Analysis and Design of Substrate Integrated Waveguide-based Antennas for Millimeter Wave Applications

Recently, there has been increasing interest and rapid growth in millimeter wave (MMW) antennas and devices for use in diverse applications, services and technologies such as short-range communication, future mm-wave mobile communication for the fifth generation (5G) cellular networks, and sensor and imaging systems. Due to the corresponding smaller wavelength, mm-wave frequencies offer the advantage of physically smaller antennas and circuits as well as the availability of much wider bandwidth compared to microwave frequencies. It is important to design millimeter wave antennas with high gain characteristics due to their high sensitivity towards atmospheric absorption losses. Moreover, millimeter wave antennas can have wide bandwidth and are suitable for applications in large frequency range. In this thesis, planar antennas are designed using substrate integrated waveguide (SIW) technology to have low losses, high quality factor, and low fabrication cost. Firstly, an antipodal fermi linear tapered slot antenna (AFLSTA) with sine corrugations at the side edges at 32.5 GHz is presented, which has a wide impedance bandwidth greater than 30 %, in order to support the high data rate channels. This antenna has a high gain of 12.6 dB and low side lobe levels (better than - 17 dB) in both E and H planes. This antenna is studied and analyzed in array and beamforming configurations to meet requirements of millimeter wave applications. In order to obtain high gain and narrow beamwidth pattern, a 1 × 8 AFLTSA array using SIW power divider network is presented. The design characteristics of the power divider network are presented in this thesis, which help in calculating the performance characteristics of this array structure. This array has an acceptable bandwidth of 14.7 % (30-35 GHz) with high gain of 20.4 dB and 8.35° 3 dB beamwidth. The side lobe levels are also improved using this SIW power divider network and are lower than -25 dB in E-plane and -15 dB in H-plane respectively. This antenna has a radiation efficiency greater than 93% over the whole bandwidth. The second research theme is beamforming of AFLTSA antenna. This beamforming is performed using multi-beam antenna concept in which the beam is rotated with a help of compact beamforming network and excitation from different input ports. The design methodology for 2 × 2 and 4 × 4 subarray beamforming networks is presented along with their current distributions illustrating the beamforming process. These subarrays possess wide impedance bandwidth between 29-36 GHz. Moreover, these subarrays are able to achieve gain between 12-15 dB with narrow beamwidth reaching till 11°. All the results along with the numerical data is presented in this thesis. This antenna is suitable candidate for millimeter wave wireless communications and imaging systems

Hybrid MIMO Architectures for Millimeter Wave Communications: Phase Shifters or Switches?

Hybrid analog/digital MIMO architectures were recently proposed as an alternative for fully-digitalprecoding in millimeter wave (mmWave) wireless communication systems. This is motivated by the possible reduction in the number of RF chains and analog-to-digital converters. In these architectures, the analog processing network is usually based on variable phase shifters. In this paper, we propose hybrid architectures based on switching networks to reduce the complexity and the power consumption of the structures based on phase shifters. We define a power consumption model and use it to evaluate the energy efficiency of both structures. To estimate the complete MIMO channel, we propose an open loop compressive channel estimation technique which is independent of the hardware used in the analog processing stage. We analyze the performance of the new estimation algorithm for hybrid architectures based on phase shifters and switches. Using the estimated, we develop two algorithms for the design of the hybrid combiner based on switches and analyze the achieved spectral efficiency. Finally, we study the trade-offs between power consumption, hardware complexity, and spectral efficiency for hybrid architectures based on phase shifting networks and switching networks. Numerical results show that architectures based on switches obtain equal or better channel estimation performance to that obtained using phase shifters, while reducing hardware complexity and power consumption. For equal power consumption, all the hybrid architectures provide similar spectral efficiencies.Comment: Submitted to IEEE Acces

Signal design for Multiple-Antenna Systems and Wireless Networks

This dissertation is concerned with the signal design problems for Multiple Input and Multiple Output (MIMO) antenna systems and wireless networks. Three related but distinct problems are considered.The first problem considered is the design of space time codes for MIMO systems in the case when neither the transmitter nor the receiver knows the channel. We present the theoretical concept of communicating over block fading channel using Layered Unitary Space Time Codes (LUSTC), where the input signal is formed as a product of a series of unitary matrices with corresponding dimensionality. We show the channel capacity using isotropically distributed (i.d.) input signaling and optimal decoding can be achieved by layered i.d. signaling scheme along with a low complexity successive decoding. The closed form layered channel capacity is obtained, which serves as a design guideline for practical LUSTC. In the design of LUSTC, a successive design method is applied to leverage the problem of optimizing over lots of parameters.The feedback of channel state information (CSI) to the transmitter in MIMO systems is known to increase the forward channel capacity. A suboptimal power allocation scheme for MIMO systems is then proposed for limited rate feedback of CSI. We find that the capacity loss of this simple scheme is rather small compared to the optimal water-filling solution. This knowledge is applied for the design of the feedback codebook. In the codebook design, a generalized Lloyd algorithm is employed, in which the computation of the centroid is formulated as an optimization problem and solved optimally. Numerical results show that the proposed codebook design outperforms the existing algorithms in the literature.While it is not feasible to deploy multiple antennas in a wireless node due to the space limitation, user cooperation is an alternative to increase performance of the wireless networks. To this end, a coded user cooperation scheme is considered in the dissertation, which is shown to be equivalent to a coding scheme with the encoding done in a distributive manner. Utilizing the coding theoretic bound and simulation results, we show that the coded user cooperation scheme has great advantage over the non-cooperative scheme

5G Uniform linear arrays with beamforming and spatial multiplexing at 28 GHz, 37 GHz, 64 GHz and 71 GHz for outdoor urban communication: A two-level approach

Multiple-input multiple-output (MIMO) spatial multiplexing and beamforming are regarded as key technology enablers for the fifth-generation (5G) millimeter wave (mmWave) mobile radio services. Spatial multiplexing requires sufficiently separated and incoherent antenna array elements, while in the case of beamforming, the antenna array elements need to be coherent and closely spaced. Extensive 28-, 60-, and 73-GHz ultra-wideband propagation measurements in cities of New York City and Austin have indicated formation of two or more spatial lobes for the angles-of-departure and angles-of-arrival even for line-of-sight (LOS) transmission, which is an advantageous feature of mmWave channels, indicating that the transmitting and receiving array antenna elements can be co-located, thus enabling a single architecture for both spatial multiplexing and beamforming. In this paper, a two-level beamforming architecture for uniform linear arrays is proposed that leverages the formation of these spatial lobes. The antenna array is composed of sub-arrays, and the impact of sub-array spacing on the spectral efficiency is investigated through simulations using a channel simulator named NYUSIM developed based on extensive measured data at mmWave frequencies. Simulation results indicate spectral efficiencies of 18.5–28.1 bits/s/Hz with a sub-array spacing of 16 wavelengths for an outdoor mmWave urban LOS channel. The spectral efficiencies obtained are for single-user (SU) MIMO transmission at the recently allocated 5G carrier frequencies in July 2016. The method and results in this paper are useful for designing antenna array architectures for 5G wireless systems