摘要： 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.