Sunday, June 22, 2008

Bandwidth enhancement of Microstrip Antennas

Microstrip antennas have become the favorite choice of antenna designers because they offer the attractive advantages of low profile, light weight, easy fabrication and easy integration with circuits. The disadvantage of microstrip antenna is its narrow bandwidth. During the recent years, the capacity issue for wireless communication applications is not easily solved, with the expansion in mobile communication systems and the number of people using their services, much effort has been devoted to the bandwidth enhancement of microstrip antennas, and many techniques have been proposed. In addition, applications in present-day mobile communication systems usually require smaller antenna size in order to meet the miniaturization requirements of mobile units. The techniques used in miniaturization further spoil the bandwidth of the antenna. A comprehensive enumeration of all the techniques used in this regard follows:

• Use of impedance matching network
• Multiple resonators arranged in stacked or co-planar structure
• Using lossy materials
• Reactive loading using U-shaped slot
• Capacitively probe-fed structure
• L-probe feeding
• Using thick foam substrate
• Using proximity-coupling
• Using a gap-coupled probe feed or a capacitively coupled feed
• Meandered ground plane
• Slot-loading
• Stacked shorted patch
• Feed modification
• Chip resistor loading
• Teardrop dipole in an open sleeve structure
• Using air substrates
• Using shorting posts between the patch and the ground plane
• Three dimensional patches like V-shaped patch or wedge -shaped patch

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