Single-resonance-based radio frequency (RF) resonators cannot detect multiple cracks simultaneously nor localize the position of a crack. To address these drawbacks, we propose a complementary split-ring resonator (CSRR)-loaded array. In this array, there are four channels and each channel consists of three CSRRs, forming a 4×3 sensing array that is developed in the ground plane of a microstrip line using a low-cost FR4 substrate. A voltage-controlled oscillator (VCO) generates three discrete frequencies: 1.88 GHz, 2.60 GHz, and 3.61 GHz to each channel, which is sequentially selected using a single-pole four-throw (SP4T) switch. The transmitted RF signals are converted into the DC voltage levels and are interpreted by a microcontroller. Aluminum sheets with cracks embedded in the surface are used to demonstrate the detection of cracks of various shapes, sizes and locations/orientations (horizontal, diagonal, and vertical) with simulations and measurements. The detection of the minimum detectable crack (Wc×Lc×Dc = 1 mm × 10 mm × 0.1 mm) is experimentally verified. Full-length longer cracks (Lc = 100 mm) are also detected using our proposed detection system with the SP4T switch in addition to our proposed algorithm that scans the CSRRs of each selected channel.

In this communication, a high-gain planar antenna with a conical beam (CB) is presented for millimeter-wave drone applications. The proposed antenna comprises a vertical monopole and a circular side reflectors. The high-gain CB is achieved by in-phase reflections from the planar annular-distributed side reflectors which is realized by a series of via walls using the printed-circuit-board (PCB) fabrication. The proposed structure was numerically and experimentally demonstrated. Full-wave analysis shows a 10 dB impedance bandwidth (BW) of 26.50–29.96 GHz, corresponding to 12.26% of the fractional BW, whereas the measured data account for 11.6% in the frequency range of 26.63–29.91 GHz. Meanwhile, a maximum peak gain of 8.51 dBi is observed at a beam-pointing angle of 22°, with a high radiation efficiency of 88.3%. Owing to these valuable features of high gain, good CB radiation performance, and simple planar structure, the proposed antenna is a promising candidate for millimeter-wave drone applications.

This paper proposes a composite right/left-handed dual-beam leaky-wave microstrip antenna with tunable operating region for V-band radiation coverage. Due to wideband excitation for second higher order modes, the symmetrically formed side-byside dual-beam initially scans in one quadrant from 52.5–65 GHz. Further, by appropriate placement of metallic via holes, a pair of back to back half-modes realizes generating two symmetrical side beams in E-plane with enhanced gain over 40–52 GHz. Mode switching is performed electronically by incorporating PIN diodes and proper biasing network. Finally, incorporating half-sinusoidal interdigital slot variations and periodically placed switching diodes enables composite right/left-handed media having frequency beam steering from backward-broadside-forward quadrant. Leaky bands in microstrip higher order modes were analyzed by dispersion characteristics, and the proposed antenna achieved - 10 dB impedance bandwidth of 29.2%, scanning range in H-plane from -65° to +69.7°, and peak gain of 18.7 dBi for the unbiased state; and 28%, -78° to +69.6° and 18 dBi, respectively for the biased state. The average side lobe level and minimum cross polar level are obtained as 13.5 dB and 23 dB, respectively. The fabricated prototype responses closely matched theoretical predictions, verifying the proposed concept.

This paper presents a high gain wideband metasurfaced magneto-electric dipole for WiGig applications. The proposed antenna achieves wide bandwidth and low cross-polarization. In addition, peak gain is increased by employing a metasurface which is working as a partially reflective surface. The proposed idea is numerically and experimentally demonstrated. Full-wave analysis shows 10 dB impedance bandwidth of 53.47–80.26 GHz, corresponding to 40.5%, while the measured data achieves 39.3% with the frequency from 47.2–70.3 GHz. Meanwhile, the simulated and measured 3-dB gain bandwidth of the proposed antenna are 52.86–66.86 GHz (23.3%) and 51.86–67 GHz (25.5%), respectively. Peak gain increased by 3.37–5.57 dB when including the metasurface; providing 11.9–13.65 dBi for 57–66 GHz, corresponding to the WiGig bandwidth.

Digital programmable coding metasurfaces (DPCMs) have recently attracted enormous attention and have been broadly applied, owing to their ability to manipulate electromagnetic (EM) wave behaviours and programmable multi-functionality. Recent DPCM works are divided into reflection and transmission types (R-DPCM and T-DPCM, respectively); however, there are only a few reported T-DPCM works in the millimetre-wave spectrum, owing to the difficulty of realising the large-phase controllable range while maintaining low transmission losses with electronic control components. Consequently, most millimetre-wave T-DPCMs are demonstrated only with limited functions in a single design. Additionally, all these designs use high-cost substrate materials that constrain practical applicability, owing to cost-ineffectiveness. Herein, we propose a 1-bit T-DPCM that simultaneously performs three dynamic beam-shaping functions with a single structure for millimetre-wave applications. The proposed structure is completely constructed using low-cost FR-4 materials, and operation of each meta-cell is manipulated using PIN-diodes, thus driving the achievement of multiple effective dynamic functionalities including dual-beam scanning, multi-beam shaping, and orbital-angular-momentum-mode generation. It should be noted that there are no reported millimetre-wave T-DPCMs demonstrating multi-function design, thus showing a gap in the recent literature of millimetre-wave T-DPCMs. Moreover, cost-effectiveness can be significantly enhanced, owing to the construction of the proposed T-DPCM using only low-cost material.

This paper proposes a single layered electronically tunable annular surface plasmon polaritons (SPP) based leaky-wave antenna at 60 GHz for continuous azimuthal beam scanning. Initially, the groundless annular SPP transmission line is designed having specialized feeding mechanism which is operational at 60 GHz under SPP mode. Periodic radiating semicircular patches are incorporated on the vicinity of the TL that form an additional momentum caused to convert the slow-wave SP mode to radiating leaky-mode and placement of extra metallic ground makes the radiated beam unidirectional. Further, implementation of the varactor diodes with imposed suitable switching conditions make the geometry electronically tunable to achieve a continuous complete azimuth coverage. The theoretical predictions, numerical simulations and the experimental validations of the proposed structure show good agreement. The proposed antenna show an overall scanning range of 275°, peak gain of 19.9 dBi with average side lobe level of -10 dB and minimum cross polar level of -20 dB. Availing the benefits from the low-profile compactness and improved performance, the proposed groundless LWA appears as a promising candidate for integration in 60 GHz mm-wave applications.