A quad-band slot antenna with spiral stub and interdigital CPW Feed

Abstract

This paper proposes a quad-band slot antenna with spiral stub and interdigital CPW feed. The antenna has a compact size and can be used for four frequency bands of 1.8 GHz, 2.45 GHz, 3.7 GHz and 5.2 GHz applicable for LTE, WiMAX and WLAN systems. The important technique designs of the proposed antenna are divided into 2 parts. The first part includes the stepped slot antenna added with square-shaped spiral stub. As a result, the resonance frequencies of the third and fourth harmonics can be controlled as desired. For the second part, the technique of interdigital capacitive CPW is employed at the feeding line, resulting in length reduction from λ/4 of the conventional one to λ/8, which is caused by the slow-wave effect. Moreover, with this technique the resonance frequency of the second harmonic can be independently controlled. The optimized antenna has good performances for all frequency bands with bandwidths of 190 MHz (1.72 GHz-2GHz) at 1.8 GHz band, 280 MHz (2.34GHz-2.53GHz) at 2.45 GHz band, 410 MHz (3.54 GHz-3.95 GHz) at 3.7 GHz band and 220 MHz (5.10 GHz-5.32 GHz) at 5.2 GHz band, respectively.