Our research activity last year has involved the exploration of new slot design for the parallel-plate leaky-wave antennas for better antenna efficiency and higher radiation directivity to meet the communication requirements in the terahertz regime. We first show that, at high frequencies, the wavelength-scale interaction with the aperture causes a nonuniform electric field distribution at the slot interface. This effect becomes more pronounced as the slot width increases and leads to the collapse of the well-known frequency-angle relationship. This observation suggests a limitation on the slot width of the leaky-wave antenna and therefore the device efficiency. To address this issue, we propose and analyze a trapezoidal slot (as an alternative to a fixed width rectangular slot) parallel-plate leaky-wave antenna using numerical simulations and experimental measurements, showing a preserved frequency-angle relationship while allowing higher output coupling efficiencies and higher directionality.
An important result involves an optimization of the geometry of leaky wave antennas. This idea (in which a waveguide contains an aperture that allows some of the guided radiation to “leak” out into free space) has been exploited for decades at lower frequencies. However, when translated to the THz realm, one enters a distinct range of parameter space, which leads to qualitatively different behavior. To be specific, we consider a parallel-plate metal waveguide with a rectangular aperture opened in one of the plates. A typical (rf) realization of this configuration would generally use a slot whose width is much less than the wavelength of the guided wave, such that the wavefront of the guided mode underneath the slot is nearly flat. However, at frequencies in the millimeter-wave and terahertz range, it is quite easy to create a situation where the slot width is comparable to, or even larger than, the wavelength. In this case, the conventional angle-frequency relation imposed by phase matching no longer strictly applies, since the wavefront underneath the slot need not be (and usually isn’t) planar. In our work, we demonstrated this departure from the conventional behavior, and then proposed a novel trapezoidal slot configuration to solve this problem. This new design preserves the valuable one-to-one coupling between frequency and angle, while also optimizing the emission efficiency (in contrast to a narrow rectangular slot, for which the frequency-angle relation is preserved but the emission efficiency is quite low). This work demonstrates true pencil-like beams from a leaky-wave aperture, for the first time. The results have been published in Applied Physics Letters.
Publications
H. Guerboukha, R. Shrestha, J. Neronha, O. Ryan, M. Hornbuckle, Z. Fang, and D. M. Mittleman, “Efficient leaky-wave antennas at terahertz frequencies generating highly directional beams,” Applied Physics Letters, 117, 261103, December 2020.