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In this communication, a time-frequency joint method is proposed to evaluate the performance of ultrawideband (UWB) antennas for the radiation of high-power (HP) electromagnetic pulses. First, conventional antenna parameters, such as the efficiency, gain, and so on, are translated to UWB pulsed antennas from the energy perspective, so as to get several scalar antenna parameters, since energy in one pulse is finite. Thus, the power-spectrum weighted efficiency ($\eta _{e}$), directivity ($D_{e}$), and gain ($G_{e}$) are proposed. Then, several electromagnetic norms of the radiating pulse are selected to characterize the sensitive parameters of the equipment under test (EUT). Based on these, several other scalar antenna parameters are proposed, which are the effective potential gain ($G_{ep}$), pulse sharpening factor (PSF), and peaking impulse gain ($G_{PI}$). Thus, a set of time-domain scalar criteria are proposed to evaluate the performance of HP-UWB antennas. These criteria can be calculated with the frequency functions of conventional antenna parameters, which demonstrate the inherent properties of one antenna. Finally, the performance of two kinds of typical HP-UWB antennas, namely the impulse radiating antenna and the combined antenna, is measured and compared with the proposed method. It indicates that, with the proposed method, one can not only get the inherent properties of one antenna in the frequency domain but also quantitatively compare the performance of different antennas with a given exciting pulse in the time domain with the proposed scalar antenna parameters. [ABSTRACT FROM AUTHOR]

In this paper, the combined antenna array is developed to maximize the effective potential gain ($G_{ep}$) within finite aperture area for the high-power ultra-wideband (UWB) radiation. The idea is to make the antenna element as small as possible, so that more elements can be arranged within the prescribed aperture area to maximize $G_{ep}$ of the UWB system. On the other hand, the antenna element should match the pulse excitation. This means that in the frequency domain, the working band of the antenna element should cover the spectrum of the radiated pulse, and in the time domain, critical parameters of the radiated field (e.g., rise time of the monopolar pulse) should not be distorted, and those can be the principles for the UWB antenna to match the pulsed excitation, based on which the minimum size of the antenna element can be determined. With this method, a four-element combined antenna array is designed. Also, an impedance transformer and power divider are designed to feed the antenna array. Also, a big combined antenna is developed with the same aperture dimensions (30 cm $\times30$ cm) as the antenna array. Then, the performances of the antenna array and the big antenna are measured and compared. Compared with the big antenna, $G_{ep}$ of the antenna array is 21% higher under the applied excitation, which indicates that the proposed method can significantly improve $G_{ep}$ of the UWB system within the prescribed aperture area. Finally, the antenna array is furthermore optimized by adjusting the distances between the elements, and $G_{ep}$ is improved by another 11%, the total improvement is 33%, and the corresponding effective potential gain is 1.49. [ABSTRACT FROM AUTHOR]

Transient electromagnetic fields can couple to overhead power transmission and distribution lines, causing damage to the connected equipment. In real cases, incident electromagnetic fields exhibit different spatial and temporal waveform distributions along the line. Normally, to ensure the accuracy of the simulation results, a large number of observation points are needed along the line, which is difficult to obtain. This paper proposes a new approach to address this problem. The proposed approach is based on Agrawal et al.’s coupling model, in which the amplitude and phase distributions of the horizontal exciting electric field along the line are, respectively, represented by the Fourier series and polynomial functions in the frequency domain using two kinds of least squares methods. As a result, the source terms along the line can be accurately evaluated starting from a limited number of observation points. The proposed approach has been validated experimentally. [ABSTRACT FROM AUTHOR]