This letter presents a broadband filtering circularly polarized (CP) folded transmitarray antenna (FTA) with a linearly polarized (LP) feed antenna based on metasurface (MS). The whole antenna mainly consists of two MSs located on the top and bottom layers and an LP feed antenna. LP to CP wave (LP-CP) conversion and phase compensation are achieved across the entire X-band with the designed top MS. The top bandpass MS is also used as a spatial filter, utilizing its out-of-band suppression characteristics and high passband edge selectivity. A fabricated prototype was measured, and the results reveal that its maximum gain is 27.8 dBi at 10.2 GHz with an aperture efficiency of 40%. It also achieves a 3-dB gain bandwidth of 24.5% and a 3-dB axial-ratio (AR) bandwidth of 41.1%, which is in good agreement with the simulation results as well. The proposed broadband CPFTA achieves a bandpass filtering response while also retaining the advantages of low profile, high gain, and low cost, which illustrates great application potential in future wireless communication systems.

A half-mode substrate integrated waveguide (HMSIW) with developed microstrip polyline unit cells etched on the waveguide surface is investigated in this letter. Modified analysis of the effective electrical parameters analysis is proposed. By applying the modified retrieval method, effective permittivity and permeability are extracted accurately to further describe the influence of the proposed structure, as well as slow-wave effect. Then, a compact 3-dB Wilkinson power divider/combiner based on polyline-patterned slow-wave HMSIW is developed for broadband microwave applications. The prototype achieves a fractional bandwidth of 91.7%, with the amplitude and phase variations less than 0.5 dB and ±4°, respectively. Compared with some reported SIW and HMSIW power divider, this letter achieves a size reduction of 40% and a bandwidth enlargement over 50%, illustrating its suitability for practical broadband applications.

A compact planar sub-wavelength array is proposed, which has planar antenna elements etched with defect oval rings on the surface. The array demonstrates a property of 1/20 wavelength super-resolution combined with time-reversed electromagnetic waves. This design is simple in structure, easy to integrate and convenient for the printing design of circuit boards.

In this letter, a method to generate multiple non-diffracting beams by a transmission metasurface is proposed. The unit cell consists of two layers of the same circular resonant patch and a medium layer in the middle. The unit cell is rotated by different angles to obtain a 360 $^{\circ }$ transmission phase shift. The method of generating multiple non-diffracting beams on the metasurface is realized by a multi-beam shared-aperture (MBSA) method. Multiple sub-arrays are used to launch non-diffracting beams that propagate in different directions in a shared-aperture manner. Each sub-array is independent and complementary to control the deflection of multiple non-diffracting beams more flexibly. In accordance with the method, three non-diffracting beams are generated by the same transmission metasurface. The metasurface is fabricated and measured, and the results validate the proposed design method.

Structurally integrated antenna is a kind of highly integrated microwave device with a loadbearing function, and it is usually installed on the structural surface of the air, water and ground vehicles. This paper presents the design, fabrication and testing of a novel structurally integrated Ka-band active antenna for airborne 5G wireless communications. The proposed antenna is mainly composed of three parts: a package layer, a control and signal process layer and a RF layer. In the RF layer, the microstrip antenna array, tile transmitting (Tx) modules, micro-channel heat sinks and a stripline feeding network are highly integrated into a functional block with a thickness of 2.8 mm. Electromechanical co-design methods are developed to design the active antenna array with the superstrates, and two schemes for designing micro-channel heat sinks are evaluated to obtain a uniform temperature distribution. The RF layer is fabricated by using the low-temperature cofired ceramic process, and the three layers are assembled to form the full-size antenna prototype. The mechanical and electromagnetic experiments are carried out, and the results demonstrate the feasibility of the structurally integrated active antenna for airborne wireless communications.

The complexity reduction of receivers in ultrawideband (UWB) communication when time reversal (TR) technique is applied makes it suitable for low-cost and low-power sensor systems. Larger antenna dispersion can generally lead to a less stable phase center and will increase the interference in UWB communications based on pulse radio, whereas a higher antenna gain will result in higher channel gain and further larger channel capacity. To find out the trade-off between antenna gain and dispersion, we performed the channel measurements using different antennas in a dense multipath environment and established the distribution of channel capacities based on the measured channel responses. The results show that the capacity loss caused by antenna dispersion cannot be compensated by antenna gain with line-of-sight transmission to some extent, the effect of phase center on the communication system is negligible, and antennas with smaller time dispersion will have a better energy focusing property and anti-interference performance in TR systems.