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"Inventi Impact: Microwave" focuses on the research and development aspects of radio frequency technology. Published quarterly in print and online, it aims to cater to the professionals and policy makers in the field, as well as the general public.
This paper pursued both the lower operating power limit and small area of on-chip rectifiers
for microwave wireless power transfer (MWPT). RF–DC charge pump rectifiers can operate in the fast
switching limit at a high frequency of 920 MHz even with a small stage capacitor Cin of 100 fF, which
contributes to an area reduction in the on-chip rectifiers. Circuit design starts with Cin determined as
small as possible, followed by the determination of switching transistors and the number of stages.
Even at an extremely low input power of 1 μW, wiring resistance in RF inputs is critical. Routing
of the RF inputs is designed in line with stage capacitors. Bonding pad structure also affects the
lower input power limit. Ground-shielded pad design can reduce the lower limit. Various types of
RF–DC charge pump rectifiers are fabricated in 65 nm CMOS. An ultra-low-power diode RF–DC
charge pump rectifier with 32 stages had a lower input power limit of −31.7 dBm at an output voltage
of 1.0 V. Its small silicon area of 0.011 mm2 allows RF–DC rectifiers to be integrated in sensor ICs.
More advanced technology providing MIM capacitors with higher capacitance density and placing
switching MOSFETs under the MIM capacitors will further reduce the area of RF–DC charge pump
rectifiers, allowing them to be integrated in sensor ICs....
A novel circular polarized rectenna with out-of-band suppression is proposed in this paper. The circular polarization is realized by\ncorner perturbation on a rectangular radiation patch and enhanced by a diagonal slim slot etched at the center of the patch. An\nopen stub connecting to the quarter wavelength impedance transformer is used to suppress out-of-band wave through harmonics\nnotching. The results of simulations and experiments agree very well, which show that the rectenna obtained Ã¢Ë?â??19 dB return loss at\n2.4GHz and Ã¢Ë?â??15.5 dB, Ã¢Ë?â??18.1 dB, and Ã¢Ë?â??11.4 dB suppression on second, third, and fourth harmonic frequency bands, respectively.The\nreflection coefficient in overall out-of-band, up to 10GHz, is limited up to Ã¢Ë?â??3 dB. Integrated with a voltage doubling rectification\ncircuit, the proposed rectenna can obtain 75.5% RF-to-DC conversion efficiency....
This paper presents a dual-band band-pass filter using modified cross-coupled step-impedance and capacitively loaded hairpin resonators for WLAN systems. The proposed filter has been designed to operate at a fundamental frequency of 2.4?GHz and the first harmonics frequency of 5.2?GHz. The techniques of step impedance and load capacitor are combined in the design of the proposed filter. In particular, the techniques of modified cross-coupling and overlap resonators are applied to improve the response of insertion losses S 21 at the first harmonic frequency of 5.2?GHz. The simulated and experimental results of insertion losses and return losses are better than 3?dB and 20?dB, respectively, at the operating frequencies....
A dual-band SiGe HBT frequency-tunable and phase-shifting differential amplifier has been developed for the future active phased\r\narray antennas with a multiband, multibeam, and multitarget tracking operation. The amplifier uses varactor-loaded, stacked\r\nLC resonators in the design of the output circuit in order to provide frequency-tunable and phase-shifting capabilities for dual\r\nfrequencies. By utilizing the varactor-loaded LC resonator, which has a variable resonant frequency and a large insertion phase\r\nvariation, frequency-tunable and phase-shifting performances become available. Moreover, by using the stacked configuration,\r\nthe frequency and insertion phase can be varied independently for dual frequencies. A dual-band SiGe HBT differential amplifier\r\nhas achieved a lower-frequency tuning range of 0.56 to 0.7 GHz for a higher fixed frequency of 0.97 GHz as well as a higherfrequency\r\ntuning range of 0.92 to 1.01 GHz for a lower fixed frequency of 0.63 GHz. A lower-frequency phase variation of 99? and\r\na higher-frequency phase variation of 90.3? have been accomplished at 0.63 and 0.97 GHz, respectively. This is the first report on\r\nthe dual-band differential amplifier with frequency-tunable and phase-shifting capabilities....
Performance evaluation is an important aspect in the study of microwave-absorbing\nmaterial coatings. The reflectivity of the incident wave is usually taken as the performance indicator.\nThere have been various methods to directly or indirectly measure the reflectivity, but existing\nmethods are mostly cumbersome and require a strict testing environment. What is more, they cannot\nbe applied to field measurement. In this paper, we propose a scheme to achieve field performance\nevaluation of microwave-absorbing materials, which adopts a small H-plane sectoral horn antenna\nas the testing probe and a small microwave reflectometer as the indicator. When the size of the\nH-plane sectoral horn antenna is specially designed, the field distribution at the antenna aperture can\nbe approximated as a plane wave similar to the far field of the microwave emitted by a radar unit.\nTherefore, the reflectivity can be obtained by a near-field measurement. We conducted experiments\non a kind of ferrite-based microwave-absorbing material at X band (8.2Ã¢â?¬â??12.4 GHz) to validate the\nscheme. The experimental results show that the reflectivity is in agreement with the reference data\nmeasured by the conventional method as a whole....
A simple metasurface integrated with horn antenna exhibiting wide bandwidth, covering
full Ku-band using 3D printing is presented. It consists of a 3D-printed horn and a 3D-printed
phase transformation surface placed at the horn aperture. Considering the non-uniform wavefront
of 3D printed horn, the proposed 3D-printed phase transformation surface is configured by unit
cells, consisting of a cube in the centre which is supported by perpendicular cylindrical rods from its
sides. Placement of proposed surface helps to improve the field over the horn aperture, resulting in
lower phase variations. Both simulated and measured results show good radiation characteristics
with lower side lobe levels in both E- and H-planes. Additionally, there is an overall increment in
directivity with peak measured directivity up to 24.8 dBi and improvement in aperture efficiency
of about 35% to 72% in the frequency range from 10–18 GHz. The total weight of the proposed
antenna is about 345.37 g, which is significantly light weight. Moreover, it is a low cost and raid
manufacturing solution using 3D printing technology....
With the rapid development of materials science and medical imaging technology, traditional optimization algorithms cannot
solve the problem of inverse scattering of complex scatterers well. Therefore, more and more imaging algorithms for solving
complex scatterers were proposed. In this paper, a novel hybrid algorithm is put forward for the microwave imaging problem.
First, the proposed algorithm improves the search path of the traditional sine cosine algorithm, which obtains better global search
capability. Second, the least square is introduced to form judging and contrasting mechanisms, which forms the parallel algorithm
simultaneously, in order to make the proposed algorithm more suitable for the diverse microwave imaging problem...........
High-spatial-resolution land-surface temperature is required for several applications
such as hydrological or climate studies. Global estimates of surface temperature are available
from sensors observing in the infrared (IR), but without ‘all-weather’ observing capability. Passive
microwave (MW) instruments can also be used to provide surface-temperature measurements but
suffer from coarser spatial resolutions. To increase their resolution, a downscaling methodology
applicable over different land environments and at any time of the day is proposed................
A microwave photonic converter based on microwave pre-upconversion is proposed
and experimentally demonstrated. Only a single Mach–Zehnder modulator (MZM) is used in
the converter system so that the complexity and bandwidth limiting of the link can be reduced.
The transmitted and received signals before entering the MZM are firstly upconverted to high
frequency (HF) by a microwave upconverter. The HF and local oscillator (LO) signals are combined
to drive the MZM. Carrier-suppressed double-sideband (CS-DSB) modulation is introduced to the
MZM for effective spectrum utilization. Then, the target signals can be obtained by photoelectric
conversion and beating. Experimental results confirm that the mixing spurs including harmonics and
intermodulation as well as original signals are all out of system frequency band from 0.8–18 GHz, and
the in-band spurious suppression of at least 40 dBc is achieved. In addition, the spurious-free dynamic
range (SFDR) reaches 86.23 dB·HZ2/3 for upconversion and 80.95 dB·HZ2/3 for downconversion.
The proposed microwave photonic converter provides a wideband and high-purity alternative for
the applications of radars and signal processing....
The absorbent resin for Cu2+ removal was prepared under microwave irradiation through grafting acrylamide (AM) and acrylic\nacid (AA) to cellulose. The initiator is a kind of redox system composed of potassium persulfate/sodium thiosulfate. The\ncrosslinking agent is...................
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