Search

This paper investigates an optimization of the conventional relay selection for multirelay environments. In contrast with previously reported selection schemes, where a selected relay accesses the channel in a dedicated cooperative slot, the proposed scheme recovers the bandwidth loss of the half-duplex constraint by allowing two relays to simultaneously access the channels. Based on an appropriate dirty-paper coding (DPC) technique among relays, the proposed scheme enables a relay to establish communication with the destination at the same time that another relay forwards the data from the source. It is proven that the interplay between relay selection and the superposition DPC weight factor provides a tradeoff between relaying and new data performance. Hence, an appropriate codesign of the superposition DPC parameter and opportunistic relay selection can achieve efficient communication for the new data without affecting the relaying performance. The proposed scheme is compared with conventional relaying approaches, and its enhancements are provided through theoretical studies and numerical results. [ABSTRACT FROM AUTHOR]

A wideband Rayleigh fading channel is considered with causal channel state information (CSI) at the transmitter and no receiver CSI. A simple orthogonal code with energy detection rule at the receiver (similar to pulse position modulation in IEEE Trans. Inf. Theory, vol. 46, no. 4, Apr. 2000 and IEEE Trans. Inf. Theory, vol. 52 no. 5, May 2006) is shown to achieve the capacity of this channel in the wideband limit. This strategy transmits energy only when the channel gain exceeds a threshold, hence only needs causal transmitter CSI. In the wideband limit, this capacity without any receiver CSI is the same as the capacity with full receiver CSI, which is proportional to the logarithm of the bandwidth. Similar threshold-based pulse position modulation is shown to achieve the capacity per unit cost of the dirty-tape channel (dirty paper channel with causal transmitter CSI and no receiver CSI), which equals its capacity per unit cost with full receiver CSI. Then, a general discrete channel with i.i.d. states is considered. Each input has an associated cost and a zero cost input “0” exists. The channel state is assumed to be known at the transmitter in a causal manner. Capacity per unit cost is found for this channel and a simple orthogonal code is shown to achieve this capacity. Later, a novel orthogonal coding scheme is proposed for the case of causal transmitter CSI and a condition for equivalence of capacity per unit cost for causal and noncausal transmitter CSI is derived. [ABSTRACT FROM PUBLISHER]

Recently, broadband optical access networks were being deployed worldwide to deliver large bandwidth to end users. Currently, the operators have been mainly deploying time-division multiplexing (TDM) passive optical networks (PON) in their networks. As bandwidth demand continues to increase, the industry further selected several next generation optical access (NGA) options to upgrade from current TDM-PON architectures. Besides increasing bandwidth requirement, current TDM-PONs suffers from limited reach and split-ratio. To further reduce the capital and operational expenditure requirements of current TDM-PON, NGA architectures must consolidate the number of central office sites. Long-reach optical access (LROA) architectures are promising solutions that employ optical amplifiers to increase optical budget to support longer reach and higher split-ratio in the distribution network. As more end users are supported over shared physical medium in LROA, access network security is of greater importance. The first part of this article reviews important LROA architectures and their enabling technologies. Moreover, few works in current literature address security weaknesses in LROA. The second part of this article reviews these security weaknesses as well as monitoring and control techniques employed in current TDM-PONs. In addition, a novel class of quasi-passive and reconfigurable devices is presented that addresses aforementioned security weaknesses and is suitable for LROA. [ABSTRACT FROM AUTHOR]

This paper presents a compact triple-band and a multiband band-pass filter (BPF) using a stepped impedance line (SIL) and a modified stub-loaded open loop resonator (MSLOR), respectively. The first proposed triple-band BPF used a new technique which involves embedding the stepped impedance line (SIL) between the feed line and the open stubs. Due to this, the proposed filter achieves an ultra wideband (UWB) and two narrow bands with a fractional bandwidth of about 12.85%, 30.38% and 2.6% for use in 4G, WLAN and satellite communication. An UWB is generated with five transmission zeros that increase the high selectivity and avoid the interference between the existing bands. The second proposed filter is triple-band to multiband BPF using MSLOR. This filter achieves five passbands with seven transmission zeros. [ABSTRACT FROM AUTHOR]

This paper presents the design and development of planar triplexer slot antenna using substrate integrated waveguide (SIW) technology. The proposed antenna is realised using 'Y' shaped slot backed by SIW cavity. SIW cavity is excited by three separate feed lines for resonance at three different frequencies of 5.7 GHz, 6 GHz and 6.4 GHz with unidirectional radiation pattern and gain of 6.26 dBi, 5.87 dBi and 5.19 dBi, respectively. Average isolation of the three ports is better than 24 dB. All the simulations are carried out using high frequency structure simulation (HFSS) software. The proposed antenna is fabricated on RT Duroid 5880substrate and measured results show better performance. The developed antenna is small in size (0.79 λ × 0.78 λ), simple to fabricate and easy to integrate with planar technology making it suitable for C-band application. [ABSTRACT FROM AUTHOR]

This paper presents the system design, calibration, and example measurements of a novel ultra-wideband, low-cost, real-time channel sounder. The channel sounder operates in the frequency range from 3 to 18 GHz with a 15-GHz bandwidth thus providing a Fourier delay resolution of 66.7 ps. It sequentially measures overlapping sub-bands of 1-GHz bandwidth to cover the whole frequency range. By using a waveform generator and a digitizer with relatively lower sample rates, the design significantly lowers the cost compared with sampling the whole band simultaneously. With the transmitting power of 40 dBm, the maximum measurable path loss is 132 dB without accounting for possible antenna gains. In this paper, we also describe the calibration procedure along with the method to stitch sub-bands into a combined channel response across 15 GHz of bandwidth. The channel sounder performance is compared with a vector network analyzer (VNA) measurements acquired in the same static channels. In contrast to VNAs, however, our channel sounder can measure the whole band in 6 ms and can, thus, operate in dynamic environments with coherence time more than 6 ms. Additionally, we present sample results from a measurement campaign performed in an indoor corridor investigating the delay spreads statistics over the range of 3–18 GHz. [ABSTRACT FROM AUTHOR]

Usually high wideband ac current and harmonics measurements are accurately achieved in industry and laboratories by using high accuracy shunts or standard shunts. For particular applications, such as power and transient measurements, it is mandatory to evaluate the shunt impedance phase and magnitude according to the frequency bandwidth of interest before to measure the current with such sensors. High electrical current shunt beyond 1 A is calibrated in magnitude up to 100 kHz and in phase angle up to 200 kHz only by a few National Metrology Institutes. The existing traceable measurement methods to characterize these sensors are limited in frequency to 100 kHz, with expanded uncertainties of the ac–dc difference (magnitude) and the phase angle of more than $5 \times 10^{-6}$ and $62~\mu $ rad at 100 kHz, respectively. A new traceable calibration method to measure and characterize current shunts at high frequencies is presented in this paper. This measurement method is based on the use of a vector network analyzer. The measurements are presented up to 60 MHz, but theoretically, the presented method does not exhibit a specific frequency limitation. Only the characteristics of the shunt under study can impose limitation in practice. While uncertainties are higher than those provided by the existing methods, the method presented in this paper is the only method able to perform in one step a broadband and simultaneous measurement of the magnitude and phase of current shunts up to few megahertz with acceptable uncertainties. [ABSTRACT FROM AUTHOR]

This paper presents an $8\times 8$ -element slot array antenna with single-layered corporate-feed based on the ridge gap waveguide (RGW) technology in the 60 GHz band. As is well known, a corporate-feed slot array antenna usually has backed cavities to increase the bandwidth and provides a space for its distribution network, and therefore three layers in total: one layer for radiating slots and two layers for feed network with one layer of back cavities and the other one of power dividers. The antenna in this paper is designed by utilizing only two separate metallic layers–a corporate-feed network layer and a radiating slot layer. Compared with the conventional three-layered slot array antennas, the proposed antenna avoids the utilization of the backed cavity layer so that its complexity and manufacture cost decrease. In order to solve the problem of the narrow bandwidth caused by taking away the backed cavities, we utilize double-ridged radiating slots instead of the conventional rectangular ones. A compact transition power divider from standard waveguide WR-15 to the RGW is introduced to excite the proposed array antenna. The $8\times 8$ -element slot array antenna has been fabricated by computerized numerical control machining technique. The measured results demonstrate that the −10 dB reflection coefficient has around 17% bandwidth covering 56.5–67 GHz frequency range, and the measured gain is better than 26 dBi with more than 70% antenna efficiency over 58–66 GHz. [ABSTRACT FROM AUTHOR]

This paper investigates the design and analysis of minimum mean square error (MMSE) turbo decision feedback equalization (DFE), with expectation propagation (EP), for single carrier modulations. Classical non iterative DFE structures have substantial advantages at high-data rates, even compared with turbo linear equalizers-interference cancellers (LE-IC), hence making turbo DFE-IC schemes an attractive solution. In this paper, we derive an iterative DFE-IC, capitalizing on the use of soft feedback based on expectation propagation, along with the use of prior information for improved filtering and interference cancellation. This turbo iterative DFE-IC significantly outperforms turbo LE-IC, especially at high-spectral efficiency and also exhibits performance improvements over existing DFE-IC variants. The proposed scheme can also be self-iterated, as done in the recent trend on EP-based equalizers, and it is shown to be an attractive alternative to linear self-iterated receivers. For time-varying (TV) filter equalizers, an efficient matrix inversion scheme is also proposed, considerably reducing the computational complexity relative to existing methods. Using finite-length and asymptotic analysis on a severely selective channel, the proposed DFE-IC is shown to achieve higher rates than known alternatives, with better waterfall thresholds and faster convergence, while keeping a similar computational complexity. [ABSTRACT FROM AUTHOR]

In this paper, a quad-mode endfire planar phased antenna array with wide scan angle and 1.2 mm clearance is proposed for 5G mobile terminals. The proposed antenna can obtain over 8 GHz of impedance bandwidth. In this paper, it is suggested to efficiently combine a multimode array element with different radiation patterns for each mode into a phased antenna array. In the array, similar and wide embedded radiation patterns are obtained for the all four modes. Furthermore, a coaxial to differential stripline transition is designed in this paper. The differential feeding structure is very compact and utilizes only MMPX connector and vias. The total scan pattern and coverage efficiency of the measured and simulated phased array antenna are calculated in the range from 25 to 33 GHz, and good agreement between measured and simulated results is observed. The mean coverage efficiency along the frequency range is very similar, but minor difference in variance of coverage efficiency is observed in the measurements. The coverage efficiency of around 50% for the threshold gain of 5 dBi is achieved in the chosen frequency range. [ABSTRACT FROM AUTHOR]

With the ever increasing demand for higher speed internet connectivity that can fulfil the application continuous need for higher bandwidth Google being the pioneer in many web-based services has launched a new UDP-based protocol named quick UDP internet connections (QUIC), which aims at providing faster data delivery without requiring upgrades or modifications to the network infrastructure. The goal of this paper is to provide an overview about QUIC protocol, propose the design and implementation of a test-bed, that is used experimentally to evaluate QUIC protocol under different network conditions and scenarios. In particular, the performance advantage of QUIC in terms of delay and throughput are examined taking into account different network conditions that resemble the real internet environment. Two scenarios are proposed, the first one investigates the protocol performance under a controlled network environment, while the second one tests the protocol in a real uncontrolled network. To achieve that, a test-bed is proposed and implemented that emulates the network impairments encountered in real-network such as packet loss, bit errors, and bandwidth limitation in a controlled manner. After that, QUIC is tested in real operational wired and wireless networks. In both scenarios, QUIC outperforms TCP in terms of delay, which strengthens QUIC position for being a potential alternative to TCP. [ABSTRACT FROM AUTHOR]

In this paper, a wideband two layer slot array antenna is proposed which operates in the frequency range of 12–14.4 GHz. The lower layer of the antenna array includes narrow rectangular slots and the upper layer consist of rectangular patches shorted on the sides of the patches with via holes. The wideband operation is obtained by making two resonances. One resonance is due to radiation of the single element and the other is the effect of mutual coupling between adjacent elements. An 8 element array is designed, simulated and fabricated with good agreement between simulated and measured results. [ABSTRACT FROM AUTHOR]

In this paper, an optical communication receiver system for 5Gbps applications is proposed concerning power consumption. An inductor-less circuit in three-stages is proposed as the trans-impedance amplifier (TIA), which benefits from the inherent low input resistance of a common gate topology as the first stage. By forming two zeros in this TIA, proper frequency response is obtained while the DC current is reduced. In order to obtain extra gain for the receiver system, three stages of conventional limiting amplifier (LA) are used. In order to verify the circuit performance, the proposed receiver is simulated in HSPICE using 90nm CMOS technology parameters. The receiver is mathematically studied and is matched with the simulations. This paper conducts the simulations, such as eyediagram, noise analysis and fabrication process analysis (Monte-Carlo). The proposed Trans-Impedance Amplifier shows 53.9dbΩ gain, 3.5GHz bandwidth, 15.2pA/√Hz and only 1.52mw power consumption for 1.2v supply voltage, and the receiver system shows 90.9dbΩ, 3.5GHz bandwidth and 6.34mw power consumption (for 2 stages of TIA and 3 stages of LA) for 1.2v supply voltage. Results indicate that the proposed receiver is suitable to work as a low-power 5Gbps optical communication receiver system. [ABSTRACT FROM AUTHOR]

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method's performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%. [ABSTRACT FROM AUTHOR]

This paper addresses the estimation and compensation of I/Q imbalance, one of the most prominent impairments found in wideband zero-intermediate frequency transceivers (TRxs). The I/Q imbalance encountered in this kind of TRx comprises not only frequency-selective gain and phase imbalance but also delay imbalance. Unless appropriate compensation is applied, the I/Q imbalance significantly degrades the performance of a communication system. This paper presents a novel compensation technique for transmitter I/Q imbalance based on built-in-self-calibration, a low cost and robust compensation technique that enables manufacturing as well as in-field calibration with low computational complexity. The method’s performance is evaluated in a TRx with 64-quadratic-amplitude modulation and 2 GHz of bandwidth implemented with real hardware. The measurements show that the proposed technique achieves an image rejection ratio greater than 35 dB in the entire 2 GHz bandwidth and an error vector magnitude lower than 3%. [ABSTRACT FROM PUBLISHER]

Satellite networks have great potential in providing global ubiquitous broadband communication. In this paper, we explore the capacity of both single-layered and two-layered satellite networks. Closed-form approximate expressions of network capacity are derived, which provide insights into the impact of different network parameters, such as number of orbits, number of satellites in each orbit, link bandwidth, existence of the seam, the relative position between the two layers, etc. We investigate the advantages of two-layered structure by comparing the capacity of single-layered and two-layered networks. The results show that the network capacity of two-layered networks is always no less than the total capacity of the two layers. Moreover, we obtain the network parameter condition under which the network capacity of two-layered networks is strictly larger than the sum capacity of the two layers. The results obtained in this paper can serve as a guideline for the design of efficient multi-layered satellite networks. [ABSTRACT FROM AUTHOR]

An ultrawideband conformal capsule slot antenna, which has a simple configuration and a stable impedance matching characteristic, is described in this paper. In the past, wideband outer-wall antennas have been proposed for capsule-type applications. However, this paper shows that the outer wall is not a good choice for placing capsule antennas, since such a choice exhibits a high specific absorption ratio, low gain, and low efficiency. Instead, the antenna proposed in this paper is conformal to the inner wall of a capsule shell, and it provides a wide impedance bandwidth ranging from 1.64 to 5.95 GHz (113.6%). Furthermore, the impedance matching remains stable even with a change in the operating environment. Since in a typical application scenario a capsule will move through the digestive system, and thus experience varying environments, a wide bandwidth and stable performance are both very desirable attributes of the antenna, whose design is discussed in this paper. Moreover, the proposed antenna continues to maintain a stable impedance match even when a battery is added inside the capsule, or when there is a change in the battery size and/or its position. Given these advantages, we argue that slot antennas are well suited for incorporation into capsule antennas for the present application. [ABSTRACT FROM PUBLISHER]

This paper presents a method for designing a power amplifier for high efficiency Class-E broadband topology using a low- pass filter of a high order is presented. A study of the state of the art regarding the design of a power amplifier Class-E performed operating within the frequency band of 0.8 GHz to 1.5 GHz. In the design accordingly ensures the attenuation of the power of the second and third harmonic, critical to achieving high efficiency amplification criterion. The design equations and simulation were made in AWR Design Environment V13. The efficiency levels achieved were 74%, the efficiency of added power (PAE) 72% power gain was more than 8 dB across the band, a bandwidth of665 MHz, and the band of 60.8% was achieved, with an efficiency drain and PAE above 50%. [ABSTRACT FROM AUTHOR]

In this paper, converters of TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{21}}$ mode and TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{01}}$ mode with similar exciting topologic structures are designed and verified for a cold test of gyro-TWT. Both the proposed converters are composed of three sections, including TE $^{\Box }_{{10}}$ to TE $^{\Box }_{{20}}$ mode converter with ridged twist waveguide, TE $^{\Box }_{{20}}$ to TE+22 mode converter with variable cross-shaped waveguide, and the last section TE+22 to TE $^{\circ }_{{21}}$ or TE $^{\circ }_{{01}}$ mode converter ($^{\Box }$ represents the rectangular waveguide, + represents the cross-shaped waveguide, and ° represents the circular waveguide). The mode converters can be designed step-by-step and exhibit excellent wideband performance and high conversion efficiency. Simulation results reveal that the proposed TE $^{\circ }_{{21}}$ mode and TE $^{\circ }_{{01}}$ mode converters have less than 0.04 and 0.03 dB loss over 13.5- and 12-GHz bandwidths, respectively, while the return loss is below −25 dB. Prototype TE $^{\circ }_{{21}}$ and TE $^{\circ }_{{01}}$ mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design. [ABSTRACT FROM AUTHOR]

Beam steering has found wide applications in many areas such as wireless communications, satellite communications, and intelligent transportation systems.Different approaches have been presented to achieve the beam steering, most of which, however, are complicated and expensive. In this paper, we propose a simple and efficient principle to realize this goal based on a partial Luneburg lens. In the experiment, a traditional Vivaldi antenna is used as the platform to test the principle, in which the partial Luneburg lens is constructed by drilled-holes dielectric composite material. The measurement results show that good beam-steering performance from -20 to 20° in a broad bandwidth (8-11 GHz) has been achieved using the proposed method, and the antenna's gain and directivity have been significantly improved in the same bandwidth after using the special lens. [ABSTRACT FROM AUTHOR]

This paper presents a new method for single-layer broadband phase shifter without needing any coupling structure. The phase shifter consists of a multimode resonator and two shunt $\lambda $ /4 stubs. Meanwhile, the bandwidth of proposed phase shifters can be achieved more than 100%. For prescribed return loss, phase shift value, and phase error, this paper develops a synthesis approach to determine all parameters of designed phase shifter. In addition, both the return-loss bandwidth and phase-error bandwidths can be considered simultaneously so as to determine the return loss and phase error for a desired bandwidth. The 45°, 90°, 135°, and 180° phase shifter are theoretically designed and presented. To validate the design method, a broadband 90° phase shifter is designed, fabricated, and measured. The synthesized, simulated, and measured results are found in good agreement with each other, and the experimental results show that the phase shifter achieves 90° ± 5°, \vert S_{11}\vert < -14 dB, and insertion loss < 0.7 dB over the bandwidth from 1.43 to 4.45 GHz (102.7%). [ABSTRACT FROM PUBLISHER]

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%–66% efficiency at a −6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%–62% while maintaining an adjacent channel power ratio below −45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs. [ABSTRACT FROM PUBLISHER]

Metamaterial based electromagnetic wave absorbers may provide perfect absorption over significant range of electromagnetic spectrum. With perfect and broadband absorption, metamaterial absorbers play an important role in stealth technology. In this paper, design, simulation and measurements of a novel X-band (8–12 GHz) metamaterial broadband absorber are presented. An absorber operating in the middle of the microwave X-band is obtained by selecting differently sized unit cells and placing their resonant frequencies close to each other. The paper presents two absorbers which consist of different number of unit cells. The first absorber has 12 unit cells (KOH12) while the other has 16 unit cells (KOH16). It is observed that the simulation results are in good agreement with the measurements. Measurement bandwidth for an absorption level of 80% is 2.73 GHz for KOH12 and 2.55 GHz for KOH16. These are the highest absorption levels for planar metamaterial absorbers at X-band. The absorption mechanism of broadband metamaterial absorber is also investigated by using electric and magnetic field distribution. Results of this study are promising for the stealth applications as absorbing elements against X-band radars. [ABSTRACT FROM AUTHOR]

In this paper, a compact microstrip fed UWB monopole antenna for dual band applications is proposed and investigated. The base of the proposed antenna is a rectangular shaped radiator. The radiator of an antenna occupies a small area of only 10.2 × 7.6 mm2 (0.081λ0 × 0.06λ0) that covers the UWB frequency range. To create a dual band antenna by etching a quarter wavelength resonator, loop strips into radiator is designed which generates the notch band characteristic. The proposed structure consists of rectangular patch shape at centre with two symmetrical loop strips. Dual band antenna is designed on FR-4 substrate whose dielectric constant is 4.4, tangent loss 0.02 and thickness 1.59 mm. The overall size of proposed antenna is 15 mm × 15 mm (0.12λ0 × 0.12λ0). The 10-dB impedance bandwidth of the antenna is 520 MHz (2.3–2.82 GHz) and 5.51 GHz (3.8–9.31 GHz). Also same configuration antenna is designed on Roger RT/Duroid substrate whose dielectric constant is 2.2, loss tangent 0.0009 and thickness 30 mil (0.762 mm). The simulated result is approximately same as FR-4. It covers the LTE, ISM, WLAN, WiMAX, X band satellite communication and ITU bands for wireless communications. To verify the proposed antenna design and response, a prototype has been fabricated on FR-4 and parameters are measured. The measured response validates the simulated response. [ABSTRACT FROM AUTHOR]

In-band full-duplex (IBFD) wireless systems offer the ability to revolutionize frequency spectrum utilization for future networks. This is only possible if the self-interference generated by each wireless node is sufficiently mitigated, and becomes more challenging as the bandwidth increases. RF cancellation is one of the critical components that enables this interference reduction, but has previously been limited to narrowband operation or restricted to distinctive environments. This paper presents a novel RF canceller that utilizes photonic components to create a wideband vector modulator architecture with tunable time-delay taps. A prototype system with 20 canceller taps has been demonstrated to provide 25 and 20 dB of cancellation over 500-MHz and 1-GHz instantaneous bandwidths, respectively, and is tunable between 0.5 and 5.5 GHz. This unique photonic-enabled RF canceller design provides a path forward to achieve the wideband operation and high tap counts that will be required to successfully deploy future wireless systems with IBFD technology. [ABSTRACT FROM AUTHOR]

In this paper, we propose a method for designing checkerboard surfaces using strategically placed artificial magnetic conductors (AMCs) for wideband radar cross section (RCS) reduction. The theoretical analysis shows that the reflection phases of the two AMCs should be linear. The cancelation conditions of checkerboard structure are analytically derived using an equivalent transmission line model, and the ideal impedance conditions of the two AMCs are obtained, which serve as guidance to select patterns of two AMCs unit. A planar checkerboard surface with two kinds of AMC elements is designed for wideband RCS reduction. A 10 dB RCS reduction is observed for approximately 91.5% of the relative bandwidth (3.77–10.14 GHz) under normal incidence. A prototype of the proposed checkerboard surface is fabricated, and the measurements results show good coincidence with the synthetic studies. The bistatic RCS of the checkerboard surface is considered for both transverse electric and transverse magnetic polarizations under oblique incidence. [ABSTRACT FROM AUTHOR]

A compact wideband high gain directional antenna is proposed in this paper for marine communications. The antenna consists of a back plane (reflector), a slot-loop antenna (driven element), and a director of rod. Based on the current distribution, the slot-loop antenna is equivalent to an array of three linear current dipoles. The dipole acts as an element of the director, which provides a high efficient director for slot-loop antenna according to theoretical analysis. Both the impedance bandwidth and the 1 dB gain bandwidth are 45% covering 1.7–2.7 GHz in this design. A gain of 11.2 to 12.2 dBi is obtained in the working band with only one set of directors. The directors have a dimension less than the antenna aperture in the H-plane, which can be seen as one director in the end-fire direction. Compared with the classic Yagi antenna with the same gain level, the newly proposed antenna is only half of the size in radiation direction, which is a breakthrough for the Yagi antenna design. This size reduction can significantly minimize the interference between ship-borne antennas. The antenna is fabricated using only metal of low cost, which is useful for the ship-to-shore/ship communicating applications and desirable for the large-scale deployment. [ABSTRACT FROM AUTHOR]

In this paper, the design of a cavity crossover with three intersecting channels is presented. The three fundamental modes of a cavity resonator, namely, TE011, TE101, and TM110 modes, are adopted to resonate at each of three channels, respectively. Due to the modal orthogonality of these fundamental modes, high isolation among three channels can be achieved. Two kinds of crossovers, for narrowband and broadband applications, are presented. For the narrowband case, the proposed crossover resonates at 2.91 GHz with the fractional bandwidth of 1.4%. For the broadband case, the proposed crossover resonates at 3 GHz with the fractional bandwidth of 24%. The isolations of both designs reach more than 50 dB. For a proof of concept, the broadband example of the cavity crossover structures is fabricated and measured. A good agreement between the simulated and the measured results verifies the accuracy of the proposed design methodology. [ABSTRACT FROM AUTHOR]

This paper describes the novel design concept of a wideband noncircular choke flange for connecting two contactless waveguide joints with the variable air gap. Resonant enhancement of transmission loss is observed in the experiment as well as the numerical simulation in Ansys HFSS software when a 2-D standing wave is excited in the narrow air gap. The shape of the choke groove is designed in such a way that ensures standing waves cannot be excited in the frequency band of interest, even considering possible linear and rotational misalignments between the connecting joints during practical operation, thereby making the design very robust. The eigenmode analysis is performed to decompose the mixed excitation mode into the fundamental and higher order modes, and for the case of misalignment, revealing why the electric field changes the direction of rotation above and below the resonant frequency. Experimental measurement results of the fabricated egg-choke flange showed that the transmission loss is less than 0.1 dB in the 2.5-GHz bandwidth from 8.5 to 11 GHz with possible misalignment which validates the design. Other choke shapes are possible following the same design methodology with different scaling parameters depending on the desired frequency band of the user application. [ABSTRACT FROM AUTHOR]

Substrate-integrated waveguide (SIW) uses rows of plated through holes to emulate the intact vertical walls of a waveguide circuit. It succeeds in the design of H-plane circuits but not the E-plane circuits because an E-plane circuit requires longitudinal current on the vertical walls that is not supported by SIW. In this paper, a novel substrate-integrated E-plane waveguide (SIEW) is presented. In SIEW, additional copper strips are inserted at the middle layer of the structure while the copper plated through holes remain unchanged. Consequently, the vertical current flows on the through holes and the longitudinal current flows along the middle strips to meet the wave propagation requirement in the E-plane waveguide circuit. The insertion loss, cutoff frequency, and propagation constant of the SIEW are investigated. As examples, an empty SIEW, a bandpass septum SIEW filter, and a dual-polarized SIEW horn antenna are designed using the SIEW technique. All of them are constructed and their performance is measured to validate the design. [ABSTRACT FROM AUTHOR]

This paper presents a broadband three-stage Doherty power amplifier (DPA) using impedance compensation for bandwidth extension. Different from the conventional design, an impedance-compensating load combiner is proposed to broaden the bandwidth of the three-stage DPA by employing the output impedances of the peaking amplifiers. Considering the load impedance of the peaking branch as an independent design variable, the Doherty load modulations are analyzed in theory, pointing out the optimized solution for the load combiner. To achieve the impedance compensation, the peaking output matching networks are deliberately designed with the dual-impedance matching topology. Experimental results show that a three-stage DPA is realized from 1.6 to 2.6 GHz (48% fractional bandwidth) with a measured efficiency of 50%–53% at 9.5-dB back-off and a saturated output power around 45.5 dBm. When stimulated by the 20- and 40-MHz modulated signals at an average output power of around 36.5 dBm, the proposed DPA can achieve the adjacent channel leakage ratio of −50 dBc over the whole frequency band after linearization, with an average efficiency of higher than 50%. [ABSTRACT FROM AUTHOR]

This paper reports a novel wideband differential antenna based on metasurface. It consists of a differential slot coupled antenna and a planar metasurface. Planar metasurface is composed of 4 × 4 elements, and a rectangular slot is embedded on the ground plane to couple energy between the differential feeding lines and metasurface. The feeding line employs the three-line coupled lines which could provide wideband filter-integrated feature. The lower and upper resonant frequencies of the proposed antenna can be adjusted independently by tuning the distance of the metasurface units and the length of the rectangular slot in metallic ground, respectively. Moreover, a differential dielectric resonator antenna is simulated for performance comparison. It is concluded that the proposed antenna has many advantages, such as low profile (0.08λ0 at 5 GHz), frequency independent, high-gain, and symmetrical radiation pattern, comparing with the differential dielectric resonator antenna. Furthermore, a differential metasurface-based antenna prototype has been fabricated to experimentally validate the principle and design approach. The measured impedance bandwidth with odd mode reflection coefficient below − 10 dB is 19.35% from 4.76 to 5.78 GHz. Meanwhile, the measured boresight gain at 5 GHz is 6.4 dB, and low cross-polarization level could be achieved. [ABSTRACT FROM AUTHOR]

In this paper, the results of the investigations on a system for energy harvesting from wideband vibrations are presented. The harvester adopts a nonlinear snap-through buckling configuration and two piezoelectric transducers, placed near the inflection points of the potential energy function that underpins the dynamics of the system. The device is capable of scavenging energy from vibration sources in the range of 0.5–7 Hz, but could be exploited up to 10 Hz with an acceptable loss of efficiency. The bandwidth of the device is compatible with applications where the vibrations occur at low frequencies, e.g., in the case of a running human. Powers of about $416~\mu \text{W}$ with root-mean-square accelerations of 13.35 m/s2 at 7 Hz and an efficiency of about 24.6% have been measured in case of a sinusoidal vibration while powers of about $250~\mu \text{W}$ and an efficiency of about 15.7%, have been measured in case of a noise input limited at 15 Hz, with a standard deviation of the accelerations of about 15.1 m/s2. The performance of the harvester is compared with a different configuration where the piezoelectric transducers are placed at the two minima of the (bistable) potential energy function that underpins the dynamics; the minima correspond to the stable states of the beam. [ABSTRACT FROM AUTHOR]

This paper presents a design procedure for a phased array feed network. The procedure is validated by designing and fabricating a set of 28 GHz 8‐element beam steerable antennas. Within the feed, a Taylor n‐bar amplitude taper is implemented using unequal power dividers. At boresight, the taper reduced the sidelobe level by 2.84 dB to −15.2 dB. Beam steering from 0° to 48° is achieved using meanders. An empirical formula for the meander widths is proposed, enabling independent control of amplitude and phase. Empirical formulae for the initial parameters of the unequal dividers are also proposed. The wide transmission lines in this feed network are compatible with low‐cost PCB fabrication techniques. [ABSTRACT FROM AUTHOR]

A compact ultra-wideband (UWB) slot antenna using narrow slots is proposed. Different from the traditional wideband slot antennas with multiple resonant modes, the proposed design of this paper utilizes the traveling-wave mode. By using a slotline–CPW transition as the convertor, which connects a slotline and four open slots, the forward wave in the slot has small reflection. The working mode keeps stable at different frequencies, i.e., operating in the traveling-wave mode. As a result, both wide bandwidth and stable radiation patterns are achieved with inherent characteristic of traveling-wave mode. The proposed antenna occupies a small area and the slot width is narrow, which make it suitable to be mounted on the edge of metallic surface for wireless devices. Given an instance for validation, a prototype is fabricated, with a slit width of 0.2 mm and a total size of $25\times 30\times 0.762 $ mm3 ($0.24\times 0.29\times 0.007 \lambda _{L0}^{3} $ , $\lambda _{L0} $ is the wavelength in free space at the lowest operating frequency). Measured results show that a relative bandwidth (VSWR < 2) of about 121% is achieved, covering the entire UWB. Besides, stable gains and radiation patterns are obtained in the operating band. The time-domain characteristic is also investigated, and a small-signal distortion is achieved. [ABSTRACT FROM AUTHOR]

A metallic patch antenna using double-tuned impedance matching is presented in this paper. The antenna mainly consists of a rectangular ground plane, a radiation patch with U-slot and two short metal cylinders, with a size of 200mm×200mm×25.5mm. The two metal cylinders are used to connect the patch and the ground. With the common effects of the U-slot and the two metal cylinders, the impedance match has become better than before. Moreover, high harmonics and cross polarization are suppressed after loading two short pins. Measured results show that the antenna has a wide impedance bandwidth from 830 MHz to 970 MHz (16%) for voltage standing wave ratio (VSWR) less than 1.5, and a high gain level about 9.3dBi in a wide band. A good agreement is achieved between simulated and measured results. Therefore, the proposed metal antenna is a good choice for UHF RFID applications. [ABSTRACT FROM AUTHOR]

This paper presents a wideband multilayer balanced-to-unbalanced (BTUB) power divider consisting of three metallic layers and two substrate layers with inherent common-mode (CM) suppression. With very simple structure, the working mechanism of the proposed power divider is investigated through even- and odd-mode equivalent circuit analysis, and the designed procedure is also summarized. For demonstration, an example of wideband BTUB power divider is implemented through standard printed circuit board process. The bandwidth of 63% of the fabricated BTUB power divider can be obtained with the best differential-mode transmission coefficient of −3.45 dB. The isolation bandwidth of approximately 63% can also be achieved. Good agreement between the simulated and measured results is observed, where the measured −15-dB CM suppression bandwidth is about 95%. Moreover, the performance is stable after adding the shielding cavity. [ABSTRACT FROM AUTHOR]

In this paper, a novel modified Doherty power amplifier (DPA) that allows for extended output back-off (OBO) range, improved power utilization factor (PUF), and increased peak power over a broad bandwidth is proposed. It starts with an in-depth analysis of the modified DPA circuitry that first revealed the ability to control the impedances seen by the main transistor versus frequency by properly setting the magnitude and phase of the ratio between the peaks of the combining currents. This is then exploited to maximize the peak power and enhance the achievable bandwidth. Furthermore, a complex-to-real output matching network is incorporated in the auxiliary path and its parameters are carefully chosen to produce proper load modulation while satisfying the required peak combining current ratio. For validation purpose, a DPA prototype is designed to operate over the frequency range of 1.35–2.05 GHz with an OBO of 9 dB. Under the continuous-wave excitation, the DPA prototype maintained the drain efficiency (DE) of 52%–55% and 65%–75% at 9-dB OBO and peak power, respectively, over the entire targeted band. In addition, the measured peak power and PUF were about 42 dBm and higher than 0.9, respectively. The linearizability of the DPA prototype using digital predistortion (DPD) with memory was assessed while being driven with a 40-MHz carrier-aggregated signal with a peak-to-average power ratio of 8.9 dB and at an average output power of 33 dBm. When the carrier frequency is swept over the entire band, the measurement revealed an adjacent channel leakage ratio of better than −46.5 dBc after DPD with an average DE of 49.3%–53%. [ABSTRACT FROM AUTHOR]

Superdirective arrays have become the key technique in enhancing the directivity of electrically small antennas. By forming an array of closely spaced unit elements, a high directivity can be achieved. Despite the high directivity, these arrays suffer from narrow bandwidth and low efficiency. In this paper, we present an approach to enhance the bandwidth of superdirective arrays using the network characteristic modes. The key step is to use an internally loaded compact wideband unit element. The loads inside the unit element are used to manipulate the characteristic modes in order to optimize its impedance bandwidth. A two-element endfire array is then formed. The modal coefficients of the characteristic fields are then optimized at multiple frequency points in order to radiate a maximal directivity in the endfire direction. The best current excitation that can maintain a constant directivity as a function of frequency is then deduced. Finally, a feeding network that can provide the desired excitation at the array ports is designed and integrated on the array system, where the 1 dB directivity bandwidth is about 23% with $D_{max}=7.1$ dBi. The antenna impedance bandwidth is equal to 15%. [ABSTRACT FROM AUTHOR]

In this paper, a wideband magnetoelectric (ME) dipole antenna with wide beamwidth both in the E-plane and H-plane is investigated. The proposed antenna, which is a differential one, has a simple structure and can realize wide beamwidth in the E-plane and H-plane in whole operating bandwidth. This antenna is easy to manufacture and low cost. The antenna consists of a pair of $\Gamma$ -shaped metal plates, a $\Gamma$ -shaped fed line, and six metal columns. The $\Gamma$ -shaped metal plates and metal columns change the current distribution which changes the radiation performance of the proposed antenna. Some parameters, which effect on the performances of the antenna, are studied. The proposed antenna achieves the impedance bandwidth (≤−10 dB) of about 81.1% (3.3–7.8 GHz). The half-power beamwidth (HPBW) of the proposed antenna is obviously broadened. The HPBW is 215° in the E-plane and 186° in the H-plane at 5.5 GHz. Besides, the cross polarization of the antenna is very low. The antenna is fabricated and measured to verify the design. The measured results are in good agreements with the simulated one. Good radiation characteristics of the new ME dipole antenna have been obtained in the whole frequency band. [ABSTRACT FROM AUTHOR]

In this paper, we present a new wideband circularly polarized (CP) antenna. It has two parts, the first part is a circular ground plane with curved branches, and the second one is a circular patch with curved branches and inverted L-shaped slots. We could obtain a wideband of impedance and axial ratio (AR) through commending inverted L-shaped slots on the patch and loading end shorting vias at the corresponding ends of the arced branches in the patch and ground plane. The realized antenna has a dimension of 43 × 43 × 3.2 mm3, equals to 0.73λ0 × 0.73λ0 × 0.054λ0 (λ0 is the wavelength at the minimum frequency). The tested results illustrated that the impedance and axial ratio (AR) bandwidth are 26.98% (5.29-6.94 GHz) and 25.33% (5-6.45 GHz), respectively. The results of the actual test are basically adjacent with the simulated one. [ABSTRACT FROM AUTHOR]

In this paper, we propose a newly enhanced Doherty combiner by adding a 180° transmission line to the stage of the peaking amplifier of a typical Doherty combiner such that the designer can easily construct a combiner having a phase deviation to be turned on within the intended bandwidth. Given such characteristics, the proposed structure provides wider phase bandwidth and better performance with respect to power combining rate than the conventional structure does. We introduce formulas for the design variables of the added transmission line and also demonstrate its validity through circuit design and experiment. [ABSTRACT FROM AUTHOR]

This paper presents a novel structure of a compact circularly polarized (CP) antenna. CP is obtained using a parasitic quasi-rectangular strip placed coplanar to the feedline. A ground plane perturbation combined with the asymmetric geometry of the coplanar waveguide ground planes is utilized to excite additional CP modes. All antenna dimensions are rigorously optimized to achieve the best possible performance in terms of the impedance and axial ratio bandwidth (ARBW). The size of the proposed antenna is only 24.7 × 25 mm2. The antenna performance is validated experimentally. A close agreement between simulation and experimental results is observed. A wide impedance bandwidth of 42.6% (3.93-6.06 GHz) and ARBW of 42% (3.96-6.03 GHz) is with 98.5% bandwidth overlap between |S11| and AR is achieved. The average realized gain of the antenna throughout the operating frequency is 3.4 dBic. Left-hand circular polarization radiation is achieved in the +z-direction.. [ABSTRACT FROM AUTHOR]

A 12-element THz wideband array antenna on a single layer is proposed in this paper. To optimize its performance, the effect of the number of array elements on the gain was investigated. With a simple planar structure, a wide bandwidth (411.2 GHz–715.9 GHz), a maximum gain of 12.2 dB, and a return loss less than −10 dB, the proposed antenna is an excellent candidate for advanced wireless communication systems. [ABSTRACT FROM AUTHOR]

In this paper, we study the achievable link-layer rate, namely, effective capacity (EC), under the per-user statistical delay quality-of-service (QoS) requirements, for a downlink non-orthogonal multiple access (NOMA) network with $M$ users. Specifically, the $M$ users are assumed to be divided into multiple NOMA pairs. Conventional orthogonal multiple access (OMA) then is applied for inter-NOMA-pairs multiple access. Focusing on the total link-layer rate for a downlink $M$ -user network, we prove that OMA outperforms NOMA when the transmit signal-to-noise ratio (SNR) is small. On the contrary, simulation results show that NOMA prevails over OMA at high values of SNR. Aware of the importance of a two-user NOMA network, we also theoretically investigate the impact of the transmit SNR and the delay QoS requirement on the individual EC performance and the total link-layer rate for a two-user network. Specifically, for delay-constrained and delay-unconstrained users, we prove that for the user with the stronger channel condition in a two-user network, NOMA prevails over OMA when the transmit SNR is large. On the other hand, for the user with the weaker channel condition in a two-user network, it is proved that NOMA outperforms OMA when the transmit SNR is small. Furthermore, for the user with the weaker channel condition, the individual EC in NOMA is limited to a maximum value, even if the transmit SNR goes to infinity. To confirm these insightful conclusions, the closed-form expressions for the individual EC in a two-user network, by applying NOMA or OMA, are derived for both users and then confirmed using Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is presented to increase microwave absorbers bandwidth. The proposed method is based on coupling resonators which consist of a graphene layer at the top, a dielectric spacer and a metallic plate in the bottom. The first resonance frequency of every resonator is calculated by the thickness and relative permittivity of the substrate and the next harmonics are odd coefficients of the first resonance. Absorption rate growth is based on the electric field reinforcement in the graphene plane via tuning graphene Fermi energy. Finally, after combining the resonators and by considering reflection amplitude lower than −10 dB, a bandwidth of 11.9 GHz is obtained from 5.3 to 17.2 GHz for Fermi energy equal to zero. Low-profile and wideband absorption of the proposed structure can be effectively used in radar cross-section applications. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a novel reformulated Auxiliary Functions of Generalized Scattering Matrix (AFGSM) method is presented for analyzing stopband characteristics of asymmetrically loaded helix Slow-Wave Structures (SWSs). In this method, the stopband problem of asymmetrically loaded helix SWS is reduced to the determination of zero transitions of J ‾ - 1 and R ‾ - 1 auxiliary functions in the vicinity of π -point frequency. Besides, Generalized Scattering Matrix (GSM) representations of a single turn of helix SWS are clearly expressed for different asymmetries which can occur with different ways due to angular offset of the rods, variations of support rod permittivity values and widths, angular offset of metal segments, variations in gap between helix to segment and segment width. In order to show the accuracy of the method, the proposed AFGSM method is verified with open literature. The applicability of the proposed method to analyze asymmetrically loaded helix SWS is quite simple and the method accurately determines Relative Stopband Bandwidths (RSBs) under different asymmetries. [ABSTRACT FROM AUTHOR]

Abstract This paper studies an eight-antenna multiple input and multiple output (MIMO) array owning a wide bandwidth to cover the 3.6-GHz (3400–3800 MHz) band for modern mobile terminal applications. The developed eight-antenna array consists of two four-antenna sub-arrays having slight different physical dimensions. The antenna elements are all based on the stepped impedance resonator (SIR) structure, which are positioned along the two long borderlines of the ground plane in the mobile terminal. A wider bandwidth can be realized by properly choosing the electrical length ratio and impedance ratio of the SIR structure, and the system performance can be consequently improved. The measured results of the fabricated prototype show that the value of the return loss is larger than 10 dB and the value of the inter-element isolation is more than 11.7 dB within the entire 3.6-GHz band. Furthermore, the envelop correlation coefficient (ECC) between arbitrary two antenna elements is smaller than 0.1 for the developed eight-antenna MIMO array. Design details of the MIMO array as well as the simulated and experimental results will be given and discussed. [ABSTRACT FROM AUTHOR]

Abstract The purpose of this paper is design of a wide band single layer reflectarray antenna using a new broadband cell. The proposed cell consists of two parts. The first part is a circular patch and the second one is a ring with some additional stubs, which are attached to the patch and ring in a symmetrical form. The circular patch and ring elements are designed at frequencies of 20 GHz and 15 GHz respectively. In order to increase the reflectarray antenna bandwidth, at first the dimensions of the patch, ring and stubs are optimized to attain uniform phase response in the frequency range from 11 GHz to 20 GHz. Then an air layer is considered under the dielectric substrate. The reflectarray antenna is designed based on this optimized wideband unit cell. A wideband horn antenna is also designed as a feed antenna for the proposed reflectarray structure. The reflectarray antenna with horn are simulated. The 1 dB gain-bandwidth of 4.66 GHz is obtained (27.4% fractional bandwidth) in the frequency band of 14.72 GHz to19.38 GHz. Finally, the reflectarray antenna is fabricated and tested. It can be seen that there is a good agreement between simulation and measurement results. [ABSTRACT FROM AUTHOR]

In this paper, a novel wideband and low-profile discrete dielectric lens (DDL) antenna is presented. The proposed unit cells of DDL with the square-pyramid structure can realize wideband antireflection at an air–dielectric interface. By increasing the phase compensation range, the DDL antenna with very large gain bandwidth but large DDL thickness would be achieved. Furthermore, based on the large gain bandwidth technology, a novel multifolded lens structure is proposed to realize the low-profile design, in which a broadband polarization rotation reflection surface is proposed, while a polarized grid is used appropriately. Finally, the proposed multifolded DDL antenna can achieve a very large gain bandwidth, while the thicknesses of the DDL unit cell and the total antenna can be greatly reduced. For demonstration, the proposed multifolded DDL antenna is fabricated and measured. The fabrication was implemented by using a simple and low-cost 3-D printing technology. The results show that the proposed lens antenna can realize a 1 dB gain drop bandwidth of 43%, thickness of less than 1/3 focal-length-to-diameter ratio, and maximum aperture efficiency of 32%. Good agreement can be observed between the measurement and simulation. [ABSTRACT FROM AUTHOR]