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A phased-array fed reflector antenna system is presented which can be used for mm-wave base station applications. The proposed system is designed to support massive-multi-input-multi-output (MIMO) scenarios within a wide coverage ( $\pm 30^\circ $ ) in the azimuth plane and a limited coverage at the elevation plane. A design and characterization methodology has been established to optimize the system for the operation in various line-of-sight conditions by adopting the maximum-ratio-transmission (MRT) and zero-forcing (ZF) MIMO algorithms. A two-user MIMO case study has been considered for the evaluation of the key system performance metrics, i.e., the effective isotropic radiated power, power consumption, signal-to-noise-ratio (SNR), and signal-to-interference-plus-noise-ratio (SINR). This study demonstrates that the phased-array fed reflector concept has a major advantage over traditional direct-radiating phased-array (DRPA) antennas to reduce energy consumption. In the present example, it requires 12-14 dB less transmitted power as compared with the MRT-beamformed DRPAs for the same SNR, and 26-27 dB less transmitted power relatively to ZF-beamformed DRPA systems for the same SINR. A prototype, employing a 55 cm diameter torus reflector and operating at 28 GHz-band, has been manufactured and tested. The measurement results agree well with simulations.

Fixed-beam, high-gain antenna systems can be used for a finer partitioning of the currently used cell-sectoring. This partitioning has the benefit of reducing the number of users seen per antenna beam, which reduces interference. Furthermore, the high antenna gain allows for a high effective isotropic radiated power while keeping the transmit power low. In this paper, we study the performance of such a fixed-beam, high gain antenna system design for millimeter-wave mobile communications. The antenna system is designed to keep the inter-sector interference in a multi-site scenario low. The performance is analyzed for single- and multi-user environments. In single-input single-output mode, the 50th percentile of the signal-to-interference-plus-noise ratio lies between 12.5 dB to 39.7 dB if 3 to 0 interferers are present, respectively. For multiple-input multiple-output transmission using zero-forcing, the signal-to-interference-plus-noise ratio increases and the 50th percentile ranges from 36.1 dB to 43.3 dB if 3 to 0 interferes are present, respectively. By using maximum ratio transmission, the best performance is achieved with no interferers present, while a plunge in performance is observed with interferers. Furthermore, the study revealed that the narrow beam antenna system can also provide a clear signal separation for small spatial separations. In the given example, the signal-to-interference-plus-noise ratio is larger than 32.1 dB with 11 active antenna elements, where 2.8 meters separate the users. Hence, the paper shows that the cell-partitioning antenna systems provide coverage in the desired area while keeping the inter-sector interference low, and the considered transmission techniques can be used for situation optimized mobile communication links.

In this letter, a uniform linear array (ULA) is proposed for line-of-sight massive multiple-input-multiple-output (MIMO). It is assumed that the number of antennas is fixed. For a given ULA with an arbitrary inter-element spacing, the probability that the correlation among the channel vectors of two users being above a threshold value is derived. The inter-element spacing of the proposed ULA is the one for which the aforementioned probability is minimized. To show the effectiveness of the proposed ULA, simulation results for two scenarios are given for a 64-Antenna ULA that serves 6 single-Antenna users. By using the proposed ULA instead of conventional half-wavelength ULA, 5th percentile sum-rate for zero-forcing precoder is improved by 9.90 bits/channel use in first scenario without dropping, and by 1.43 bits/channel use in second scenario with dropping 1 user.

A novel and compact millimeter-wave (mm-Wave) spatial power combiner is developed integrating a silicon-based integrated circuit (IC) in a metal waveguide (WG). As an initial step toward integrating a silicon-based active IC in a WG, a passive back-to-back (B2B) transition incorporating a four-way spatial power splitter and combiner is realized at E -band (71-86 GHz). In contrast to existing solutions, the proposed design considers power splitting and combining using a low-loss wireless transition between the IC and the WG. The proposed B2B structure comprises an IC implemented using the Institute for High Performance Microelectronics (IHP's) 0.13- \mu \text{m} SiGe BiCMOS technology integrated into the H -plane of a WG. The IC is postprocessed and assembled in the WG prototype. The measured prototype shows a return loss better than 13 dB, an average insertion loss of 1.7 dB for a single transition, and a fractional bandwidth of 26.4% (69-90 GHz).