Abstract
This paper presents an absorptive microstrip-fed slot antenna with a wide reflectionless band and high radiation efficiency. The proposed antenna consists of a microstrip-fed slot antenna, a quarter-wavelength coupled-line bandstop filter (BSF), and absorptive resistors attached to a grounding pad. The BSF and absorptive resistors are connected to the end of the microstrip feedline. The slot antenna and the BSF are designed to work at the same frequency. In the working band, the high input impedance of the BSF exactly matches the slot antenna for effective radiation. While out of the working band, since the input impedance looking towards the end of the slot antenna matches well with that of the BSF, the energy will flow through the BSF and then be absorbed by the absorptive resistors. In this way, the energy both in and out of the working band will not be reflected back to the input port, which presents a wide reflectionless band. To demonstrate this idea, a prototype operating at 3 GHz is designed, fabricated, and measured. The measurements show that the proposed antenna is well matched ( $|S_{11}| dB) in a wide frequency band from DC to 5.3 GHz, the 3-dB gain bandwidth covers from 2.85 GHz to 3.24 GHz with a peak gain of 4.54 dBi, the peak radiation efficiency can reach 93%, and a bidirectional radiation pattern is realized with more than 20 dB cross-polarization suppression in main radiation directions.
Highlights
INTRODUCTION1HIGHER requirements of the out-of-band performance of antennas are put forward to adapt to the current complex communication environment [1]-[4]
This paper presents an absorptive microstrip-fed slot antenna with a wide reflectionless band and high radiation efficiency
This is because the energy reflected by the bandstop filter (BSF) can not be totally radiated by the slot antenna when the BSF bandwidth is too large
Summary
HIGHER requirements of the out-of-band performance of antennas are put forward to adapt to the current complex communication environment [1]-[4]. The achievements of the non-reflecting/reflectionless characteristics are at the expense of the antenna gain and radiation efficiency. This is because the absorption effect still exists in the working band. Compared to a conventional patch antenna, the modified antenna can maintain a high radiation efficiency and gain in the working band, and achieve a reflectionless characteristic within adjacent unworking bands. To realize broadband reflectionless characteristics out of the working band and high radiation efficiency in the working band simultaneously, a novel absorptive microstrip-fed slot antenna is proposed in this paper. Considering the structural features of a conventional microstrip-fed slot antenna, a narrowband coupled-line bandstop filter, with one port terminated by absorptive resistors, is connected to the microstrip feedline. The absorptive resistors are modeled as the second port in the design procedure, which greatly facilitates the design
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