A Very Compact Ultrawideband Printed Omnidirectional Monopole Antenna

A new form of the microstrip-fed monopole antenna with truncated ground plane is presented. In comparison to the previous monopole structures, the miniaturized antenna dimension is only about 11 (0.11 lambda(r)) x 16 mm(2) (0.17 lambda(r)), where lambda(r) is the wavelength of the lowest frequency of the band (i.e., 3.2 GHz). By only sequentially inserting the three notches with proper sizes and positions in two corners of the quasi-square radiating patch, very good radiation and impedance characteristics are obtained. The measured impedance bandwidth of the realized antenna with optimal parameters is from 3.9 to 21.4 GHz (5.5:1, 138%) for VSWR <1.5. Moreover, unlike the conventional omnidirectional monopole antennas, the stability of the H-plane radiation patterns of the proposed antenna is maintained in omnidirectional form within the frequency bandwidth up to 16 GHz. The improvement process of the impedance and radiation properties is completely presented and discussed.