Multiport Network Model of Double–stub Loaded Microstrip Ring Antenna for Tri–band Operation

Abstract

A microstrip ring antenna has a single broadside fundamental radiating mode. In this communication one of the arms of the ring has been loaded with two stubs, so that the perturbation in the fields results in broadside radiation in the next two higher order modes. This results in three broadside radiating modes. Gap coupled excitation is chosen to achieve impedance matching in all the three frequency bands. Linearly polarized radiation with gain of 2.88 dB, 4.67 dB and 6.07 dB and half-power beamwidth of 89.6°, 76.3° and 79° in the φ=90º plane has been achieved at the center frequencies of 0.9526 GHz, 1.833 GHz and 2.468 GHz respectively. This structure has been analyzed using multiport network modeling. The modeling is vindicated by experimental results.