A multiplexed Cassegrain reflector antenna with a 2 × 2 open-ended rectangular waveguide (OERW) matrix feed and an orbital angular momentum (OAM) mode mux is proposed for the simultaneous generation of three OAM modes (l = 0, ±1). The OAM mode mux (OMM) was designed using sequential combinations of quadrature hybrids, crossovers, and phase shifters to multiplex and demultiplex three OAM modes at the same time. The 2 × 2 OERW matrix feed and the OMM were separately measured and their performances were verified according to proposed theories. A near-field antenna measurement for a multiplexed Cassegrain reflector antenna was conducted to obtain the far-field magnitude and phase patterns around polar elevation angle θ and azimuthal angle ϕ, thus confirming that our antenna can produce three OAM modes simultaneously. We also measured the communication link characteristics of two identical multiplexed antennas. The measurement results show that the channel isolation of three OAM modes is more than 12.7 [dB] and 17 [dB] for fixed and compensated receiver positions, respectively, indicating that the proposed antenna system can be used for independent communication links with the same frequency and polarisation.
A parabolic reflector antenna with an azimuthally deformed Cassegrain subreflector is proposed to effectively generate arbitrary orbital angular momentum (OAM) modes. The Cassegrain dual-reflector antenna was fabricated for 18 GHz and measured in the near-field range. The nearfield to far-field transformed radiation phase around a full azimuth shows that the proposed antenna generates fields with the l = 1 OAM mode. Simulated and measured feed reflection coefficients are below −10 dB for 15.1-21.2 GHz, even though the distance between a horn feed and a deformed subreflector is 15.6 mm, thus it is expected that the proposed structure can be used for a broadband low-profile antenna.Introduction: Various researches based on orbital angular momentum (OAM) modes have been extensively studied in optics [1]. Recently, communication systems analogous to the optical one were demonstrated in radio frequency [2][3][4]. To utilise OAM characteristics for radio communications, generating and detecting arbitrary OAM modes is essential. In [2], a helicoidally parabolic reflector, which is similar to [5], is used as the main reflector to transmit electromagnetic waves with a fundamental OAM mode (l = 1). From the standpoint of reflector antenna design, fabricating the main parabolic surface as a helicoid [2, 5] is expensive and inefficient, because ordinary main reflectors should be modified for the generation of non-zero OAM modes. Therefore, we need a simple and efficient method to generate arbitrary OAM modes while keeping the main reflector unchanged. In this Letter, we propose an alternative structure [6] in which a Cassegrain subreflector is azimuthally deformed instead of the main parabolic reflector. A parabolic reflector antenna with an azimuthally deformed Cassegrain subreflector enables us to process small area of a subreflector without modifying a large main reflector. Owing to this merit, we can adopt a variety of ordinary main reflectors for the efficient generation of arbitrary OAM modes. In addition, the proposed antenna has very good reflection characteristics due to the fact that a deformed subreflector radiates higher-order OAM modes which cannot be received by a normal feed horn.
This paper presents a novel 90 GHz band 16-quadrature amplitude modulation (16-QAM) orthogonal frequency-division multiplexing (OFDM) communication system. The system can deliver 6 Gbps through six channels with a bandwidth of 3 GHz. Each channel occupies 500 MHz and delivers 1 Gbps using 16-QAM OFDM. To implement the system, a low-noise amplifier and an RF up/down conversion fourthharmonically pumped mixer are implemented using a 0.1-μm gallium arsenide pseudomorphic high-electronmobility transistor process. A polarization-division duplex architecture is used for full-duplex communication. In a digital modem, OFDM with 256-point fast Fourier transform and (255, 239) Reed-Solomon forward error correction codecs are used. The modem can compensate for a carrier-frequency offset of up to 50 ppm and a symbol rate offset of up to 1 ppm. Experiment results show that the system can achieve a bit error rate of 10 -5 at a signal-to-noise ratio of about 19.8 dB.Keywords: W-band, PDD, OFDM, 10 Gigabit Ethernet, error correction code. Manuscript received Sept. 22, 2013; revised Feb. 10, 2014; accepted Feb. 13, 2014. Hyung Chul Park (corresponding author, hcpark@seoultech.ac.kr) is with the Department of Electronic and IT Media Engineering, Seoul National University of Science and Technology, Seoul, Rep. of Korea. I. IntroductionAs high-speed wireless data services, such as 3G/4G mobile communications, IEEE 802.11ac/ad wireless LAN, and wired Gigabit Ethernet, are becoming more widespread, multi-gigabit Ethernet networks are needed. Compared to wired multigigabit Ethernet networks, wireless multi-gigabit Ethernet networks have the advantage of an easy installation and low construction cost. bandwidth of 3 GHz. In our previous work, we presented a single carrier 16-QAM based E-band (71 GHz to 76 GHz and 81 GHz to 86 GHz) wireless point-to-point broadband communication system [7]. In the previous system, the FDD scheme was used because the spectrum is divided into a lower band (71 GHz to 76 GHz) and an upper band (81 GHz to 86 GHz). However, since a bandwidth of 3 GHz (92 GHz to 95 GHz) is allocated in the 90 GHz band, the proposed system herein utilizes a polarization-division duplex (PDD) architecture to achieve both full-duplex communication and a multi-Gbps data rate. By using a PDD scheme, the spectral efficiency of full-duplex communication can be increased by two times compared to that of the FDD-or TDD-schemebased existing millimeter wave wireless communication. In addition, an OFDM technique and equalizer are used to reduce the effects of inter-symbol interference caused by multipath propagation.II. System Architecture and Function Blocks Figure 1 and Table 1 produces 1 Gbps of binary data. Figure 2 shows a detailed block diagram of the RF/IF transceiver. In the IF transmitter, the digital-to-analog converted signal is low-pass filtered by a seventh-order Butterworth filter with a cutoff frequency of 288 MHz. A passive type I/Q mixer is used for the up conversion, with a conversion loss of 7 dB.Six IF channel sig...
In this paper, we propose a convenient microwave orbital angular momentum (OAM) mode generation and multiplexing method operating in the 18 GHz frequency band, based on a 2×2 uniform circular array and a 4×4 Butler matrix. The three OAM modes −1, 0, and +1 were generated and verified using spatial S‐parameter measurements; the measured back‐to‐back mode isolation was greater than 17 dB in the full 17 GHz to 19 GHz range. However, the radiated OAM beam centers were slightly dislocated and varied with both frequency and the mode index, because of the non‐ideal characteristics of the Butler matrix. This resulted in mode isolation degradation and transmission distance limitations.
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