Low-Profile Dual-Band Filtering Patch Antenna and Its Application to LTE MIMO System

This paper presents a low-profile dual-band filtering antenna element and its application to long-term evolution (LTE) multiple-input multiple-output (MIMO) system for wireless customer premise equipments (CPEs). The proposed element consists of two separate U-shaped patches operating at different frequencies and a multistub microstrip feed line. For size miniaturization, the smaller U-shaped patch is embedded in the larger one. In addition, the multistub feed line can generate two controllable resonant modes as well as two nulls in realized gain at the boresight direction. Since the modes of the patches and multistub feed line can be controlled individually, the two operating bands can be tuned to desired frequencies. Also, the radiation nulls in boresight gain can be controlled, high roll-off rate and out-of-band radiation rejection levels are thus obtained. For demonstration, a low profile (0.009λ
₀
) dual-band filtering antenna element operating at 1.9 and 2.6 GHz for TD-LTE applications (B39 and B38-bands) is implemented. Dual-band bandpass responses and four radiation nulls are observed in the experiment. Measured in-band gains are 6.7 and 7.3 dBi, whereas out-of-band gains are less than -10 dBi. Based on this element, a four-element MIMO antenna is further designed for LTE CPEs, where low profile and high integration of multiple components are required. A low mutual coupling of less than -19.2 dB and the low envelope correlation coefficients of better than 0.2 are obtained with a small edge-to-edge spacing of 0.15λ
₀
.