This paper introduces a new volumetric conical notch-band antenna. Structure of this antenna is in contrast with planar and printed band rejection antennas currently existing in almost all of the literatures. The radiation pattern of the proposed antenna is symmetrical and stable against frequency variation, while planar and printed antenna types suffer from high variation of their radiation pattern with frequency, and consequently asymmetric and unstable omnidirectional behavior. The frequency band of the antenna is notched with two slots implemented on the antenna structure. Uniform various frequency band rejections are achieved by changing the slots dimensions and position. Both measured and simulation results of manufactured antenna show the frequency bandwidth of the antenna is from 3 to 4.9 GHz and from 6.2 to 11 GHz with reflection coefficient less than −10 dB. Moreover, the antenna notches the frequency band from 4.9 to 6.2 GHz with nearly uniform reflection coefficient level of approximately −3 dB. Stable radiation pattern and proper range of frequency band rejection make the designed antenna an appropriate candidate for the use in UWB and indoor communication systems.

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In this paper, very compact (12mm?17mm) and simple UWB antenna is proposed. The achieved bandwidth of the presented antenna is from 3.05 GHz to 12.5 GHz and in the most of the bandwidth, the return loss is less than -20dB. In addition to frequency characteristics, time characteristics such as group delay variations for three different antenna positions, namely, front to front, back to back and side by side using CST MW studio are simulated and discussed. To improve the group delay variations, by changing the radius of the circle on the back side of the antenna, the antenna gain in different frequencies will be tuned, therefore, the time domain characteristics of the proposed antenna are greatly improved.

In this paper, a novel gap-groove folded-waveguide slow-wave structure (SWS) for high-efficiency G-band travelingwave tube (TWT) is presented. In this novel tube, a sheet electron beam passes through the small gap between a bed of nails and a folded groove realized in a metallic plate. The bed of nails and the metallic plate form a high impedance structure-perfect electric conductor parallel plate waveguide, which prevents the fields from leaking transverse to the propagation direction. The phase velocity of the proposed SWS has been analytically calculated and the results show good agreement with those obtained using Eigenmode solver of computer simulation technology (CST). Meanwhile, the simulation results indicate that the interaction impedance of the proposed SWS is considerably higher than the conventional folded-waveguide SWS. Furthermore, employing a proper phase velocity taper in the end section of circuit leads to increasing the efficiency of the proposed TWT. According to Particle-in-cell simulations performed by the CST Particle Studio, the designed TWT can generate a peak power of 225 W at 220 GHz, corresponding to the maximum gain and efficiency of 42.7 dB and 14.9%, respectively. IndexTerms-Folded waveguide (FW), gap-groove waveguide (GGW), slow-wave structure (SWS), travelingwave tube (TWT).

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