A new fading reduction technique applicable to small shipborne antennas in the future maritime satellite communications is proposed. This technique has simple hardware construction and a good fading reduction effect. In this paper, the principle of the proposed fading reduction technique and the theoretical reduction effects of the technique are presented, comparing with those of the Polarization Shaping Method.

It is expected that software receivers will be widely available for radio communication, broadcasting and radio monitoring applications because they are able to be equipped with multimode, multirate and multiband functions in a single hardware platform. This paper describes the basic techniques required for software receivers for both hardware and software. The evaluation items and methods were studied and some evaluations done with an experimental software receiver model fabricated for radio monitoring applications. Future concepts in radio communication, broadcasting and radio monitoring applications where software receivers are thought to be suitable, were studied, and problems for realization identified.

Short backfire (SBF) antenna developed by H.W. Ehrenspeck is experimentally well-known to have high efficiency radiation characteristics in spite of its small size so far. Therefore this antenna is expected to be one of the candidates of single antennas and an element of array antennas for several types of communications. For example, this antenna has been proposed for shipborne antenna of INMARSAT-M system for maritime satellite communications. Although many efforts to analize and/or optimize this antenna has been made mainly experimentally, rigorous design procedure has not been almost established even now because of its complex configuration. In 1980, an approach to analyze this antenna was tried by Kawakami, H. and et al. which was the first attempt to obtain the theoretical characteristics by more rigorous process, however, from the view points of practical designing, the calculated values in their paper were insufficient because of the lack of strict numerical consideration. Upon the above circumferences, analysis of SBF antenna is performed in this paper by using method of moment with wire-grid model from the view points of establishing the design technique. This paper presents the analytical results of the radiation characteristics of this antenna and also the comparison with the experimental results. From this study, it can be noticed that the radiation characteristics of this antenna can be almost exactly analyzed and also there exists the good agreements between the theoretical and experimental results.

Four sets of on-board experiments regarding the measurements of 1.5 GHz multipath fading on propagation paths with low elevation angles and evaluation of fading reduction effects using the polarization shaping method were carried out. This paper describes the outline of the experiments, results obtained, and the comparison with theoretical values of the model presented by the authors. Results indicate that fading depth hardly depends on the wave height when the wave height is higher than 1 m, and that the polarization shaping method is effective for both up-link and down-link fadings for sea conditions with a wave height of up to at least 3 m.

Interference suppression is one of the important functions for mobile communications and software radio. First, this paper shows a new type of interference suppression method by P-RCE (Probability-Restricted Coulomb Energy) which is applicable to mobile communications and software radio. P-RCE is one of the neural networks and mainly used in the field of pattern classification. Secondly, this paper presents several characteristics of this method. For example, it is found from our studies that good suppression effects can be performed even when the interference signals exist closely adjacent to the desired signal and/or total number of signals is more than that of the antenna elements. Next, this paper discusses two types of improvement of processing speed for new suppression method. One is the setting up the learning and non-learning intervals, and the other is the restriction of the number of prototype cells. According to the results, fairly good improvement is realized.

This paper describes the characteristics of multipath fading in aeronautical satellite communications by mainly applying the maritime fading model.

This letter presents experimentally that the power gain of axial-mode helical antenna can be improved by installing a relatively thin dielectric cylinder outside the helix, and also presented in some theoretical consideration to clarify the above effect approximately.