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A full-passband linear-phase band-pass filter (BPF) equalized with negative group delay circuits (NGDC) is proposed. The NGDCs are utilized to suppress the salient group delay at the edge of the passband of the traditional BPF for achieving the full-passband linear-phase characteristic. To obtain input- and output-port impedance matching, two BPFs loading NGDCs are center symmetrically configured by Wilkinson power dividers. To verify the design concept, a 3-order full-passband linear-phase BPF is designed and fabricated. From the measured results, the GD fluctuation is reduced by 74% from 0.57 to 0.15 ns, return loss is better than 10 dB, and the insertion loss variation is less than 3 dB within the frequency range from 2.142 to 2.804 GHz. The proposed BPF achieves a flat group delay in the whole passband and realizes the full-passband linear-phase characteristic.

This paper presents a new type of miniaturized base station antenna array, which consists of a metal reflector, six upper-band dipoles, and a couple of ladder sidewalls, operating over 1.71-2.69 GHz (DCS/PCS/UMTS/LTE). Meanwhile, this paper also proposes a novel miniaturized phase shifter with one input and five outputs to enable the antenna array to achieve electrical downtilt (0°-10°) in the operating frequency band. Three different sidewalls are applied in the proposed antenna array to compare their performance. Simulated results demonstrate that the antenna array with ladder sidewalls can achieve an excellent performance, and this proposed phase shifter also has good electrical properties to help the proposed antenna array realize downtilt. The proposed antenna array and phase shifter are fabricated and measured, and the measured results show that the antenna array has good radiation characteristics, including low-voltage standing wave ratio (31 dB), low third-order passive intermodulation (3 30 dB), and high cross-polarization discrimination at ±60° azimuth (>11.5 dB) in all frequency bands and electrical downtilt angles. The proposed antenna array exhibits an acceptable gain of 15 ± 1.1 dBi across the operational frequency band.

The performances of plane spiral orbital angular moment (OAM)-based MIMO (PSOAM-MIMO) systems are investigated in a non-line-of-sight (NLoS) channel. Two analytical models, known as specular reflection model and circular scattering model, are applied to evaluate the reflection and scattering effects of wave propagating in the NLoS channels. The performances of the PSOAM-MIMO system in the NLoS channel are compared with those of the conventional MIMO system and in LoS channel. It is found that the capacity gain of the PSOAM-MIMO over MIMO is mainly determined by a direct path. In the NLoS channel, the capacity gain of PSOAM-MIMO over MIMO decreases compared with that in LoS, however, the multi-path effects improve the absolute capacity of PSOAM-MIMO system, and the worst case are comparable with those in an MIMO system. As a result, the PSOAM-MIMO system demonstrates the strong robustness in wireless communications.