In this letter, an ultrawideband (UWB) antipodal tapered slot antenna with reflectionless notched band is proposed and investigated. The proposed antenna uses an integrated absorptive bandstop filter, consisting of two quarter-wavelength open-circuit stubs and a 50 Ω resistor, to form a reflectionless notched band. Consequently, the input energy at the notched frequency is absorbed by the resistor rather than reflected. An antenna prototype is designed and fabricated to validate the design. Both simulated and measured results present that the realized gain drops over 40 dB at 5.5 GHz, and the reflection coefficient is below –10 dB from 3.1 to 10.6 GHz. Besides, a low ringing level of –23.4 dB of the measured reception pulse shows a good time-domain performance. Therefore, the proposed antenna could be applied in UWB short-pulse system to inhibit the 5 GHz WLAN interference.

An antipodal tapered slot antenna (ATSA) with wideband reflectionless filtering characteristic is proposed in this work. The ATSA incorporates a wideband absorptive bandpass filtering network, which consists of a parallel-coupled line (CL), a stepped impedance open stub (SIOS), and a resistively terminated T-shaped bandstop filter. This network is designed using the frequency-complementary diplexing concept, where in-band input energy is selected by the CL and SIOS and radiated by the ATSA, out-of-band energy is dissipated on the resistor through the bandstop filter. The SIOS also enhances out-of-band absorption and suppression by introducing additional gain nulls. A prototype was fabricated and measured, yielding a 3-dB gain bandwidth from 3.2 to 6.8 GHz and a wide impedance bandwidth from DC to 11.8 GHz with an out-of-band absorptive ratio greater than 80%. Additionally, the realized gain exhibits a sharp bandpass radiation characteristic with measured out-of-band suppression higher than 25 dB in the lower stopband and 16 dB in the upper stopband.

A circularly polarized (CP) endfire antenna is proposed and designed based on the sequentially rotated corrugated Goubau lines. The open-ended corrugated Goubau lines serve as endfire radiators, and simultaneously realize phase transforming function for phase control. A pair of corrugated Goubau lines could be etched on two edges of a common metal strip, and four corrugated Goubau lines with different corrugations along two perpendicular metal strips provide sequentially rotated radiated fields, establishing the CP radiation. Complexity and space occupation of the feeding structure could be reduced by applying the phase-transforming element radiators, which is significant especially in array design. A prototype antenna is fabricated and measured to verify the design. The measured axial ratio is below 3 dB and the return loss is over 15 dB from 8.9 to 9.5 GHz. Peak gain is 8.6 dBic and the cross-polarization level is around -20 dB at 9 GHz.

A spoof surface plasmon polariton (SSPP) antenna with dual-band endfire gain and small frequency ratio (FR) is presented. It uses asymmetric structure to support two independent surface waves with different nonlinear phase constants. Due to the different phases of the superposed E-field at the terminal of the proposed structure, dual-band endfire gains and endfire radiation null are achieved. The odd-mode and even-mode feedings, providing additional phase differences, are also investigated. Three prototypes, with FRs of 1.06, 1.11 and 1.5, are designed, simulated and measured respectively. All results validate the mechanism and demonstrate that the FR of the proposed antenna can be achieved easily in the range of 1.06 to 1.5 by choosing different unit cells and feeding modes. Moreover, the measured endfire out-of-band gain suppression, over 17 dB, presents a good directional interference inhibition. This small-FR endfire antenna shows a broad prospect for band coverage and directional noise inhibition with very close operating frequencies.

A monopulse feeding network is proposed for transmitting and receiving time-domain short pulse with high fidelity. The network consists of coplanar waveguides (CPWs), slotlines, microstrip lines, and transitions. Both the sum and the differential performances of the network depend mainly on the transverse structures of these transmission lines rather than their lengths, providing the capability of short-pulse transmission with high fidelity. Moreover, the normalized Euclid distance is employed to characterize and optimize the time-domain performance of the proposed network. A prototype is designed, fabricated, and measured, and linear phase response and stable transmission coefficient are achieved in ultrawide bandwidth. Time-domain performances are evaluated using an input differential Gaussian pulse, with a frequency spectrum of 4-12 GHz. The fidelity between input and output signals is over 0.96, and the amplitude of received signals is nearly the same, showing potential in short-pulse monopulse applications of the network.

This work proposes a ultrawideband (UWB) monopole antenna with multiple integrated narrow reflectionless notched bands (RNBs). A multi-mode resonant slot is etched in the monopole radiator to generate high-impedance open-circuit characteristic at the antenna feeding point. Multiple coupled and embedded absorptive stubs are integrated into the microstrip feed line to dissipate the input notched-band energy, enabling RNBs characteristics. A single RNB antenna is initially analyzed and designed to demonstrate the operating mechanisms of the resonant slot and coupled absorptive stubs, as well as the conditions for RNB. Then, a triple RNBs antenna is designed based on the conceptual circuit model of multiple RNBs to inhibit the interference from 3.5 GHz (WiMAX), 5.5 GHz (WLAN) and 7.4 GHz (Satellite communications). All the results validate the mechanism and indicate that the proposed antenna can significantly reduce the radiation efficiency and the realized peak gain in the multiple narrow notched bands while maintaining the reflection coefficient below -10 dB from 3-10 GHz.