A method of triple-mode operation by capacitive slot loading is proposed for bandwidth enhancement of single-fed circularly polarized (CP) patch antennas. Instead of using even-numbered linearly polarized (LP) modes with quadrature phase, three orthogonal LP modes are used for CP bandwidth enhancement, where the middle mode is shared by two cross-polarized modes with the same polarization. The advantages include reduced constraints, lower complexity, and a higher degree of freedom for antenna design. Guided by the method, a U-slot antenna and an E-shaped antenna are proposed and designed with characteristic mode analysis (CMA). Both antennas work with a TM ₁₀ -like mode and a TM ₀₁ -like mode. Differently, the U-slot antenna works with an additional slot mode and the E-shaped antenna works with an additional TM ₁₁ -like mode. The operating modes are manipulated by the slot loadings for creating phase difference. As a result, wideband CP radiation is achieved with a single feeding. CMA-based empirical formulas are derived for fast design. The proposed method and antennas are experimentally validated. Both antennas measure a bandwidth exceeding 21% for 10 dB return loss and 3 dB axial-ratio (AR), a significant improvement compared with conventional corner-truncated U-slot patch antennas of similar thickness or volume.

A phase gradient metasurface (PGM) array with beam converge characteristic in reflection direction at 15 GHz and transmission direction at 5.6 GHz is proposed in this letter. Compared with the traditional unidirectional PGM, the proposed PGM can achieve bidirectional radiation at two frequencies. A horn is used as the feed placing at a focal length of 200 mm of PGM array. Simulation results show that the horn has a peak gain enhancement of 11.9 dB at 15 GHz with a -3 dB beamwidth reduction of 33° in reflection direction and a peak gain enhancement of 7.9 dB at 5.6 GHz with a -3 dB beamwidth reduction of 30° in transmission direction. The proposed PGM array achieves beam converge in two directions at two different frequency and has a potential use for communication system consisting of receivers with multi-frequency and multi-location characteristic.

This letter proposes a novel center-fed (CF) triple-mode wide-band circularly polarized (CP) array using characteristic mode analysis (CMA). The proposed antenna can not only achieve the wide-band CP property, but also obtain more symmetrical patterns than traditional off-center fed (OCF) patch antennas. The influence of the symmetry of the element pattern on the array scanning performance is analyzed further in this work. Two 36-element arrays consisting of proposed CF elements and traditional chamfered OCF elements are fabricated and measured for comparison, respectively. The measurement results show that the proposed CF patch array can increase the peak gain almost 1.8 dB higher and greatly improve the axial ratio (AR) almost 3.5 dB better than the traditional OCF CP patch array when scanning to a large angle.

In this article, a novel method of achieving a single-layer, dual-band, dual-circularly polarized (CP) shared-aperture phased array antenna with wide beam scanning coverage is presented. The space antenna was designed to provide direct-to-cellular communications services at S-/C-bands with a frequency ratio of 1:1.8. Using novel ceramic substrates with high dielectric constants for antenna miniaturization, the optimum interelement spacing can be ensured in one single layer to meet the large-angle scanning demand. The CP characteristic of the phased array is improved by the sequential rotation technique. A prototype of phased array, which is composed of an 8 × 8 S-band Rx array and a 16 × 16 C-band Tx array, is fabricated to verify this design. The measured results show that the shared-aperture phased array can provide ±50° beam scanning coverage at both the S- and C-bands simultaneously to meet the direct-to-cellular communication demand in low earth orbit (LEO) satellites.