This paper presented the microstrip-fed circular disc monopole antenna with defected waveguide structure. First, the microstrip-fed circular disc monopole antenna was designed. Next, the monopole antenna was designed with waveguide and lastly followed by the defected waveguide structure where the uniplanar compact (UC) structure was used. CST Microwave studio software was used for simulation and parametric studies process. Initially, the microstrip-fed circular disc monopole antenna was designed to achieve return loss less than -10dB for wideband frequencies. Then, the gain and directivity was improved with the integration of waveguide. The highest directivity of 11.38dBi found at 13.5GHz. However, low efficiency and narrower bandwidth were obtained. Next, uniplanar compact defected waveguide structure (UC DWS) was designed at inner surface of waveguide. The bandwidth achieved 3.09GHz where it covered from 10.91GHz to 14GHz. Meanwhile, the directivity maintained higher than the monopole antenna with highest directivity of 8.84dBi at 10GHz. The gain was also improved from 11GHz to 14GHz with highest gain of 6.38dB occurred at 13.5GHz.
This paper presented the effects of Defected Waveguide Structure (DWS) toward wideband monopole antennas. Ultra-wideband (UWB) technology was introduced to support high data rate and maximum bandwidth utilization. Monopole antenna received great attention owing to its appealing features of planar in the structure and is easy to manufacture in miniaturized sizes. Yet, poor gain and directivity are always the drawbacks of the miniaturized antennas. It was found that there was no research work done on the monopole antenna design with DWS. Two wideband monopole antennas with a microstrip feed line and coplanar waveguide (CPW) feed line were proposed. Two waveguides with full copper and square DWS were designed at all the inner walls. Monopole antennas were then integrated in the waveguides. The antenna parameters studied were return loss, efficiency, gain, directivity and radiation pattern to investigate the effects of DWS toward monopole antennas. Both monopole antennas achieved wide bandwidth from 2.5 GHz to 11 GHz and higher efficiency of more than −2 dB. Monopole antennas with waveguide presented a narrower bandwidth from 6 GHz to 11 GHz but a significant directivity improvement of 5 dBi at a lower frequency of 4.5 GHz. Monopole antenna with square DWS demonstrated high directivity and gain in a wide bandwidth of 8.5 GHz. Higher gain was improved around 4 dB at the frequency of 4.5 GHz, and high efficiency of more than −2 dB was achieved. The DWS design served as a guide for future communication system based on the smart technology system.
This article presented defected waveguide structure (DWS) designs and characteristics with microstrip‐fed circular monopole antenna for ultrawideband applications. Typically, waveguide is often designed and employed as antenna and filter application in its rigid dimension. The reconfigurable design toward the waveguide in terms of structural alteration with DWS was found less concerned among researchers although defected ground structure and defected microstrip structure have been applied widely. The motivation of this article was to propose the different DWS designs and characteristics in terms of the S‐parameters result. DWS in basic square geometry with different configurations of straight lines were introduced and compared with FR4 substrate waveguide. Simulated S‐parameters results were modeled in terms of equivalent circuit and measured for validation. For practical measurement, waveguide ports at both open‐ended surface of waveguide were replaced by the monopole antenna. For the modeled S‐parameters results, the square DWS design and square DWS with horizontal straight lines showed quite similar characteristics with higher S11 and lower S21 above frequency 9 GHz. Whereas square DWS with vertical straight lines and square DWS with both horizontal vertical straight lines showed higher S11 and lower S21 below frequency 3.5 GHz. Square DWS with vertical straight lines achieved the lowest S21 around −70 dB below 3.5 GHz and lower S21 around −50 dB at frequency 10.3 GHz. Thus, DWS is proposed for the future smart antenna technology as it can be further modified to meet the different requirements without changing the antenna configuration.
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