Abstract
The paper describes the development of passive, chipless tags for a novel indoor self-localization system operating at high mm-wave frequencies. One tag concept is based on the low-Q fundamental mode of dielectric resonators (DR) which exhibits peak scattering at its resonance frequency. As the radar cross-section (RCS) of DRs at mm-wave frequencies is far too low for the intended application, arrays of DRs and combinations with dielectric lens and corner reflectors are investigated to boost the RCS while keeping the scattering retro-directive over wide-angle incidence. Satisfactory results are demonstrated experimentally in W-band with metal corner reflectors combined with planar arrays of DRs; the tags produce a high RCS level over a moderately broad angular range and a wide frequency range where they exhibit a notch at the resonance frequency of the dielectric resonators. These designs suffer from low coding range of 3 to 6 bit, degradations of RCS in angular range, and a difficult separation of the tag response from strong clutter. Both the suppression of large clutter interference by using time gating of the tag response and a larger coding range are promised by a chipless tag concept based on multiple high-Q resonators in photonic crystal (PhC) technology. Experimental samples are characterized as transmission resonators and as retro-directive tags at the 230 GHz band. As a concept to boost the retro-directive RCS with a truly wide-angle response, the integration of PhC resonators with a Luneburg lens is discussed.
Highlights
Automation in logistics and industrial processes increasingly requires highly precise, autarch self-localization of, e.g., robots or autonomous vehicles in an indoor environment
This paper has presented the evolution of tag landmark designs for a novel selflocalization system
Tags based on single dielectric resonators were found to provide retro-directive scattering but with far too low radar cross-section (RCS) levels for our system application
Summary
Automation in logistics and industrial processes increasingly requires highly precise, autarch self-localization of, e.g., robots or autonomous vehicles in an indoor environment. It is found that, for optimum notch depth, the DRs must be placed at a distance from the metal reflector of approximately half-wavelength or multiples These designs combine high RCS level with a useful frequency position coding by a notch signature; they are still not satisfactory as they are limited in incidence angle to the near-broadside directions. This design allows corner reflector sizes as large as required to overcome the clutter while providing its high RCS and deep notch signature over a wide range of incidence angle As in this example, the freedom to place the two distinct spectral notch positions by choosing suitable DR sizes increases the frequency position coding range for tag identification to equivalent 5-bit over the equivalent 3-bit when only a single DR size is used. As demonstrated in [13] and indicated in Fig. 8, a spherical lens reflector could be an
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