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A compact wideband dual-polarized filtering antenna based on tightly coupled cross dipoles is presented in this letter. The enhancement of impedance bandwidth is realized by introducing four impedance equalizers to equalize the input resistances of the two inherent resonant modes of tightly coupled cross dipole antenna. The enhancement of the selectivity is realized by introducing two radiation nulls in 5G sub-6 GHz n77 and n79 bands. The radiation null in n77 band is obtained by introducing the cross strips in the center of the antenna. The radiation null in the n79 band is achieved by the introduction of open-end branches. The manipulation of their key parameters allows for independent control over both radiation nulls. The validity of the antenna's design principle was confirmed by carrying out fabrication and measurements. The results obtained showcase the antenna's broad fractional bandwidth of 63.4% and exceptional port isolation of 31 dB. High out-of-band rejection levels in n77 and n79 bands are also obtained. In addition, since the whole radiator of the presented antenna is coplanar, it offers the advantage of a simple structure and convenient manufacturing, making it highly suitable for the use in base stations operating across multiple bands.

In this communication, a novel four-port slot antenna designed for both 5G New Radio (NR) and WiFi operations is introduced. Wideband NR antennas are achieved using a hybrid mode concept. Then, two NR slot antennas are co-designed as a radiative bandstop structure. By moving the resonance frequencies of the hybrid modes close to the band-reject points of this bandstop filter, a wideband decoupled dual-antenna structure is achieved. To enhance functionality, two additional ports are incorporated into the dummy slot area between these two NR ports, resulting in a quadruplex antenna. In this final configuration, two of the antennas are optimized for 5G NR applications, covering the 5G N77, N78, and N79 bands (3.3 GHz-5.0 GHz), while the remaining two antennas serve the WiFi band (5.15 GHz-5.8 GHz). Compared to other presented works, the simulation and experimental results demonstrate that this work not only, for the first time, achieves simultaneously wideband in-band and small frequency ratio (1.05) out-of-band duplex in one single module, but also has the advantages of high isolation, compact size, and low cost.

A dual-polarized antenna with wide impedance bandwidth and high selectivity is presented for the use of 5G sub-6GHz base stations. By strategically introducing a novel coupled dual-mode grid structure, two additional resonant modes (One is in-band, another one is out-of-band) as well as two radiation nulls can be obtained to enhance the impedance bandwidth and out-of-band rejection level of the widely used tightly coupled cross-dipole antenna. The two radiation nulls introduced by the grid structure are located at the two edges of the desired frequency band. To further improve the gain suppression level in higher out-of-band, a new radiation null is obtained by symmetrically introducing four T-shaped strips. Apart from these additional radiation nulls, this antenna also exhibits two inherent radiation nulls originating from its feed structure and reflector. The measured results demonstrate that the proposed antenna exhibits a wide impedance bandwidth of 39.5% (ranging from 3.07 GHz to 4.58 GHz), excellent isolation of over 31 dB, and a notable out-of-band rejection level exceeding 17.6 dB and 19.2 dB in the frequency bands of 1.7 GHz-2.7 GHz and 4.8 GHz- 5.0 GHz.

In this paper, a novel method for the decoupling between two filtering antennas is presented. The mutual coupling between two filtering antennas is investigated and a coupled-resonator decoupling network (DN) is developed. This coupled-resonator DN is co-designed with the coupled filtering antennas with little effect on the original filtering responses. By connecting this network to the coupled antennas in parallel, the mutual coupling between two 2 nd order filtering antennas can be suppressed dramatically. A step-by-step realization of the DN is provided. To verify the concept, a prototype using the proposed DN was fabricated and measured. Full-wave simulations and measurements indicate that this coupled-resonator DN can enhance the isolation between two filtering antennas up to 30 dB without significantly affecting the filtering performance of each antenna, at a cost of 1.15 dB efficiency drop.

A dual-polarized antenna with multimode resonance and high selectivity is proposed in this paper to cover the 5G sub-6 GHz bands. The proposed antenna achieves dual wide impedance bandwidth characteristics by incorporating a dual mode coupled patch and four planar coupled strips around the driven patch. Through the four resonant modes of these structures, the antenna effectively covers the two desired frequency bands. Moreover, the electric/magnetic coupling between the driven patch, dual mode coupled patch, and planar coupled strips enables the creation of three radiation nulls that suppress unwanted radiation. To further improve the out-of-band rejection level and half power beamwidth, four shorted strips are introduced around the radiator. The introduction of these strips results in a 4th radiation null at higher out-of-band frequencies and expands the antenna's half power beamwidth from 52° to 62°. To demonstrate the feasibility of the design, both the proposed antenna and its array were manufactured and tested. Measured results show that the filtering element was able to operate within frequency bands of 3.24-3.83 GHz (16.7%) and 4.74-5.30 GHz (11.2%) with a reference of |Sdd11| < -14 dB. The input ports exhibited a high level of isolation, measuring 40 dB. Furthermore, the four radiation nulls proved effective in suppressing out-of-band radiation.

This study introduces a wideband and compact filtering antenna with dual-polarization for 5G base station usage. The proposed design, which combines meander lines and parasitic grid structures, achieves a broad operating bandwidth and an excellent gain suppression level in the unwanted 2/3/4G band. To verify the design concept, a prototype of the design was fabricated and tested. According to the test results, the proposed design can cover 3.16 GHz to 4.75 GHz. The isolation between the two ports exceeds 30 dB in the target n77 band (3.3-4.2 GHz). Additionally, the gain rejection level is higher than 13 dB in 1.7-2.7 GHz.

This paper introduces novel dual-polarized/duplex filtering antennas with a novel filtering feeding network. The feeding network consists of an all-resonator structure, which shares a common dualmode resonator. This structure facilitates the isolation of two well-isolated channels through the exploitation of the even and odd modes of the dual-mode resonator. By applying balanced excitation to the odd mode and unbalanced excitation to the even mode, the two modes can be separated, creating a hybrid-like feeding structure. Despite the common resonator, the channels exhibit high isolation, and the overall size of the filtering circuit is much smaller than conventional cascaded-resonator designs. To demonstrate the effectiveness of the proposed feeding network, we have designed, fabricated, and measured a dual-polarized and a duplex filtering antenna. The simulated and measured results agree well, showing isolations greater than 34 dB and 38 dB for dual-polarized and duplex cases, respectively. Our proposed antennas are compared with state-of-the-art developments, demonstrating the advantages of compact size, flexible decoupling frequency ratio, and high isolation.

this article presents a novel method for decoupling two patch antennas. Instead of using the TM 10 mode of a conventional patch, TM 20 mode is utilized as the operation mode of the antenna. By loading stubs at the radiating edge of the patch, the resonance frequency of the TM 20 mode is moved down to the same band as the original TM 10 mode. Then, the mutual coupling between two such patch antennas is suppressed simply by physical placement, even when they are placed extremely close to each other. Without using any extra decoupling elements, isolation is improved by up to 20 dB using this method. Furthermore, this method can also be applied to multielement multi-input -multi-output (MIMO) array and dual-antenna system with different operating bands. The proposed method is verified with three different application scenarios, including a two-element MIMO array, a two-antenna system with adjacent operating bands, and a four-element MIMO array. Reasonable agreements between simulated and measured results can be observed, showing the advantages of simple structure, low cost, high isolation, and good radiation performance.

Dual-band dual-polarized arrays (DBDPA) using interleaved configuration have drawn industry attention as a promising way to improve channel capacity in a package that has a minimum width. By integrating high-performance filtering elements, a novel interleaved DBDPA for base station use is presented in this paper. For the first time, a radiation null is introduced into the low-band (LB) antenna using the intrinsic suppression mode of folded dipole. Then, to enhance the gain-suppression level in out-of-band to 16 dB, four rectangular loops are introduced under the radiator. To achieve high selectivity for high-band (HB) antenna, a meander line loop is introduced and analyzed for the first time in this paper. Simulations indicate that the presented HB antenna achieves 17 dB of out-of-band rejection and 243 dB/GHz of roll-off rate. The combined use of these two filtering elements finally enables the realization of a DBDPA with low mutual coupling and low cross-band scattering. According to the measurements, this antenna covers two wide frequency ranges of 2.26- 2.73 GHz and 2.98- 4.3 GHz with a 25 dB cross-band isolation level.

The theory, design and experiments of a wideband dual-polarized filtering antenna are presented. A novel technique, which combines the use of open loops, parasitic loop, and extended ground plane, is proposed to realize two upper band radiation nulls and a lower band radiation null. Thanks to these radiation nulls, the proposed antenna obtains a sharp cut-off at the edges of the operating band. To achieve wideband performance, another novel technique of exciting multiple resonant modes of the crossed dipoles and parasitic loop is proposed. The measured results demonstrate that this antenna achieves a wide impedance bandwidth from 1.7 to 3.01 GHz (56%), high isolation of 38dB, low cross-polarization within the working frequency band and also filtering performance. At 3.17 GHz, the gain of the antenna will drop rapidly to -18.1 dBi, which is 26.4 dB lower than the average in-band gain. These advantages make the proposed antenna a good candidate for base station applications.

A dual-polarized filtering antenna with steep cut-off and compact size is developed for base station applications. In this design, four controllable radiation nulls are obtained by utilizing split rings, slotted T-shaped branches, a single-stub tuner, and a parasitic loop. Split rings are firstly used as the dipole arms to obtain the 1st radiation null at upper out-of-band. Four T-shaped branches working as DGS are printed under the crossed dipoles to achieve the 2nd radiation null. The connected outer conductors of the differential feed structure acting as a single-stub tuner can provide the 3rd radiation null to further enhance the upper-band rejection. Finally, a parasitic loop is incorporated around the split rings, and the out-of-band rejection of the lower-band is further enhanced by the 4th radiation null. More importantly, the impedance bandwidth of the antenna can be expended with two newly introduced resonant modes. As a result, a compact filtering antenna with a wide operational bandwidth of 1.7- 3.01 GHz (56%) is realized for |Sdd11| < -15 dB with the isolation higher than 38 dB. The out-of-band suppression is higher than 18.4 dB in 3.1-4.5 GHz and more than 47 dB in 0.8-1.1 GHz.

An interleaved shared-aperture dual-band dual-polarized base station array antenna is proposed in this paper. The lower-band (LB) element is realized by using a multiple folded-dipole antenna (MFDA) and four parasitic loops. To interpret the working principle of the MFDA, a double folded-dipole antenna (DFDA) is firstly analyzed by using the transmission line model. Then, by combining two bended DFDAs and introducing four parasitic loops, a low cross-band scattering LB element with a high out-of-band rejection level of 16 dB is obtained to cover 2.3-2.7 GHz. The higher-band (HB) element with a wide impedance bandwidth of 42.5% (3.0-4.6 GHz), a high roll-off rate (RoR) of 249.2 dB/GHz, and a high out-of-band rejection level of 17 dB is obtained by introducing a meander line loop, a rectangular loop and V-shaped strips near the dipole arms. By combining the proposed low scattering low-pass LB element and the high RoR high-pass HB element, a novel interleaved shared-aperture dual-band dual-polarized array antenna with a small frequency ratio of 1.46 and a high cross-band isolation level of 25 dB is realized. Due to the low-scattering characteristic and filtering response of the LB element, the radiation patterns of the wideband HB sub-arrays are almost unaffected.

A comprehensive study of developing a novel printing system using a low-cost open-source printer for fully 3D printing frequency selective surface is presented in this paper. The novel printing setup employs a low-cost printer to print a plastic based filament and a conductive silver ink paste simultaneously. As there were no printers available in the market for this application, the open-source Fused Filament Fabrication (FFF) printer was modified to accommodate two extruders mounted on the same extruder carriage. Techcon TS250 air pressure dispenser was employed for the extrusion of silver ink. Extension pieces for the extruder carriage were also 3D printed using a Fused Deposition Modelling (FDM) printer to reduce the production costs. A bandstop FSS comprising of square loop elements was designed to demonstrate the full fabrication. The FSS operated at a central frequency of 2.55 GHz and provided a good angle of response with wide bandwidths. Surface profiles of the printed FSS and substrate demonstrate the reliable fabrication of the FSS design. This full 3D printing method provides an economical, eco-friendly, swift, reliable, and viable substitute for the fabrication of FSS designs that could be highly customised in terms of fabricating three-dimensional FSS designs with reliable performances. The designs can be printed and deployed to reduce the drop in signal within an enclosed environment.

Dual operations of AC current sensing and Bluetooth transmission using a reconfigurable slot antenna are described here. The novel current sensing setup comprises of a tunable antenna connected to a current transformer and AC/DC converter to create a smart AC current sensing mechanism. The tunable antenna consists of a double-layer slot antenna on a thin, flexible substrate with a tuning circuit consisting of capacitive-coupled biasing tracks on the backside. Capacitive coupling isolates circuits at DC while providing connectivity at radio frequency (RF). Tracks act as the capacitors for the tuning biasing circuit. A double-sided copper clad Mylar substrate is etched to produce the slot antenna on one side and the biasing circuit using inexpensive Varactor diodes on the other side. The antenna tunes over a wide frequency range of approximately 2:1. The antenna is able to sense currents by providing a frequency response when connected to the sensing system. The current sensing antenna can also detect the operational or non-operational states of the appliances and devices. This low-cost setup of antenna on a flexible substrate can assist in detecting the power and current monitoring in household electrical devices providing an energy-efficient solution while also operating as a transmitter via Bluetooth. The measured reflection coefficients and radiation patterns are in a good agreement with the simulated results and noticeably clear sensing of current is achieved.