Abstract
A dual-channel 3D quasi-optical network (QON) system is analyzed and compared by theoretical and experimental results. It is divided into dual-channel signals by frequency selective surface (FSS) or wire grid polarizer (WGP) for transmitting the 324 GHz signal on the top layer while diverting the 183 GHz signal to the bottom layer. The system structure based on the beam radius is traced by the complex beam parameter and system transfer matrix for deciding the positions of cascade mirrors. The design principles and test results of FSS with perforated hexagonal array and WGP printed on the dielectric substrate are discussed together. In order to evaluate channel performance, the output planar near-fields of QON system are simulated and tested by the four reflections and three transmission results, respectively, where both scalar and vector conversion efficiencies are used to evaluate the quality of output beams. For the distortion phenomenon and energy loss in planar field, the aperture modes of corrugated horn feeds are analyzed by spherical wave expansion (SWE) to explain the asymmetrical pattern characteristic. The cut section of the far-field pattern is also directly measured in the compact antenna test range (CATR), comparing with the far-field patterns that are indirectly obtained based on the principle of near-to-far-field transformation and ideal aperture field integral of quiet zone (QZ). The differences between the near- and far-field test in QON have been compared, and discussion that the corresponding experimental results verify the WGP has better work performance in the good pattern symmetry, high cross-polarization isolation, low energy loss, and side-lobe level.
Highlights
In recent years, along with the rapid development of millimeter wave (MMW) and submillimeter wave technology, the quasi-optical network (QON) system with the features of multifrequency and multipolarization is widely applied in the radio astronomy, meteorological satellites, remote sensing, and imaging system [1]
This paper mainly focuses on the design principle, measurement, and contrast method towards the dual-channel 3D QON system between frequency selective surface (FSS) and polarizer
According to the size of beam radius calculated in the filter position, the dimension of FSS structure is selected as the 24.89 mm × 24.89 mm and can satisfy the condition that the length is larger than the four-time beam radius both in double channels
Summary
Along with the rapid development of millimeter wave (MMW) and submillimeter wave technology, the QON system with the features of multifrequency and multipolarization is widely applied in the radio astronomy, meteorological satellites, remote sensing, and imaging system [1]. In the higher frequency band, limited by high machining accuracy in the grooves and junction, the machining quality of corrugated horn can affect its far-field pattern that leads to nonuniformity symmetrical Gaussian distribution due to the decreasing of main mode HE11 This problem often appears on the manufacturing during the process of spark erosion, classical milling, and electroforming [18]. The FSS comprises periodic arrays of metallic patches (reflection) or apertures (transmission) that are fabricated in a conductor surface directly or printed on a dielectric-slab indirectly, where the different periodic structures contain center connected, loop, solid interior, or combination types They can finish a frequency selection perfectly with low-pass or high-pass features, obtaining a narrow band in the MMW range and very rapid cut-off characteristic outside the working frequency band is difficult [19, 20], so it is necessary to introduce the polarizer due to its frequency irrelevant attribute. We share relevant design and testing experience about the QON system
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