Soji Sajuyigbe

Experimental demonstration of 16-Gbit/s millimeter-wave communications link using thin metamaterial plates to generate data-carrying orbital-angular-momentum beams

We present the design and performance characterization of a thin metamaterial plate for generation of orbital angular momentum (OAM) modes of a millimeter-wave beam, which can carry independent data streams over the same physical medium. The plate has a thickness of 1.56 mm, and consists of 3.06 × 0.68 mm rectangular apertures with spatial variant orientations. It generates OAM beams l = +1 and l = +3 with mode purity larger than 77.5% over a bandwidth of 6 GHz (25-31 GHz). We then use these streams to experimentally demonstrate a 16-Gbit/s millimeter-wave wireless communications link using two multiplexed OAM modes, each carrying a 2-Gbaud 16-QAM signal. A channel crosstalk less than -20 dB over a bandwidth of 4 GHz (26-30 GHz) and biterror-rates (BER) less than 3.8 × 10-3 are achieved.

Experimental measurements of multipath-induced intra- and inter-channel crosstalk effects in a millimeter-wave communications link using orbital-angular-momentum multiplexing

This paper reports on an experimental measurement and analysis of multipath-induced intra- and interchannel crosstalk effects in a mm-wave communications link using orbital angular momentum multiplexing at 28 GHz. The reflection is from an ideal reflector parallel to the propagation path. The intra-channel crosstalk effect is measured when a single OAM beam is transmitted, and inter-channel crosstalk effect is measured when 2 multiplexed OAM beams are transmitted. Both simulation and experimental results show that OAM channels with larger OAM number ℓ tend to have stronger intra-channel crosstalk because less power is received from the direct path and more power is received from the reflected path. This effect is caused by OAM beam divergence, as OAM beams with larger ℓ spread into a larger beam size and have less power in the beam center. For the same reason, OAM beams of larger ℓ lead to stronger inter-channel crosstalk with the other OAM channels.

A Wideband Frequency-Shift Keying Modulation Technique Using Transient State of a Small Antenna (Invited Paper)

The rate of wireless data transmission is limited by the antenna bandwidth. We present an e-cient technique to realize a high-rate direct binary FSK modulation by using the transient properties of high-Q antennas. We show that if the natural resonance of a narrowband resonant-type antenna is switched at a high rate, the radiating signal follows the variation of resonant frequency and provides a high-rate data-transmission regardless of the narrowband characteristics of the antenna. The bit-rate in this method is dictated by the switching speed rather than the impedance bandwidth. Since the proposed technique employs the antenna in a time-varying arrangement, carrier frequencies are not required to be simultaneously within the antenna bandwidth. When demanded, the antenna is tuned to required carrier frequency according to a sequence of digital data. Moreover, if the switching frequency is properly chosen such that the stored energy in the near-zone is not dramatically disturbed, any variation in the antenna resonance will instantaneously appear in the far-fleld radiation due to the previously accumulated energy in the near fleld. Therefore, depending on the Q factor and switching speed, radiation bandwidth of the antenna can be improved independently from the impedance bandwidth. Furthermore, we show that a single RF source is su-cient to excite both carrier frequencies and the need for a VCO is obviated. Experimental results are presented to validate the feasibility of the proposed technique.

Heat-Sink Modeling and Design With Dipole Moments Representing IC Excitation

Electromagnetic field coupling and radiation from a heat sink is a challenging issue in the electromagnetic compatibility design of high-speed circuits. In order to accurately predict the fields excited by a heat sink, an approach is proposed in this paper to include the equivalent excitation of the heat sink, which is described by some dipole moments constructed from the near-field scanning of the integrated circuit beneath the heat sink. With both the dipole moments and the passive heat-sink structure incorporated in a full-wave model, near-field coupling and far-field radiation can be estimated, and the heat-sink structure can be optimized for mitigating unintentional interferences. Two examples are used to validate and demonstrate the proposed approach.

A dual-channel 60 GHz communications link using patch antenna arrays to generate data-carrying orbital-angular-momentum beams

We present a short-range experimental orbital-angular-momentum (OAM) multiplexing millimeter-wave communication system using patch antenna arrays. The dependence of the evolution of OAM beams on the number of array elements and array radius are analyzed. We also find phase delay deviation of 30 degrees leads to mode purity degrading to ~1% and power deviation of 6 dB reduces the purity by <;40%. An obstruction of size <;10mm has not much influence on the evolution of OAM beams generated from antenna arrays with r = 8mm, which enables the stacking of multiple antenna arrays. We also use these patch antenna arrays to demonstrate a 60 GHz wireless communication link using two multiplexed OAM modes, each carrying a 500-Mbaud 16-QAM or 2-Gbaud QPSK signal. A channel crosstalk of less than -20 dB and bit-error-rates (BER) of less than 3.8 × 10-3 are achieved.

32-Gbit/s 60-GHz millimeter-wave wireless communication using orbital angular momentum and polarization multiplexing

This paper reports an experimental demonstration of a 32-Gbit/s wireless link using orbital angular momentum (OAM) and polarization multiplexing in a millimeter-wave regime at 60 GHz. Results of the analysis show that a higher carrier frequency reduces the propagation loss as well as the size of the transmitter and receiver, particularly for OAM channels with higher OAM values. Further, two different OAM channels (with l = +1 and l = +3) on each of the two polarizations are spatially multiplexed, and each channel carries 2-Gbaud signals with 16-QAM modulation. Spiral phase plates are used to generate 60-GHz OAM beams. The simulation results show that a higher carrier frequency plays a more significant role in reducing both the aperture size and the transmission loss for channels with higher OAM values. The bit error rates (BERs) of 4 channels are measured, and the raw BERs are found to be less than 3.8 × 10-3.

Tunable generation and angular steering of a millimeter-wave orbital-angular-momentum beam using differential time delays in a circular antenna array

In this paper, the generation and steering of beams carrying orbital angular momentum utilizing a custom-designed circular antenna array has been demonstrated at 28 GHz. A steering angle as large as 30 degrees for an orbital angular momentum (OAM) beam has been achieved. The effect of number of antennas and the distance from antennas to the array center to the quality of beam generation and beam steering is investigated through both experiments and simulations. Our results indicate that: (1) As the steering angle increases, the mode purity of the generated OAM beams decreases; (2) Increasing the number of antennas improves the OAM mode purity; (3) For a fixed number of antennas, high mode purity is observed for lower order OAM modes; (4) Placing the antennas farther away from the array center allows for reduced divergence of the generate OAM beams.

Mitigation techniques for RFI due to broadband noise

Mobile computing devices such as Laptops, tablets, smartphones and the like mostly have GPS, WLAN, and cellular capabilities whose performance could be degraded in the presence of broadband noise in the receiver antennas vicinity due to integrated high speed buses and digital circuitry. Shielding, as a passive technique, has become a convention in the mobile wireless industry and we present here a study of its effectiveness particularly in the near-field (as inside a smartphone for instance). We also present some novel active techniques such as bus activity control and RFI data encoding. In the former one, the correlation that exists between the activity level of the bus and its noise coupled to the radio is used in an adaptive algorithm that indirectly estimates the noise affecting the data transmission and controls the bus activity level to meet some require SNR. In the latter one, line encoding is used to reduce the spectral contribution to RFI of a data bus at some specific frequency band. Using K to N (K <; N) codes, simulations show a reduction of the noise of more than 10dB.

OFDM over mm-Wave OAM Channels in a Multipath Environment with Intersymbol Interference

This paper reports an experimental investigation of using orthogonal frequency division multiplexing (OFDM) on orbital-angular momentum (OAM) channels when there is intersymbol interference (ISI) caused by multipath effects. The impulse response measurement indicates that due to the divergence of OAM beams, channels of larger OAM number are more affected by the ISI caused the reflections from surrounding objects. Channel performance of three different OAM numbers l = 0, +1 and +3 are studied. When a single QPSK channel is used, the more channel performance degradation in term of BER and EVM is observed for higher OAM channels. OFDM with 4 sub-carriers is used on the OAM channels to help reduce the ISI and improve the channel performance to some extent.

Demonstration of Tunable Steering and Multiplexing of Two 28 GHz Data Carrying Orbital Angular Momentum Beams Using Antenna Array

In line-of-sight communication systems, accurate alignment between the transmitter and receiver is important to guarantee sufficient signal power at the receiver. Such alignment is even more important for orbital angular momentum (OAM) multiplexing systems since misalignment between the transmitter and receiver may cause crosstalk among channels. In this paper, we demonstrate the simultaneous generation and tunable steering of two OAM beams utilising a custom-designed circular antenna array at 28 GHz. We achieve a steering angle of up to 35 degrees from the antenna array normal. We find that (i) the steering angle of the generated OAM beams is limited by the emitting angle of the antenna elements, and (ii) a larger steering angle may degrade the mode purity of the generated OAM beams as well as induce inter-symbol-interference to each of the individual channels. Moreover, we demonstrate the transmission of two 1-Gbaud quadratic phase shift keying (QPSK) signal over the two steerable OAM beams with both multiplexed channels achieved bit error rates (BERs) of <3.8 × 10−3.