Low sidelobe level circularly polarised monopulse slot waveguide antenna array for Ka‐band application

Abstract

A circularly polarised (CP) monopulse waveguide antenna array for Ka-band wireless communication is proposed. The antenna structure can be divided into six layers from top to bottom, including radiating layer, aperture layer, cavity layer, aperture layer, feeding layer and monopulse comparator. The upper radiating layer allows two transmission modes of the transverse electric (TE) wave and the transverse magnetic (TM) wave to pass through. The 90° phase difference can be obtained by adjusting the horizontal and vertical angles of the horn radiator, which realises the CP radiation pattern. Besides, the 0° or180° phase difference produced by the monopulse comparator enables the antenna to obtain a monopulse radiation mode. In order to obtain the low sidelobe characteristics, the coupling parameters of the coupling layer are weighted by the Taylor distribution. The overall size of the antenna is 194 × 25 × 31 mm3. The slot waveguide antenna is fabricated and measured to validate the proposed design. The measured results show that the monopulse system can achieve an impedance bandwidth of 3.7% (34.5–35.8 GHz) in the Ka-band at the centre frequency of 35 GHz. The sum-pattern maximum gain and radiation efficiency are 23.3 dBic and 75% at 35 GHz, and the gain of the whole bandwidth is >20 dBic. The axial ratio and the sidelobe level is less than 1.2 and −28 dB, respectively. The difference-pattern amplitude imbalance is <0.2 dB and the null-depth lower than −30 dB. Also, the isolation is better than 30 dB. Besides, the pure metal structure of waveguide has incomparable advantages in a harsh environment.