In general, Micropower Impulse Radar (MIR) depends on Ultra-Wideband (UWB) transmission systems. UWB technology can supply innovative new systems and products that have an obvious value for radar and communications uses. Important applications include bridge-deck inspection systems, ground penetrating radar, mine detection, and precise distance resolution for such things as liquid level measurement. Most of these UWB inspection and measurement methods have some unique qualities, which need to be pursued. Therefore, in considering changes to Part 15 the FCC needs to take into account the unique features of UWB technology. MIR is applicable to two general types of UWB systems: radar systems and communications systems. Currently LLNL and its licensees are focusing on radar or radar type systems. LLNL is evaluating MIR for specialized communication systems. MIR is a relatively low power technology. Therefore, MIR systems seem to have a low potential for causing harmful interference to other users of the spectrum since the transmitted signal is spread over a wide bandwidth, which results in a relatively low spectral power density.

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Response to FCC 98-208 notice of inquiry in the matter of revision of part 15 of the commission's rules regarding ultra-wideband transmission systems

In-band full-duplex (IBFD) technology can enable unique system capabilities and network architectures by allowing devices to transmit and receive on the same frequency at the same time. While previously considered impossible, this ability can now be used to optimize resource sharing within the crowded frequency spectrum for various communication systems, including 5G new radio. The potential of these IBFD systems can only be realized if each device incorporates a sufficient number of self-interference cancellation techniques to ensure that its receivers do not saturate. This tutorial survey offers the most comprehensive collection to date of these techniques and discusses how all of them can be implemented within the different domains of a typical transceiver. In addition, the results of a novel IBFD system study are presented for more than 50 demonstrated communication systems with more than 80 different measurement scenarios. The various system parameters are then combined into a new figure of merit, which can be used to propel future research and accelerate the inclusion of IBFD technology within an upcoming wireless standard.

In-Band Full-Duplex Technology: Techniques and Systems Survey

Microwave pyrolysis (MP) has emerged as a promising technique to valorize agricultural wastes (AW) into biofuels, comprising biochar, bio-oil, and syngas. To fill the research gap, we review the state-of-the-art MP conversion of AW into value-added biofuels, including the influence of feedstock composition, new reactor designs, operating conditions, catalytic applications, and reaction mechanisms. The techno-economic and environmental impacts are discussed together with key implications for future development. Microwave valorization of AW to biofuels represents an economically viable cum environmentally-benign approach by virtue of (i) high availability of AW, (ii) scalable process, (iii) great potentiality for continuous operation, and (iv) thermochemical process with positive energy ratio. For continuous MP, the microwave heating distribution, products yield, and reactor design have not yet fully explored due to the limited understanding on microwave propagation pattern, materials handling, and varying feedstock compositions. The utilization of AW as biofuels feedstock offers several environmental advantages in terms of improved biomass utilization, enhanced carbon sequestration, and lower sulphur emission. The toxicity of bio-oil can be reduced by adding metal oxide catalysts (CaO, CuO, MgO, and NiO) to lessen its content of polycyclic aromatic hydrocarbons. The process of continuous MP can be optimized by coupling shaftless auger and multiple magnetron to improve the quality of the biofuel, and uniformity of microwave heating. It is envisaged that continuous conversion of AW to biofuels is a sustainable, low carbon footprint, and alternative energy generation route, provided that the appropriate catalyst, effective condenser, and self-purging condition are chosen.

Progress in microwave pyrolysis conversion of agricultural waste to value-added biofuels: A batch to continuous approach

Impedance matching networks for nonlinear devices such as amplifiers and rectifiers are normally very challenging to design, particularly for broadband and multiband devices. A novel design concept for a broadband high-efficiency rectenna without using matching networks is presented in this paper for the first time. An off-center-fed dipole antenna with relatively high input impedance over a wide frequency band is proposed. The antenna impedance can be tuned to the desired value and directly provides a complex conjugate match to the impedance of a rectifier. The received RF power by the antenna can be delivered to the rectifier efficiently without using impedance matching networks; thus, the proposed rectenna is of a simple structure, low cost, and compact size. In addition, the rectenna can work well under different operating conditions and using different types of rectifying diodes. A rectenna has been designed and made based on this concept. The measured results show that the rectenna is of high power conversion efficiency (more than 60%) in two wide bands, which are 0.9–1.1 and 1.8–2.5 GHz, for mobile, Wi-Fi, and ISM bands. Moreover, by using different diodes, the rectenna can maintain its wide bandwidth and high efficiency over a wide range of input power levels (from 0 to 23 dBm) and load values (from 200 to 2000 Ω). It is, therefore, suitable for high-efficiency wireless power transfer or energy harvesting applications. The proposed rectenna is general and simple in structure without the need for a matching network hence is of great significance for many applications.

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Matching Network Elimination in Broadband Rectennas for High-Efficiency Wireless Power Transfer and Energy Harvesting

Wireless power transmission was conceptualized nearly a century ago. Certain achievements made to date have made power harvesting a reality, capable of providing alternative sources of energy. This review provides a summ ary of radio frequency (RF) power harvesting technologies in order to serve as a guide for the design of RF energy harvesting units. Since energy harvesting circuits are designed to operate with relatively small voltages and currents, they rely on state-of-the-art electrical technology for obtaining high efficiency. Thus, comprehensive analysis and discussions of various designs and their tradeoffs are included. Finally, recent applications of RF power harvesting are outlined.

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RF power harvesting: a review on designing methodologies and applications

A transmission-line-based decoupling technique for dual-polarized multiple-input and multiple-output (MIMO) antenna arrays is presented and analyzed. The proposed scheme enables well-canceled coupling for the adjacent elements under co-polarization, without degrading the isolation of the cross-polarized ports. First, a decoupling network based on the presented method for a $2 \times 2$ MIMO array is provided, along with a comprehensive design procedure. Calculations and simulations are operated to verify decoupling performance. For further verification, a $2 \times 2$ dual-polarized patch array with the proposed decoupling method is developed. The decoupling network characterizes low profile, compact size, and low insertion loss, which is realized in a single layer. Measurements denote that the isolations between the co-polarized elements are improved from 16 to 20 dB to over 30 dB after decoupling at the center frequency of 2.45 GHz. Subsequently, based on the proposed $2 \times 2$ decoupling method, a decoupling network for large-scale dual-polarized MIMO arrays is presented. A design example of a $4 \times 4$ dual-polarized patch antenna array is established. Full-wave simulations indicate that the isolations are enhanced to better than 30 dB with a small insertion loss of less than 0.45 dB and can widely be used for phased array and massive MIMO array systems.

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A Transmission-Line-Based Decoupling Method for MIMO Antenna Arrays

In this paper, a stub-loaded transmission line that is used to design Wilkinson power dividers with arbitrary power division ratios is discussed in depth. Power division is always required in most wireless/wireline communications such as industrial systems and consumer electronics. However, the design of an unequal Wilkinson power divider, particularly with a large division ratio, becomes a challenge in engineering because of the impractical realization of the high- or low-impedance transmission lines on a dielectric substrate. In this paper, we first introduce a transmission-line structure and perform theoretical analysis. The derivations reveal that the studied structure can be utilized to design Wilkinson power dividers with equal or unequal power divisions. For demonstration purposes, two power dividers with division ratios of 1 : 1 and 1 : 9, respectively, and operating in the popular industrial, scientific, and radio-frequency identification frequency bands are implemented by loading distributed transmission-line elements, namely, open- or short-circuited stubs. The demonstrators are also fabricated and validated by measurements, and good agreement between the experimental results and the simulated responses is observed.

Novel Design of Wilkinson Power Dividers With Arbitrary Power Division Ratios

A compact reconfigurable rectifying antenna (rectenna) has been proposed for 5.2- and 5.8- GHz microwave power transmission. The proposed rectenna consists of a frequency reconfigurable microstrip antenna and a frequency reconfigurable rectifying circuit. Here, the use of the odd-symmetry mode has significantly cut down the antenna size by half. By controlling the switches installed in the antenna and the rectifying circuit, the rectenna is able to switch operation between 5.2 and 5.8 GHz. Simulated conversion efficiencies of 70.5% and 69.4% are achievable at the operating frequencies of 5.2 and 5.8 GHz, respectively, when the rectenna is given with an input power of 16.5 dBm. Experiment has been conducted to verify the design idea. Due to fabrication tolerances and parametric deviation of the actual diode, the resonant frequencies of the rectenna are measured to be 4.9 and 5.9 GHz. When supplied with input powers of 16 and 15 dBm, the measured maximum conversion efficiencies of the proposed rectenna are found to be 65.2% and 64.8% at 4.9 and 5.9 GHz, respectively, which are higher than its contemporary counterparts.

A Compact Frequency Reconfigurable Rectenna for 5.2- and 5.8-GHz Wireless Power Transmission

A broadband polarization reconfigurable rectenna is proposed, which can operate in three polarization modes. The receiving antenna of the rectenna is a polarization reconfigurable planar monopole antenna. By installing switches on the feeding network, the antenna can switch to receive electromagnetic (EM) waves with different polarizations, including linear polarization (LP), right-hand and left-hand circular polarizations (RHCP/LHCP). To achieve stable conversion efficiency of the rectenna ( $\eta_{r}$ ) in all the modes within a wide frequency band, a tunable matching network is inserted between the rectifying circuit and the antenna. The measured $\eta_{r}$ changes from 23.8% to 31.9% in the LP mode within 5.1–5.8 GHz and from 22.7% to 24.5% in the CP modes over 5.8–6 GHz. Compared to rectennas with conventional broadband matching network, the proposed rectenna exhibits more stable conversion efficiency.

Polarization Reconfigurable Broadband Rectenna With Tunable Matching Network for Microwave Power Transmission

A new microstrip ultra-wideband (UWB) bandpass filter (BPF) with two sharp notches using E-shaped resonator is proposed in this letter. The circuit topology and its corresponding electrical parameters of the initial microstrip UWB BPF are achieved by a variation of genetic algorithm (GA). Then, the resonance properties of the E-shaped resonator are studied. Results reveal that the multiple-mode property of the E-shaped resonator can be utilized in the UWB BPF design to achieve dual band-notched performance. To validate the design concept, a microstrip UWB BPF with two notched bands respectively centered at frequencies of 5.9 GHz and 8.0 GHz is designed and fabricated. Both simulation and experimental results are provided with good agreement.

Jia-Lin Li

Papers

A Transmission-Line-Based Decoupling Method for MIMO Antenna Arrays

Novel Design of Wilkinson Power Dividers With Arbitrary Power Division Ratios

A Compact Frequency Reconfigurable Rectenna for 5.2- and 5.8-GHz Wireless Power Transmission

Polarization Reconfigurable Broadband Rectenna With Tunable Matching Network for Microwave Power Transmission

Compact Microstrip UWB Bandpass Filter With Dual Notched Bands Using E-Shaped Resonator