Читать книгу Fundamentals of Terahertz Devices and Applications - Группа авторов - Страница 33

In this section, we will show different example implementations of leaky‐wave antennas feeding silicon lenses. Figure 2.18 shows the photograph of the different prototype examples we will comment on.

Figure 2.26a and b show two prototypes of leaky‐wave microlens antennas fabricated at 550 GHz. The first lens was fabricated using laser micromachining, while the second lens was fabricated using DRIE silicon micromachining. Even though both antennas obtained a good agreement with the expected results, the DRIE silicon micromachined lens portrayed some aberrations that were visible in in the radiation pattern measurements showing an increase in the secondary lobes and a small tilt.

Figure 2.26c shows a microlens antennas at 1.9 THz integrated with a 1.9 THz Schottky‐based tripler all in the same wafer. The antenna was synthesized on 12 resistivity silicon wafers and the tripler waveguide circuit was synthesized on three wafers. All the wafers, including the lenses, were fabricated using DRIE silicon micromachining process, aligned using the silicon compressive pin technique, and finally glued together. An alignment better than 2 μm was achieved across the wafer stack [26]. Even though in this case, the lenses suffered from aberrations caused by the lack of the surface control in the fabrication process, well‐focused beam patters very similar to the design ones were achieved.

On another note, new efforts are now being investigated to enable lens beam‐scanning capabilities in the system front end. Figure 2.26d shows a highly integrated beam scanning lens‐antenna using a piezo‐electric motor demonstrated operating at 550 GHz presented in [48]. A hemispherical lens was glued on top of a silicon wafer containing alignment marks processed using DRIE silicon micromachining. The piezoelectric motor displaced the lens around ±1 mm from the center position of the lens, providing a beam scan of ±25°. Not only this method can be employed for improving the alignment of the lens with the feed, but it also has the potential to enable beam‐scanning capabilities on the system front end for future terahertz imaging systems.

The results achieved so far show a great potential to use these dielectric lens antennas in the development of future focal plane arrays at terahertz frequencies. By using the leaky‐wave waveguide feed, we only need a small part of the surface of the lens, which reduces the reflection losses and phase errors that these type of lenses suffer. But most of all, it allows the use of photolithographic process when fabricating the lens. The fabrication of the lenses using photolithographic process reduces the cost, with the same performance achieved with other fabrication methods, such as laser micromachining.