낮은 SLL과 넓은 대역폭을 위한 비균일 간격 및 급전 밀리미터파 마이크로스트립 안테나 어레이

Abstract

In the first part of my thesis, I demonstrate theoretical backgrounds of the microstrip antenna with parasitic patches, corporate feeding, array factor, and antenna radiation pattern and reviewed conventional methods to reduce side lobe level (SLL). The SLL reduction is necessary to reduce noise and cochannel interference in wireless communication. Usually, the SLL reduction of the microstrip antenna array can be realized by the tapering of the microstrip lines or radiating elements to feed the corresponding antenna elements with non-uniform power distribution. This tapering technique results in numerous tapered branches which eventually increase the cross-polarization of the array. In contrast, a systematic way can be employed to realize the non-uniform distribution of power by using the different levels of power split in the junction of the power divider. This method can eliminate the necessity to taper the transmission line or radiating elements. In addition to the non-uniform power distribution, recently, the spacing between the antenna elements was controlled in a non-uniform fashion to reduce SLL and the related examples are overviewed. In the second part of my thesis, we designed a non-uniformly powered and spaced corporate feeding network to feed a 12-element parasitic patch-integrated microstrip antenna array for SLL reduction at 28 GHz in the millimeter-wave band. In the feeding network, we arranged two one-to-six-way power dividers from the opposite sides and two opposite input ports were fed 180° out-of-phase. This feeding technique demonstrated high isolation and lower mutual coupling between the adjacent antenna elements. The non-uniform power distribution was realized by using the different levels of power split in the junction of the power divider, whereas non-uniform spacing for the lowest SLL was determined using the analytical array factor. Due to the consideration of the coupling effect of the parasitic patch, the non-uniform spacing was further optimized using full-wave simulations. To verify the SLL reduction effect from the non-uniform spacing in the array, we designed two non-uniformly excited antenna arrays with uniform half-wavelength spacing and non-uniform spacing. To feed all of the antenna elements with identical electrical phase, we optimized the power split junction of both antenna arrays. Besides, non-uniform spacing introduces higher phase mismatch compared to uniform spacing, to compensate for this we introduced a meander line in the power divider section of the non-uniform spaced array. We fabricated and measured both antenna arrays, where the non-uniformly powered and spaced patch antenna array demonstrated a nearly 16.56 dBi boresight gain and −17.27 dB SLL, which is nearly 2 dB lower than the uniformly spaced counterpart. For future implementation, beamforming performance for the uniform and the non-uniform spaced array was also analyzed. Finally, we expect that the non-uniformly powered and spaced high gain patch antenna array with a low SLL will be suitable for millimeter-wave communication application.