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An innovative IoT-based system utilizing a modified slotted microstrip patch antenna with enhanced coupling is presented for precise measurement of leaf moisture content. The antenna employs a rectangular slot above the feed point with an advanced coupling technique to enhance sensitivity. The antenna, fabricated on a 0.8 mm F4B substrate, is designed to resonate within the 2.40 to 3.0 GHz range under unloaded conditions. A parametric analysis focusing on leaf permittivity ranging from 20 to 30 is conducted to determine the antennas' sensitivity. Experimental measurements of the reflection coefficient (S11) with respect to resonant frequency shift are performed with leaf samples as the samples under test (SUT). Experimental results reveal that the proposed patch antenna's sensitivity is significantly enhanced, ranging from 0.57 to 1.67 times greater than that of traditional patch antennas for the five leaf samples tested. The antenna exhibits a sensitivity of 0.06 GHz and 0.02 GHz for the modified and enhanced coupling designs, respectively. The mean relative error between predicted and measured moisture content values is low at 0.038. The findings highlight the antenna's increased sensitivity in detecting leaf moisture content and illustrate the potential of the proposed IoT-based system for real-time agricultural monitoring, marking an advancement in precision farming practices. The study validates the microstrip patch antenna's capability as a moisture sensor through detailed sensitivity analysis, frequency shift measurements, and regression modeling. [ABSTRACT FROM AUTHOR]

A modified slotted microstrip patch sensor antenna has been developed for sensitivity enhancement to measure the moisture content of leaves. The design incorporates a rectangular slot positioned above the feed of a rectangular patch antenna. The antenna achieves resonant frequency at a lower range than the operating frequency of a traditional patch antenna without slot while maintaining a miniaturized form factor. To evaluate the sensitivity of the proposed modified slotted patch antenna, the variation in the resonant frequency and the reflection coefficient (S11) is observed with the sample under test (SUT), i.e., leaf is placed above the patch. A comparative analysis with regard to sensitivity and shift in frequency is performed between the designed antenna structures. The designed antenna is fabricated on a 0.8 mm F4B substrate in order to resonate within the 2.40–2.80 GHz range under unloaded conditions. The antenna's sensitivity is tested by performing parametric analysis with respect to the permittivity of the leaf ranging from 20 to 30. The experimental results reveal that the sensitivity of the proposed patch antenna is enhanced by a factor of 1.67 as compared to traditional patch antenna for the four levels of SUT, demonstrating an enhanced sensitivity in detecting the moisture content of leaves. [ABSTRACT FROM AUTHOR]

Most planar absorbers are designed under normal incidence, leading to a sharp decline in absorber performance under oblique incidence, especially when the incidence angle exceeds 30°. Three‐dimensional structured absorbers ensure the performance of the absorber under oblique incidence, but they lack practicality due to their complex processing and assembly. In this letter, a tightly‐coupled planar absorber (TCPA) is proposed. Its design method combines the reciprocity principle and tightly‐coupled structure, incorporating a wide‐angle matching layer and interdigitated structures to improve planar absorber's performance under oblique incidence. A sample is fabricated and measured for verification. The measurement results show that the absorber has a fractional bandwidth of 102.0% with an absorption rate of at least 90% under normal incidence. When the incident angle reaches 50°, the absorber maintains good performance under both transverse electric and transverse magnetic polarization. [ABSTRACT FROM AUTHOR]

In this paper, a frequency selective surface (FSS) based shared-aperture antenna is designed for 5G/Wi-Fi applications. The 5G and Wi-Fi channel are separated to achieve different polarizations and simultaneous work. The proposed antenna is of ±45°-polarization in the 5G N79 band and vertical polarization in the Wi-Fi5.8 GHz band. The antenna is vertically stacked with the N79 band antenna located above the Wi-Fi band antenna. The N79 antenna is composed of FSS units with transmissive characteristics in the Wi-Fi band, and serves as an electromagnetically transparent surface to avoid blocking the Wi-Fi antenna. A prototype of our design is fabricated, assembled and tested, and measured results show that the prototype is able to cover the entire N79 band (4.1–5.2 GHz, 23.7%) and Wi-Fi5.8 GHz band (5.73–5.89 GHz, 2.8%). Measured average gain is 8.2 and 7.8 dBi in the N79 and Wi-Fi band, respectively, and radiation efficiency is over 86 and 80%. The proposed design exhibits separated channels, tri-polarizations, high gain and compact size, which is sufficient for regular 5G/Wi-Fi applications. The antenna also achieves a relatively wide and highly consistent signal coverage in the two bands, making it suitable for 5G/Wi-Fi multi-function communication and indoor 5G blind compensation. [ABSTRACT FROM AUTHOR]