-
[show abstract]
[hide abstract]
ABSTRACT: A physical limitation on the power transfer efficiency between two electrically small antennas in the near-field range is presented. By using a Z-parameter which describes the interaction between two antennas for spherical modes in connection with antenna parameters, the maximum power transfer efficiency and the optimum load impedance are shown as functions of the distance between two antennas, the radiation efficiency and the input impedance of the isolated antenna. The theory is verified by a simulation with a small helical antenna, which generates and modes, simultaneously.
IEEE Transactions on Antennas and Propagation 12/2010; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An on-off keying (OOK) receiver for wireless capsule endoscope application is presented, which comprises low-noise amplifier (LNA), band-pass filter, envelope detector, automatic-gain control (AGC) and output buffer. The common-drain-feedback LNA provides wideband input matching. Moreover, a high-frequency envelope detector has been implemented, which is based on OTA-rectifier-peak-detector open loop structure. The storage capacitor of the envelope detector is optimized to obtain good sensitivity and high data rate. A discrete-step AGC is applied for wide input dynamic range, which adopts forward gain-control technique to enhance the settling speed. The carrier frequency is 480 MHz. Sensitivity of the proposed receiver is measured to be -83 dBm, -81 dBm and -80 dBm with data rates of 10 Mbps, 20 Mbps and 40 Mbps, respectively.
Microwave Conference, 2009. EuMC 2009. European; 11/2009
-
[show abstract]
[hide abstract]
ABSTRACT: The effective area for a receiving antenna in a lossy medium is derived by solving a receiving problem of an insulated Hertzian dipole with its gain obtained beforehand. As a result, the effective area in a general medium is found to be the product of the gain and pi/Re[omegaradic{epsivmu*}]<sup>2</sup> . The latter term becomes same as the previous formula, pi/Re[omegaradic{epsivmu}]<sup>2</sup>=4pi/lambda<sup>2</sup> when the medium is only electrically or magnetically lossy. A simulation result of power transmission between two insulated small dipoles validates the theory.
IEEE Transactions on Antennas and Propagation 07/2009; · 2.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An efficiency-enhanced power-amplifier system using dynamic bias switching method is presented. The presented system generates two different voltage sources from one source for drain bias of a RF power amplifier. The drain of the RF power amplifier is biased at low voltage level while the input RF signal is detected to be small. The drain bias is rapidly changed to high voltage level when the input RF signal reaches a certain threshold level. The measured drain bias at V<sub>H</sub> state is 4.6V with the efficiency of the bias switching system, 49% and at V<sub>L</sub> is 2.94V with 86%. The measured result shows that the overall efficiency of the proposed RF power amplifier is improved by 62% compared to that of the fixed bias amplifier, when OFDM signal with bandwidth 8.46MHz is applied.
Microwave Conference, 2008. EuMC 2008. 38th European; 12/2008
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, a possibility of applying the method of auxiliary sources (MAS) in analyzing the characteristics of insulated wire antennas in layered media has been explored. The existing DGF-MAS technique for the analysis of bare antenna in layered media has been revisited and extended to analyze insulated antennas, which has been overlooked by other researchers. Numerical examples have been presented for several interaction problems to demonstrate validity, accuracy, and efficiency of the proposed technique. The proposed method can also be applied to the analysis of antennas immersed in arbitrary shaped insulation layer. Furthermore, analysis of the wire antenna with a spherically layered insulator which is eccentric to a spherically layered medium and more practical case of insulated antenna problem such as the wire antenna with a spherically layered insulator in a cylindrically layered medium, which models the wireless capsule endoscopy application roughly, is under investigation.
Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
-
[show abstract]
[hide abstract]
ABSTRACT: The concept of double-Lorentz (DL) transmission lines (TL) provides two additional degrees of freedom in realizing triband microwave devices. The triband operation is accomplished by the flexible phase slope characteristic of the DL TL with the frequency. In this article, the theory, design procedure, and implementation of the triband quarter-wave (λ/4) DL TL are presented. Moreover, the triband λ/4 open-circuit stub and triband branch-line coupler (BLC) are introduced for the application of mobile TV service. The simulated and measured results of these triband components are also presented. The λ/4 DL TL open-circuit stub demonstrates insertion loss larger than 17 dB at each target band. The triband BLC has S-parameters of output larger than −4.569 dB, return losses larger than 14 dB, isolations larger than 15 dB, phase differences of output 90° ± 5° at each target band. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1174–1177, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23311
Microwave and Optical Technology Letters 04/2008; 50(5):1174 - 1177. · 0.62 Impact Factor
-
IEICE Transactions. 01/2008; 91-C:1969-1970.
-
[show abstract]
[hide abstract]
ABSTRACT: Quality factors (Q) of small insulated antennas in a lossy dielectric medium are evaluated using Chu's equivalent circuits of TM<sub>01</sub> and TE<sub>01</sub> spherical waves. Using the evaluated Q, the upper limit of radiation efficiency for the required bandwidth is calculated for the link loss estimation. The result shows that a magnetic type antenna has much higher Q and the advantage in its radiation efficiency is sacrificed at low frequency for the required bandwidth.
Microwave Conference, 2007. KJMW 2007. Korea-Japan; 12/2007
-
[show abstract]
[hide abstract]
ABSTRACT: A 60-GHz coplanar waveguide (CPW)-fed dielectric-resonator-above-patch (DRAP) antenna using micromachining technology is presented. In the proposed structure, the patch is elevated in the air with support of a dielectric-post, and a rectangular dielectric resonator antenna (RDRA) is fixed above the patch. The size of the RDR is 1 × 0.8 mm2. We introduce a novel use of micromachining technology (solder ball bumping and flip chip bonding) for the first time to exactingly align and bond a small RDRA with a feed-slot. The fabricated antenna shows broadband characteristics such as −10-dB bandwidth of 17.5 GHz from 54 to 71.5 GHz, corresponding to a fractional bandwidth of 29.2%. Moreover, the radiation pattern could be measured by integrating the proposed antenna with a 60-GHz VCO. An antenna gain of about 3.6 dBi at 60 GHz is measured. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1859–1861, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22632
Microwave and Optical Technology Letters 07/2007; 49(8):1859 - 1861. · 0.62 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: There has been much interest in accurate and fast numerical analysis of 1-D periodic planar structures. Recently the efficient method to obtain 1-D periodic Green's functions in planar structure was proposed (Baccarelli et al., 2006). Here we propose the efficient method for the evaluation of impedance matrix in applying the method of moment.
Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: A new structure of on-off keying(OOK) transmitter with low power consumption and high data rate is proposed using a current-reused CMOS differential LC-VCO for wireless capsule endoscope application. The carrier frequency (440 MHz) of the transmitter is determined as the minimum loss frequency point considering the antenna loss and the loss property of human body, etc. The transmitter is able to output 0 dBm of power at the single-ended output to a monopole 50-Ohm antenna to meet the demands of high-data rate speed (40 Mb/s) and short range (15-cm) wireless communication. This transmitter, has been fabricated using 0.18-mum CMOS technology, consumes only 860-muA of current from a 3 V supply.
Microwave Symposium, 2007. IEEE/MTT-S International; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: A novel harmonic-suppressed microstrip low-pass filter (LPF) is proposed which is composed of defected ground structures and stepped-impedance shunt stubs as series L and shunt C components in the pass-band. Due to the attenuation poles of two kinds of resonators, it is found that harmonic responses are not only suppressed effectively, but the rejection in the stop-band is also deep and wide. Besides, the proposed LPF can be compactly implemented since both kinds of resonators have slow-wave characteristics
IEEE Microwave and Wireless Components Letters 07/2007; · 1.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A novel bias-switching scheme for a high-efficiency power amplifier is proposed. Two voltage levels for the drain bias of the RF power amplifier are generated using a combination of a class E dc/ac inverter and a class E rectifier with offset voltage. When signal peaks occur, the output of the class E dc/ac inverter is rectified and the rectified dc is added to the offset voltage by the class E rectifier, which boosts the drain bias of the RF power amplifier. Except during peaks, the drain bias of the RF power amplifier is connected to the offset voltage directly. Since the efficiency when there are no peaks is very high due to the direct connection between the offset voltage and drain bias, the overall efficiency of the RF power amplifier can be improved dramatically in high peak-to-average power ratio (PAPR) systems. The measured results show that the drain bias of the RF power amplifier is boosted up to approximately 1.8 times the offset voltage when the RF peaks generate. The overall efficiency of the proposed bias-switching amplifier is improved by 62% compared to that of the fixed bias amplifier in high PAPR systems
IEEE Transactions on Microwave Theory and Techniques 05/2007; · 1.85 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The dyadic Green's function in spherically layered media is considered by assuming that source and field points can be located anywhere. After manipulations from the expression of the dyadic Green's function based on the reflections and transmissions of the scalar waves, the dyadic Green's function in terms of the spherical vector wave functions is newly constructed and also the coefficients of the scattering dyadic Green's function are derived in a simple form. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1142–1143, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI.10.1002/mop.22374
Microwave and Optical Technology Letters 04/2007; 49(5):1142 - 1143. · 0.62 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This letter presents a power re-use technique for pulsed oscillating amplifiers. By rectifying the upconverted switching harmonics of the pulsed oscillating output, some portions of wasted power can be returned to the power supply. The efficiency of the amplifier can be enhanced without degradation of the linearity. The measured results show that the overall efficiency of the amplifier with power re-use is improved up to 22% compared to the pulsed oscillating amplifier without the power re-use at the PCS band
IEEE Microwave and Wireless Components Letters 11/2006; · 1.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: It was demonstrated that a field from a large phase conjugate array is a statistical estimate of the spatial correlation of the wave propagation channel. In many situations the spatial correlation is known, and decays very fast. Hence the focusing of electromagnetic field within a few wavelength distances can be achieved by time reversal as seen in simulations, and the lowest limit of the beamwidth of the focused pulse can be estimated without any effort.
Antennas and Propagation Society International Symposium, 2005 IEEE; 08/2005
-
[show abstract]
[hide abstract]
ABSTRACT: This letter presents a novel high-efficiency linear transmitter using pulse-width modulation (PWM). An envelope of radio frequency (RF) input signal is modulated by the PWM. The modulated signal is applied to the gate bias of a class F injection-locked power oscillator and switches it on and off. By filtering the pulsed oscillating output signal of the injection-locked oscillator using high-Q bandpass filter, the input signal is restored. This technique enables the transmitter to have high efficiency with good linearity. Also, there is little distortion near saturation point of an active device. The measured results show efficiency of 54.6% and very good linearity in PCS band at 26.4-dBm output power.
IEEE Microwave and Wireless Components Letters 05/2005; · 1.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The method of auxiliary sources (MAS) has been used for the numerical solution of a variety of electromagnetic problems successfully. Since MAS can be considered as a modified or generalized version of the standard surface integral equation technique (SIE), it has the interior resonance problem, but the remedies to this problem have not been investigated yet. In this letter, it is shown that the interior resonance problem in applying MAS can be completely removed using combined-source solution (CSS).
IEEE Microwave and Wireless Components Letters 04/2005; · 1.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This letter presents a new method to reduce the phase noise in oscillator based on the loaded Q improvement approach. A hairpin resonator is weakly coupled to the two microstrip lines to improve the loaded Q of it and the dual feedback topology is used to enable the start-up oscillation condition to be satisfied. The high loaded Q property of the resonator in the proposed oscillator circuit is analyzed using the CAD simulation. For comparison the phase noise performances of the conventional hairpin resonator oscillator and the oscillator using the dual feedback are measured. Measurements show that the oscillator using the dual feedback exhibits a low phase noise performance of -109.1 dBc/Hz at 100-kHz offset at 10 GHz, which is reduced by about 10 dB compared to that of the conventional one.
IEEE Microwave and Wireless Components Letters 02/2005; · 1.72 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper presents a new technique to design high-Q active resonators. The active resonators are then used in the design of low phase-noise oscillators. The proposed new technique uses an amplifier to generate a negative resistance, which compensates for the resonator losses and increases the Q factor. The active resonator using this technique shows a high loaded Q factor of 548.62 from measurement at the fixed 10-GHz resonant frequency. Considerations to design a voltage tunable active resonator is given and measurements show that the loaded Q factors exceed 500 with a 120-MHz tuning range. A low phase-noise free-running and voltage-controlled oscillator (VCO) were designed as an application of the proposed active resonators. The phase noise of the free-running oscillator using the active resonator is -114.36 dBc/Hz at 100-kHz offset, which is 14 dB lower than the phase noise of the passive resonator oscillator. In the case of a VCO using the active resonator, the phase-noise performance is below -110 dBc/Hz over the whole tuning range, which is lower 13 dB compared to the passive resonator VCO. The total dc power consumptions are approximately 500 mW.
IEEE Transactions on Microwave Theory and Techniques 12/2004; · 1.85 Impact Factor
