In this paper, a 3 dB H-plane substrate-integrated waveguide (SIW) power divider/combiner with improved isolation is reported. By adding two isolated ports into the Y-junction, it will perform like a multi-port coupler, so that the isolation between its dividing ports can be effectively improved as the newly-added ports are properly matched. To verify the availability and effectiveness of this concept, two prototypes, one is terminated by coaxial terminations and the other is loaded with lumped resistors, are developed. Their measured results are separately in good agreement with their corresponding simulations. Meanwhile, isolations better than 16 dB with fractional bandwidth (FBW) of 35 and 25% are achieved, respectively, as well as low phase and amplitude imbalances. Compared with some reported similar SIW power dividers, the proposed ones exhibit wider FBW with similar isolation, insertion loss, phase, and amplitude balance performance.

This paper presents the characterization and modeling process of MASMOS structures by means of a classical compact three-port electrical non-linear model approach. From DC and S-parameters measurements, a large signal model (LSM) has been developed for two different MASMOS structures. The proposed LSM and associated modeling approach have been validated through load pull measurements with different harmonic load conditions. Then, generic multi-tone measurements have been carried out making use of an innovative test bench to quantify linearity performances of MASMOS structures. The model is used in a power amplifiers design flow for LTE applications and is expected to allow a significant reduction of simulation time, compared with technological-oriented model as BSIM3.

We present a new ultra-wideband (UWB) band-pass filter (BPF) configuration with a stepped impedance short-circuited stub (SISS)-loaded triple-mode resonator (TMR) and stepped impedance radial stub (SIRS). The novel SISS-loaded TMR and SIRS improve the roll-off ratio at both ends. Even though this UWB BPF is based on a single resonator, the measured results show excellent in-band performance with a small insertion loss less than 0.6 dB and return loss greater than −16 dB. The proposed UWB BPF has sharp roll-off ratio of 96 and 43 dB/GHz, respectively, at the lower and upper edges of the pass-band, and a wide stop-band from 10.8 to 15.6 GHz with the rejection greater than 20 dB.

In this paper, a slow-wave transmission line implemented in coplanar waveguide technology, based on simultaneous inductive and capacitive loading, is presented for the first time. The shunt capacitors are achieved by periodically etching transverse strips in the back substrate side, connected to the central strip through metallic vias. The series inductors are implemented by etching rectangular slots in the ground plane. The effect of these reactive elements is an enhancement of the effective shunt capacitance and series inductance of the line, leading to a significant reduction of the phase velocity (slow-wave effect). Consequently, the guided wavelength is also reduced, and these lines can be applied to the miniaturization of microwave components. Moreover, due to periodicity, these artificial lines exhibit stop bands (Bragg effect) useful for spurious or harmonic suppression. A compact harmonic suppressed power splitter, based on a slow wave 35.35 Ω impedance inverter, has been designed and fabricated in order to demonstrate the potential of the proposed approach. The length of the inverter is 48% the length of the conventional counterpart, and measured power splitting at the first (3f0) and second (5f0) harmonic frequencies is rejected more than 49 and 23 dB, respectively.

A modified compact Y-junction substrate-integrated waveguide (SIW) four-way power divider (PD)/combiner is proposed in this paper. The proposed approach is based on the traditional Y-junction waveguide. By using direct transition structure from SIW to half-mode SIW, four-way PD that provides equal power split to all four output ports is achieved. The even- and odd-mode equivalent circuits are given to analyze and design the PD. The measured results validate the proposed design methodology and show good agreement with the simulation results. The measured 17 dB return loss bandwidth and 1.2 dB insertion loss bandwidth of this four-way PD are both about 2.5 GHz.

A 1.1-m reflectarray antenna has been designed, manufactured, and tested to fulfill the requirements of a satellite antenna in Ku-band that provides South-American coverage in Tx and Rx. The reflectarray cells consist of four dipoles for each polarization in two dielectric layers, selected because of their simplicity and high performance. The dipole dimensions are optimized in all the reflectarray cells to accomplish the prescribed radiation patterns, by iteratively calling an analysis routine based on method of moments in spectral domain and local periodicity. The measured radiation patterns of the manufactured antenna have been satisfactorily compared with simulations and with a three-layer reflectarray previously designed, manufactured, and tested for the same mission.

A dual closed-loop stepped impedance resonator (DCLSIR) is investigated and used in designing a compact microstrip bandpass filter (BPF). The proposed DCLSIR is symmetrical; as a result, the symmetric characteristics of the resonator have been used. The design equations are derived and used to support the circuit design. The center frequency, position of transmission zeros, and fractional bandwidth (FBW) are easily tuned by changing the physical dimensions of the resonator. Three transmission zeros are generated to improve the performance in the upper stopband. A DCLSIR prototype BPF is fabricated with a center frequency of 9.3 GHz, and evaluated to validate the design concept. The measured FBW is 9.25%, the insertion loss is 1.58 dB, and the return loss is over 17 dB. The measurement results agree well with the simulation results.

A novel Gysel power divider with high power-handling capability based on half-mode substrate integrated waveguide (HMSIW) has been presented in this paper. A HMSIW ring is used and good input/output impedance matching is achieved based on HMSIW-microstrip taper transition. Two microstrip stubs are introduced in HMSIW ring to assemble two isolation resistors to improve the isolation between the output ports. The even- and odd-mode analysis method is used for the presented circuit. A prototype of the presented power divider is designed, fabricated, and measured. The measured results show a reasonable agreement with the simulated ones.

In this paper, a high-gain dual-band distributed amplifier (DBDA) based on the metamaterial transmission line (TL) is proposed. To have two separate frequency bands in the distributed amplifiers, the composite right/left-handed (CRLH) TLs are used instead of conventional TLs. Although both forward and reverse gains of the distributed amplifiers are available in this case, they suffer from their low gains. In this paper, to increase the DBDA power gain, a new circuit architecture for the CRLH TL is introduced. By using the proposed CRLH TL, a lower wave attenuation coefficient at the forward band of the DBDA is achieved than the conventional structures, which causes a higher forward power gain. Simulation results also show that the power gain of the proposed DBDA is about 28.5 dB at the desired frequency bands, and good agreement between the measurement and simulation results confirms the accuracy of the design method.

In this work, a simple and efficient approach to design a microstrip diplexer is proposed. It is based on the combination of two compact Square Open Loop Resonator band pass filters. These filters are designed for Radio Frequency Identification application at 2.45 GHz frequency. Using the Chebychev approximation, the two filters and diplexer are designed, simulated, fabricated, and measured. The results show that the diplexer presents a high selectivity, a good insertion loss and high isolation (>40 dB) with the compact size. The diplexer also shows a good performance when associated with the patch antenna operating at 2.45 GHz.

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.

Sentinel-1A is a space-borne synthetic aperture radar (SAR) system developed in the frame of the Copernicus Program. The German Aerospace Center supported the radiometric and polarimetric calibration of Sentinel-1A by the analysis of point target responses of several acquisitions considering different modes, beams, and polarization channels. An elevation dependent bias, which had not been properly predicted by the used antenna model, was found for all investigated modes. Offsets of up to 2 dB were determined during the SAR instrument calibration phase, in particular, for low and high elevation angles. Therefore, in order to correct these elevation biases, a radiometric refinement was carried out by European Space Agency in November 2015. After that, Sentinel-1A radiometric accuracy and long-term stability were analyzed over a period of 1.5 years. For this period, the absolute calibration factor and the channel imbalance were determined for the main imaging mode. Moreover, a slight drift of the derived calibration factor was observed starting from July 2016. At the same time an anomaly was detected in the front-end affecting several transmit and receive modules in one tile. The radiometric behavior of Sentinel-1A should therefore be monitored for a longer period of time, especially to detect potential degradation effects of the SAR instrument.

This paper presents a procedure for the design of tensorial metasurface antennas radiating polarized beams through aperture field synthesis. The aperture field is generated using the surface wave to leaky wave conversion resulting from metasurface modulation. The design procedure of the feeder is presented with a description of the geometrical parameters affecting the antenna matching. Numerical solutions for single beam and multi-beam metasurface antennas working respectively, at 12.25 and 20 GHz are presented. In addition, a metasurface prototype working at 12.25 GHz is manufactured and measured.

This paper focuses on assessing the limitations in the direction-finding process of radio sources with directional antennas in an urbanized environment, demonstrating how signal source antenna parameters, such as beamwidth and maximum radiation direction affect bearing accuracy in non-line-of-sight conditions. These evaluations are based on simulation studies, which use measurement-tested signal processing procedures. These procedures are based on a multi-elliptical propagation model, the geometry of which is related to the environment by the power delay profile or spectrum. The probability density function of the angle of arrival for different parameters of the transmitting antenna is the simulation result. This characteristic allows assessing the effect of the signal source antenna parameters on bearing error. The obtained results are the basis for practical correction bearing error and these show the possibility of improving the efficiency of the radio source location in the urbanized environment.

In this paper, a self-actuated frequency-selective radome is presented and applied to a microstrip antenna. The radome acts as a self-triggered switchable screen to achieve adaptive electromagnetic protection in the L band. A prototype of the radome is fabricated to measure its transmission performance. The switchable characteristic is verified by a high-power radiation experiment carried out in a waveguide system. Besides, the antenna is placed under the radome to realize integration analysis, and the radiation performance of the composite antenna radome is measured in the anechoic chamber.

An optically transparent and electrically small frequency modulation (FM) radio receiving antenna has been designed and fabricated from a mesh silver layer printed onto a glass substrate. The studied FM antenna consists of a transparent meandering monopole associated with a micrometric size MEtal Semiconductor Field Effect transistor. An optical transparency of 87% and a sheet resistance lower than 0.22 Ω/sq are obtained. The received signal strength indicator and the signal-to-noise ratio are both measured and compared with those of a commercial monopole antenna (a quarter-wave wire antenna). The transparent FM antenna exhibits similar radiofrequency performance with, in addition, a low visual impact.

Microwave ablation is widely recognized as a promising minimally invasive tool for treating cancer. Real-time monitoring of the dimensions of the ablation zone is indispensable for ensuring an effective and safe treatment. In this paper, we propose a microwave imaging algorithm for monitoring the evolution of the ablation zone. Our proposed algorithm determines the boundary of the ablation zone by exploiting the time difference of arrival (TDOA) between signals received before and during the ablation at external antennas surrounding the tissue, using the interstitial ablation antenna as the transmitter. A significant advantage of this method is that it requires few assumptions about the dielectric properties of the propagation media. Also the simplicity of the signal processing, wherein the TDOA is determined from a cross-correlation calculation, allows real-time monitoring and provides robust performance in the presence of noise. We investigate the performance of this approach for the application of breast tumor ablation. We use simulated array measurements obtained from finite-difference time-domain simulations of magnetic resonance imaging-derived numerical breast phantoms. The results demonstrate that our proposed method offers the potential to achieve millimeter-order accuracy and real-time operation in estimating the boundary of the ablation zone in heterogeneous and dispersive breast tissue.

In this paper, a compact metamaterial inspired ultra-thin polarization independent quad-band microwave absorber for electromagnetic interference (EMI)/ electromagnetic compatibility (EMC) applications have been discussed. The proposed absorber structure offers four different absorption peaks having absorptivity of 97.02, 94.07, 91.72, and 98.20% at 3.40, 8.23, 9.89, and 11.80 GHz, respectively. Due to the four-fold symmetry of the designed unit cell, the proposed absorber structure shows polarization independent behavior. In addition to above, the absorption curve for the designed structure has been also analyzed under different angles of incidence for both transverse electric and transverse magnetic polarization states. In order to confirm the metamaterial behavior of the proposed absorber unit cell, dispersion plot has been studied. Further, input impedance plot, electric field, and surface current distribution plot have been discussed to explain the absorption mechanism of the proposed absorber structure. The designed absorber unit cell shows compactness of 0.136 λ0 × 0.136 λ0 with the ultra-thin thickness of 0.0113 λ0, where λ0 (free space wavelength) corresponds to the lowest absorption peak of 3.40 GHz. In order to calculate the measured value of absorptivity, the designed absorber structure has been fabricated. Further, it has been observed that simulated and measured results perfectly match with each other. The ultra-thin and compact nature of the proposed absorber structure suggests its potential use in the field of various EMI/EMC applications.

This paper illustrates the different possibilities given by additive manufacturing technologies for the creation of passive microwave hardware. The paper more specifically highlights a prototyping scheme where the 3D-printed plastic parts can be used as initial proofs of concept before considering more advanced 3D-printed parts (metal parts, for instance). First, a characterization campaign has been made on common plastics used by a 3D printer using the fused deposition modeling and material jetting (Polyjet©) technologies. The impact of the manufacturing strategy (high-speed or high-accuracy) on the part roughness, as well as on the dielectric material permittivity and loss tangent, has been specifically studied at 10 and 16 GHz. Based on a specifically optimized and deeply explained characterization method, the conductivity of a coating based on silver paint has also been characterized on such plastic parts at 10 and 40 GHz. These plastic materials and coating have been used for the creation of quasi-elliptic and tuning-free bandpass filters centered at 6 and 12 GHz and compared with a similar filter made of stainless steel by selective laser melting. Finally, a compact rectangular TE10 to circular TE01 mode converter also undergoes one prototyping step out of plastic before moving to an advanced part made out of stainless steel. This mode converter, which is made in a single part, is designed to operate from 28 to 36 GHz as a tuning-free final demonstrator.

A compact monopulse comparator with complete nulling in all DELTA channels is designed and fabricated. The proposed comparator has small dimension and consists of interconnections of four broadband branch-line couplers and several 90° phase shifters with multistage Schiffman coupled-lines. This comparator has been characterized by its eight-port S-parameters to generate the SUM and DELTA channel frequency responses. Over 30-dB null depth was achieved in DELTA channels across the SUM channels in pass band from 14.8 to 18.2 GHz frequency range.