Design and Analysis of a Dual-Band Inverted-F Antenna With Orthogonal Frequency-Controlled Radiation Planes

A dual-band inverted-F antenna design operating at 433/868 MHz ISM bands is reported. The structure is planar, fed by a coplanar waveguide and easily integrated into a PCB. The device has the ability to produce radiation in two different orthogonal planes with respect to the operation frequency. This frequency-controlled radiation property offers a spherical coverage in space. A transmission line model based on the asymmetrical coplanar waveguide is used to analyze the critical parameters of the design and can be used to estimate its performance. Analytical equations are provided confirming the model and the simulations. The design procedure can be used to adjust the structure to the desired operating frequencies and to achieve the required frequency ratio (f_H/f_L). Measured data from a fabricated prototype show return loss greater than 10 dB at both frequency bands and are compared to simulations. Measured and simulated radiation patterns demonstrate the reconfiguration of the radiation planes with frequency that can be used for more reliable mobile communications.