Dual-Band Omnidirectional CoCo Antenna With a Large Frequency Ratio

In this letter, a dual-band omnidirectional coaxial colinear (CoCo) antenna with a large frequency ratio is proposed. It consists of two metal layers which alternate periodically via metal crossover lines to form a Coplanar Waveguide (CPW) CoCo antenna. The antenna operates in the folded dipole mode at low bands (LB) and in the CoCo mode at high bands (HB). A metal sheet functions as a series capacitor to achieve impedance matching for both bands, eliminating the need for additional matching elements that could increase design complexity. A prototype of the antenna is fabricated to validate the concept. The measured -10 dB impedance bandwidths are 438-470 MHz and 4.6-5.7 GHz. The peak gains at LB and HB are 1.8 dBi and 8.4 dBi, respectively. The gain variation in the H-plane remains within 3 dB across both bands, achieving dual-band omnidirectional radiation. The proposed antenna is well-suited for applications in next-generation wireless communication system.