An Evaluation of Distortion and Interference Sources originating Within a Millimeter-wave MIMO Testbed for 5G Communications

This paper presents an evaluation of distortion and interference sources, namely, the harmonic distortion and antenna crosstalk, originating within a 2 x 2 millimeter-wave (mm-wave) multiple-input-multiple-output (MIMO) testbed. The experience gained through the insight into the built testbed could be fed into the design of future mm-wave massive MIMO testbeds.Comment: 2nd URSI Atlantic Radio Science Meeting (URSI AT-RASC 2018

Millimeter-Wave Over-the-Air Signal-to-Interference-plus-Noise-Ratio Measurements Using a MIMO Testbed

In this paper, over-the-air experiments with external and internal interferences were performed using Chalmers millimeter-wave multiple-input-multiple-output testbed MATE. The resulting SINR for both interference experiments are compared and discussed.Comment: 2nd URSI Atlantic Radio Science Meeting (URSI AT-RASC 2018

Hybrid Beamforming Transmitter Modeling for Millimeter-Wave MIMO Applications

Hybrid digital and analog beamforming is an emerging technique for high-data-rate communication at millimeter-wave (mm-wave) frequencies. Experimental evaluation of such techniques is challenging, time-consuming, and costly. This article presents a hardware-oriented modeling method for predicting the performance of an mm-wave hybrid beamforming transmitter. The proposed method considers the effect of active circuit nonlinearity as well as the coupling and mismatch in the antenna array. It also provides a comprehensive prediction of radiation patterns and far-field signal distortions. Furthermore, it predicts the antenna input active impedance, considering the effect of active circuit load-dependent characteristics. The method is experimentally verified by a 29-GHz beamforming subarray module comprising an analog beamforming integrated circuit (IC) and a 2 times 2 subarray microstrip patch antenna. The measurement results present good agreement with the predicted ones for a wide range of beam-steering angles. As a use case of the model, far-field nonlinear distortions for different antenna array configurations are studied. The demonstration shows that the variation of nonlinear distortion versus steering angle depends significantly on the array configuration and beam direction. Moreover, the results illustrate the importance of considering the joint operation of beamforming ICs, antenna array, and linearization in the design of mm-wave beamforming transmitters

An active load-pull technique creating time-variant impedances to emulate coupling between power amplifiers

A method for emulating antenna array coupling effects, based on active load-pull, to present time-varying impedances to power amplifiers is presented. An entire array, given identical elements, can be emulated using a single device-under-test. The method is demonstrated and verified by studying two scenarios, where the resulting adjacent channel power ratio and error-vector magnitude are given as function of delay and coupling for a 6W GaN power amplifier. Differences in adjacent channel power ratio and error-vector magnitude can be attributed to time-variant load impedances

Designing and characterizing MATE, the Chalmers mm-wave MIMO testbed

In this paper, we report on the design and characterization of MATE, the mm-wave testbed at the Chalmers University of Technology. We elaborate around design choices of various parts of the testbed, baseband hardware, required software and RF frontend. We also perform a thorough characterization of the testbed, in terms of I/Q imbalance, stability, frequency offset, DC offsets, and ADC/DAC clock rate offset. The study shows that the utilized design techniques for baseband and RF frontend hardware are feasible, and also that many hardware imperfections are possible to accurately characterize, for subsequent calibration and digital compensation

Measurement Technique to Emulate Signal Coupling Between Power Amplifiers

A measurement technique to emulate coupling between power amplifiers (PAs) such as that in an antenna array is presented. The case that the technique aims to emulate is referred to as the target array. The technique provides emulation of the distorted output signal for each PA under the coupling effect without the requirement for constructing the target physical coupling network or antenna array. Furthermore, given that the target array contains identical elements or PAs, transmitting either identical or different signals, the technique merely requires one PA as the device-under-test (DUT) to produce all output signals. The technique has direct connection to active load-pull, and aims to present the output of the DUT with corresponding time-varying impedances of each transmission path in the target array. The emulated output signals can then be analyzed, for example, in terms of adjacent channel power ratio, error vector magnitude, and normalized mean square error. Such measurement technique provides insight into the distortion and the impairment generated in the target array without the requirement to realize an actual array, and can be used, as an example, during the design stage of an array. The technique is theoretically motivated. The procedure is thoroughly described. The technique is experimentally demonstrated and verified under various usage cases and scenarios. Subsequent comparison to conventional active load-pull is provided

A Generic Theory for Design of Efficient Three-stage Doherty Power Amplifiers

An analytical load-pull based design methodology for three-stage Doherty power amplifiers (PAs) is presented and demonstrated. A compact output combiner network, together with the input phase delays, is derived directly from transistor load-pull data and the design requirements. The technique opens up a new design space for three-stage Doherty PAs with reconfigurable high-efficiency power back-off levels. The method is designed to enable a high transistor power utilization by maintaining full voltage and current swings of the main and auxiliary amplifier cells. Therefore, a wide efficiency enhancement range can be achieved also with symmetrical devices. As a proof of concept, a 2.14-GHz 30-W three-stage Doherty PA with identical GaN HEMT active devices is designed, fabricated and characterized. The prototype PA is able to linearly reproduce 20-MHz long-term evolution signals with 8.5- and 11.5-dB peak-to-average power-ratio (PAPR), providing average efficiencies of 56.6% and 46.8% at an average output power level of 36.8 and 33.8 dBm, respectively. Moreover, an average efficiency as high as 54.5% and an average output power of 36.3 dBm have been measured at an adjacent power leakage ratio of -45.7 dBc for a 100-MHz signal with 8.5-dB of PAPR, after applying digital pre-distortion linearization

Temperature-dependent Characterization of Power Amplifiers Using an Efficient Electrothermal Analysis Technique

In this paper, we propose an efficient methodology for the electrothermal characterization of power amplifier (PA) integrated circuits. The proposed electrothermal analysis method predicts the effect of temperature variations on the key performances of PAs, such as gain and linearity, under realistic dynamic operating conditions. A comprehensive technique for identifying an equivalent compact thermal model, using data from 3-D finite element method thermal simulation and nonlinear curve fitting algorithms, is described. Two efficient methods for electrothermal analysis applying the developed compact thermal model are reported. The validity of the methods is evaluated using commercially available electrothermal computer-aided design (CAD) tools and through extensive pulsed RF signal measurements of a PA device under test. The measurement results confirm the validity of the proposed electrothermal analysis methods. The proposed methods show significantly faster simulation speed comparing to available CAD tools for electrothermal analysis. Moreover, the results reveal the importance of electrothermal characterization in the prediction of the temperature-aware PA dynamic operation

Wireless energy and information transmission in FSO and RF-FSO links

We propose and analyze a wireless energy and information transmission scheme in free-space optical (FSO) links. The results are presented for both quasi-static and fast-fading conditions. We derive closed-form expressions for throughput, outage probability, and optimal power allocation optimizing the system throughput/outage probability. Finally, we complement the FSO link with an additional radio frequency (RF) link to create a hybrid RF-FSO system and reduce the system outage probability. The results show that joint implementation of the RF and FSO links leads to considerable performance improvement, compared to the cases with only FSO-based communication

Vector-corrected Nonlinear Multi-port IQ-mixer Characterization using Modulated Signals

In this paper, large-signal operation of IQ-mixers isstudied using a vector-corrected four-port measurement setup with modulated signals as stimuli. The measurement setup presents unique characterization possibilities since it has two ports at low/baseband frequencies and two ports at RF, making it ideal for characterization of frequency-translating devices such as mixers. A commercial upconverting IQ-mixer is studied, with the I and Q input signals residing at incommensurate frequencygrids, enabling separation of the nonlinear distortion generated in the I and Q branches. Frequency-domain and time-domain measurements reveal imbalances between the I and Q branches in terms of conversion gain and nonlinear distortion. It is also shown for the same mixer that operating the I and Q branches concurrently has limited influence on both conversion gain and nonlinear distortion, compared to non-concurrent operation