A number of recent works have shown that moment-method solutions of Hallén's and Pocklington's equations with the approximate kernel present undesirable and unphysical oscillations near the ends of the antenna and possibly (depending on the feed model) near the driving point. Such oscillations have been associated with the nonsolvability of the underlying integral equations. They necessarily occur when the number of basis functions is sufficiently large and cannot be blamed on finite computer wordlength or matrix ill-conditioning effects. In the present paper, we show that similar phenomena occur when one uses the "extended" thin-wire kernel, originally proposed by Poggio and Adams in the 1970s and currently used by the Numerical Electromagnetics Code (NEC), which is an antenna modeling software suite that has many variants (e.g., GNEC, EZNEC Pro, SuperNeC, MiniNEC). We discuss the nature and properties of the oscillations. In particular, we show that they are milder and less rapid than those with the approximate kernel. Our main tools of study are (i) numerical investigations that carefully distinguish from effects due to roundoff, (ii) an analytical study for the case of the antenna of infinite length. We finally apply the so-called effective-current method as a remedy to the issues arising from the said oscillations. ).1 These are usually referred to as Hallén-type integral equations or thin-wire integral equations. 2 The fact that oscillations are caused by nonsolvability is conclusive for the case of the oscillations near the center because an argument that is analytical in nature has been developed in [1] and [6]. No such analytical argument exists for the case of the oscillations near the ends; here, the existing evidence is numerical (but, in our opinion, overwhelming). The present communication will re-illuminate these issues.
This paper examines the multiple-input multiple-output (MIMO) characteristics of the vehicular MIMO channel at 5.9 GHz by analyzing the correlation of multipath components (MPCs) in the case of high antenna separation and the angular characteristics of the same scenario. The scenario is selected as crossing traffic on urban intersections. The 2 × 2 channel measurements with a wideband channel sounder are employed for the correlation analysis, and in parallel, the same scenario is simulated with a ray-tracing tool for the analysis of the angular domain. We introduce measures and tools to describe the relevant characteristics and the performance; the limitations of the ray-tracing simulation are also subdued to critical evaluation. The focus of this paper is set on the evaluation of the presented method on one selected experiment (combination of measurement and ray-tracing simulation) rather than on an exhaustive statistical analysis of many scenarios. The combination lies in the higher level of analyzing the MIMO characteristics of the channel using two different methods. The results provide that the MIMO channels show a similar power level in terms of mean MPC power, but the linear correlation stays relatively low. Specifically, discrete MPCs tend to be more highly correlated than diffuse MPCs. Furthermore, the angular spread is highly dynamic but small and substantially increases when both vehicles are near the center of the intersection. Significant power contributions caused by buildings along the roadside are identified
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