$4\times4$ -Element Cavity Slot Antenna Differentially-Fed by Odd Mode Ridge Gap Waveguide

A differential feeding for a cavity slot antenna is presented. The proposed feeding is based on a simple mechanism rather than the traditional complex networks that suffer from high losses. It is based on exciting the first higher order mode (TE10) of the ridge gap waveguide (RGW) by enlarging the ridge width. This enlargement would excite some undesired even modes that are suppressed by inserting a vertical perfectly electric conducting (PEC) wall in the middle of the waveguide based on the concept of magic tee operation. The proposed $4\,\,\times 4$ cavity slot antenna is implemented using substrate integrated waveguide (SIW) technology. Two horizontal slots on the top of proposed wide RGW, representing the differential feeding approach, are implemented to feed the cavity slot antenna. The slots couple the fields with same amplitudes and 180° phase difference to the cavity. The electric fields of the two coupling slots have odd symmetry in the x-axis, and subsequently, uniform electric field distribution of the TE440 mode of a cavity can be excited. The 4/4 radiating slots are etched on the top of the cavity in a specific distribution to ensure having in-phase fields for broadside radiation with low-cross-polarization levels. The measurement and simulation results of the proposed cavity slot antenna are in a good agreement. The obtained results confirm that the proposed antenna achieves a relative bandwidth of 7.1% for −10-dB return loss, a gain of about 16.5 dBi, and a side lobe level about −17 dB in E-plane and −13.8 dB in H-plane. Moreover, the proposed antenna provides low cross-polarization levels (−35 dB in E-plane and −27 dB in H-plane) within the operating frequency band of 32.5 to 34.9 GHz. With this achieved low profile, high gain, and high efficiency of the proposed cavity slot antenna, it may have a great potential for millimeter-wave (MMW) applications.

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