Design, simulation and measurement results of the integrated compact up-converter MMICs (microwave monolithic integrated circuits) are presented and discussed. The design is performed to achieve low cost and high performance transmitter system for the Ka-band frequency applications. It is designed using anti-parallel diode pair sub-harmonic single sideband mixer and three stage RF (radio frequency) amplifier. Microstrip lines and lumped elements are used together to achieve a compact chip size. The layouts of the circuits are designed with careful EM (electromagnetic) simulations to avoid inter-component couplings and effect of the microstrip bending discontinuities. The chip is operated for the wide bandwidth of the RF frequency from 22-38 GHz. Due to sub-harmonic mixing the required local oscillator frequency (LO) is reduced to half (10-19 GHz) to that of the RF frequency. The conversion gain of the chip is 9-15 dB and P-1dB output power is 7-12 dBm. The single sideband and anti-parallel diode pair suppress the in-band unwanted sideband and second harmonic of the local oscillator (2LO), respectively. The suppression of sideband and 2LO signals is typically 20-35 dB and 20-30 dB, respectively. The size of the chip is as compact as 4.2 mm2 on a 100 μm-thick GaAs substrate.
Radiation pattern, impedance characteristics, and gain of a probe-excited rectangular ring antenna are investigated by the Method of Moments with the Rao-Wilton-Glisson (RWG-MoM) basis functions. The analysis is carried out for different lengths and positions of the probe as well as various lengths, widths and heights of the ring. In addition, the distribution of the surface current is also illustrated. Consequently, the suitable parameters are determined. It is obvious that the proposed antenna offers a bidirectional pattern with the impedance bandwith (|S11|< -10 dB) of 17%. Along the direction of the ring aperture, the gain is 5.28 dBi. Furthermore, the prototype antenna was fabricated and measured to verify the validity of the numerical calculation. It is found that the numerical and measured results are reasonably in good agreement.
The effect of copper on the microwave absorption, conductivity and complex permittivity of fritless Ni(1-x)CuxMn2O4 (x=0,0.4,0.8,1) thick film on alumina have been investigated in the 8-18 GHz frequency range. The structural changes have been identified by scanning electron microscope (SEM), FTIR and RAMAN scattering spectroscopy. The microwave conductivity and permittivity increase as copper content increases. The fritless Ni(1-x)CuxMn2O4 (0≤x≤1) thick film with x=0.4 shows best absorption properties, though all the other compositions also show good absorption in a large frequency range. The microwave conductivity increases from 1S/cm to 951 S/cm due to copper and the dielectric constant (ε) increases from 7 to 19.5.
In this paper, models of metallic absorbers for electromagnetic waves in the infrared to microwave frequency range are reported and discussed. The Hadley's formalism (1D model) of transmission, reflection and absorption for semi-infinite layers, which allows to design all configurations of unstructured absorber films and dielectrics is generalized. To make the micro-fabrication of the metallic absorbers easier (that means to have layers thick enough), the metallic layers need to be structured (grid for example). We developed a model that allows us to consider the structure of metal as a homogeneous layer, where the diffraction is negligible. This new layer can be used with the previous model. When diffraction effects must be taken into account, we modified an electrical model made by Ulrich. We further developed it for the configuration of a dielectric before the metallic grid. The results showed the importance to take into account all the dimensions of the grid, the dielectric layer parameters and the wavelength to design the best absorber.
Modifying the rate equations of an injection-locked semiconductor laser, we have analyzed its optical bistability with the effect of frequency chirping of injected light. Comparison between the bistable steady-state characteristics of the laser in two cases: with and without frequency chirping is done by studying the effect of parameters such as frequency detuning, carrier injection rate, and cavity length. Then we have made a comparison between the bistable dynamic characteristics of the laser for these two cases. The results of the analysis show that the effect of frequency chirping on the bistability behavior is negligible.
An equilateral triangular microstrip antenna is proposed for circularly-polarized synthetic aperture radar (CP-SAR) systems operated in L-Band (1.27 GHz). For airborne application, a prototype antenna patch is designed, fabricated and tested. Electromagneticallycoupled, dual-feeding method is applied to generate the circularly-polarized wave radiating from the patch. The fabricated patch exhibits an axial ratio bandwidth (< 3 dB) of about 0.58% (7.4 MHz), which is consistent with the value of 0.57% (7.24 MHz) from the simulation.
Ultra Wideband (UWB), an impulse carrier waveform, was applied at HF-VHF frequencies to utilize surface wave propagation. Due to the low duty cycle of the pulse, the energy requirements are significantly reduced. UWB involves the propagation of transient pulses rather than continuous waves which makes the system easier to implement, inexpensive and small. The use of surface wave propagation (instead of commercial SHF UWB) extends the communication range. The waveform, transmitter, receiver, modulation and channel characteristics of the novel system design will be presented.
This paper presents a novel multi-objective optimization of printed microstrip-fed monopole antenna for ultra wideband (UWB) applications. Two objective functions are minimized in this design: return loss and transient distortion. Using this method, a set of optimum antennas are achieved instead of a single design. Optimization is performed to reduce distortion in different scenarios. When distortion reduction only in E-plane or in both of E- and H-planes is considered, the obtained set of applying this algorithm dominates reported UWB antennas. Therefore, the obtained result provides a set of proper designs for UWB systems with random physical orientationt.
A new antenna structure with lower side lobe pattern and higher gain was designed by combining a microstrip rectangular planar antenna array with the separated feed network technique. In this paper, the side lobe behaviors of two different radiating structures have been studied and compared. The first antenna configuration ("Structure 1") is a 16-element planar antenna array whose feed line is printed on the same plane as the radiating elements. The second one ("Structure 2") is a 16-element planar antenna array whose feed network is separated from the radiating elements by an air gap. This technique enables one to reduce the unwanted spurious effects from the feed line. Both antennas are designed at 5.8 GHz. Compared to "Structure 1" we show that the optimization of "Structure 2" allows reducing the side lobe level and increasing the antenna gain. The experimental results are shown to be in very good agreement with the numerical simulations.
Generalized cross-coupled filters require implementation of both positive and negative cross-coupled elements. A positive element frequently uses inductive coupling, while a negative one uses capacitive coupling. Traditional methods for realizing capacitive couplings, which are difficult to adjust in practice, have included the use of capacitive probes in coaxial cavity. And this kind of n-order cross-coupled filters without the coupling between input and output ports can only produce 2-n transmission zeros at most. In this paper, we present a convenient method for capacitive coupling. Based on the method a four-order cross-coupled filter is realized, and the measured results match well with the theoretical prediction. Especially, there are three transmission zeros near the pass band.
The strip-line frequency-domain technique for permeability measurement is compared to the field domain technique. The combined setup for microwave measurement of thin film permeability with both techniques is proposed. The field-domain technique is less affected by inhomogeneity of measurement strip cell and has significantly higher signal-to-noise ratio, but the obtained parameters are affected by film thickness and may differ from that of the frequency-domain technique. Analysis of the field-domain data obtained at a set of frequencies makes it possible to determine the saturation magnetisation, the anisotropy field and the damping factor without the knowledge of the amount of substance under study. In case of a simple permeability spectrum the data on metal thickness make it possible to estimate the effective skin-depth as well. The technique is tested by simulation and is applied to determine permeability of Fe-based films vacuum-sputtered on glassceramic and polymer substrates.
A new subspace method based on spatial-temporal structure is presented for estimation of directions-of-arrival (DOA's) and ranges of multiple near-field sources impinging on an array of sensors. The arrival angle and range parameters are directly given by the eigenvalues of a set of constructed matrices and the computational complexity of the proposed method is lower than those of several available methods which do not require search operation. Simulation results show that the proposed method outperforms an ESPRIT-like method.
A method of acquiring clear three-dimensional image of human tooth in vitro, which is based on optical coherence tomography, is described. The background noise of the cross-section image is eliminated by image preprocessing algorithms, then the three-dimensional image is reconstructed by ray-casting algorithm, and gives the whole view of dental crown which contains dentin and enamel. A plane can be used to cut the tooth interactively to observe the inner tissue. This image is convenient for doctors to locate lesions and has a great potential for the clinical diagnosis of early dental caries.
Design aspects of high efficiency profiled circular horns feed with smooth wall for the high-power microwave (HPM) system are presented in this paper. The modal content at the circular aperture of horn necessary to closely approximate a linear polarized Gaussian distribution is established. Slope discontinuities along the axis of the horn are then used to generate the necessary waveguide modes with the appropriate amplitudes and phases at the aperture. The performance of the horn is calculated using the mode matching technique. Significant improvement in the performance of radiation over a straight conical horn can be achieved on the premise of high power capacity. The excellent correspondence between the predictions and simulated result by CSTMWS (CST microwave studio) supports this conclusion.
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