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We describe a new type of ultrawideband feed antenna based on nested coaxial waveguides. The feed is for radio astronomy applications and covers two closely spaced bands: 400–800 and 900–1800 MHz. New design techniques are described for a three-cavity choke, a wideband iris matching network, and printed circuit board (PCB) excitation structures. The design methods were developed to improve broadband impedance matching, to control radiation patterns, to separate bands, and to suppress unwanted waveguide modes. The feed has nearly constant beamwidth over the entire 4.5:1 frequency range and a stable phase center. On an $f/D=0.43$ reflector antenna, the aperture efficiency exceeds 70% and the phase efficiency exceeds 95%. Other features include low ohmic loss and a compact, lightweight, and low-cost structure. Experimental results are shown for a scaled prototype to verify the design methodology. The methods described are general and can be applied to continuous frequency coverage on reflectors of different geometries. [ABSTRACT FROM AUTHOR]

The design of a 2.2 to 4.4 GHz coaxial waveguide feed antenna for radio telescopes is described. An iris matching network is designed to improve the unmatched aperture reflection coefficient from $-$ 6.7 to $-$ 12 dB over a 2:1 bandwidth ratio. An efficient method of optimizing the irises over a wideband is presented. The properties of wideband iris matching networks including their behavior as bandpass structures are discussed. The far-field beamwidth of the feed is held constant across the octave band by a corrugated choke. Measured radiation properties agree closely with simulation. [ABSTRACT FROM AUTHOR]

Distributed data-centers have emerged as a key architecture for future optical networks. This architecture relies on power and cost-efficient high-speed fiber optical connections over distances up to 80 km which can be densely wavelength-division multiplexed (WDM) in the C-band. Recently, single-polarization single sideband (SSB) direct detection (DD) has been considered as an attractive transmission scheme for achieving data rates beyond 100 Gb/s per channel over 80 km. The advantages of SSB DD transmission includes the simple transceiver architecture and the capability of electronic dispersion compensation. However, the required digitizer's bandwidth in a single-polarization SSB transmission is around four times higher than in those of a conventional dual-polarization coherent detection system offering the same data rate. This critical issue prevents the practical implementation of high-speed SSB digital signal processing (DSP) in CMOS ASIC. To address this problem, we consider in this work a 112 GSa/s SiGe HBT BiCMOS ADC frontend. Using this ADC front-end, we experimentally demonstrate a WDM SSB DD transmission at a net data rate of 200 Gb/s per channel over 80 km while using only 14 GHz of digitizer's bandwidth which is comparable to those of a full-coherent counterpart. [ABSTRACT FROM AUTHOR]

Market forecasts for intra and inter data center interconnects predict high growth rates in the upcoming years. This is associated with increasing requirements in terms of costs, power consumption, and bit rate per wavelength. Today, PAM4 systems are frequently used at up to 100 Gb/s per wavelength. The next logical step is to double the symbol rate to allow bit rates of 200 Gb/s at the same modulation format and at the same direct detection scheme. Such systems require three-digit gigasample analog-to-digital converters with bandwidths larger than 50 GHz, which are not available today as CMOS components. To extend the bandwidth of CMOS converters, we suggest the use of ADC frontends, which sample and demultiplex the analog input signals simultaneously. At the outputs of such ADC frontends, the signals can then be digitized by parallel converters with lower bandwidth and at a lower conversion rate. In this article, we present the circuit implementation of a 1-to-4 ADC frontend in IHP 130 nm SiGe HBT BiCMOS and demonstrate its integration into a 100 GBaud PAM4 transmission system with only 14 GHz of digitizer bandwidth. For optimum performance, the mitigation of intersymbol and interchannel interferences is mandatory in the transmission system. We describe and compare two different receiver DSP architectures for reduction of these interferences and evaluate their performances in electrical and optical back-to-back experiments. Furthermore, we report on transmission experiments over 500 m, 10 km, and 40 km SMF at 1550 nm wavelength. With linear equalization, we obtained a BER below the HD-FEC threshold of 3.8 × 10−3 and with 3rd order Volterra equalization, we even achieved a BER below the KP4 threshold of 2.3 × 10−4. [ABSTRACT FROM AUTHOR]

Location information and positioning technology are important to some Internet of Things (IoT) applications. The accuracy of indoor positioning using WiFi can be substantially enhanced by appropriate access point (AP) placement strategies, i.e., in a given indoor environment to deploy the WiFi APs at the locations where the mobile devices can work out their location more precisely. The plan of AP placement needs to be generated automatically by algorithms, especially for large-scale indoor environment. This paper presents an indoor map system that provides coordinate system and graphic representation. The detailed map information such as walls can be explicitly expressed and used to assist the AP placement algorithm. In this paper, AP placement is formulated into an optimization problem in which the sum of Euclidean distance of fingerprints among all the reference points (RPs) is maximized. The fingerprint at RP is predicted by an indoor radio propagation model which takes the attenuation of walls into consideration with the assistance of our indoor map. The optimization problem is solved by particle swarm optimization (PSO) and evaluated by k-nearest neighbors positioning algorithm in a real-world environment. The experimental results show that our map-assisted AP placement can provide higher positioning accuracy. [ABSTRACT FROM PUBLISHER]