Millimeter-Wave Filtering Circularly Polarized Antenna Using Hybrid Radiation Modes for Satellite Applications

A novel millimeter-wave filtering circularly polarized (CP) antenna is proposed for Ka-band satellite applications. The antenna element mainly consists of an L-shaped feeding microstrip line, a radiating slot, and a stacked patch. The parasitic structure is used on the radiating slot and stacked patch to achieve filtering performance. In addition, the proposed antenna uses two hybrid radiation modes and achieves wideband CP performance. The L-shaped feeding microstrip line excites the radiating slot with two orthogonal degenerate TE10 and TE01 modes, and one minimum axial-ratio (AR) point is realized. The upper stacked patch is chamfered with two orthogonal degenerate TM10 and TM01 modes to generate another minimum AR point. Four short-circuited patches are designed around the stacked patch to generate a radiation null in the lower band. Four symmetrical stubs protruded at the four corners of the radiating slot to generate another radiation null in the higher band. To further validate the feasibility of the proposed antenna, a $2\times 2$ CP antenna array using a well-established sequential-phase feeding network is designed. The measured results demonstrate that the proposed antenna array has an AR bandwidth of 28–33 GHz (16.4%), a realized gain of about 13 dBi, and an out-of-band suppression of over 14 dB.