Department Publications

The 6-24 GHz upper midband - FR3 range - is the next generation spectrum for mobile wireless applications. Traditionally allocated for defense and scientific use cases, the possible adoption of FR3 frequencies for commercial applications opens the possibility for severe interference between different commercial and scientific/defense systems. We demonstrate lowcomplexity adaptive array processing in the FR3 range using realtime implementation in the 10.7-10.8 GHz band, with 100 MHz of bandwidth using Xilinx Virtex-6 Sx475T FPGA technology. The demonstration supports a uniform linear array with 8 Vivaldi antennas (6-24 GHz) and can provide up to 6 nulls in the aperture pattern in addition to the desired RF beam. The FPGA back-end utilizes sampling at 200 MS/s and exploits digital signal processing to furnish up to 100 MHz of bandwidth at IF.

A low-complexity multibeam wideband transmit beamformer using a 2D sparse FIR filter design capable of multiple beams is proposed as a digital building block for fully digital beamformers. The 2D sparse FIR filter has multiple trapezoid-shaped passbands pertaining to wideband beams aimed at particular directions. The proposed multibeam digital beamformer drives a uniform linear array of wideband antenna elements to achieve the wideband multibeam transmit-mode signals desired by the communication system. The 2D sparse FIR filter is designed to be optimal in the minimax sense using convex optimization techniques. Full-wave electromagnetic simulations using real antenna models confirm that the proposed wideband transmit beamformer can achieve multibeam transmission in the 1.3–2.8 GHz frequency range, with more than 70% fractional bandwidth. Furthermore, the adoption of the wideband transmit multibeam beamformer leads to a significant reduction in digital arithmetic (computational) complexity compared with previously reported wideband transmit beamformers of similar transfer function type, without deteriorating beam directionality and causing increases in the side-lobe level. The proposed sparse 2D FIR multibeam beamformer architecture is well-suited for both sub-6 GHz (legacy) band transmit beamforming, frequency range three (FR3) beamforming up to 28 GHz, and mmWave operation for emerging 5G/6G applications.

This paper describes a technique for de-embedding electromagnetic mutual coupling effects between nearest neighbors of a ULA receiver. Measured S-parameters across a range of frequencies of interest are used in a closed-form mathematical model that relates measured S-parameters, measured LNA reflection coefficients, and transmission line parameters to digital beamformer design equations, such that the beam shape distortions arising from mutual coupling can be compensated in the DSP algorithm. A 5.8 GHz 32-element receiver array with custom receivers and 32-channel Xilinx Virtex-6 Sx35 FPGA based DSP system implementing a real-time complex-valued Frost beamformer operating at IF is proposed to show the benefits of de-embedding mutual coupling for far-field side-lobe suppression. The worst-case side-lobe level is reduced by 11.2 dB, and the average side-lobe level is reduced by 5.2 dB, for …

The objective of this study is to propose a heuristic model of energy propagation due to an anomaly; electromagnetic (EM) field penetration into a continuously covered conducting enclosure (Faraday shield) from an external radio frequency source, violating the accepted model in the EM field theory. In this study, at an arbitrarily selected frequency, range of 26.965–1,800 MHz, of an external frequency source, an EM field inside the conducting enclosure was observed, contrary to expectations, which was followed by a systematic examination. Although no induced voltage could be expected inside the enclosure according to the classical theory, the experiment revealed a clear induced voltage inside, an attenuated induced voltage of −18.0 to −1.0 dB (for the range of frequencies 26.965–1,800 MHz) was observed. Hence, these results apparently contradict the established notion that an EM field cannot …

A low-complexity wideband transmit beamformer is proposed using a digitally-fed uniform linear array of broadband Vivaldi antennas operating in the S-band. The proposed transmit beamformer employs a novel DSP feeding network based on a transmit-mode 2-D sparse finite-extent impulse response (FIR) filter having a planar passband in the 2-D frequency-wavenumber space. Electronic beam steering is achieved by changing the filter coefficients defined in closed-form and hard-thresholding (HT) is employed to obtain a sparse 2-D impulse responses of the filter. Full-wave electromagnetic simulations are used to obtain the far-field beam patterns produced by the 2-D sparse FIR filter in the frequency range 2-2.8 GHz for wideband signals with 33% fractional bandwidth. Computational complexity, beam directionality and side-lobe performance are investigated with varying HT along with quantitative comparisons …

The paper presents the development and the experimental verification of a technique for the identification of obstructions in the line-of-sight path between two or more radio transceivers in a multipath radio environment. The objective of this technique is to use RSS measurements from a mesh of simple sensor nodes to identify intrusions.

The study of empirical propagation models for mobile channels has been done extensively, but the applicability of those models to a Fixed Wireless Access (FWA) System is not appropriately tested. The candidate models include Hata - Okumura, COST 231 Hata, COST-Walfisch-Ikegami and Erceg. From those models Erceg model seems to be the most suitable. In this paper field measurements are taken for the 3.5GHz Fixed WiMAX network in Katubedda, Sri Lanka. Those are used to validate the applicability of the above mentioned propagation models in a sub urban environment in Sri Lanka.

5.1 Discussion: One of the most cumbersome and difficult problems associated with obtaining solutions for electromagnetic integral equations has been the manipulation of large matrices resulting from numerical methods such as MoM. Unfortunately, such situations are unavoidable in practical problems where the analysis (such as electro-magnetic wave scattering or radiation characteristics) has to be made in respect of objects of complex shapes and sizes. As mentioned in the introductory chapter, several techniques have been developed over the years in order to address this problem. Objective of this research work has been, to investigate the possibility of addressing the above-mentioned problem through wavelet transform techniques that started gaining popularity among the research community over a decade ago. Though there is evidence that wavelet transform techniques have been invented in early 20t h …

The paper describes the design and implementation of a controller, which rotates an antenna in the optimum direction for reception of signals at the installed loca-tion. The antenna controller can be programmed on-site, with the direction of best reception for each channel. During operation, when a particular channel is selected, the controller will align the antenna in the direction to which it is programmed. This device is ideally suited for TV reception in Sri Lanka, where broadcast stations are placed at a variety of different geographic locations. However, the device is suitable for any application where a requirement exists for antenna re-aligning with geographic location.

MAGI array is a very popular antenna for ITIE/UHF applications due to its simple construction. It is extensively used in television and FM radio reception. However, design of MAGI arrays to meet a given set of specifications is a very difficult task. This paper presents a genetic algorithm based design technique for MAGI arrays for receiving applications

Measurement of rainfall level in a certain place is a key requirement in recording meteorological data. The current measurements of the rainfall is done by a conventional volumetric vessel and a manual reading of the amount of water collected within a specific period of time. This research is focused on developing a methodology to measure the rainfall or the precipitation using a purely electrical method. The main drawback in the conventional method is the difficulty in interfacing the reading from the rainfall sensor with an electronic device. Using a weight sensor or a volume estimation method is not ideal for an integrated and robust digital weather station.