This paper presents the Received-Signal-Strength-Indicator (RSSI) based living-body radar, which uses only a single RF front-end and a few parasitic antennas. This radar measures the RSSI variation at the single active antenna while varying the terminations of the parasitic antennas. The propagation channel is estimated from just the temporal transition of RSSI; our proposal reconstructs the phase information of the signal. In this paper, we aim to estimate the direction of living-body. Experiments are carried out and it is found that most angular errors are within the limit of the angular width of the living-body.

Single front-end architecture with parasitic antenna element (PAE) in compact array system has been proposed for enhancing spectral efficiency and miniaturizing the receiver. Although most of studies paid attention to design optimal receiver with antenna mutual coupling on fading correlation, relatively little attention has been paid to noise. In this paper, we propose a low noise model for single front-end MIMO receiver system with PAE which includes arbitrary signal and noise coupling. The proposed model articulates physical noise sources and relates their spatial correlation with array receive antennas, parasitic element, front-end and matching circuit. A matching circuit is designed to achieve minimum noise figure. After that, the optimal PAE value is derived to maximize channel capacity. We present numerical analysis to verify the proposed system on certain conditions.

In recent years, wireless communication technology has been studied intensively. In particular, MIMO which employs several transmit and receive antennas is a key technology for enhancing spectral efficiency. However, conventional MIMO architectures require some transceiver circuits for the sake of transmitting and receiving separate signals, which incurs the cost of one RF front-end per antenna. In addition to that, MIMO systems are assumed to be used in low spatial correlation environment between antennas. Since a short distance between each antenna causes high spatial correlation and coupling effect, it is difficult to miniaturize wireless terminals for mobile use. This paper shows a novel architecture which enables mobile terminals to be miniaturized and to work with a single RF front-end by means of adaptive analog beam-forming with parasitic antenna elements and antenna switching for spatial multiplexing. Furthermore, statistical analysis of the proposed architecture is also discussed in this paper.

This paper proposes a channel capacity maximization method for Multiple-Input Multiple-Output (MIMO) antennas with parasitic elements. Reactive terminations are connected to the parasitic elements, and the reactance values are determined to achieve stochastically high channel capacity for the environment targeted. This method treats the S-parameter and propagation channel of the antenna, including the parasitic elements, as a combined circuit. The idea of the 'parasitic channel,' which is observed at the parasitic antenna, is introduced to simplify the optimization procedure. This method can significantly reduce the number of necessary measurements of the channel for designing the antenna. As a design example, a bidirectional Yagi-Uda array, which has two driven antennas at both ends of the linear array, is measured in an indoor environment. The resulting design offers enhanced channel capacity mainly due to its improved signal-to-noise ratio compared to the antenna without the parasitic antennas.

To cut down the sidelobe level of radiation pattern, a novel adaptive algorithm is proposed for electronic steering parasitic antenna. The composite objective function in this algorithm takes both directivity and sidelobe level of pattern into account, and the steepest gradient algorithm is selected to search the optimum value of reactive load. Simulations are carried out to validate the algorithm, simulated results show that the levels of sidelobe are both below -4 dB in different beamforming cases, and the front to back ratios are better than 10 dB.