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The graphic of Figure 3 represents the rectangular microstrip antenna with the various parameters identified. Note specifically the radiating electric field configuration at each edge of the microstrip conductor. Because the effective length of the microstrip conductor is a half- wavelength, the electric field is a maximum at the left and right edges due to the effective open-circuit and the repeating field pattern at half-wavelength intervals. The radiation intensity is significantly influenced by the conductor length, L, and width, W, and to a lesser extent by the substrate height, h. The microstrip conductor is located at the boundary of two dielectric materials: the substrate below the conductor and air above. Since part of the electric field is located within the substrate material and part in air, the relative dielectric constant of the substrate must be modified to accommodate the influence of the dielectric boundary. The accommodation is represented by the mathematical definition of the effective dielectric constant. Eq. 1 In addition to the influence of the dielectric substrate and air boundary, the impact of fringing of the electric field at the edges of the conductor must be accommodated. Electric field fringing at conductor edges may be accurately modeled by lumped element capacitors which effectively increase the electrical length of the conductor at each edge by an incremental length, DL. The incremental length is represented mathematically: 5 Eq. 2 Therefore, the effective, electrical length of the conductor may be written: Eq. 3 As mentioned earlier, the electrical length of the microstrip conductor at resonance is l/2. Therefore, accounting for the fringing, the resonant frequency, f o , or corrected operating frequency, f rc , may now be written: Eq. 4 5 Balanis, C. A., Antenna Theory, 3rd Ed., John Wiley and Sons, Hoboken, NJ, 2005, p. 818. 1 12 1 1 2 1 2 1 > + × - + + = h W W h r r eff for e e e ( ) ( ) h . h W . . h W . . L eff eff × ÷ ø ö ç è æ + - ÷ ø ö ç è æ + + × = D 80 0 258 0 264 0 3 0 412 0 e e L L L eff D + = 2 ( ) eff rc eff eff o L L c f L c c f e e l D + = = × × = = 2 2 2 2 Figure 3 – Rectangular Microstrip Antenna – Radiating Edges Microstrip Antenna Design 5 www.cadence.com/go/awr