Abstract
This work presents novel techniques to realize a retrodirective millimeter wave antenna array with wide field of view. High gain arrays in phase conjugate configuration are used in combination with orthogonal polarization states and a novel pulse modulation technique to improve backscattering which finds its application in localization and enabling data transmission from sensor nodes. The proposed approach avoids the use of amplifiers thereby reducing the cost, complexity and power consumption of sensor nodes while providing a wide field of view. The basic building blocks of the proposed antenna array are compact one-dimensional (1D) slot arrays that can be designed with orthogonal linear polarizations. Their compact size limits the grating lobes under −10 dB level with respect to the main beam to enable 120° retroreflective field of view, thus, eliminating the reflections in undesired directions while providing 90° rotated linear polarization for the reflected signal with respect to the incident signal polarization. The orthogonal polarization states and compact size are achieved by using a two-layer structure and exploiting the characteristics of substrate integrated waveguide and rectangular cavities. Arrays are designed, prototyped and characterized to validate the proposed concepts. −6pt
Highlights
A N amplifier-less backscattering retrodirective tag finds its application in several low power radio frequency (RF) systems such as senors to sense displacement [1] and humidity in confined environment [2], data communication nodes [3], [4], as target in automotive radar [5] and millimeter wave imaging [6]
A retroreflective tag design featuring improved backscattering, amplitude modulation, orthogonal incident and reflected polarization states and wider FoV with suppressed grating lobes is introduced in this article
The tag design procedure is presented with the description of the radiating elements, elevation plane beamforming arrays and delay lines connecting the radiating elements to form a retroreflective array
Summary
A N amplifier-less backscattering retrodirective tag finds its application in several low power radio frequency (RF) systems such as senors to sense displacement [1] and humidity in confined environment [2], data communication nodes [3], [4], as target in automotive radar [5] and millimeter wave imaging [6]. The proposed tag operates in X-band with inter-element spacing of 1.5λg with phase modulation realized by switching between different length transmission lines using PIN diode. K is the free-space wavenumber, n is an integer ranging from 1 to 8 representing each antenna element in the array, d is the spacing between the antenna elements and θ is an independent variable in the AF varying from −90o to +90o It can be derived from this figure that around the design frequency, the reflected beam squints with an approximate rate of 22o/GHz. It is important to mention that the phase slope of the line increases with its length. The measurement setup and tag characterization are discussed
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