In order to improve the operating bandwidth and achieve a compact design of the combined antenna, the Klopfenstein impedance taper method is adopted to implement the structure of the combined antenna in this paper. The effects of Klopfenstein taper with different parameters are compared and analyzed with simulation method. Also, the quantity of the magnetic moment of the combined antenna is optimized to improve the low-frequency performance. The relationship between the performance and the structural parameters for the combined antenna is concluded based on the research results. Finally, an optimized combined antenna with length of 30 cm is designed and measured. The impedance bandwidth [voltage standing wave ratio (VSWR) < 2] of the antenna is 180 MHz to 7 GHz, which means that the band ratio is about 40. The ratio between the antenna length and the wavelength of the lower cut-off frequency, L/ $\lambda $ , is reduced to 0.18. The weighted radiation efficiency within 0–7 GHz is 93.7%. Both numerical and experimental results show that the antenna exhibits uni-directional patterns within the frequency range of 0.5–7 GHz. With a short ultra-wideband pulse excitation, gain of the antenna is measured and derived within the spectrum of the excitation, i.e., 0–3 GHz. The corner frequency of the antenna gain is about 200 MHz, which is close to that of VSWR. Moreover, the radiation efficiency is 76.1%, and the pulse fidelity factor is 0.82 with the applied excitation.

In this paper, the combined antenna array is developed to maximize the Effective Potential Gain (Gep) within finite aperture area for the high-power (HP) ultra-wideband (UWB) radiation. The idea is to make the antenna element as small as possible, so that more elements can be arranged within prescribed aperture area to maximize Gep 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; in the time domain, critical parameters of the radiated field (rise time of the monopolar pulse, e.g.) 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 4-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 × 30 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, Gep of the antenna array is 21% higher under the applied excitation, which indicates that the proposed method can significantly improve Gep of the UWB system within the prescribed aperture area. Finally, the antenna array is furthermore optimized by adjusting the distances between the elements, and Gep is improved by another 11%, and the total improvement is 33%, the corresponding Effective Potential Gain is 1.49.

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.

The traveling-wave Marx generator was first proposed by Carl Baum to analyze the switch-closure propagation process in fast pulsed-power systems. To improve the performance of the transistorized sub-nanosecond pulse generator, the traveling-wave Marx circuit with inter-stage transmission lines is studied. Simulations indicate that the delay time and the impedance of inter-stage transmission lines [microstrip lines on printed circuit board (PCB)] are main factors affecting the pulse waveform. Based on it, the series connection of modularized Marx circuits is proposed, which has the advantages of adjustable amplitude and bendable circuit layout. A compact high-amplitude pulse generator is developed with the amplitude of 8.2 kV, the rise time of 150 ps, and the PCB length of 35 cm. For higher pulse repetition rate, the heat dissipation design of PCB is necessary; however, due to the variations in the microstrip line structure, the commonly used metallic heat sink may cause a significant decrease in pulse amplitude. Thus, a novel heat dissipation design is proposed by optimizing the layout of metallic sinks and introducing heat-conducting ceramic sinks. A high-repetition-rate pulse generator is developed with the maximum pulse repetition rate of 600 kHz, the amplitude of 1.1 kV, and the rise time of 160 ps.

In this paper, a kind of tightly coupled array (TCA) with non-uniform short-circuited branches (NSCB) is proposed. It indicates that, the introduction of the NSCBs fundamentally changes the working principle of the TCA, and makes it operate like an electromagnetic combined antenna. Arms of the array elements, the short-circuited branches, together with the ground plane, compose current loops, which act as magnetic dipoles, and the array elements themselves are electric dipoles, so the TCA becomes an array of electromagnetic combined dipoles in theory. Thus, the backplane short-circuited effect and the edge truncation effect which limit the working band of the TCA are avoided simultaneously. Therefore, working band of TCA remarkably improves, so that it can be applied to radiate the UWB pulses with band ratio over 10:1. Then, based on the theory of electromagnetic combined dipoles, the TCA with NSCBs is designed and optimized. A practical such TCA integrated with feeding baluns is developed and measured. The developed TCA with NSCBs has a working band of 287 MHz to 6.45 GHz, and the band ratio is 22.5:1. The distance between the array and the ground plate is 20 mm, and the total height of the array antenna is 35 mm, which is only 3.4% of the wavelength of the lower-cut-off frequency, which makes a low-profile UWB antenna. Finally, the TCA is excited by a UWB pulse with an amplitude of 3.06 kV, and the performance is measured and calculated in the pulse mode. It indicates that the UWB pulse radiating system has an effective potential of 3.54 kV, and the effective potential gain is 1.16.

In this paper, a high-power ultra-wideband radiation system, composed of multiply radiation modules, is developed based on the space-synthesis method. The radiation module mainly consists of a transistorized pulser, a 2 × 2 combined antenna array, and a power divider. To improve the out parameters [the amplitude, the pulse repetition frequency (PRF), and the rise time] of the transistorized pulser based on the Marx circuit, the influence of the traveling wave process on the output pulse must be concerned. Based on the theoretical analysis, the printed circuit board circuit parameters and the circuit structure of the pulser are optimized. To improve the power synthesis efficiency, the pulse jitter characteristic of the pulser is improved by replacing the conventional base triggering mode with the collector voltage ramp triggering mode for the first-stage avalanche transistor in the pulser. The previous optimized antenna array is utilized in this radiation system, which has a better radiation performance in the prescribed aperture area. In addition, based on the gradient microstrip structure, the power divider integrated with the pulser is designed, which has the advantages of wide bandwidth, low loss, and light weight. Experimental results show that the peak effective potential rE_p of the radiation system of 20 radiation modules is 221.8 kV, the maximum PRF could reach 10 kHz, and the half-power radiation angles of its radiation field are about 5° in both the E plane and the H plane. More radiation modules could be integrated into the system to achieve a higher electric field in the future.