Dual-polarized Loop Research Articles

Broadband Dual-Polarized Loop Cross-Dipole Antenna for 5G Base Station Applications

A broadband dual-polarized base station antenna is proposed in this paper. The antenna consists of loop cross-dipoles, Y-shaped coupling feeding lines, and a metal box reflector. An equivalent circuit model including a signal flow diagram is established to analyze the mechanism of the proposed antenna in detail. Moreover, the Y-shaped coupling feeding lines are introduced to control the coupling with the antenna to achieve broadband and good impedance matching. The prototype of the antenna is fabricated and measured. The measured results show that the antenna with simple structures can operate at the band of 3.2–5.22 GHz (48%) with high port-to-port isolation (35 dB) and stable gain (9 ± 1 dBi). The measured results show good agreement with simulated results, especially in cross-polarization discrimination ratio (>27 dB) and the half power beam width (61° ± 3° at the E-plane, 68° ± 3° at the H-plane). In summary, the proposed antenna could be a good candidate for 5G sub-6 GHz base station applications.

Wideband Dual-Polarized Omnidirectional Antenna Array for Base-Station Applications

A compact wideband dual-polarized omnidirectional antenna array for base-station applications is proposed. It consists of ten antenna units. To generate ±45° dual-polarized ominidirectional radiation with low gain variation for each unit, three close-in crossed-dipole elements are uniformly arranged in a regular triangle shape and excited by two 1-to-3 power dividers with equal magnitude and phase, acting as a dual-polarized loop antenna. To obtain wide impedance bandwidth for each unit, the dipole element and power divider are designed to operate in a wide and well-matched band. Moreover, the unit features steady structure, easy fabrication, and high scalability, which makes it convenient to form an antenna array. To achieve a high gain for base-station applications, a ten-unit antenna array is designed, fabricated, and measured. A wide impedance bandwidth of 52.3% (1.62–2.77 GHz) for standing-wave ratio (SWR) < 1.5 and a high port-to-port isolation of 26 dB are realized. It also features a high gain of 10.3 ± 0.9 dBi and a small gain variation of less than 2.5 dB in the horizontal plane. Additionally, the sidelobe suppression of 18 dB and null filling below the main vertical beam are obtained by the designed feeding networks. These results make the proposed design attractive in base-station applications.

Study of the Colocated Dual-Polarized MIMO Capacity Composed of Dipole and Loop Antennas

The colocated dual-polarized dipole (DPD) and dual-polarized loop (DPL) MIMO channel performances are compared. Computation results show that, for the ideal electric and magnetic dipoles, the dual-polarized MIMO systems have identical channel capacity. But the contour plots of the capacity gain of the realistic DPD and DPL are different, due to the difference in antenna patterns. The cumulative distribution function (CDF) of the capacity gain in the two-mirror (TM) channel shows that, for small distance, the capacity gain obtained by the DPD is obviously smaller than that of the DPL, but, with the increase of the distance, the difference gets smaller. A DPL with low mutual coupling is fabricated. Measured results show that high MIMO capacities can be obtained by this DPL in both the anechoic chamber (AC) and the realistic office room. The capacity gain of the DPL antenna is 1.5–1.99, which basically coincides with the theoretical and numerical results. Furthermore, the capacity of the virtual DPL antenna with no mutual couplings is also investigated. It is shown that, in the AC, the mutual coupling will generally decrease the dual-polarized MIMO capacity; however, in the office room, the effect of mutual coupling is not always negative.

HEXA-BAND HIGH-ISOLATED DUAL-POLARIZED LOOP ANTENNA FOR MOBILE COMMUNICATIONS

This paper presents a broadband hexa-band dual-polarized loop antenna for mobile communications. Two orthogonal one-wavelength-perimeter modes of a rectangular loop are excited by two orthogonal feedings. One mode for vertical polarization is excited by a circular monopole, and the other mode for horizontal polarization is excited by a slot-coupled microstrip line. By optimizing the antenna structure and the orthogonal feedings, the orthogonal polarizations can be achieved in a wide bandwidth with high ports isolation. The overall size of the proposed antenna is only 58 × 53 mm 2 (0.43λ0 × 0.39λ0, λ0 is the free-space wavelength at 2.2 GHz). A prototype of the proposed antenna is built and tested. The measured bandwidth with reflection coefficient less than −10 dB is 61.4% (1.65-3 GHz) for both orthogonal polarizations, covering the DCS, PCS, UMTS, WLAN, LTE2300, and LTE 2500 operation. The measured ports isolation is better than 28 dB over the entire band. In addition, the radiation patterns, gains and diversity performance are also discussed.

MIMO CAPACITY COMPARISONS OF THREE TYPES OF COLOCATED DUAL-POLARIZED LOOP ANTENNAS

The 2 × 2 multiple-input-multiple-output (MIMO) capacities of three types of colocated dual-polarized loop (DPL) antennas with different current distributions and isolations are investigated in the free space (FS) channel, the corridor with perfect electric conductor walls (PEC corridor) and the corridor with concrete walls (CON corridor), separately. Capacity results show strong dependences on both the structure and the position of the DPL antenna, in addition to the propagation conditions. For all the three propagation scenarios, the largest capacity can be reached is in the PEC corridor, employing the DPL antenna with a uniform current distribution and a high isolation. Specifically, for a 20 dB signal-to-noise ratio (SNR), the maximum dual-polarized MIMO capacity is 13.1 bps/Hz, which is 1.97 time of that obtained by the one-polarized loop. It is also noted that, the rich-multipath environment can increase the robustness of the DPL MIMO system and the difference of the MIMO capacity obtained by different antenna structures will get smaller with respect to that in the FS channel.