New zeroth‐order resonators (ZORs) were utilized as parasitic elements to enhance bandwidth of microstrip antenna. By utilizing one, two and three resonators, extra corresponding numbers of resonances were generated. Then, by merging the resonances of the resonators with that of the microstrip antenna, the measured impedance bandwidth can be increased from 56 MHz of the reference microstrip antenna to 101, 120, and 133 MHz of the ZORs loaded antennas. As the ZOR is very small (approximately λ0/10), the antenna area ratio of the proposed bandwidth enhanced antennas to the referenced microstrip antenna (RMA) is only approximately 1.33. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:1096–1100, 2017

Antipodal Vivaldi antenna (AVA) with five sandglass‐type director elements is proposed in this research for radiation characteristics improvement. The impedance bandwidth of the proposed antenna ranges from 2.85 to 12 GHz (9.15 GHz, 123.2%). The five director elements have different sizes and they form a symmetrical linear array in front of the antipodal Vivaldi antenna. Therefore, the director elements are responsible for secondary radiations of different frequencies, thereafter, the gain improvement of the AVA is achieved in a broad frequency band. In the 2.85 to 12 GHz frequency band, the antenna gain is increased by 1 to 2.65 dBi and the 3 dB beamwidths are reduced. Thus, a high gain AVA is achieved with gains of 6.52 to 11.55 dBi in the whole frequency band. A prototype of the proposed antenna is fabricated and measured, and the simulated and measured results agree well with each other.