Abstract: A novel slop-loop antenna is proposed. Using the nonlinear phase shift characteristic of the interdigital capacitor, the resonant frequency of this antenna with the interdigital capacitor loading can be reduced. The theoretical analysis and experiment elaborate the relationship between the electrical performance and the interdigital capacitor: theoretical analysis shows that the resonant frequency can be reduced by decreasing the finger spacing of interdigital capacitor; the experiment results indicate an obvious improvement in electrical performance, that is, the resonant frequency is decreased by 500MHz, the bandwidth increased 50MHz and the cross polarization ratio increased 8.17dB.