A Wideband Filtering Antenna Array With Harmonic Suppression

In this article, a wideband $2\times 2$ filtering antenna array is proposed and studied for fixed beam applications. The device is composed of a patch antenna array, and a slotline-based four-way filtering power divider has served as the feeding network. The integration of the antenna and the feeding parts is not a simple combination but a cosynthesis, where the characters of the two parts are both involved during the integration. First, the presented network is analyzed through an equivalent-circuit study to verify the frequency selectivity. Subsequently, integration synthesis of the network and the patch array is carried out to realize the filtering antenna array. For demonstration purposes, a filtering antenna array centered at 3 GHz is developed and fabricated. The measured absolute impedance bandwidth is 1.13 GHz, corresponding to a fractional bandwidth of 37.1%, and out-of-band rejection of up to 9.5 GHz is achieved. Compared with the array fed by a traditionally T-junction-based power divider, the absolute impedance bandwidth of the filtering array is significantly increased by 47%. The in-band gain of the proposed array is higher than 9.7 dBi, which is over 12.1 dBi from 2.75 to 3.25 GHz. The results denote that compared with the previously reported literature, the proposed filtering antenna array features sharp cutoff response, wide impedance bandwidth, high gain, and low cross-polarization level, with the harmonic suppression of up to three times the center frequency.