Inset Fed Patch Antenna Calculator

In this article, we will dissect the theory behind the inset feed, derive the critical equations, explore the variables that affect performance, and—most importantly—show you how to use a dedicated calculator to go from substrate parameters to a fabrication-ready design in under 60 seconds.

Consider a rectangular microstrip patch antenna fed at its edge. The input resistance at the edge, ( R_in ), is typically very high (e.g., 200 Ω for a common FR4 substrate). Directly connecting a 50 Ω transmission line creates a massive impedance mismatch, leading to high return loss (poor ( S_11 )). inset fed patch antenna calculator

) :The input impedance at the edge of the patch is very high ( ) and drops toward the center ( ). You must calculate the depth where the impedance matches your 50 Ωcap omega feed line: In this article, we will dissect the theory

If ( y_inset ) approaches L/2, the feed point is near the center where impedance is near 0 Ω. This never matches 50 Ω. The calculator must output ( y_inset \leq 0.45L ). If not, the substrate is too thin or ( \varepsilon_r ) too high. Directly connecting a 50 Ω transmission line creates

A: No—the cosine-squared impedance variation is specific to rectangular patches. Circular patches require Bessel function solutions.

[ \varepsilon_\textreff = \frac4.4+12 + \frac4.4-12\left(1+12\frac1.637.3\right)^-0.5 \approx 4.18 ]