Compact Offset-Beam Four-Layer X-Band Proximity-Coupled Array Antenna in Triangular Grid

In this paper, a compact four-layer offset-beam X-band triangular grid microstrip array antenna with proximity coupled feed patch element is presented. The feed network is in the lower substrate and the radiation elements are in the upper substrate of the array antenna structure, which is isolated by the ground plane in the middle substrate. The feed network is in parallel planar format and utilizes a 1x4 phase shifter power divider to realize a progressive phase shift needed to control the beam direction. The isolation of the feed network from patch elements reduces cross-polarization and side-lobe-levels (SLLs). The patch antenna elements are excited by proximity coupling which increases bandwidth, flexibility in the impedance matching, and simplicity of fabrication also reduces spurious response. A triangular arrangement is used to reduce mutual coupling and to limit the grating lobes. Moreover, a 4x4 element array antenna with a fixed scan angle at 30° is designed with 1 GHz impedance bandwidth with a center frequency of 9.5 GHz, peak gain of 15.1 dBi, and side lobe level (SLL) less than -10 dB in principle planes. Besides, the proposed power supply network structure enables easy PIN and varactor diode phase shifters, which can be used to improve antenna performance by providing reconfigurable and tunable scanning.