This paper presents the design of an asymmetrical Doherty power amplifier (DPA) with improved linearity and efficiency performance. Resonator-type drain bias networks, providing high impedances at the carrier frequency and low impedances with small variation at the envelope frequency, are introduced to reduce the DPA's memory effects when transmitting wideband signals. The general criteria for DPA design are summarized, and the approach to obtain optimum fundamental and harmonic impedances is proposed to achieve back-off efficiency enhancement. For experimental validation, the asymmetrical DPA is designed and implemented using two identical GaN HEMTs. Measured with continuous wave (CW), the proposed DPA delivers a saturation power greater than 49.3 dBm from 3400 to 3600 MHz, along with high drain efficiency of over 62% and 48% at peak and 8-dB back-off power, respectively. Driven with 100-MHz LTE-advanced signals, the adjacent channel leakage ratio (ACLR) asymmetry of the DPA at 20-MHz offset is lower than 1-dB. After digital predistortion (DPD) linearization, the proposed DPA achieves an ACLR of better than -48 dBc at an average output power about 41 dBm and the drain efficiency over 45% across the frequency band.
A right-angled waveguide bend using conformal transformation optics is proposed which guides the input electromagnetic wave smoothly through the waveguide, reduces the reflections and broadens the bandwidth of the device significantly. The isotropic material parameters are obtained through solving Laplace's equations with Dirichlet and Neumann boundary conditions. It is shown that the performance of the proposed bend is mainly determined by refractive indices lower than one. Utilizing this, the approximated resulting medium is implemented by drilling hole arrays in a dielectric background. In order to take advantage of planar technology, it can be implemented in a substrate integrated waveguide.
Active Magnetic Bearings (AMBs) are advantageous due to their active control on rotor position, but are disadvantageous due to their high initial as well running costs. The running cost of AMB can be reduced by improving design of electromagnet so that the same magnetic field can be generated with reduced supply of electric current. In the present paper, analyses of various arrangements of electromagnets using 2D finite element (FE) have been presented. To validate the results of magnetic flux density obtained from theoretical study, experiments were performed, and comparisons have been presented. The electromagnet using Halbach winding arrangement provides the best results.
In this article, a matching pursuit algorithm is developed to improve the performance of a passive multiplexing technique based on compressed sensing. This deconvolution technique is applied to RADAR imaging in the microwave range, starting from previous studies based on a compact coding device and L1-norm regularizations. This study demonstrates that in this context, the quality of the reconstructed RADAR images can be improved using an algorithm close to Hogbom's Clean, and based on a dictionary built with Tikhonov pseudo-inversions. The theoretical principle of this new algorithm is developed, followed by a parameters study. Finally, an experimental validation is presented to demonstrate the efficiency of this iterative algorithm.
A novel design concept of dual-band 180° hybrid ring coupler is presented in this paper. Coupler is a key element in front-end building blocks of wireless transceiver systems such as industrial systems and consumer electronic devices. The proposed design is realized by combining multiple arbitrary length transmission lines operating at two frequencies with one dual-band 180° phase shifter. The even-odd mode method is applied to derive the design equations for proposed dual-band 3 dB 180° directional coupler. Based on the analysis, it is found that the realizable frequency ratio of the proposed coupler is very flexible (i.e. the ratio between the two operating frequencies). Moreover, the 180° phase shifter features arbitrary characteristic impedance (i.e. its characteristic impedance can be arbitrarily chosen), which further ensures the easy implementation of proposed structures. To prove the design concept, full-wave electromagnetic simulations are performed to design a dual-band ring hybrid coupler working at 0.9 and 1.98 GHz. An experimental prototype is fabricated on Rogers RT/Duroid 5880 board. The measurement results match well with the theoretical and numerical ones.
We propose a framework based on the use of a flat-base Luneburg lens antenna with a waveguide array for Direction-of-Arrival (DOA) estimation, and also present a hybrid approach which combines waveguide mode extraction and signal processing techniques for enhancing the angular resolution of the lens antenna. The hybrid method involves sampling the electric field at specified positions when the lens is operating in the receive mode, and extracting the weights of the possible propagating modes in each waveguide. Following this, we correlate these weights with the known ones that have been derived by either simulated or measured signals from single targets located at different look angles, to make an initial estimate of the angular regions of possible DOAs. We then apply an algorithm based on the Singular Value Decomposition (SVD) of the simulated or measured database to estimate the angles of incidence. Numerical results show that the proposed framework, used in conjunction with the hybrid approach, can achieve an enhanced resolution over the conventional limit base on the 3 dB beamwidth of the lens antenna. Furthermore, it is capable of locating targets with different scattering cross-sections and achieving an angular resolution as small as 2˚, for a Luneburg lens antenna with an aperture size of 6.35λ and a Signal-to-Noise Ratio (SNR) of 30 dB.
Ring resonators are very commonly used for the design of frequency selective surfaces (FSSs). But, for some particular design, the spacing between the resonators becomes very small. So it leaves no space to shift the reflection band towards the lower side of the spectrum. It also becomes very difficult to realize large PCBs. In this paper, an improvised design of the ring resonator using stubs is reported. This provides the designer with some flexibility. Two different configurations using this concept have been fabricated. Measured results are compared with the configuration using conventional ring resonators. These results indicate good performance with tune-ability in the response without major change in the design or in the substrate.
This paper presents for the first time a systematic algorithm to optimise the bandwidth for a semiconductor junction circulator with minimum magnetic bias requirements. The behaviour of the gyroelectric parameters was studied to describe the optimum biasing magnetic field for millimetre wave operation with maximum bandwidth. Perfect circulation conditions derived using a Green's function approach were analysed to determine the optimum radius and coupling half-angle for the semiconductor disk forming the circulator. Previously measured data for InSb at 77 K were used to find design parameters for optimum bandwidth of circulation at millimetre wave frequencies. The performance of the design was verified using a full-wave electromagnetic simulation package, where up to 90% 10 dB bandwidth centred at 200 GHz was achieved with magnetic biasing as low as 0.214 T.
This paper presents the design, simulation and measurements of wideband two-stage LNAs using commercially available discrete components and targeting Square Kilometre Array (SKA) focal-plane-array verification studies. The design optimization was implemented through simulations based on theoretical work that shows that low wide-band noise figures and power match are achievable by inner-stage component selection and device bias. In contrast to the conventional practice of having each stage of a discrete LNA matched to 50 Ω, the inner stage was designed with a mismatching capacitor between the two stages. The measured results are presented for 0.7-1.4 GHz and achieve noise figures below 0.4 dB, gain of at least 28 dB, mid-band input return loss of 7 dB, output P1dB of 18.3 dBm, input-referred IP3 of -15.47 dBm, and power consumption of 500 mW with a supply voltage of 5 V.
A novel range-instantaneous-Doppler (RID) algorithm of inverse synthetic aperture radar (ISAR) imaging based on adaptive Doppler spectrum extraction is proposed in this paper. Regarding maneuvering targets, such as military aircraft, the ISAR image is blurred on cross-range domain when the range-Doppler (RD) algorithm is applied. The RID imaging method is often used to resolve the Doppler ambiguity, but there are some scatterers that could be lost because the sliced time is fixed in traditional RID imaging. To the method proposed in this paper, the optimal Doppler spectrum of each range bin is extracted by gradient energy function (GEF) after time-frequency (TF) analysis, and then all of the optimal Doppler spectrums are combined to obtain a final 2-D RID image of the target. Compared with the traditional RID method, the novel algorithm can obtain image with better focused quality. The results obtained from simulated and field-measured data verify the superiority of the proposed algorithm.
We report the results of a high-output power unbalanced tripler at 225 GHz, in which a pair of discrete Schottky varactor chips in parallel is adopted. Considering the present situation of domestic processing technology, the advantage of unbalanced structure is that it could provide bias to the diodes without a on-chip capacitor, which is essential in the balanced tripler scheme. The whole circuits are built on a 50 um-thick quartz substrate, and the novel field-circuit method is applied to the design process that enables us to calculate the impact of the parastics. The measured results indicate that the output power is more than 7 dBm in 215~228 GHz, and the output power is 12.3 dBm at 224 GHz when driven with 23.8 dBm of input power at room temperature. In general, this tripler has important practical value.
To achieve broadband microwave absorption, a three-layer structure is designed and manufactured. It involves a resistive frequency selective surface (FSS) sandwiched between two layers of magnetic sheets. The measurement results reveal that this structure exhibits -13 dB reflectivity in the frequency range of 7.9-18 GHz while the thickness is only 1.7 mm. The reflectivity bandwidth at the level of -10 dB is 11.4 GHz which is much wider than that of magnetic sheets with non-resistive FSS or the magnetic sheets without FSS. The effect of resistive FSS on the performance of the multilayered absorber is discussed in detail. It is concluded that an embedded resistive double loops FSS can result in a secondary resonance peak which obviously broadens the reflectivity bandwidth of the magnetic sheets.
A planar, printed multiple-input multiple-output (MIMO) antenna for slim mobile handset is presented. The dual-antenna system, comprises two symmetric antenna elements, is printed on a printed circuit board (PCB) of mobile phone. Each antenna element consists of coupled-fed loop antenna. The loop antenna is formed by a quarter wavelength (at 762 MHz) meandered loop strip with end terminal short-circuited to the ground plane. A Tshaped protruded ground is deliberately designed to enhance the impedance matching and decoupled the two closely deposed antenna elements (distance between antenna elements are 0.03λ at 762 MHz). The integrity of the T-shaped decoupling structure and coupled-fed loop antenna array covers LTE700 (0.747 GHz−0.787 GHz) and WWAN (1.7 GHz-3.04 GHz) based on -6 dB reflection coefficient and achieves isolation between elements well below -10 dB over all the operating bands. The application platform is LTE700, GSM1700, GMS1800, UMTS, Wi-Fi, Bluetooth, LTE2300, and LTE2500 bands for the 2G/3G/4G mobile terminals. The effect of user proximity by considering the actual mobile environment is also studied in the form of total radiated power (TRP), specific absorption rate (SAR), diversity performances, and radiation performances. Finally, a prototype is fabricated and tested with network analyser. The measured results are found in good agreement with simulated ones.
This paper presents the design of a novel wideband gap coupled sectoral antenna for communication systems. The circular patch is placed in the aperture of four sectoral rings. The antenna parameters are optimized using various simulations to attain good return loss and corresponding resonant frequency. The antenna operates in X-band at 10.35 GHz showing wideband characteristics along with high directivity and reduced side lobe level to a good extent. The antenna has also been studied using fuzzy inference system (FIS). The return loss and analogous frequency obtained from simulated results and fuzzy system are compared and in good agreement. Design is extended to an array of nine elements mutually coupled to the active fed patch. The antenna is fabricated, and the simulated results are found to be in good agreement with experimentally measured ones. A bandwidth of 900 MHz at resonant frequency of 10.35 GHz with a directivity of 7.0 dBi and reduced side lobe level of -18.9 dB is therefore obtained.
A novel printed reconfigurable square slot antenna with switchable right/left-handed circular-polarization (CP) and switchable dual-band performances for use in DCS/WiMAX applications is designed and manufactured. In the proposed antenna, in order to create a reconfigurable structure with switchable dual-band performance, a meander-line shaped radiating stub is utilized. This radiating stub can select between two operating frequency bands with respect to the number of its steps, and also right- or left-handed circular polarization at one of the operating bands (WiMAX) is determined by the growth direction of this meander-line structure. Moreover, through embedding an L-shaped slot on the ground section, circular polarization can be provided for the other operating frequency band (DCS). Having right or left handed circular polarization at this frequency band can be determined by the location and orientation of the L-shaped slot on the ground plane. In order to achieve a reconfigurable antenna structure with simultaneous switchable dual-band and circular polarization functions, six PIN diodes were utilized. The designed antenna has a small size of 30×30 mm. Simulated and experimental results obtained for the designed antenna reveal good radiation behavior within the DCS (1.85 GHz) and WiMAX (3.5 GHz) frequency ranges.
In this paper, a multiband circularly polarized capacitive coupled stacked microstrip antenna is proposed. The multiband circular polarization (CP) is achieved by corner truncation, embedding slits and inclined slots on a three layered antenna structure. The proposed antenna also shows wideband behavior with an impedance bandwidth of 52.13% in the frequency range of 4.85 GHz to 8.27 GHz, while 3 dB axial ratio bandwidths in five CP bands are 0.51%, 4.54%, 0.33%, 0.83% and 1.29% in the frequency range of 5.12 GHz to 5.15 GHz, 5.45 GHz to 5.70 GHz, 5.90 GHz to 5.92 GHz, 6.25 GHz to 6.31 GHz and 7.68 GHz to 7.78 GHz, respectively. The antenna prototype is fabricated, and simulated results as axial ratio, radiation pattern and the reflection coefficient are validated with measured result.
In this paper, the design of a class-F radio frequency power amplifier with a multiharmonic input transmission line network is presented. Harmonic signal components at the gate come from several sources including nonlinear device capacitances and imperfect output harmonic terminations that create harmonic components that are fed back to the gate through the gate-drain capacitance. The effect of these harmonic generation mechanisms and the potential to shape the gate waveform to improve power efficiency are investigated. The study shows that a second harmonic short is most beneficial and the effect of a third harmonic termination is small. The concepts are applied to the design of a 10 W GaN class-F amplifier and the design is supported by theoretical, simulation and experimental results. The fabricated design has a measured drain efficiency of 78.8% at an output power of 40.5 dBm for a frequency of 990 MHz. The amplifier was also tested with a 8.8 dB peak-to-average power ratio 5 MHz WCDMA signal. With the modulated signal, the adjacent channel power ratio was -33.1 dBc at a drain efficiency of 46.1% without predistortion correction.
A planar UWB antenna with added GSM 1800/WMTS and UMTS bands is presented. A CPW-fed circular patch is used to obtain wideband characteristic covering the UWB range. A novel slot formed by merging the alternate sides of a hexagon with isosceles triangles is inserted in the patch to obtain dual-band operation with the lower band suitable for GSM 1800 operation. By inserting a bent monopole in the space created by the slot, a triple-band antenna is developed with two lower bands suitable for WMTS and UMTS operation. The antenna prototype is fabricated and tested. Simulated and experimental results are in good agreement. The antenna exhibits stable radiation characteristics and nearly constant group delay in the UWB range.
Slotted waveguide antenna (SWA) arrays offer clear advantages in terms of their design, weight, volume, power handling, directivity, and efficiency. For broadwall SWAs, the slot displacements from the wall centerline determine the antenna's sidelobe level (SLL). This paper presents a simple inventive procedure for the design of broadwall SWAs with desired SLLs. For a specified number of identical longitudinal slots, and given the required SLL and operating frequency, this procedure finds the slots length, width, locations along the length of the waveguide, and displacements from the centerline. Compared to existing methods, this procedure is much simpler as it uses a uniform length for all the slots and employs closed-form equations for the calculation of the displacements. A computer program has been developed to perform the design calculations and generate the needed slots data. Illustrative examples, based on Taylor, Chebyshev and the binomial distributions are given. In these examples, elliptical slots are considered, since their rounded corners are more robust for high power applications. A prototype SWA has been fabricated and tested, and the results are in accordance with the design objectives.
An equivalent circuit model of a finite ground plane coplanar waveguide (FGCPW) interconnect in a metal-insulator-semiconductor (MIS) system for an ultra-broadband monolithic IC is proposed and illustrated. An effective substrate considering Maxwell-Wagner Polarization is suggested and demonstrated. The method of modeling the weak skin effect of the conductor is presented. The accuracy of the equivalent circuit model is evaluated. This proposed FGCPW interconnect equivalent circuit model enables a quick and efficient time domain simulation to estimate the time delay and bandwidth of the ultra-broadband ICs.