The goal of this study is to propose a wideband circularly polarised (CP) psi‐shaped antenna of high gain and wide bandwidth as necessitated by intelligent transportation system applications. A wide impedance bandwidth of 2 GHz (40%) centred at 5.3 GHz is achieved through the combination of modified TM01, TM20, and TM21 modes with three slots on either radiating edge in the simple rectangular geometry of the antenna. The stacked patch configuration helps to achieve a minimum gain of 7 dBic in the entire bandwidth. The CP psi‐shaped antenna has an impressive axial ratio bandwidth of 1 GHz, which is >19% of its centre frequency 5.3 GHz. The proposed antenna can be used for detection of the blind spots of a vehicle at 5.88 GHz (DSRC frequency band), vehicle‐to‐vehicle communication at 5.2 GHz (WLAN IEEE 802.11a frequency band), and vehicle to roadside communication at 5.5 GHz (WiMAX IEEE 802.16 frequency band).

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Abstract-The present paper analyses and documents the merits of incorporating fractal design in microstrip antenna intended to be mounted on and integrated into the design of smart vehicles. A novel design is proposed for a compact tri-band hexagonal microstrip antenna to be integrated with the body of a smart vehicle for short range communication purpose in an Intelligent Transport System (ITS). This antenna can be used at 1.575 GHz of GPS L1 band for vehicle to roadside communication, at 3.71 GHz of mobile WiMAX band (IEEE 802.16e-2005) for blind spot detection and at 5.9 GHz of DSRC band (IEEE 802.11p) for vehicle to vehicle communication. At 3.71 GHz, the two major lobes of the antenna radiation beam, tilted by 35 • on both sides from its broadside direction, help the vehicle to detect blind spots efficiently. The largest dimension of the proposed antenna corresponds to the lowest resonating frequency, 1.575 GHz. Compared to the conventional hexagonal patch, the modified Sierpinski fractal proposed herein reduces the overall area, at 1.575 GHz, by 75%, with 5.2 dBi gain. In comparison with other popular fractals, the proposed fractal structure achieves demonstrably better antenna miniaturization. When the antenna is mounted on the vehicle, considered an electromagnetically larger object, the simulated and on-vehicle experimental results show antenna gains of more than 5.5 dBi at 1.575 GHz, 8 dBi at 3.71 GHz and 9 dBi at 5.9 GHz in the desired direction with negligible amount of electromagnetic interference inside the car.

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A new class of switchable bandpass filter using PIN diodes is presented in this paper. The design aims at achieving a multistate switchable bandpass filtering characteristics between the passbands centered at 2.4, 3.5, and 5.2 GHz. The proposed filter is designed by assembling two λg/2 open-ended and four short-ended λg/4 uniform impedance resonators. The open-ended resonator generates a fixed passband at 3.5 GHz, whereas the short-ended resonators loaded with PIN diodes are independently controlling the ON and OFF characteristics of the passband centered at 2.4 and 5.2 GHz. The transmission zeros around each passband are produced without employing any additional circuit. The filter sample is fabricated and tested for experimental verification. A good agreement has been observed between EM-simulated and measured results. The designed filter has a compact size of 0.20 λg × 0.15 λg at 2.4 GHz.