A Broadband Flipped-Stair Conical Filtering Dielectric Resonator Antenna With Independently Controlled Radiation Nulls

In this letter, a broadband flipped-stair conical filtering dielectric resonator antenna (FDRA) using fusion design approach with independently controlled radiation nulls is proposed. The DRA is fabricated into a flipped-stair conical shape to widen the bandwidth as well as generate a radiation null. Besides, a simple microstrip stub and a pair of slotline are elaborately designed and loaded to provide two radiation nulls at the edges of the passband. Consequently, a good filtering response is obtained without extra filtering circuits. In addition, three radiation nulls can be controlled independently by adjusting the length of the microstrip stub and slotline and the dimension of flipped-stair conical DRA. A prototype is fabricated and measured for demonstration. The measured results are in reasonable agreement with the simulated ones. The prototype owns a 10-dB impedance bandwidth of 37.7% (4.26–6.24 GHz), a peak realized gain of 8.6 dBi and an out-of-band suppression level of 17 dB, respectively. Besides, a cross-polarization discrimination of more than 25 dB in each plane is obtained.