A 2-way symmetrical Doherty power amplifier (PA) with high efficiency is presented. This amplifier delivers 49.2 dBm (83 W) of saturated output power and 63% drain efficiency with 38.2 dB of power gain at 460MHz. The drain efficiency at 6 dB backed-off power level shows about 62%. After digital pre-distortion (DPD) system corrected, about 48% power-added efficiency (PAE) at 42.2 dBm (16.6 W) average output power has been demonstrated, while achieving -52 dBc (-28 dBc before linearization) Adjacent Channel Leakage Ratio (ACLR) at 20 MHz offset using a LTE-Advanced input signal with 6.5 dB peak to average ratio (PAR) to meet the IMT-Advanced system requirements. We also used a π type structure network based on lumped elements to replace the traditional Doherty amplifier 1/4λ transmission line, and compared the performance.
A compact multimode bandpass filter with low insertion loss, high stopband rejection and wide stopband bandwidth is introduced by using cascaded multimode resonators and compact loading cells in combination. The measured minimum insertion loss is of 1.7dB including the connector loss in the input and output ports in the passband of 5.7~8 GHz. Through the use of cascaded multimode resonators, steep skirt selectivity and wide stopband up to 18 GHz can be achieved. When incorporated with the lowpass loading cells, which have elliptical low-pass response by using the source-load coupling, the stopband of the proposed filter can be further extended up to 40 GHz, with only negligible influence on the passband performance.
An analysis for circularly-polarized (CP) ring slot antennas fed by a coupling strip with resistive loading is presented. By treating the antenna as a two-port circuit, the amplitudes and phases of two orthogonal modes excited from the slot antenna can be found and expressed in terms of the S parameters of the circuit. The axial ratio calculated through the S parameters has a good agreement with that obtained from the pattern simulation of IE3D. The effects of varying key parameters of the coupling strip on the amplitudes and phases of the dual orthogonal modes are investigated in detail.
This paper presents a practical direction finding receiver based on six-port networks. To expand beam direction angles, improve measurement accuracy, and avoid phase ambiguity, we introduce a dual-baseline architecture into the direction finding receiver. We also propose a calibration technique based on support vector regression (SVR) for the following reasons: The nonlinearity of diode detectors and the asymmetry of six-port junctions can cause measurement phase errors. Moreover, the transmission parameters of two microwave channels differ with changes in received power. Results show that the SVR model can achieve a direction finding accuracy of 0.2932°.
Preparing the 3D-geometry models to perform electromagnetic compatibility (EMC) numerical simulations can be tedious and time consuming. Furthermore, the need to include the test setup in the models, in order to validate the software, by comparing the numerical results with the measured data, may lead to unwieldy simulation models with often unaordable computational costs. In this paper, we provide strategies for optimizing and simplifying the modeling process, together with guidelines for achieving the most unfavorable case in the simulation of EMC problems, as required for a certication process. A test case from the European FP7 HIRF-SE project is analyzed in this paper as an example of how to identify the unnecessary elements for the simulation, while retaining the essential physics of the problem.
In this paper, we report on the design, fabrication and characterization of a slot antenna on quarter wavelength silicon substrate coupled to a Titanium microbolometer for detection at 94 GHz. The detector was fabricated using conventional photolithographic and microfabrication techniques. The detector exhibited a responsivity of 0.779 V/W, a noise equivalent power (NEP) of 10.2 nW/√Hz, and a time constant of 3.88 μsec.
In this paper, a new design of a dual-polarized antenna with high isolation and low cross polarization is proposed. The main radiation structures comprise two pairs of petaloid patches, which are fed by coaxial lines. Behind the patches, a U-shaped ground is placed to improve the front-to-back ratio of the antenna. Stable and symmetric radiation patterns at slanted ±45° polarization have been obtained within the frequency band 1.71-2.17 GHz. A return loss of -14 dB is achieved and measured isolation between the two input ports is over 31 dB. The 3 dB beamwidths of the two polarizations is stable (65°) and the average gain of the proposed antenna is about 9dBi across the whole frequency band.
In this paper, a filter based on Composite Right/Left Handed (CRLH) structures is presented, wide pass band is obtained due to the balanced CRLH properties. Besides, it has Complementary Split-Ring Resonator (CSRR) units etched on ground plane, which improves signal rejection in its upper stop band. The CSRRs work as a stop band filter in a band near the main pass band of the filter and bring in equivalent negative permittivity. CSRRs and CRLH units occupy the two sides of substrate respectively and have little mutual affection in the pass band, so either structure can be designed independently, without considering the effect from the other. The improvement occupy no additional space, the size is as large as the original filter. Detailed design procedure is illustrated. Good agreements among simulation and measurement results are achieved. In addition, the filter has a semi-enclosed structure and compact size, and the performance is greatly improved.
A time-domain approach for distortion analysis of electromagnetic eld senors is developed in Laguerre functions subspace. Using Laguerre convolution preservation property, it is proved that every electromagnetic eld sensor corresponds to an equivalent discrete-time LTI system. The equivalent discrete-time system is compared to a reference system as a measure of distortion. Further, this analysis may be performed repeatedly to obtain a bandwidth-limited distortion characteristic. The method is employed to compare the distortion characteristic of an asymptotic conical dipole (ACD) to wire monopoles of various lengths. A time-domain simulation is performed in order to nd the distortion characteristics by solving an electric eld integral equation (EFIE) using the method of moments (MoM).
A compact microstrip-line dual-band bandpass filter using a short stub-loaded resonator is presented. The resonator is formed by loading one short stub in shunt to a simple uniform impedance line. A key merit of the filter configuration is that the center frequency and bandwidth of the first passband can be conveniently controlled by properly adjusting the lengths of the short stubs and the coupling between the short stubs, whereas those of the second passband are fixed. To illustrate the concept, a third-order dual-band filter is designed, fabricated and measured. Simulated and measured results are found to be in good agreement with each other.
A compact dual-band CPW-fed triangle-shaped antenna is proposed for applications in 2.4/5 GHz WLAN and RFID. The designed antenna, including ground plane, is only 28 mm in height and 26 mm in width. By introducing a Π-shaped slot and a T-shaped strip, the proposed antenna can generate two separate impedance bandwidths. Prototypes of the proposed antenna have been constructed and tested. The measured impedance bandwidths, ranging from 2.36 GHz to 2.50 GHz and from 5.01 GHz to 6.33 GHz separately, are obtained with return loss less than -10.00 dB, which meet the required bandwidths specification of WLAN and RFID. Good omni-directional radiation and appropriate gain characteristics in the desired frequency bands have been achieved.
The effect of temperature on the photonic band gap has been investigated. One dimensional photonic crystal in the form of Si/air multilayer system has been studied in this communication. The refractive index of silicon layers is taken as a function of temperature and wavelength both. Therefore, this study may be considered to be physically more realistic. It may be useful for computing the optical properties for wider range of wavelength as well as temperature. We can use the proposed structure as temperature sensing device, narrow band optical filter and in many optical systems.
In this paper, a bandwidth enhancement technique of asymmetrical slot antennas with two different excitation methods is presented. One method of excitation is the microstrip line feed, and the other is the coplanar waveguide feed. The rectangular slot excited by microstrip line feed gives an impedance bandwidth of 14.76% (|S11| < −10 dB). When the rectangular slot is excited by a coplanar waveguide (CPW), it gives an impedance bandwidth of 26.61%. Both impedance and radiation characteristics of these antennas are studied.
A Gunn mounted active microstrip slot-ring antenna (ASRA) has been investigated for the reception of FM microwave signal. Current well/valley phenomenon has been successfully utilized to demodulate the modulation information. The monolithic behaviour of an active slot-ring antenna as a lock-in amplifier, FM (Frequency Modulation) to AM (Amplitude Modulation) converter and square law detector has been demonstrated in this paper. Theoretical analysis coupled with experimental results has been presented. The proposed receiving scheme is unique in the sense that it does not require IF electronics for the purpose of demodulation. It also works well in a multi-channel environment due to the excellent noise-squelching property of an Injection Locked Gunn Oscillator.
A novel circular slot antenna with two pairs of T-shaped slots is proposed for satisfying WLAN and WiMAX applications simultaneously. The proposed antenna consists of a 50 Ω microstrip feed line with a tuning stub on the top and a circular slot ground plane with an embedded straight strip and two pairs of etched T-shaped slots on the bottom side. By carefully adjusting the length of the straight strip, the proposed antenna can operate in two separate bands. With the use of two pairs of T-shaped slots, a new resonant frequency has been excited, and the impedance bandwidth can be widened. The measured results show that the 10 dB return loss bandwidths of the proposed antenna are 760 MHz (3.18-3.94 GHz) and 1002 MHz (5.05-6.07 GHz), which can cover both 5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. The design evolution and parametric study of the proposed antenna are presented to provide information for designing and optimizing such an antenna. Furthermore, good omnidirectional radiation patterns with appreciable antenna gain are obtained over the operating bands.
Reinforced concrete structures (RCS) have potential application in civil engineering and with the advent of nuclear engineering RCS to be capable enough to withstanding a variety of adverse environmental conditions. However, failures/loss of durability of designed structures due to premature reinforcement corrosion of rebar is a major constrain. Growing concern of safety of structure due to pre-mature deterioration has led to a great demand for development of non-destructive and non-contact testing techniques for monitoring and assessing health of RCS. This paper presents an experimental investigation of rebar corrosion by non-stationary thermal wave imaging. Experimental results have been proven, proposed approach is an effective technique for identification of corrosion in rebar in the concrete samples.
This work studies the impact of estimating soil wave number in Underground Focused SAR imaging for tunnel detection applications. It is demonstrated that neglecting wave refraction at the ground surface results in poor underground imaging; however, by considering refraction with inexact, yet sufficiently high, estimates of soil dielectric constant, clear target images can be produced. In addition, using a wrong wave number for the soil incorrectly predicts the tunnel's depth, but gives positive identification of its transverse extent.
A novel broadband monopole antenna design with wideband circular polarization (CP) characteristic is presented. This antenna consists of a feed line and a step-shaped ground plane which is formed by cutting a notch in the upper left corner of an asymmetric ground plane. The asymmetric ground plane is capable of exciting two orthogonal electric field vectors with equal amplitude and 90° phase difference (PD) for CP. By cutting a notch, the impedance-bandwidth can be enhanced greatly and the 3-dB axial ratio (AR) bandwidth is improved meanwhile. The measured impedance-bandwidth is about 5.96 GHz (84.7%) from 4.06 to 10.02 GHz, and the measured AR-bandwidth is about 2.64 GHz (36.5%) from 5.91 to 8.55 GHz. The results show that the antenna can achieve wide impedance-bandwidth and wide AR-bandwidth simultaneously.
A polarization-dependent mutiband radar absorbing material (PDM-RAM) composed of polarization-dependent multiband AMC (PDMAMC) and perfect electric conductor (PEC) cells is proposed. The PDMAMC is realized by etching a complementary split ring resonator (CSRR) on the patch of a conventional AMC. Around the two/three operational frequencies of the PDMAMC-elements for different electric field polarizations, the reflections of the PDMAMC and PEC have opposite phases, so for any normal incident plane wave the reflections cancel out. The basic principle is discussed, and a sample is measured. The results show that the proposed method is feasible and effective for the polarization-dependent multiband radar cross section (RCS) reduction.
This paper proposes a 10:1 unequal Gysel power divider using a capacitive loaded transmission line (CLTL). For obtaining a high dividing ratio of divider, the CLTL is proposed to realize a low characteristic impedance line below 10 Ω. A design method using a CLTL which consists of a small transmission line with shunt open stub at periodic intervals is newly suggested for power divider with the high power division ratio. For the validation of the CLTL power divider, the high dividing ratio of the fabricated Gysel divider is measured at a center frequency of 1 GHz. The measured performances are in good agreements with simulation results.