The design of a high-stability radiometer is presented in this paper. It is used to characterize the stability of a microwave active cold load at L-band. The two-load radiometer takes advantage of a noise injection technique to improve its sensitivity. A temperature-stabilized enclosure is used to minimize gain and noise temperature fluctuations of the receiver. The radiometer sensitivity is 0.031 K and the gain fluctuations are less than 0.005 dB during 1 day. The total gain and the receiver noise temperature of the radiometer exhibit very small variations (<0.03 dB and 1 K, respectively) on the long term.

In this paper, an algorithm for extracting and localizing a radar pulse in a noisy environment is described. The algorithm combines two powerful tools: wavelet denoising and the short-time Fourier transform (STFT) analysis with statistical-based threshold. We aim to detect radar pulses transmitted by any radar in blind mode regardless of the intra-pulse modulation and parametric features. The use of the proposed technique makes the detection and localization of radar pulses possible under very low signal-to-noise ratio conditions (−18 dB), which leads to a reduction of the required signal power or alternatively extends the detection range of radar systems. Radar classes pattern-based analysis is used in blind mode to decrease the probability of false alarm.

The direct measurement of the radiation pattern of an antenna is often unreachable. A near-field sampling followed by a near-field/far-field (NF/FF) transformation is therefore substituted. This process is, in most cases, applied to antennas placed in free-space or over a perfect electric conductor. On the contrary, few results concern real environment conditions. Nevertheless, it is well known that the nature of the soil can drastically change the radiating characteristic of an antenna. The lack of information about the behavior of the antenna in real conditions can give rise to substantial errors in the evaluation of the performances of electromagnetic devices. The aim of this paper is then to propose a new NF/FF transformation able to reliably supply the field radiated by an antenna placed over a plane, homogeneous, dielectric, and lossy interface. The method is based on the cylindrical-wave expansion of the electric field. The real soil is taken into account by means of its reflection coefficients. First results are given for simple antennas and for both transverse magnetic and transverse electric polarizations.

In this paper, the design methodology of a flat reflector composed with standard dielectric material and using transformation electromagnetics (TE) is presented. First, the mathematical relation between a flat reflector and a parabolic one is described. The TE principle is then described. Some realization issues are highlighted, leading to approximations and compromises in order to design a more realistic structure. In this way, a flat reflector made only with standard dielectric materials is presented, using an original method to achieve the desired spatial permittivity variation. The simulation results of different configurations for the flat reflector are presented and compared to classical solutions in order to prove the thickness reduction and the improvement of radiation characteristics in terms of gain and half-power beamwidth.

This work presents the design of two compact multi-standard low-noise amplifier (LNA) in a 28 nm low-power bulk CMOS process. The transistor parameters were optimized by the gm/ID method taking into account the parasitics and the behavior of highly scaled transistors. To cover the industrial science medical (ISM)-bands around 2.4 and 5.8 GHz, the WLAN band as well as the Ku band a bandwidth enhancement is required. Two versions of LNAs, one with vertical inductors and one with active inductors, are implemented and verified by measurements. The noise figure (NF) exhibits 4.2 dB for the LNA with active inductors and 3.5 dB for the LNA with vertical inductors. The voltage gain reaches 12.8 and 13.4 dB, respectively, with a 3 dB-bandwidth of 20 GHz. Both input referred 1-dB-compression points are higher than −12 dBm making the chips attractive for communication standards with high linearity requirements. The chips consume 53 mW DC power and the LNA with active inductors occupies a core area of only 0.0018 mm2, whereas the version with vertical inductors requires 0.021 mm2.

This paper investigates metamaterials composed of resonant particles with negative electric polarizability located in a three-dimensional net. The main problem in fabricating these materials is the spread of the resonant frequencies of particular planar resonators. This spread is caused by the tolerances of the fabrication process for planar resonators. The simulation shows that there is a limit to the dispersion of resonant frequencies that allow the metamaterial to behave as a metamaterial with negative effective permittivity. Two metamaterials with a negative real part of the effective permittivity were designed on the basis of simulations. The first metamaterial has a regular periodic structure. The second is a metamaterial in which the resonant particles are randomly distributed both in space and in orientation, and it offers an isotropic response. This metamaterial was fabricated by inserting planar resonators into plastic shells that can be poured into any volume and ensure a random distribution of the resonant particles in space. The results of the simulations have been verified by measurements.

A suspended-stripline Gysel low-insertion-loss power combiner is presented in this paper. The multi-layer cavity structure reduces the circuit size and increases power density, composed of suspended strip lines and coaxial lines. The transmission-line theory is used to analyze this proposed power combiner, and the equivalent circuit model is developed to investigate the characteristics and design of the power combiner. The measured input return loss is greater than 20 dB from 7.15 to 9.35 GHz. The measured insertion loss is less than 0.36 dB, and the power-combining efficiency is greater than 92% from 7.39 to 9.19 GHz. The maximum power-combining efficiency is 98.8% at 8.1 GHz. Besides, the measured isolation is greater than 20 dB from 7 to 10 GHz. The power capacity is analyzed, and the cross-sectional power density is greater than 3.57 kW/cm2. The measured and simulated results show reasonable agreement with each other.

A novel dual-band planar antenna with a low profile for mobile communication system is proposed in this paper. The antenna is composed of one shorted patch with two radiating notches for low frequency resonance and one square patch for high frequency resonance. The low profile is achieved via the shorting patch, which introduces the parallel electrical field between the reflector and antenna. A step-impedance microstrip line is used to feed the antenna. The coupling between the square patch and microstrip line cancels out the inductance of shorting probe, which increases the working bandwidth of proposed antenna. A prototype with a low profile of 0.0286λ is fabricated and measured. The antenna achieves dual impedance bandwidths of 1.6% for the low frequency band and 60% for the high frequency band, covering the frequency range 851–865 MHz and 1.97–3.65 GHz, respectively. The measured results show good agreements with the simulated ones.

This paper presents a miniaturized tri- and quad-band power divider (PD)based on substrate integrated waveguide (SIW). By adopting different types of modified circular complementary split-ring resonators on the top surface of SIW, multiple passbands are generated propagating below the SIW cut-off frequency. The working principle is based on evanescent mode propagation that decreases the operating frequency of the PD and helps in the miniaturization of the proposed structure. The operating frequency of the proposed PD can be individually controlled by changing the dimensions of the resonator. To verify the proposed concept, a tri-band and a quad-band PD exhibiting 3 dB equal power division at 2.41/3.46/4.65 GHz and 2.42/3.78/4.74/5.8 GHz are designed using the full-wave simulator, validated through circuit model, fabricated and experimentally verified. The measured results agree well with the simulations. The proposed PDs have good performance in terms of reasonable insertion loss, isolation, minimum amplitude and phase imbalance, smaller footprint, easy fabrication and integration. The size of the fabricated prototype is 18.3 mm × 8.4 mm, which corresponds to 0.205λg × 0.094λg, λg being the guided wavelength at the first operating frequency.

In through-wall radar system, the wall parameters, including permittivity, and wall thickness are of crucial importance for locating targets precisely. Recently, to obtain a quick and accurate estimation of wall parameters, an approach based on machine learning was introduced. However, these approaches are less reliable as only simulations results are presented. One of the major concerns with machine learning-based approaches is the generation of training and testing data which require fabrication of wall with different permittivity, thickness, and conductivity. Creating walls with different permittivity, thickness, and conductivity can really be challenging and expensive. Therefore, an effort has been made in this paper to establish a cost-effective and robust machine learning-based wall parameter estimation process with the usage of transmission line method and artificial neural network. The implementation and efficacy of proposed approach have been demonstrated through simulation and experimental results. The proposed approach quickly and accurately predicted the wall relative permittivity and thickness of real building wall. The merit of proposed approach is that it is less complex and computational efficient as it can extract wall parameters from only one measurement and therefore can be used in conjunction with any commercial through-wall radar systems.

In this work, three successive filter models based on defected ground structure (DGS) techniques are designed, fabricated, and tested to be utilized for different wireless applications. The filters are printed on a RO5880 substrate of an overall size of 22 × 11 × 0.8 mm3. Three DGSs are etched from the ground plane to achieve the suggested band stop features for all frequencies above 10 GHz. The first model is a low-pass filter that succeeded to pass all frequencies below 10 GHz, the second model is a bandpass filter that operated at 4.5 and 9 GHz after using a pair of interdigital capacitors, and the third model covered all ultra-wideband frequency range when a pair of lumped capacitors is utilized instead of the interdigital capacitors. Good consistency between simulated and measured outcomes is achieved for each of the three filters confirming their suitability to be embedded in small-sized wireless devices.

A super-wideband (SWB) omnidirectional antenna is reported in Lau et al. in 2005 and 2008, but the antenna structure was complex and the radiation properties were unsatisfactory. In this paper, a SWB omnidirectional antenna with simple structure and improved radiation properties is presented. The antenna just consists of a two-stage inverted cone and two shorting pins. The proposed two-stage cone can improve the impedance matching in super-wide bandwidth, and the optimized shorting pins can reduce the cut-off frequency more than 50%. The calculated and measured results are investigated to confirm the antenna performances. The impedance bandwidth of the antenna for voltage standing wave ratio ≤ 2 achieves more than 1:22.1, covering 0.905 GHz to the above band. The smaller sizes than those referred by Lau et al. in 2008 are obtained. The profile of the antenna is 0.078λc, and the diameter of the radiation body is 0.217λc (λc is the wavelength of the cut-off frequency of the antenna). In addition, the radiation properties of the kind of SWB omnidirectional antenna are improved obviously. In the whole band, the ripple levels in horizontal radiation patterns are not more than 6.6 dB, and the cross-polarized levels are reduced by 9 dB.

In this paper, a dual-band 8 × 8 multi-input multi-output (MIMO) array antenna operating in 3.5 GHz band (3400–3600 MHz) and 5.5 GHz band (5150–5925 MHz) for 5G mobile handset is presented. The proposed hybrid antenna includes a comb-shaped monopole and an L-shaped open slot antenna which are symmetrically located on the inner surface of the side-edge frame of smartphone. Pattern diversity is achieved that can mitigate envelope correlation coefficients (ECCs) and improve the MIMO system performances. The prototype of proposed dual-band eight-element MIMO antenna is fabricated and experimentally measured. The results show that isolation <−10 and <−15 dB, respectively in the lower band and high band without any additional decoupling element are achieved and the desired bands are satisfied under the condition of −6 dB impedance matching. Moreover, the essential parameters for evaluation of the MIMO system performance such as the ECC, mean effective gain (MEG), and ergodic channel capacity are calculated. Furthermore, the influence of user's hand on the radiation characteristics of proposed MIMO antenna are also investigated and discussed. Based on the result, the proposed MIMO antenna is a good candidate for use in future 5G applications.

In this paper, a microstrip lowpass filter adopting two main resonators with steep transition band and wide rejection band has been introduced. The first main resonance cell consists of meandered transmission lines which are loaded by modified T-shaped patches. The second main resonator is composed of high-impedance lines loaded by polygon patches. To obtain a steep skirt performance, the first and second resonators have been combined. Moreover, employing eight high–low impedance folded stubs and two rectangular open-stubs as suppressing cells has resulted in improving the stopband features. To comprehend the frequency behavior of the employed resonators and also their combination, the formulas of the transmission coefficient, reflection coefficient, and the transmission zeros of their equivalent LC circuits have been extracted, separately. According to the measurement results, the −3 dB operating frequency of this filter is 1.65 GHz. Moreover, a relative stopband bandwidth equal to 166% with a corresponding attenuation level of 23 dB and a sharp roll-off rate (393.61 dB/GHz) have been achieved. In the passband region from DC to 1.632 GHz, the insertion loss and return loss are better than 0.0763 and 15.85 dB, respectively, proving an acceptable in-band performance. Finally, the implemented structure brings about a high figure-of-merit equal to 81 672.

Multiplexer design is a challenging task due to the high number of variables involved, raising the difficulty as the numbers of filters increase. Numerical computing tools provide a suitable environment to evaluate topologies and technologies before starting the long journey to the device. A direct scattering matrix solution for a star-junction multiplexer, based on the circuit theory, is presented in this work. The resulting star-junction matrix is introduced in a matrix system with the scattering matrix of each filter to evaluate the overall multiplexer response. This approach allows the acquisition of main multiplexer parameters like transmission, reflection, and cross-isolation response in a compact way, achieving a good starting point for the further full-wave optimization procedure. Furthermore, an approach for the design of a star-junction multiplexer is tackled based on the reflection coefficient phase. A triplexer under this interpretation is presented and evaluated using lumped elements.

A solution to the problem of Gaussian beam scattering by a circular perfect electric conductor coated with eccentrically anisotropic media is presented. The incident Gaussian beam source is expanded as an approximate expression in the simple form with Taylor's series. The transmitted field in the anisotropically coated region is expressed as an infinite summation of Eigen plane waves with different polar angles. The unknown coefficients of the scattered fields are obtained with the aid of the boundary conditions. The addition theorem for cylindrical functions is applied to transfer from the local coordinates to the global ones. The infinite series can be truncated under the prerequisite of achieving the solution convergence. Only the case of transverse-electric polarization is discussed. The similar formulation of transverse-magnetic polarization can be obtained by adopting a similar method. Some numerical results are presented and discussed. The result is in agreement with that available as expected when the eccentric geometry comes to the concentric one.

Magnetic coupling resonance wireless power transfer technology has attracted worldwide attention in recent years due to its mid-range, non-radiative, and high-efficiency power transfer. However, in regard to its practical applications, there are still some issues that need to be considered and studied with respect to coil design, such as coil structure, and parasitic parameter extraction. This paper investigated the characteristics of magnetic coupling resonance wireless power transfer systems with different coil structures, including circular coils and rectangular coils arranged in parallel. We calculated the magnetic field distributions and mutual inductances by subdividing the receiving coils and computing the magnetic flux density of each subdivision. The proposed analysis was validated by means of the finite element analysis and the experimental results. We investigated the effects of the coil's structure, and topological structures, on the power transfer efficiency. The results demonstrate that using circular coils in parallel is more advantageous than using rectangular coils.

A compact circularly polarized (CP) rectenna with low profile and high efficiency based on the artificial magnetic conductor (AMC) is proposed in this paper. The receiving CP antenna is a coplanar stripline fed dual rhombic loop with an AMC reflector. The proposed AMC reflector not only improves the antenna gain to 9.8 dBi but also decreases the profile to 0.1 λ0. The AMC reflector also makes the antenna have a harmonic suppression function so the low pass filter between the rectifying circuit and the antenna could be omitted and the rectenna has a compact structure. According to the measured results, the rectenna has the highest conversion efficiency of 76% on the load of 240 Ω with the received power of 117.5 mW. When the linearly polarized transmitting antenna is rotated, the conversion efficiency of the CP rectenna maintains a constant high conversion efficiency of 74%. The compact structure and CP operation of the rectenna made it a good candidate of the wireless battery for some electronic devices and far-distance microwave power transmission.

The high millimeter-wave (mmW) frequency range offers new possibilities for high-resolution imaging and sensing as well as for high data rate wireless communication systems. The use of power amplifiers of such systems boosts the performance in terms of operating range and/or data rate. To date, however, the design of solid-state power amplifiers at frequencies about 210 GHz suffers from limited transistor model accuracy, resulting in significant deviation of simulation and measurement. This causes cost and time consuming re-design iterations, and it obstructs the possibility of design optimization ultimately leading to moderate results. For verification of the small-signal behavior of our in-house large-signal transistor model, S-parameter measurements were taken from DC to 220 GHz on pre-matched transistors. The large-signal behavior of the transistor models was verified by power measurements at 210 GHz. After model modification, based on process control monitor (PCM) measurement data, the large-signal model was found to match the measurements well. A transistor model was designed containing the statistical information of the PCM data. This allows for non-linear spread analysis and reliable load-pull simulations for obtaining the highest available circuit performance. An experimental determination of the most suitable transistor geometry (i.e. number of gate fingers and gate width) and transistor bias was taken on 100 nm gate length metamorphic high electron mobility transistor (mHEMT) transistors. The most suitable combination of number of fingers, gate width and bias for obtaining maximum gain, maximum output power, and maximum power added efficiency (PAE) at a given frequency was determined.