Investigation into a size-reconfigurable ground slot for multiband folded coplanar inverted-F antenna

This paper presents an investigation into a coplanar inverted-F antenna with a ground slot whose electrical size is varied by turning ON and OFF PIN diode switches. Initially, a quarter wavelength coplanar inverted-F radiator is designed to operate at 900MHz. To minimize its size, the radiator is folded to occupy an area of approximately 10 × 40mm². Next, a ground slot is introduced to excite another resonance at 1850MHz without affecting the 900MHz operation. An investigation is then carried out to tune the size of the slot using three pairs of PIN diode switches with simple biasing circuits. The varying slot size generates new resonances around 1850MHz. The proposed reconfigurable antenna is fabricated and experimentally tested. A good agreement is achieved between the simulated and measured return loss of the antenna showing the experimental impedance bandwidth covering GSM900, PCS1900 and UMTS2100 services. In these frequency bands, the antenna offers nearly omni-directional radiation patterns with measured peak gain between 1.4dBi and 3.5dBi.