## 1 Introduction  
Microwave signals operating in the L/S bands (1-4 GHz) have been prioritized for maritime satellite communication systems due to their low-elevation transmission stability and strong diffraction characteristics [1, 2, 3]. This frequency regime not only suppresses multipath fading through omnidirectional coverage but also enables shipborne mobile terminals to achieve three critical functionalities: (1) robust LEO satellite signal acquisition, (2) dynamic Doppler shift compensation [4], and (3) integrated navigation enhancement services exemplified by BeiDou short message communication. As the critical component of communication links, antenna performance directly determines system stability. Circularly polarized waveguide slot antennas [5, 6, 7] have emerged as a research focus owing to their structural reconfigurability and simplified feeding networks.  
Conventional designs predominantly employ rectangular configurations. As reported in [8], a single-cavity dual-mode structure achieves an axial ratio \(\leq\) 3 dB through prism-isolated multimode resonance and X-shaped slot implementation. However, the inherent asymmetric current distribution along the rectangular waveguide edges induces transverse field phase mismatch, resulting in a significant E-H plane beamwidth discrepancy (>15\({}^{\circ}\) typical) that restricts applications to directional scenarios [9]. In contrast, circular waveguides inherently ensure field uniformity in omnidirectional radiation patterns through their axisymmetric geometry.  
Circular waveguide slot antennas have evolved into diversified configurations through decades of development [10, 11]. Early work in [12] realized circular polarization via orthogonally etched slots on cylindrical cavities through parametric optimization of slot dimensions, spacing, and tilt angles, yet suffered from a narrow impedance matchingbandwidth (<5%) and limited multiband integration capability. The cross-slot design in [13] achieved dual-band omnidirectional radiation at the expense of a deteriorated axial ratio (>6 dB) and narrowed half-power beamwidth (<60\({}^{\circ}\)) due to a dense array configuration. Although [14] implemented dual-band circular polarization using choked grooves with inclined slots, the design exhibited limited maximum gain (<2 dBi) and 30% lateral size expansion, failing to meet the spatial constraints of marine installations.  
To address the inherent limitations of conventional waveguide slot antennas and meet practical application requirements, this work proposes a novel marine cable-conformal satellite communication antenna based on circular waveguide technology. The proposed architecture incorporates an integrated X-shaped slot radiator with a three-stage coaxial impedance matching network, enabling omnidirectional circularly polarized radiation and dual-band operation. Through meticulous optimization of the slot configuration and matching network dimensions, the antenna achieved a 14.5% improvement in impedance bandwidth (1.61-1.85 GHz L-band) with a peak realized gain of 4.1 dBi. The operational bandwidth fully covers both the uplink (1610-1625.5 MHz) and downlink (2483.5-2500 MHz) frequency specifications mandated by the BeiDou-1 satellite navigation system. Experimental results demonstrated stable radiation patterns with axial ratios below 3 dB across the entire azimuth plane, validating the effectiveness of the X-slot configuration in generating symmetric circular polarization characteristics. This compact design ensures spatial compatibility with submarine cable infrastructure while maintaining satisfactory radiation performance, offering a viable solution for integrated marine communication systems requiring robust satellite links.