Bandwidth Enhancement of the Millimeter-Wave Microstrip Linear Array With Loading of Shorting Pins

A broadband, series-fed, millimeter-wave (MMW) microstrip linear array is investigated. This array is evolved from a stub-loaded microstrip line, which has two resonant modes in the passband and an impedance bandwidth of about 26%. By simply inserting three pairs of shorting pins at the two ends of the microstrip line to regulate the field/current distributions, four additional resonances can be excited, significantly increasing the operating bandwidth to 63.5%. In addition, the original gain dips caused by anti-phase (equivalent) magnetic current disappear and the gain becomes quite stable, showing the maximum value of 12.82 dBi and a 3 dB bandwidth of 53.8%. Also, the first sidelobe level (FSLL) is lower than -10 dB from 26.6 to 44.2 GHz (49.7%) and lower than -20 dB from 26.6 to 30.7 GHz (14.3%). Therefore, the proposed array features great advantages, such as a simple structure and an enhanced bandwidth with good sidelobe suppression.