Proximity fed circular microstrip antennas

The broadband microstrip antenna is realized by fabricating the patch on lower dielectric constant thicker substrate. The proximity feeding is a more commonly used technique to realize broadband microstrip antennas for substrate thickness greater than 0.06λ₀. In the proximity fed configuration the coupling rectangular strip is either placed below the patch or it is placed inside the slot which is cut on the patch. However, design guidelines for the coupling strip parameters, to realize broadband response are not available. In this paper, a broadband proximity fed circular microstrip antennas at various frequencies over 800 to 8000 MHz frequency band are designed. By using those optimum designs the formulations for the strip dimensions and its position below the patch for the given substrate thickness are proposed. The proximity fed configurations were further designed using these formulations at different frequencies in the 800 to 8000 MHz frequency bands. They gives broader bandwidth with the formation of loop in the impedance loci at the center and inside the VSWR = 2 circle. Thus, these formulations can be used at any other frequencies for designing broadband proximity fed antennas.