Nrusingha Charan Pradhan

1. Antennas, traditionally employed for wireless communication, are increasingly being explored as multifunctional components capable of both signal transmission and environmental sensing, thereby ...

This paper presents the design and performance evaluation of a novel 3D-printed microwave sensor for dielectric characterization. The sensor utilizes a modified complementary split-ring resonator (CSRR) structure integrated within the ground plane. The sensor’s ability to measure both solids and liquids is demonstrated, with solid samples placed in proximity to the resonator and fluids injected into the embedded channel, thereby avoiding additional materials for fluidic channels. The sensor’s performance is evaluated based on changes in resonant frequency due to variations in dielectric constants. For solids, the resonant frequency shifts from 4.24 GHz to 2.66 GHz with increasing permittivity. For liquids, the frequency ranges from 4.24 GHz to 3.27 GHz for permittivity values between 1 and 80. An equivalent circuit model is developed to validate the sensor’s performance. The sensor is fabricated using the Fused Deposition Modeling (FDM) method with conductive layers applied via copper aerosol spray. The sensor’s versatility is demonstrated through testing with a range of solid substrates, such as Rogers 5880, FR4, Rogers 3006, and Rogers 6010, as well as four liquid samples—methanol, ethanol, propanol, and distilled water. The sensor effectively measures dielectric constants by monitoring shifts in resonant frequency, which vary with the permittivity of the tested samples. With an overall compact design of 30 mm × 40 mm × 1.6 mm, the sensor requires minimal liquid volume and achieves comparable sensitivity, with 4.05% for solids and 0.3% for liquids. The sensor’s resolution, accuracy, and low fabrication cost make it a promising tool for precise dielectric constant measurement.

This paper proposes a cavity-backed substrate-integrated-waveguide dual-feed self-diplexing MIMO antenna for Internet of Things (IoT) applications. To implement a self-diplexing operation, the half-mode SIW cavity is loaded with a rectangular slot carved on the top metal cladding. This causes the cavity to be divided into two unequal apertures, resulting in the development of a quarter-mode SIW. The patch has orthogonally positioned feed lines that provide two distinct resonant frequencies, 5.18 GHz and 5.8 GHz, with respect to the fundamental mode $TE_{110}$. Employing metallic vias on the cavity improves the self-isolation between the orthogonal ports. Furthermore, a square aperture between orthogonal patches can achieve maximum isolation without additional units. The proposed compact MIMO antenna with a self-diplexing feature using an aperture slot achieves maximum isolation of 46.84 dB at 5.17 GHz and 42.76 dB at 5.8 GHz between patches, inter-port isolation of 28.6 dB at $f_{L}$ and 27.6 dB at $f_{H}$ among ports, an impedance bandwidth of 130 MHz (5.236 - 5.106 GHz) and 174 MHz (5.88 - 5.72 GHz), and high gain of 4.5 dBi, and 5.46 dBi was achieved at 5.17 GHz and 5.8 GHz, respectively. In addition, the MIMO antenna's performance metrics are envelope correlation coefficient $< $ 0.01 and diversity gain $>$ 9.9 dB was assessed. The proposed MIMO antenna's performance is evaluated through full-wave EM analysis and physical measurements of the fabricated prototype.

This article presents the design and analysis of an all-metal frequency selective surface (FSS), aimed at achieving triple-bandpass filtering applications. The proposed structure is manufactured using a laser cutting method on a 1.2 mm thick stainless steel sheet. The proposed design is a slot-type element, making it ideal for all-metallic FSS designs. In each unit cell, slots are created by etching complementary split-ring resonator (CSRR) structures. These unit cells are arranged such that adjacent cells are rotated by 90°. The overall 2x2 configuration of these rotated unit cells forms the final unit cell of the proposed FSS design. The proposed design is polarization-insensitive for both TE and TM modes. This configuration demonstrated measured resonances at 5.67 GHz, 9.04 GHz, and 10.47 GHz, with an insertion loss of less than 1.4 dB across all frequency bands. The overall size of the filter is 0.75λ₀ × 0.75λ₀. The all-metal design offers high robustness and durability, making it an attractive solution for harsh environmental conditions and advanced communication systems.

This work demonstrates the development of an additive manufacturing-based transition from a microstrip to an empty substrate integrated waveguide (ESIW). An expanded ESIW section with a sharp dielectric taper allows for wideband impedance matching. The proposed transition is validated by simple, inexpensive and reduced complexity using additive manufacturing (AM) technique. The top and bottom of ESIW are covered with copper-coated polylactic acid (PLA) substrate of 0.5 mm thickness. The via holes in the ESIW are replaced by spraying copper on the internal walls. The proposed model’s veracity was further established by evaluating it against a subtractive manufacturing (SM) prototype. The measured results obtained using AM (SM) have an insertion loss of less than 2.24 dB (0.92 dB), a return loss better than 17.7 dB (18.08 dB), and 73.4 (60.8) % fractional bandwidth (FBW) over 10-21.6 (10-18.75) GHz.

This paper presents a novel frequency-reconfigurable self-diplexing antenna (SDA) utilizing a hybrid substrate-integrated waveguide (SIW). The antenna comprises a radiating slot, a feeding network, and a hybrid SIW cavity featuring half-mode circular and half-mode rectangular SIW structures. The unique feature of this antenna lies in its fine-tuning capability of each resonant frequency by inserting or injecting solid and liquid dielectrics into designated etched pockets. Experimental results demonstrate that the proposed structure can be effectively tuned within the frequency range of 2.7 to 3.47 GHz for the lower band and 4.05 to 4.96 GHz for the upper band. The mutual coupling between the ports is better than 20.4 dB, and the antenna maintains consistent radiation patterns across the entire operating range. The proposed tunable antenna, featuring precise frequency tuning capability, compact size, and stable radiation patterns, is well suited for various applications, including wireless communication systems, biomedical telemetry, microwave imaging, WiMAX, and Wi-Fi.