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Miniaturised microstrip‐line‐fed slot antennas with ring‐shaped metallic strips for dual‐band and broadband operations are investigated and verified in this study. The proposed designs implemented on a 0.8‐mm FR‐4 substrate show that the ring‐shaped metallic strips and the feeding structure yield multiple resonant modes, achieving 66.3% size reduction. The proposed dual‐band design reveals two operating bandwidths (12.4 and 46.5%) at the central frequencies of 2445 and 4813 MHz, respectively. The broadband design indicates the maximum bandwidth of 2511 MHz (69.6%) at 3606 MHz. This large operating bandwidth is obtained by choosing suitable combinations of feeding structure and multi‐ring slot shapes. Simulated and experimental investigations are clearly conducted to understand their behaviours and optimise them for dual‐band and broadband operations.

A compact coplanar waveguide (CPW)-fed multifrequency circular slot antenna design loaded with arc-shaped metallic strips is investigated and verified in this letter. The proposed design implemented on a 0.8-mm FR-4 substrate shows that the arc-shaped metallic strips yield the multiple resonant modes for multiband vision. Unlike other multifrequency antennas whose sizes are determined by the lower resonant frequency, the compact size of the proposed slot is determined by the upper resonant frequency. Other operating frequencies are obtained by inserting arc-shaped metallic strips without increasing the overall antenna area. The prototype for different applications examined by modifying the angles of the arc-shaped metallic strips reveals that the input impedance bandwidths of the operating frequencies range from 5.0% to 64.7%. Moreover, these operating resonant bands exhibit the broadside radiation patterns with efficiency better than 45%.Index Terms-Multifrequency antennas, slot antennas.

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