This paper presents a novel tri-band, dual-polarized and shared-aperture antenna with frequency selective function for Sub-6 GHz base station applications. The proposed antenna is composed of a dual-polarized square loop antenna with two parasitic loops for 2G/3G/4G (1710-2690 MHz) and a differentially fed dual-polarized planar antenna for 5G (3300-3600 MHz and 4800-5000 MHz) base station applications. These two antennas are placed coaxially but different altitude for saving the installation space. In order to achieve good individual performance for these two antennas in the same aperture without interference or blocking, the lower-band (LB) antenna is designed as a frequency selective surface (FSS) for the nether mid/upper-bands (M/UBs) antenna. Measured results show that the proposed antenna achieves a high port isolation (> 20 dB) between LB and M/UBS and a -10-dB impedance bandwidth of 50.4% (1.60-2.70 GHz), 14.9% (3.28-3.80 GHz) and 8.6% (4.75-5.18 GHz), respectively. To further validate the design concept, an antenna array composed of 4 LB elements and 8 M/UBs elements with correspond spacing is fabricated and measured, which demonstrates the application of the tri-band shared-aperture antenna in array form.

A compact-size low-profile wideband circularly polarized (CP) omnidirectional antenna with reconfigurable polarizations is presented in this communication. This design is based on a low-profile omnidirectional CP antenna which consists of a vertically polarized microstrip patch antenna working in TM ₀₁ /TM ₀₂ modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field. The combined radiation from both the microstrip patch and the slots leads to a CP omnidirectional radiation pattern. The polarization reconfigurability is realized by introducing PIN diodes on the slots. By electronically controlling the states of the PIN diodes, the effective orientation of the slots on ground plane can be changed dynamically and the polarization of antenna can be altered between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The proposed antenna exhibits a wide-operational bandwidth of 19.8% (2.09-2.55 GHz) with both axial ratio below 3 dB and return loss above 10 dB when radiates either LHCP or RHCP waves. Experimental results show good agreement with the simulation results. The present design has a compact size, a thickness of only 0.024λ and exhibits stable CP omnidirectional conical-beam radiation patterns within the entire operating frequency band with good circular polarization.

A novel polarization-reconfigurable planar antenna is presented. The antenna consists of an electronically reconfigurable polarizer integrated with a printed slot. By changing the states of the p-i-n diodes on the polarizer, the linearly polarized (LP) waves radiated by the slot can be converted into either right-hand circularly polarized (RHCP) or left-hand CP (LHCP) waves. The polarizer contains 16 unit cells arranged as a 4 × 4 array. The antenna radiates RHCP waves if the p-i-n diodes on the top side of the polarizer are switched ON, while LHCP waves are radiated if the p-i-n diodes of the bottom side of the polarizer are switched ON instead. The physical mechanisms of the antenna are discussed and the parametric study is carried out by full-wave simulations. To verify the concept, one prototype at 2.5 GHz is designed, fabricated, and measured. Good agreement between the measured and simulated results is obtained. The antenna achieves a gain ≥8.5 dBic in both RHCP and LHCP with an aperture efficiency of 70%. Advantages of the proposed design include electronically reconfigurable polarizations for RHCP or LHCP, low profile, low cost, high isolation between the dc bias circuit and RF signals, high power handling capability, and easy extension to large-scale arrays without increasing the complexity of the dc bias circuit. To the best of our knowledge, this is the first report of an electronically polarization-reconfigurable CP antenna with a single-substrate polarizer.

This communication proposes a novel method to design a dual-band circularly polarized (CP) transmitarray (TA) antenna with a linearly polarized feed. By using this method, a shared-aperture dual-band TA is developed, which forms independent beams with right-hand circular polarization (RHCP) or left-hand circular polarization (LHCP) in two frequency bands with a single linearly polarized feed antenna. Four different CP TA prototypes operating at 12 GHz and 14.2 GHz with different senses of CP and different beam directions are designed, and two of the prototypes are fabricated to validate the design concepts. A good agreement is obtained between the radiation patterns, gain curves, polarizations, and cross polarization levels measured and computed in both frequency bands. The proposed single-source dual-band CP TA design has advantages of simple structure, lightweight, easy fabrication, low cost, and high performance, making it a good candidate for varied applications.

In this communication, a novel wideband differentially-fed dual-polarized stacked patch antenna with tuned slot excitations for base station application is proposed. The antenna is composed of a driven patch excited by tuned slot excitations, a parasitic patch to enhance the impedance bandwidth, and a ground plane to obtain unidirectional radiation. Two pairs of the slot excitations etched on the opposite edges of the driven patch are used to obtain dual polarizations. Each tuned slot excitation has an open-ended slot and a Γ-shaped feeding line. To connect to the differential circuit easily, a rotated feeding mechanism is adopted. A prototype of the proposed antenna is fabricated and tested. Measured results show that the antenna has a wide differential impedance bandwidth of 49.4% (1.66 to 2.75 GHz) for |Sdd11|<-15 dB. In addition, a high differential port isolation of more than 37 dB, a stable radiation pattern with a 3-dB beamwidth of 61°±5°, and a stable gain around 8.7 dBi are obtained within the operational band. The proposed antenna features wide band, high port isolation and stable gains, and it is a promising candidate for base station systems using differential signals.

In this paper, an antenna interference cancellation chip (AICC) with a high-pass response is proposed to mitigate the mutual coupling of two antennas resonating in contiguous frequency bands. Using the most up-to-date low temperature co-fired ceramic (LTCC) technology, the chip only occupies a compact volume of 1.6 × 0.8 × 0.6 mm ³ . Two external tuning capacitors and two shunt inductors together with the LTCC AICC device which are in shunt with two coupled antennas, are able to improve the antenna isolation near band-edge by more than 15 dB without sacrificing antenna performance in its useful resonating bands. The high-pass property of the AICC device prevents the decoupling design near 2.4GHz affecting the successful operation of GPS at 1.575 GHz. The superiority of the proposed method is verified with active measurement of a Mi-Fi (mobile Wi-Fi) device in Wi-Fi hotspot mode using the AICC device. The proposed AICC device and corresponding decoupling method with the device can find plenty of applications in long-term-evolution and future 5G wireless platforms.