sector have been identified. They include the inability to meet domestic food requirements and the inability to export at quality levels required for market success. We envisage that these problems can be solved by using internet of things (IoT) and data analytics (DA). In this paper, the application of IoT technologies and DA in agriculture are discussed. The benefits and challenges of deploying the IoT and DA are presented. Finally, methods that can be adopted towards solving the problems facing Nigeria's agriculture sector are proposed.

Traditional design of 4 × 4 Butler matrix (BM) uses couplers, phase shifters (PSs), and crossovers. Due to some troublesome issues related to PS and the crossovers involved in the design of BM, which degrades its performance, this paper presents a planar 4 × 4 BM without PS and crossovers. It is accomplished with the help of a modified coupler. The modified coupler is realized to have a 45° output phase difference, which replaces the function of the 45° PSs. The 45° output phase differences obtained from this type of coupler combined with quadrature coupler give the desired phase differences required at the output of the BM. The BM is meant to operate at 6 GHz. The simulated and measured reflection coefficients and isolations at all ports are below -17 dB at the center frequency. The result also shows an amplitude imbalance within ±3 dB with phase mismatch of about ±3° at the center frequency. The -10-dB reflection coefficient bandwidth is 37.10%, and the transmission bandwidth between -5 and -9 dB is about 31.0%. Both the simulated and experimental radiation patterns obtained by exciting the input ports (P1-P4) of the BM produce four orthogonal beams deposed at +15.3°, -47.6°, +47.6°, and -15.3°. This beam steering depicts a stable beam scanning angle of the BM, which is in good agreement with the theoretical predictions.

A multiband microstrip-fed wideband (WB) antenna with filtering notches is described for 3G/4G/5G applications. The proposed antenna comprises three notch bands by etching a modified inverted U-slot, a square ring slot, and an interdigital inductor slot on the patch element and feedline. The antenna resonates at 1.9, 2.3, and 3.5 GHz due to the resonant components’ mutual interaction, which eliminates interference at other frequencies. The antenna’s measured S ₁₁ are 18.79 dB at 1.9 GHz,–24.8 dB at 2.4 GHz, and –40.6 dB at 3.5 GHz, showing a multiband function with a band-reject level of 0.4 dB. The VSWR is less than two at all resonant frequencies. The effects of altering the notch dimensions on the S ₁₁ and VSWR were explored. The antenna was developed and tested using a Rogers RT/Duroid 5880 substrate. The agreement between measured and simulated results was satisfactory. The S ₁₁ result was validated using the ADS schematic and machine learning techniques. The proposed triband-notched antenna offers encouraging results, with radiation patterns exhibiting omnidirectional characteristics and effective performance within the required frequencies. Current distribution analysis reveals how notches disrupt surface current and lower radiation at specific frequencies. The antenna’s gain and efficiency performed satisfactorily in the stated frequency ranges.

This letter presents a wide-angle scanning multibeam planar inverted-E antenna (PIEA) array for vehicle-to-everything communication. The compact four-element PIEA array is designed with 0.3λ _o spacing, which achieves 90 $^{\circ}$ wide-angle scanning when a 135 $^{\circ}$ phase shift is applied obtained using a 4 × 4 Butler matrix (BM). The closeness of the array elements causes high mutual coupling and high cross polarization at wider scan angles. Therefore, three novel techniques are employed to overcome the high cross polarization and mutual coupling between the antenna elements in this array. To feed the antenna array, a low-cost miniaturized beamforming 4 × 4 BM circuit is designed without the use of phase shifters and conventional crossovers. The total dimensions of the compact PIEA array are just 0.456λ ₀ × 1.12λ ₀ × 0.036λ ₀ , while the overall dimensions of the multibeam array, including BM, are 2.731λ ₀ × 2.2λ ₀ × 0.046 λ ₀ . This multibeam array achieves for the first time the wide-angle scanning angles of ±87 $^{\circ}$ with a 3 dB beam scanning range of ±120 $^{\circ}$ along with the scanning angles of ±20 $^{\circ}$ . This array design can be scaled to use as an antenna array for millimeter-wave applications.