The device, which the authors call a Funnel Morph Antenna, gets its name from a distinctive hybrid geometry that combines a narrow tapered neck with a flared upper section, resembling the profile of an industrial funnel. That shape is not merely aesthetic. In millimeter-wave antenna design, one of the central challenges is impedance matching: the antenna must present a consistent 50-ohm load to the feeding circuitry across a wide range of frequencies, or else a large fraction of the captured signal simply reflects back instead of being delivered to the rectifier. The funnel profile solves this by providing a gradual electromagnetic transition from the narrow neck, which concentrates surface currents toward the radiating aperture, to the wide flared portion, which extends the effective radiating area. Because the current path changes smoothly rather than abruptly, discontinuities that would normally cause reflections are minimized, and the antenna maintains a reflection coefficient below minus 10 dB across the full operating band.

The physics behind the wideband behavior is a story of overlapping resonances. Simulations of the surface current distribution at 28, 33, and 38 GHz reveal that different parts of the structure dominate at different frequencies. At 28 GHz, current concentrates around the narrow neck and lower radiating sections, corresponding to a low-frequency resonant mode. By 33 GHz, the current spreads into the flared upper portion, indicating the formation of additional resonant modes, and at 38 GHz the maximum current density shifts to the upper flare and the cavity regions, where shorter current paths support the highest-frequency operation. The superposition of these multiple modes is what stretches the usable bandwidth to a full 14 GHz, an unusually wide span for a compact millimeter-wave element. A multilayered cavity embedded in the ground plane adds further control, confining the electromagnetic fields and stabilizing the directional radiation pattern.

Perhaps the most provocative engineering decision in the study is the choice of substrate. Millimeter-wave devices almost always use specialized low-loss laminates such as Rogers RT/duroid, because ordinary FR4, the fiberglass material found in countless consumer circuit boards, suffers from significant dielectric losses and dispersion at frequencies above 26 GHz. The team deliberately chose 1.6-millimeter FR4, with a dielectric constant of 4.3 and a loss tangent of 0.02, to test whether a genuinely low-cost design could still perform. Despite the higher insertion losses, careful optimization of the flare and feed geometry allowed the antenna to achieve wideband matching, and the geometry proved robust against the etching tolerances of standard printed circuit board fabrication, holding its performance even with dimensional deviations of plus or minus 0.05 millimeters. The single element measures only about 17.5 by 20.3 millimeters and delivers a simulated peak gain of roughly 5 dBi with radiation efficiency above 85 percent, figures that measurements closely confirmed.

A single antenna, however, captures only a modest amount of power, so the researchers replicated the element into a four-element array. To feed all four elements uniformly, they designed a 1-to-4 Wilkinson power divider, a classic microwave component built from three cascaded two-way dividers, each using quarter-wavelength transmission lines with a characteristic impedance of twice the system impedance and a 100-ohm isolation resistor between output ports. The divider performed impressively across the band, with insertion loss between roughly minus 6 and minus 6.2 dB, meaning each output port receives almost exactly one quarter of the input power, and port-to-port isolation exceeding minus 45 dB around 30 GHz, indicating negligible signal leakage between channels. The array elements were spaced 5 millimeters apart, half a wavelength at the operating frequency, to maximize gain while suppressing unwanted side lobes.

The assembled array, measuring 78.25 by 70.57 millimeters, delivered a measured peak gain of 10.25 dBi and an efficiency of about 93 percent at 28 GHz. The theoretical maximum gain for four ideal elements with a single-element gain of 4.8 dBi would be 10.82 dBi, so the measured value falls only 0.57 dB short, a gap the authors attribute to feed network losses, conductor losses in the microstrip lines, and the dielectric losses inherent to FR4. The aperture efficiency, a measure of how effectively the physical area of the array is used, remained a steady 78.5 percent despite mutual coupling between elements and phase errors across the wide band. The beam pattern is notably narrow, with a half-power beamwidth of about 9 degrees at 28 GHz and 10 degrees at 38 GHz in one plane, and side lobe levels between minus 7 and minus 9 dB, giving the array a focused, directional sensitivity well suited to harvesting energy from distant base stations.

Converting captured radio waves into usable electricity falls to the rectifier, and here the team navigated some practical constraints. They selected the 1SS351 Schottky diode from ON Semiconductor, chosen because its electrical characteristics closely match the widely used HSMS-2852 diode, which has recently become obsolete. Using Keysight Advanced Design System software, the researchers modeled the diode with harmonic balance and S-parameter simulations to extract its input impedance, finding a value of 47.4 minus j20 ohms near 28 GHz. Matching that impedance to the antenna required careful design work. The team compared half-wave and full-wave rectifier topologies and found that the full-wave bridge significantly raises the imaginary component of the input impedance, which would degrade efficiency without elaborate matching. A matched half-wave rectifier using microstrip lines emerged as the practical choice, especially after lumped-element matching proved infeasible because it required component values, such as a 53-ohm resistor and a 2.7-nanohenry inductor, that are difficult to source off the shelf.

The full system was validated experimentally in an anechoic chamber, with a broadband vector signal generator driving a standard gain horn antenna as the transmitter and the fabricated rectenna prototype as the receiver, separated by one meter, comfortably within the far-field region for these frequencies. Both antennas were carefully polarization-aligned, and the incident power density was calibrated with a broadband power sensor before characterization. When the array harvested 68.7 microwatts of incident RF power, the system produced an output voltage of 250 millivolts across a 2-kilohm load, corresponding to an overall RF-to-DC conversion efficiency of 45.5 percent. That figure is competitive with, and in several respects superior to, prior millimeter-wave rectennas, many of which required expensive substrates, waveguide structures, or far higher input power levels to reach comparable efficiency.

The comparison with earlier work underscores why the low-cost approach matters. Previous millimeter-wave rectennas have relied on Duroid substrates, substrate-integrated waveguides, liquid crystal polymer packaging, on-chip CMOS integration, and even air-filled waveguide Fabry-Perot resonators. Some achieved higher peak gains or higher conversion efficiencies, such as a waveguide-fed 35 GHz design reaching 68.5 percent, but typically with narrower bandwidth, more complex manufacturing, or substantially greater incident power. Others, like CMOS folded dipoles, achieved extreme miniaturization at the cost of negative gain. The new design occupies a distinctive middle ground: a full 26 to 40 GHz operating range, a respectable 10.25 dBi gain, a narrow 9-degree beamwidth, and 45.5 percent conversion efficiency, all on ordinary FR4 fabricated with standard PCB technology.

The implications reach beyond the laboratory. As 5G and future 6G networks densify urban radio environments, the ambient millimeter-wave energy available for harvesting will only grow, and devices that can scavenge it without batteries could power IoT sensors, wearables, and backscatter tags indefinitely. The authors suggest that future work will explore miniaturization techniques and adaptive beamforming to improve integration into compact real-world devices. If battery production costs, which are high relative to the energy those batteries actually store, continue to drive the push toward green electronics, a funnel-shaped patch of fiberglass that drinks from the 5G spectrum may prove to be one of the more elegant shortcuts to energy-autonomous wireless devices.

Subject of Research: A wideband funnel-geometry rectenna array for radio-frequency energy harvesting in the 26–40 GHz 5G millimeter-wave band

Article Title: Wideband funnel geometry rectenna array for RF energy harvesting in 26–40 GHz 5G networks

Article References: Megahed, A. A., Mousa, M. E., Al-Gburi, A., & Elabd, R. H. (2026). Wideband funnel geometry rectenna array for RF energy harvesting in 26–40 GHz 5G networks. Results in Optics, 25, Article 101178. https://doi.org/10.1016/j.rio.2026.101178

Image Credits: AI Generated

DOI: Not provided

Keywords: rectenna, RF energy harvesting, 5G, millimeter-wave, antenna array, Wilkinson power divider, Schottky diode, FR4 substrate, wireless power transfer, impedance matching, IoT, Results in Optics

A new analysis published in Communications Engineering examines how two familiar wave phenomena, reflection and transmission, can be harnessed systematically to keep terahertz links alive when the direct path between transmitter and receiver is blocked. The work argues that non-line-of-sight terahertz communication should not be treated as an afterthought or a failure mode, but as a first-class design objective, engineered deliberately into the architecture of future sixth-generation networks. By treating reflective surfaces such as walls, ceilings, glass facades, and even road signs as passive allies, and by exploiting controlled transmission through materials such as drywall and window glass, the study sketches a pathway toward terahertz coverage that survives the shadows cast by everyday obstacles.

The scale of the challenge is rooted in fundamental electromagnetics. As frequency increases, the free-space path loss between two antennas grows with the square of the frequency, so a terahertz link at 300 gigahertz suffers dramatically more spreading loss than a microwave link carrying the same distance. Diffraction, the phenomenon that allows lower-frequency radio waves to bend around corners and fill rooms with coverage, becomes vanishingly weak at terahertz frequencies because the wavelengths, on the order of a millimeter or less, are tiny compared with the edges and gaps of ordinary objects. Scattering from rough surfaces, which would smear energy in many directions at lower frequencies, becomes more specular and directional, meaning that a terahertz wave bounces off a flat wall much the way a billiard ball bounces off a cushion: predictably, but only along a narrow geometric path determined by the law of reflection.

This directional character is a double-edged sword. On one hand, it means that a blocked terahertz link cannot rely on the diffuse, multipath-rich propagation that made older cellular systems robust. On the other hand, it means that reflected paths are stable, identifiable, and potentially very high quality. A signal that bounces once off a well-positioned wall arrives with a predictable delay, a predictable angle of arrival, and, if the surface is sufficiently smooth and conductive, only a modest additional loss. The new analysis emphasizes that in many indoor and street-canyon scenarios, first- and second-order reflected paths can deliver received power levels well within the sensitivity range of modern terahertz receivers, provided that the antenna beams are steered to illuminate and collect from those paths deliberately.

Beam steering is therefore the linchpin of the approach. Terahertz systems almost universally employ highly directional antennas, often implemented as phased arrays of many small radiating elements, to concentrate their limited power into a narrow pencil beam and to overcome path loss. In a line-of-sight world, pointing such a beam is straightforward. In a non-line-of-sight world, the network must first discover which reflective or transmissive paths exist, then select the best one, and then keep the beam locked onto it as people move and doors swing open. The analysis highlights beam management as a central research problem: hierarchical search procedures, machine-learning-assisted path prediction, and the use of out-of-band or sub-6-gigahertz control channels to cue the terahertz beam are all candidate techniques for finding a viable reflected route in milliseconds rather than seconds.

Reconfigurable intelligent surfaces, sometimes called smart metasurfaces, extend this idea from accidental reflectors to engineered ones. These are thin panels studded with subwavelength elements whose electromagnetic response can be tuned electronically, allowing the panel to act as a programmable mirror that redirects an incoming terahertz beam toward a chosen receiver, or even to shape the wavefront in ways a plain wall never could. Mounted on ceilings, building facades, or interior walls, such surfaces could serve as deliberate relay points, stitching together coverage in courtyards, corridors, and factory floors where no natural reflection geometry happens to work. The study situates these engineered surfaces alongside natural reflections as complementary tools in the non-line-of-sight toolkit, noting that their low power consumption and passive operating principle make them attractive for dense deployment.

Transmission, the second pillar of the analysis, is often dismissed at terahertz frequencies because many common building materials attenuate the signal severely. Concrete and brick are effectively opaque, and even wood and glass introduce losses that grow rapidly with frequency and thickness. Yet the picture is nuanced. Drywall, plasterboard, and standard window glass can pass usable fractions of the incident power at the lower end of the terahertz range, particularly near 100 to 140 gigahertz, where several standards bodies are now defining early commercial allocations. A signal that passes through a single interior wall may arrive attenuated but decodable, especially when the transmitter can boost power or the receiver can integrate over longer symbol durations. The analysis argues that material-aware network planning, in which the propagation database records not only reflectivity but also transmissivity of the surfaces in a given environment, allows the network to choose intelligently between penetrating an obstacle and bouncing around it.

The interplay between reflection and transmission also shapes how channel models must evolve. Classical statistical channel models, built for scattering-rich microwave environments, poorly describe terahertz links, which are dominated by a small number of deterministic geometric paths. Ray-tracing simulations, seeded with accurate three-dimensional models of buildings and streets and with measured material parameters, emerge as the preferred planning tool. The analysis stresses that measurement campaigns at terahertz frequencies remain comparatively sparse, and that closing this gap between modeled and measured channel behavior is essential before operators can trust simulated coverage maps. Hybrid approaches that combine sparse measurements with ray-tracing interpolation, updated in real time from the feedback that connected devices report, offer a pragmatic middle path.

The implications reach well beyond faster smartphone downloads. Terahertz non-line-of-sight techniques are critical for industrial wireless networks, where metal machinery guarantees that direct paths will be blocked, and where deterministic, ultra-reliable low-latency communication is a hard requirement for replacing factory cabling. They matter for vehicular networks, where the geometry of a street canyon creates rich reflection opportunities off building walls and parked vehicles, and for integrated sensing and communication, in which the same reflected terahertz signals that carry data can simultaneously image the environment. They also underpin the vision of wireless data centers and chip-to-chip links, where racks and heat sinks create a maze of reflective metal surfaces that a well-designed terahertz system can exploit rather than suffer.

Considerable engineering hurdles remain before reflected and transmitted terahertz paths can be managed at network scale. Phased arrays with thousands of elements consume significant power, and the phase shifters and amplifiers behind them are still costly at these frequencies. Beam alignment protocols must become faster and more energy-efficient, and handover between line-of-sight and non-line-of-sight states must be seamless enough that users never notice the network quietly rerouting their connection around a passing pedestrian. Standardization bodies are actively working to define the measurement, signaling, and beam-management procedures that would let multiple vendors implement interoperable non-line-of-sight behavior. What the new analysis makes clear is that the physics need not be an enemy. The same specular, mirror-like behavior that makes terahertz waves unforgiving also makes them predictable, and predictability is precisely what a carefully engineered network needs. If future 6G systems learn to treat every wall and window as potential infrastructure, the terahertz frontier may arrive not despite the obstacles in its path, but because the network has learned to use them.

Subject of Research: Non-line-of-sight terahertz communications using reflection and transmission for future 6G networks

Article Title: Non-line-of-sight terahertz communications enabled by reflection and transmission

Article References: Liu, F., Seddon, J., Belio-Apaolaza, I., G. Huggard, P., Wang, H., Lia, E., Deborgies, F., Wu, J. E., Munshi, M. N., Fice, M., & Seeds, A. (2026). Non-line-of-sight terahertz communications enabled by reflection and transmission. Communications Engineering. https://doi.org/10.1038/s44172-026-00782-6

Image Credits: AI Generated

DOI: 10.1038/s44172-026-00782-6

Keywords: terahertz communications, non-line-of-sight, 6G, beam steering, reconfigurable intelligent surfaces, reflection, transmission, channel modeling, millimeter wave, wireless networks, Communications Engineering, phased arrays