Quasi-static analysis of microstrip lines with variation of substrate thickness in transverse direction (original) (raw)

mm is inset 19.25 mm from the center of a patch edge. The coaxial aperture has radius 1.75 mm. The resonant frequency, resistance, and reactance were measured as 1.55 GHz, 128.1 ⍀, and 48.6 ⍀, respectively. A circular capacitor patch is added. The probe is now penetrating the radiating patch and is connected to the center of the capacitor patch. The radius of the hole in the radiating patch is 2 mm. The impedance was calculated for a range of structures. Four different antenna elements were fabricated and measured. For the fabricated structures the distance between the patch and the capacitor patch is 3.4 mm. The measured resonant frequency in all cases stayed at 1.55 GHz, as expected. In Figure 3, the resonant impedance is given for several distances d 2 between the radiating and capacitor patch and for capacitor patch diameters ranging from 5 to 35 mm. The agreement is very good for the resistance. A small shift is seen in the reactance. It is probably due to the use of the approximate slot model. It is clearly seen that the inductance of the probe can be canceled out by selecting the configuration with zero inductance and 50 ⍀ resistance. This allows the bandwidth to be broadened considerably. IV. CONCLUSION A network model is given for the calculation of the effect of a top capacitor patch on the impedance of a microstrip antenna. The main advantages of the procedure are that it is a very fast a posteriori procedure, it is easily implemented, and it gives full physical insight. Therefore, it is a very practical tool for antenna designers that want to use the concept of capacitive feeding.