Planar, self-complementary, and wideband antennas with polarization diversity

Summary form only given. With the ever-growing technology progress in wireless communication systems, from cell phones, wireless computer tablets, and multimode Global Positioning Systems (GPS) to modern satellite and radar applications, the channel capacity enhancement is in increasing demand during the recent decades. One remedy, that has long been used, is to transmit and or receive signals over the same band of frequency, well known as frequency reuse systems. In these systems, two orthogonal waves are utilized for each transmit and or receive channel, thereby leading to a significant increase in the channel capacity. The orthogonality can be realized by two perpendicularly linearly polarized waves or two circularly polarized ones with opposite senses of polarization. In radar applications, the circular polarization not only improves the radar cross section response of the objects, but also helps better clutter suppression due to the raindrops. Therefore, antennas with the capability of generating both senses of circular polarization (CP) are of great importance in polarization diversity applications. The planar self-complementary antenna structures, such as spirals and helices, are the best candidates. As it is well known, the sense of polarization in a spiral antenna is determined by the direction of its winding. Therefore, a given spiral geometry presumably produces CP waves with a right- or left-handed sense. In the literature, an orthogonal mode helical antenna with dual senses of polarization was reported by (H.P. Coleman and B.D. Wright, IEEE Trans. Antennas Propag., 414-415, 1984), when it was fed from its both arm ends. This, however, results in a complex feeding network and increases the overall antenna weight and volume, when applied to N-arm spiral or helical antennas.In this paper, a planar, self-complementary, four-arm Archimedean spiral antenna is investigated. The proposed antenna is only center-fed and produces both righthanded and left-handed - P waves over the same frequency band of nearly 13GHz, with the spiral winding preset to the right direction. Based on the band theory, the dominant mode produces a CP axial beam, whose sense of polarization accords with the winding direction of the spiral. The opposite sense of polarization is then generated using higher order modes. The higher order modes, however, have boresight-null beams. Therefore, the proposed spiral antenna is carefully designed to always radiate broadside beams for both senses of polarization. Moreover, linear polarization, either vertical or horizontal, can be achieved by signal processing technique from the resultant CP waves with two senses of polarization. All the corresponding results of such a reconfigurable antenna with polarization diversity will be discussed and presented in the conference.