The concept of self-mixing antenna arrays is presented and analyzed with respect to its beneficial behavior of large gain over a wide angular range. The large gain is attained by an antenna array with large element spacing, where all array element signals are combined approximately coherently over the entire angular receiving range. This functionality is achieved by the self-mixing principle, where an exact description via an intermediate frequency (IF) array factor is derived. For verification purposes, a 4 × 2 self-mixing array is fabricated and measured in the frequency range from 34 GHz to 39 GHz. A multiple-resonances millimeter-wave microstrip patch antenna has been especially developed to achieve large bandwidth and a wide angular receiving range. The broad beamwidth is achieved by two parasitic patches and suitable radiation characteristics of the resonant modes. The self-mixing of the receive signal is realized at each antenna element by a Schottky diode with an optimized operating point. The down-converted array element signals are then combined and measured at the IF. The receive power is increased significantly over a large angular range as compared to conventional array feeding techniques. The simulation results are verified by measurements, which show very good agreement.Index Terms-Active antenna arrays, broad bandwidth, frontend circuitry, intermediate frequency (IF) beamforming, microstrip patch antenna, nonreciprocal receiving antenna, wide beamwidth. I. INTRODUCTIONF OR THE increasing demand of ever-expanding data rates in wireless communications, millimeter-wave (mm-wave) frequencies are widely investigated, e.g. for the fifth generation mobile communication standard [1]-[3] or the Wifi standard WiGig [4], [5]. Data links at such high radio frequencies (RF) enable higher data rates, corresponding to an increased channel capacity obtained by the utilization of wide-band radio channels. Yet, mm-wave communication suffers significantly from the high path loss according to the Friis transmission equation [6]. Therefore, antennas or antenna arrays should have a large gain to compensate for the path loss [7]- [10].
Two novel decoupling and matching networks (DMNs) in microstrip technology for three-element uniform circular arrays (UCAs) are investigated and compared to a more conventional DMN approach with simple neutralization lines. The array elements are coaxially-fed quarter-wavelength monopole antennas over a finite groundplane. Three-element arrays are considered since UCAs with an odd number of elements are able to provide an almost constant maximum array factor over the whole azimuthal angular range. The new designs are explained from a theoretical point of view and their implementations are compared to four-and three-elements UCAs without DMN in terms of decoupling and matching bandwidth as well as beamforming capabilities. In addition to excellent decoupling and matching below −16 dB, a broader bandwidth is obtained by the two DMNs. The reasons for the enhanced bandwidth are similar in both cases: By introducing several circuit elements offering additional degrees of freedom, matching of the monopole input impedances at different frequencies becomes feasible. One of the presented designs offers a larger bandwidth, while the other design is able to provide a better total efficiency. Scattering parameters, radiation patterns, beamforming capabilities, and enhanced gain are all verified by measurements over the operating bandwidth.
Abstract. A tracking solution for collision avoidance in industrial machine tools based on short-range millimeter-wave radar Doppler observations is presented. At the core of the tracking algorithm there is an Extended Kalman Filter (EKF) that provides dynamic estimation and localization in real-time. The underlying sensor platform consists of several homodyne continuous wave (CW) radar modules. Based on In-phase-Quadrature (IQ) processing and down-conversion, they provide only Doppler shift information about the observed target. Localization with Doppler shift estimates is a nonlinear problem that needs to be linearized before the linear KF can be applied. The accuracy of state estimation depends highly on the introduced linearization errors, the initialization and the models that represent the true physics as well as the stochastic properties. The important issue of filter consistency is addressed and an initialization procedure based on data fitting and maximum likelihood estimation is suggested. Models for both, measurement and process noise are developed. Tracking results from typical three-dimensional courses of movement at short distances in front of a multi-sensor radar platform are presented.
Abstract. A new receiving scheme for self-mixing receivers is presented that overcomes the disadvantages of the selfheterodyne concept. Generally speaking, the self-mixing receiver offers immunity to phase noise and frequency offsets, especially at very high frequencies, since it does not require radio frequency local oscillators. Our proposed technique eliminates the drawbacks of the self-heterodyne transmission scheme, which are the poor power efficiency and the strong dependence on the continously transmitted carrier.A nonlinear system of equations is constructed that describes a phase retrieval problem for the reconstruction of the original transmit signal before self-mixing. Two different solution strategies, with restrictions in time and frequency domain, are presented. As a consequence, the self-mixing equation system is shown to be solvable with some a-priori information about the transmit signal. With this novel approach, the transmitted information is distributed over the full available bandwidth, and there is no special dependence on a certain subcarrier for the down-conversion.The general performance, regarding bit error ratio over signal to noise ratio, is improved by at least 2 dB as compared to the self-heterodyne transmission scheme. In the case of frequency selective channels, e.g. multi-path propagation, this improvement is shown to be much larger, because the presented approach is able to reconstruct the received subcarriers without the necessity of receiving all subcarriers.
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