No abstract

Using the quad‐antenna linear (QAL) array as a building block, the 8‐antenna and 16‐antenna arrays for the 3.5‐GHz long term evolution multiple‐input multiple‐output (MIMO) operation in the smartphone are demonstrated. The QAL array has a planar structure of narrow width 3 mm (0.035λ) and short length 50 mm (0.58λ), with λ being the wavelength at 3.5 GHz. For the 8‐antenna array, two QAL arrays are disposed along two opposite side edges (denoted as Array A) or the same side edge (denoted as Array B) of the system circuit board of the smartphone. The obtained envelope correlation coefficient values of the antennas in Array A and B are shown. The calculated channel capacities for Array A and B applied in an 8 × 8 MIMO system are also analyzed. The 16‐antenna array formed by four QAL arrays disposed along two opposite side edges (denoted as Array C) is then studied. For operating in a 16 × 16 MIMO system, the calculated channel capacity of Array C can reach about 66–70 bps/Hz with a 20‐dB signal‐to‐noise ratio. The obtained channel capacity is about 5.7–6.1 times that (11.5 bps/Hz) of the upper limit of an ideal 2 × 2 MIMO system with 100% antenna efficiency for the antennas therein. Details of the proposed Array A, B, and C are described, and the obtained results are presented. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:174–181, 2016

Progress in metal-organic chemical vapor deposition of high quality ( ) 0001 ¯N-polar (Al, Ga, In)N films on sapphire, silicon carbide and silicon substrates is reviewed with focus on key process components such as utilization of vicinal substrates, conditions ensuring a high surface mobility of species participating in the growth process, and low impurity incorporation. The high quality of the fabricated films enabled the demonstration of N-polar (Al, Ga, In)N based devices with excellent performance for transistor applications. Challenges related to the growth of high quality N-polar InGaN films are also presented.

A 10‐antenna array operating in the 3.6‐GHz band (3400–3800 MHz) for multi‐input multi‐output (MIMO) operation in the smartphone is presented. Each antenna in the proposed array is a microstripline‐fed open‐slot antenna with same small dimensions of 3 × 8 mm2 (0.036λ × 0.096λ, λ is the wavelength at 3.6 GHz). The proposed array consists of two symmetric five‐antenna arrays disposed, respectively, along two long side edges of the system ground plane of the smartphone. The proposed array is expected to be placed in the narrow spacing between the display panel and the long side edges of the smartphone. Acceptable isolation (better than about 10 dB) and good envelop correlation coefficient (ECC) of less than 0.1 for any two antennas in the proposed array is obtained. The maximum channel capacity of the proposed array in a 10 × 10 MIMO system is calculated to reach about 47 bps/Hz at 20‐dB signal‐to‐noise ratio, which is larger than four times that (11.5 bps/Hz) of the upper limit of an ideal 2 × 2 MIMO system with 100% antenna efficiency and zero ECC between antennas. Details of the proposed 10‐antenna array are described, and the experimental results are presented and discussed. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1699–1704, 2015

This paper reviews the progress of N-polar (000 1) GaN high frequency electronics that aims at addressing the device scaling challenges faced by GaN high electron mobility transistors (HEMTs) for radio-frequency and mixed-signal applications. Device quality (Al, In, Ga)N materials for N-polar heterostructures are developed using molecular beam epitaxy and metalorganic chemical vapor deposition. The principles of polarization engineering for designing N-polar HEMT structures will be outlined. The performance, scaling behavior and challenges of microwave power devices as well as highly-scaled depletion-and enhancement-mode devices employing advanced technologies including self-aligned processes, n+ (In,Ga)N ohmic contact regrowth and high aspect ratio T-gates will be discussed. Recent research results on integrating N-polar GaN with Si for prospective novel applications will also be summarized.