Characteristic Mode Analysis of Circular Microstrip Patch Antenna and Its Application to Pattern Diversity Design

Abstract

In this paper, a highly-isolated microstrip patch antenna (MPA) is presented for pattern diversity applications. The physical insight of MPA is investigated without the influence of external exciter by using the theory of characteristic modes (TCMs). Shorting pins are added to manipulate the resonant frequencies of eigenmodes. TM 11 , TM 01 , and TM 02 modes are clearly tracked and identified. For the first time, all the three modes are simultaneously utilized to enhance the performances of MPA. To be specific, TM 01 and TM 02 modes have conical pattern, thus are combined to increase the bandwidth, while TM 11 mode has broadside pattern, and is used to provide pattern diversity. A two-port feed network, consisting of probe feed and aperture coupling, is designed to excite the three modes. The measured -10 dB bandwidth of the two ports is 720 MHz and 130 MHz. The simulated port isolation reaches 42 dB, and the measured value is higher than 27 dB. The proposed MPA has the advantages of clear operating principle, flexible mode tuning and high port isolation, thus is attractive in MIMO systems.INDEX TERMS Microstrip antenna, theory of characteristic mode, pattern diversity, wideband antenna.

Broadband inhomogeneous lens with conical radiation pattern

“…Recently, different methods have been proposed to design a wideband conical pattern antenna, such as some shapes of the planar monopole 14 – 16 , substrate-truncated microstrip circular patch 17 , open-ended coaxial waveguide 18 , mode conversion in a circular waveguide 19 , and radially arrayed slot antenna 10 , 20 . Different resonant modes of circular patch antennas can be excited to radiate broadside and conical patterns 21 , 22 . Adopting two separate ports with different radiating modes for a single patch antenna is another method to have pattern diversity 23 .…”