A closely located dual-band meander-line antennas with isolation enhancement by inserting novel split electromagnetic bandgap (EBG) uniplanar structure is proposed. The meander-line antenna is coupled to a parasitic rectangular patch to achieve the dual-band operation. Splits are applied on the surface of an EBG structure to cause decoupling at the first resonant mode and utilizing an EBG structure to decouple at the second resonant mode. The prototype of the proposed structure achieves a dual band of 180 MHz (3.42-3.6 GHz) and 400 MHz (4.7-5.1 GHz). The mutual coupling is significantly reduced by 26 and 44 dB at 3.48 and 4.88 GHz, respectively, compared to the reference antenna. In addition, the structure has high front-to-back ratio radiation characteristics.

This paper presents a novel design of high-isolation dual-band antenna with a close distance for 5G applications. The proposed antenna consists of two symmetrical monopole antenna elements. The two resonance frequencies of the monopole antenna are independently tunable. A defected ground structure (DGS) and grounded branches are loaded to reduce mutual coupling of the lower band by changing the current distribution on the ground plane. And a T-shaped parasitic element is placed between the two antenna elements. The parasitic element introduces an inverse path for mutual coupling cancellation, which greatly increases the iso-lation of the higher band. As a result, the proposed antenna achieves 5G dual-band of 3.409-3.601 and 4.76-5.04 GHz (S11&S22<-10 dB, S12&S21<-26 dB). Compared with the single monopole antenna, the bands of the proposed antenna don't shift and the impedance matching is improved. With the decoupling structure, the isolations are -29 and -41.4 dB at 3.5 and 4.85 GHz, respectively. In addition, the proposed antenna also has the advantages of small size, more flexibility, and simple structure.

A dual-band multi-polarized aperture-shared antenna array is presented, achieving Ku-band dual linearly polarized (LP) operation and Ka-band dual circularly polarized (CP) operation. Its dual-band aperture-shared structure is fed by two groups of independent feed networks, from the side and the bottom, using the quasi-planar coaxial waveguide line (QCWL) and the hollow-waveguide (HW) feed structure, respectively. Ku-band antenna and Ka-band antenna are carried out through the same quad-ridge waveguide aperture, and have the same array spacing. Thus, the large element spacing at high-frequency band inevitably leads to high sidelobes. The parasitic elements are adopted to suppress the high sidelobes in the E-plane and H-plane, and the realized gain of the high-frequency antenna is increased accordingly. In addition, a 1/2λ short-circuited stub is designed in the QCWL-based feed network for isolation enhancement. To demonstrate, a 4×4-element Ku/Ka-band multi-polarized antenna prototype is fabricated and measured. Experimental results show that the impedance bandwidths of 19.4% (14.4–17.5 GHz) for dual LP and 7.4% (32.5–35 GHz) for dual CP are achieved. The peak gains of the dual LP are 18.4 dBi and 18 dBi respectively while those of the dual CP are 23.4 dBic and 22.9 dBic.

In this article, a flexible high-selectivity single-layer coplanar waveguide (CPW) bandpass filter using interdigital spoof surface plasmon polaritons (SSPP) of bow-tie cells is proposed, simulated, and fabricated. The low and high cut-off frequency can be adjusted independently, which is one of the characteristics of the presented bandpass filter. The SSPP of bow-tie cells is used to adjust the high cut-off frequency, while the interdigital coupling structure of the SSPP is designed to adjust the lower one. The proposed filter also has advantages of single-layer structure and high selectivity. Simulated results of the proposed filter show a theoretical 3-dB bandwidth from 2.28 to 5.12 GHz (about 76.8%) with high selectivity (| S₁₁| < -15 dB and -0.4 dB >| S₂₁| > -1.1 dB in the passband), and measured results agree well with simulated ones. Since the filter in this article is designed based on the flexible printed circuit (FPC) board, the circuit can be tested in bent, folded, and even twisted states, and these measured results are all basically consistent with the test result of the flat state circuit. This characteristic can greatly reduce the size of the filter and increase the flexibility of the circuit application.

In this article, an ultraminiaturized bandpass-filtering matching network based on GaAs substrate integrated passive device (IPD) technology is proposed, which is suitable for frequency-dependent complex source and load. The presented bandpass filter (BPF) is derived from an equal-ripple Chebyshev low-pass filter prototype through frequency transformation and impedance scaling. The susceptance required by the source and load is extracted from the adjacent susceptance blocks, and the final reactance/susceptance block is equivalent to a series/parallel LC circuit at the two edge frequencies. Therefore, the proposed design has both bandpass high-selectivity and impedance matching functions, and simultaneously, the bandwidth can be flexibly controlled. Finally, a wideband BPF example with the center frequency of 3.5 GHz was simulated and fabricated with the IPD process, showing satisfactory performances.

In this paper, a dual-band bandwidth-enhanced filtering phase shifter is proposed, which can achieve two different predetermined phase-shifting values with the single-layer structure. The proposed phase shifter is composed of two stub-loaded transmission lines (SLTLs) and two delay lines. The loaded stubs provide three transmission zeros to realize dual-band working and filtering function. Based on the even-and odd-mode network analysis, the theoretical formulas can be obtained. According to the theoretical analysis and design method, several dual-band phase shifters are achieved. A dual-band phase shifter example, which can provide the phase shift of 90∘ and 270∘ in two bands, is simulated, manufactured, and measured for demonstration.