Dual Band Folded Microstrip Patch Antenna for Omnidirectional Radiation

A new planar folded microstrip patch antenna with vertical polarization is presented for dual band omnidirectional radiation. The antenna is composed of two layer stacked substrates with the ground plane buried between them. On the top layer substrate, a rectangular patch is folded around the side edges of both substrates. The proposed folded structure is along the H-plane of the antenna for broadening the impedance bandwidth. A 50 Ω coaxial probe is used to directly feed the antenna for simplicity. Simulated omnidirectional radiation with gain variation of less than 1.8 dB and 2.3 dB in the horizontal plane can be obtained at 1.45 GHz and 2.5 GHz respectively. The measured 10-dB impedance bandwidths are 3 MHz and 500 MHz with center frequency located at 1.44 GHz and 2.6 GHz, and the agreement between the simulated and measured |S
₁₁
| can be observed.