Dazhi Piao

Characteristics of the Hexapolarized MIMO Channel over Free-Space and Three Non-Free-Space Scenarios

The eigenvalues and channel capacity of the hexapolarized MIMO system in free-space (FS) and three non-FS scenarios are investigated, based on the exact determinant electromagnetic field expressions. Computation results show that there are generally 6 nonzero eigenvalues in all the four scenarios. However, the values of the eigenvalues are affected strongly by the link distance, the antenna position and the scattering condition, thus some of the eigenvalues are too small to contribute to the overall channel capacity. Interestingly, the smallest two eigenvalues and the corresponding hexapolarized MIMO channel capacity can be increased obviously with the increasing of the number of scattering planes, especially in the far field. Furthermore, more scattering can increase the robustness of the multipolarized MIMO system over the location of the array. However, in those non-FS channels, a threefold increase of the capacity over that in the FS channel is not obtained, and the maximum capacity gain is 2.15. Fortunately, a threefold capacity gain of using the tri-polarized electric dipoles over the one-polarized electric dipole can be obtained in most cases of the three-mirror (3M) channel. Finally, some numerical simulations were conducted, the theoretical predicted hexapolarized MIMO capacities agree well with that obtained from the simulations.

Measurement-Based Performance Comparison of Colocated Tripolarized Loop and Dipole Antennas

In this paper, a colocated tripolarized loop (TPL) antenna is proposed and a colocated tripolarized dipole (TPD) antenna is also designed for multiple-input multiple-output (MIMO) performance comparison. Both antennas have satisfactory performances of impedance bandwidth and isolation. The channel measurements are conducted in a nonlossy reverberation chamber (RC), a lossy RC, a corridor, and an office room. For both antennas, the measured average correlation coefficients (CCs) in the nonlossy RC are the smallest, close to 0.1, in the lossy RC are the largest, 0.3-0.5, and in the two indoor scenarios are slightly larger than that in the nonlossy RC. Except for the signal correlation, the relative path loss (RPL) should also be included to fairly compare the channel capacities. If the RPL is considered, a strong dependence of the channel capacity on the propagation properties can be seen. For both antennas, the channel capacities in the two indoor scenarios are 20%-30% smaller than that in the nonlossy RC. Interestingly, both antennas have similar condition numbers (CNs) in all the four scenarios, whose PDFs are close to that of the independent identically distributed (i.i.d.) complex Gaussian channel, which reveals that both antennas can obtain nearly three independent parallel subchannels and good multiplexing performance.

Two novel colocated dual-polarized antennas with extremely low mutual coupling for polarization diversity MIMO applications

This paper presents two novel colocated cross-polarized multiple-input-multiple-output (MIMO) antennas. One consists of two modified printed loop (MM) antennas with ideal impedance matching and port isolation, which can provide a wide bandwidth of 750 MHz. The simulated isolation between the two loops was -30 dB or less within 2.25-3.0 GHz. The other one is composed of an electric dipole and a magnetic dipole (EM), and ideal port isolation (better than -60 dB) is achieved within the entire band of 1.5-3.5 GHz. Computation results show that in the free space channel, a nearly twofold capacity gain can be obtained over the one-polarized single-input-single-output (SISO) system for both of the two dual-polarized antennas. The capacity gain obtained by the MM antennas is 1.975 and by the EM antennas its 1.995, for the communication distance larger than 0.1 m. In the ground reflected channel, the maximum capacity gain close to 2 can also be obtained for both of the two dual-polarized MIMO antennas, however, the capacity gains fluctuate with the communication distance. We get the conclusion that the characteristics of the multipolarized MIMO system is not only influenced by the antenna properties, but also influenced strongly by the propagation characteristics of the channel.

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.

A High isolated Dual-polarized MIMO Antenna Composed of a Loop and a Coplanar Dipole with EBG

In this paper, a low coupled, colocated orthogonal dual-polarized MIMO antenna consisting of a loop and a coplanar dipole is presented. To reduce the high mutual coupling between the two antennas, some electromagnetic band gap (EBG) material was used. Simulation results show that the mutual coupling between the coplanar loop and dipole can be effectively reduced, from −6 dB without EBG to −30 dB with EBG at the resonate frequency of 2.15 GHz.

Measured Performance Comparisons between Spatial Multiplexing and Beamforming Arrays in the 28 GHz Band

A spatial multiplexing (SM) array and a beamforming (BF) array with similar antenna size working at 28 GHz are designed and fabricated. In the SM array, a 4 × 4 MIMO system is realized with each port composed of a four-element subarray. In the BF array, the whole 16 elements are used to formulate a high-gain array. The measured S-parameters are in agreement with the simulated results. For both arrays, the channel capacities are computed by the measured channel matrix and signal-to-noise ratio (SNR) in an office room. Results show that capacity of the SM system is larger than that of the BF system, although the gain of BF array is about 5 dB larger than that of the SM array. However, the capacity of the SM array depends heavily on SNR; specifically, for the 1 dBm transmit power, communication distance  cm, the ergodic capacity of the SM system is 2.76 times that of the BF system, and if  cm, the capacity gain is reduced to 1.45. Furthermore, compared with the BF array, the SM array has a more robust performance over antenna misalignment, because of the wider beamwidth.

Design of a dual-polarized MIMO antenna with high isolation

Summary form only given. Multipolarized MIMO antennas can effectively increase the channel capacity of wireless communication systems and also provide a compact design of the MIMO antenna for the space limited applications. However, if the dual-polarized antenna is composed of a coplanar loop and dipole, the mutual coupling between the two antennas are generally very high, which causes the decrease of the performance of MIMO antenna. In this paper, a dual-polarized MIMO antenna with a dual-layer mushroom EBG structure is presented working at 2.4 GHz bands. The MIMO antenna consists of a loop and a coplanar dipole placed in the middle of the loop In order to retain the radiation characteristics of a magnetic dipole, the electric loop should have a constant current distribution, thus the loop is constructed based on a structure of dash line which is an artificial zerophase transmission line and can ensure that the current is of equal magnitude and in-phase along the loop. The antenna elements are printed on an FR4 (relative dielectric constant of 4.4, loss tangent of 0.02) substrate with dimensions of 70mm × 75mm × 1.6 mm. Isolation enhancements are achieved by introducing a dual-layer mushroom EBG structure. Based on the concept of slow-wave propagation, the dual-layer mushroom EBG structure performs well in both antenna miniaturization and mutual coupling mitigation. Its upper layer acts as a band-stop filter at the antennas resonant frequency and reduces the unwanted surface waves occurs in the substrate, while the inner layer aids in the antenna miniaturization. Simulation results show that the amplitude of S21 is below -17 dB at the resonant frequency, which is 12.1 dB lower than that of the MIMO antenna without an EBG structure.

A wideband segmented line dipole antenna with stable radiation patterns

In this paper, a wideband segmented line dipole antenna with stable radiation patterns in E-plane was proposed and simulated. The configuration of the segmented line helps to reduc the phase lag of the following current which flows toward the same direction consequently. According to the simulated results, the designed antenna covers a wide impedance bandwidth of about 1.34 GHz (2.16–3.5 GHz, 47%). Compared to the conventional dipole with the same dimension, the proposed antenna shows a more stable performance in E-plane radiation pattern.

A high-gain resonant cavity antenna with orthogonal polarizations working at 28 GHz

In this paper, a high-gain resonant cavity antenna (RCA) with orthogonal polarizations working at 28 GHz is presented. This antenna is composed of a patch-type frequency selective surface (FSS) as RCA superstrate and a dual-feed dual-polarized microstrip patch antenna as the feeding system. The FSS is located at a designated height above the ground plane of the microstrip patch antenna. By adjusting the size of the FSS unit and the height of resonator, the electromagnetic waves can reflect inside the cavity continuously, thus the gain can be enhanced when the partial rays projected though the space have equal phases in the normal direction. According to the simulation, the proposed design has both vertical polarization (V-pol) and horizontal polarization (H-pol) at 28 GHz with low cross polarization, better than −27 dB. The gains in two polarizations can reach 16 dB at 27.5 GHz over the impedance bandwidth of 1.8 GHz (27.2–29 GHz).

Measured MIMO channel capacity of a virtual colocated tri-polarized loop antenna

The channel matrix of a MIMO (multiple-input multiple-output) system composed of a virtual colocated tripolarized loop (TPL) antenna is measured in an anechoic chamber and an office room. Results show that in both scenarios, the TPL antenna can obtain a nearly 3 fold capacity increase over the one-polarized loop (OPL) antenna, and can obtain a nearly 1.5 fold capacity increase over the dual-polarized loop (DPL) antenna. Furthermore, in both scenarios, using the TPL antenna can obtain 3 nonzero eigenvalues, which indicates that three effective parallel channels can be generated. Numerical computations are also conducted by commercial software Ansoft HFSS, the simulated capacity results agree basically with the measured results.