This letter presents a novel design of patch antenna arrays in X-band for wideband operation. The proposed patch arrays are achieved by using unequal resonance arms fed by a coplanar waveguide (CPW). In this design, three unequal arms fed by the CPW-to-slotline through a coupling system of 100-Ω Tshaped slotline transitions produce three resonances to broaden the impedance bandwidth. The proposed structures are used for the designs of 1 × 2 and 1 × 4 patch arrays, which cover the measured frequency ranges (S11 −10 dB) from 8.48 to 11.45 and 8.50 to 11.31 GHz, respectively. By varying the length of unequal arms, the resonance tuning within the impedance bandwidth can be obtained. The proposed antenna arrays present outstanding features such as resonance tuning ability, comparatively simple structures with low fabrication cost and enhanced impedance bandwidth with unidirectional radiation patterns. In this letter, an equivalent circuit model for the proposed 1 × 2 array is also introduced to predict the behavior of its bandwidth enhancement. The lumped elements used in this suggested model are optimized in order to make conformity between the obtained results of the model and the full-wave simulation results.
