In this paper, a low-temperature co-fired ceramic (LTCC)-based E-shaped planar in-verted-F antenna (PIFA) is proposed for circularly polarized (CP) at D-band (110-170GHz). For stable CP radiation characteristic, a densified self-sequential rotation feeding (DSRF) technique is applied for 2×2 subarray. Certain perturbance of field distribution is achieved by arranging the coupling feed disks properly. Hence, a TE410-mode/quasi-TE330 high-order-mode (HOM) substrate integrated waveguide (SIW) cavity is excited with four coupling feeding slots properly arranged to obtain equal amplitudes and sequential 90°-phase shifts, which can be deemed as high-order-mode based densified self-sequential rotation feeding (HOM-DSRF) configuration. Thanks to the proposed HOM-DSRF configuration, the overall dimension of the 2×2 CP subarray is only 1.05λ×1.05λ with a simulated aperture efficiency up to 96%, which is significantly superior to conventional sequentially rotation feeding methods in terms of overall dimension and aperture efficiency. Finally, a 4×4 antenna array is designed, fabricated and measured. The measured impedance bandwidth and 3-dB axial ratio bandwidth are 10.4% from 145.7 to 161.7 GHz and 10.5% from 144 to 160 GHz, respectively. The measured peak gain is 15.1 dBic, with measured aperture efficiency up to 71%. The measured results agree well with the simulated ones. The proposed HOM-DSRF configuration has potential applications for terahertz (THz) CP antenna array designs.

A high-gain circularly polarized (CP) magnetoelectric dipole (ME-dipole) radiating element is demonstrated at a millimeter-wave (MMW) 5G band of 37–43.5 GHz. Each ME-dipole radiating element, consisting of two pairs of ring-shaped and L-shaped metal posts is excited by a cross-shaped substrate-integrated waveguide (SIW) coupling slot to achieve CP radiation. Through the use of all-metal radiating structures with a height of 3.4 mm, high-gain and high-efficiency radiation performances are achieved. For proof of concept, a 4 × 4 antenna array with a SIW feeding network is designed, fabricated, and measured. The measured impedance bandwidth of the proposed 4 × 4 CP antenna array is 19.2% from 33.9 to 41.1 GHz for |S11| ≤ −10 dB. The measured 3 db AR bandwidth is 10.3% from 37 to 41 GHz. The measured peak gain is 20.3 dBic at 41 GHz. The measured and simulated results are in good agreement.

In this letter, a chamfered pyramidal Potter horn antenna is designed with both low sidelobe level (SLL) and low cross polarization level (XPL). Firstly, a stepped discontinuity structure is introduced to excite the TM₁₂ mode. By precisely controlling the amplitude and phase of the TM₁₂ mode through structural adjustment, low SLL and low XPL performances are achieved. In addition, simple chamfered structures are also applied to change the electric field distribution across the horn aperture, which further reduces the XPL of the pyramidal horn antenna. Finally, the antenna is fabricated and measured. Measurements demonstrate excellent E-plane and H-plane symmetry with low SLL across 23.5–29.5 GHz, achieving a bandwidth of 22.6% with XPL lower than −30 dB. The E-plane SLL remains below −25 dB throughout the operating band. Note that the proposed pyramidal Potter horn achieves an unprecedented minimum measured XPL of −37.8 dB.

In this letter, a hybrid dielectric-metallic-loaded (HDML) broadband horn array antenna is proposed, which achieves extremely high aperture efficiency (AE) and covers the entire Ka-band. The proposed antenna array is composed of four distinct components: a bottom full-corporate feeding network configuration, a second horn array layer, a third lattice structure acting as metallic loading, and a top embedded multi-step rectangular block (MRB) structure acting as the dielectric loading. High gain and high AE are achieved owing to the HDML technique. Additionally, the embedded MRB structure reduces the reflections between the air and the radiation configuration, which effectively enhances the impedance bandwidth (IBW). Ultimately, an HDML 8×8 horn array antenna was simulated, fabricated, and measured. The prototype achieves a 42.28% IBW ranging from 26.32 to 40.43 GHz. Thanks to the proposed HDML technique, the measured peak gain of the 8×8 horn array is 27.4 dBi and the AE is as high as 96.3%.