This paper presents the design of a compact, planar, single layer, tri-section ultra-wideband (UWB) branch-line (BL) coupler. The prototype offers 10 dB return loss characteristics from 3.1 to 13.7 GHz. Over a major portion of the band, phase imbalance of ±10° is achieved. The method of deploying multi stage impedance feed has been used to achieve improved bandwidth. To enhance the power output through the coupled port throughout the operating band, ring shaped slots have been introduced in the ground plane beneath the series arms. The performance of the fabricated prototype has also been validated experimentally.

Multi-device radio frequency power amplifiers (PAs) often exhibit strongly non-linear behavior in combination with long-term memory effects, leading to an extremely challenging model development cycle. This paper presents a new, dynamic, behavioral modeling technique, based on a combination of the real-valued decomposed piecewise method and concepts from the field of machine learning. The underlying theory of the proposed modeling technique is provided, along with a detailed modeling procedure. Experimental results show that the proposed decomposed piecewise support vector regression (SVR) model leads to significant performance improvements when compared with standard SVR models for both single transistor and multi-transistor PAs. Different model thresholds are used to test the proposed model performance for both PA types. For the single-transistor PA, modeled using only one partition, an approximately 10 dB normalized mean square error (NMSE) reduction is seen when compared with the standard SVR model. For the same PA, when utilizing two partitions, the reduction improves to 14 dB. When applied to a multi-device Doherty PA, the NMSE between model and measurement data is −50 dB, representing more than 10 dB improvement compared with the standard SVR model.

The possibility to characterize infinite and periodic frequency-selective surfaces (FSS) filters that have two orthogonal axes of symmetry inside a waveguide is reported. Thus, preliminary measurements can rapidly be obtained at low cost with few elementary cells instead of using a large FSS panel in free space. This is possible because of the equivalence that exists between the electromagnetic fields of two symmetric and oblique plane waves incident on and reflected from an infinite periodic surface and the incident/reflected fields that exist inside a single-mode rectangular waveguide containing a finite number of elementary cells. Comparisons of the measurements with some full-wave simulations for FSS belonging to the first three groups as they were defined by Munk confirm the good agreement between them. This is an interesting and simple assessment tool concerning the fabrication quality of FSS. The extension of this technique to non-symmetric FSS patterns is also discussed and supported by experimental and simulation results. The limitations of the technique are finally discussed.

This paper presents application of split ring resonators (SRR) in conventional waveguide slot array antenna to achieve performance improvement and multiband characteristics. Three SRRs have been placed on the transverse plane of a conventional slotted waveguide and has been simulated and measured. The measured results show that the antenna has dual band response with respective 10 dB return loss bandwidth 8.23–9.23 GHz (11.45%) and 9.68–11.01 GHz (12.87%). The measured gain and radiation pattern reveal that the proposed antenna has higher gain and front to back radiation ratio as compared with a conventional slotted waveguide antenna. Equivalent circuit of the proposed antenna also has been presented.

Multiple Input Multiple Output (MIMO) Radar has many advantages compared with conventional Radars including improved target parameters estimation, improved angular resolution while keeping a small number of antennas. Nevertheless, these advantages can be obtained when probing simultaneously the scattering matrix with orthogonal transmit signals. Recently, a passive orthogonal waveform generation technique was introduced using a 1 × M ports Mode-Mixing microwave cavity whose transfer functions are uncorrelated. This approach makes MIMO Radar system able to satisfy transmit beamforming constraint with a cost-efficient architecture. In this paper, more conceptual clarifications are brought and the orthogonality metrics are assessed. Furthermore, the proposed method is experimentally compared with a conventional MIMO Radar based on frequency hopping waveforms.

This paper presents wideband split-ring antenna arrays based on substrate integrated waveguide (SIW) for Ka-band (26.5–40 GHz) applications. The antenna array is fed by a 2.92 mm coaxial connector (K-connector) and the power is equally distributed to each split-ring resonator. The designed coplanar waveguide (CPW), SIW, CPW-to-SIW transition, coaxial-to-CPW transition, and two-stage SIW power divider are described in detail. By using a thin Rogers 6002 substrate with silver epoxy-filled vias, a transition prototype is designed, fabricated, and tested in a back-to-back configuration. A wideband split-ring resonator is developed as a single element and four possible arrangements of antenna arrays are introduced. By combining the designed components and routing paths, two full layouts of the antenna arrays with four split-ring resonators are addressed. As a demonstrator, a 2×2 antenna array prototype in a compact format is designed, fabricated, and tested. The fabricated antenna array achieves a measured directivity of 15.0 dBi with a fractional bandwidth of 23.0% centered at 30.5 GHz.

To achieve a high IIP2 level on a mixer, static calibration techniques have been developed. Most of them are based on an intentional introduction of a calibrated mismatch in the structure of the mixer. They are performed at production stage. It is also possible to automate them but their activation is strongly limited in portable devices because of system restrictions. Furthermore, IIP2 is sensitive to system variations, thereby degrading the calibration operation. The challenge is so to make the calibration system dynamic, i.e. performing an online calibration. This paper presents a perturbance-based algorithm as part of an automatic calibration system to track the optimum IIP2 level. Measurements validate the algorithm behavior and indicate the feasibility of using it in a complete calibration system for a future on-chip implementation.

Passive location techniques have always been considered an important topic and recently, thanks to digital signal processing (DSP) advances, new methods are being studied and experimented with. The possibility to passively locate radar emitters avoiding transmission is crucial in a variety of military applications, in particular when a flying platform (aircraft or helicopter) is entering an unknown and potentially hostile area. Elettronica SpA (ELT) gave start in 2004 to an experimental campaign in this field with the support and collaboration of the Italian Ministry of Defence (MoD). In this context the following activities were carried out:

• – theoretical study (with analytically derived and simulated results) of a passive location algorithm,

• – design and development of a passive location demonstrator (PLD) qualified for flight,

• – field tests (July 2006) performed in Sardegna (Salto di Quirra).

New technologies have resulted in transmission lines that deviate significantly from the intended rectangular cross sections. Trapezoidal cross sections and roughness that penetrate a significant depth into the surface in comparison to the skin-depth of the conductor can cause a very significant deviation in transmission line parameters from predicted values. Proximity effect further complicates the analysis by increasing losses and changing the impact of surface roughness by changing the current distribution. A skin-effect filament model that combines a traditional skin-effect filament modeling concept with traditional surface roughness modeling concepts is presented that accounts for surface roughness effects and non-ideal cross sections. The new technique models the transmission line non-idealities in a combined way with the current density in the signal and return current paths. This adapted filament model shows an average deviation of less than 2% above 1 GHz with one given transmission line measurement and does not have the computational challenges seen in a 3D full-wave solver.

This paper presents the design, implementation, and validation tests of a C-band analog-front-end (AFE) for the frequency modulated continuous wave (FMCW) radar. The system was designed to be used in various radar applications, including short rage mode, synthetic aperture radar (SAR) and moving target indication (MTI) mode. The AFE presented here was based on commercial off-the-shelf radio frequency components, and designed as a homodyne system, so the final applications were based on the FMCW radar. Validation tests and experiments were carried out in the laboratory and in open-air environments. The authors present tests of the AFE, including MTI and SAR trials, conducted using a ground moving platform (a car) and an airborne platform (a small aircraft). The results are discussed with the prospect of future work and further improvements in mind.

An axially slotted cylinder coated with two different types of inhomogeneous coating layers is considered. These inhomogeneous coatings have decreasing permittivity profiles. The effects of various parameters of these coatings upon the gain pattern have been investigated using numerical simulations. It is studied that the gain at certain observation angles can be enhanced or diminished by controlling the inhomogeneity parameters of these considered profiles. It is further studied that for specific type of considered inhomogeneous coatings, the forward direction gain can be enhanced significantly.

This paper presents a compact multilayer substrate integrated waveguide (SIW) bandpass filter with wide stopband. The square SIW cavity resonators in multilayer substrates are horizontally and vertically coupled with magnetic coupling. By properly designing the coupling structure, the couplings between the higher-order resonant modes can be suppressed. Compared with the conventional single-layer SIW filters, the proposed multilayer SIW filter also exhibits a compact size. To verify the design concept, a double-layered SIW filter is fabricated and measured. The measured results agree well with the simulations. The measured results show that the upper stopband of the filter is extended to 2.73 times of the center frequency 8.02 GHz.

In this study, a single-sideband time-modulated phased array (STMPA)-based hyper beamforming (HBF) system for automobile radar is suggested. The left beam and the right beam are generated once the improved STMPA is split into two subarrays. The HBF method is then used to produce the hyper beam. The switching sequence may be adjusted to generate the hyper beam in the desired direction. This study's benefits may be summed up as follows: (1) The hyper beam's sidelobe level is lower and its beamwidth is narrower than the conventional beam, which can help with estimating the direction of arrival. (2) The HBF can be achieved over a very wide scanning range. (3) With time as an additional controllable variable, the system's control mode is flexible and only two channels are needed, which lowers the system's cost and complexity. The effectiveness of the algorithm is tested through simulation, and the results highlight the system's potential when used with automobile radar.

Step-impedance resonators and step-impedance capacitor coupling pads are introduced to microstrip band-pass filters to suppress spurious stop-band responses up to the ninth order, thereby providing a very wide stop band. Combined with improvements in existing suppression techniques, the overall suppression in one of the filters, with 1 GHz center frequency and 42% bandwidth, is −54 dB, up to 8.9 GHz. By also using suitably placed resistors, spurious levels are now depressed to −67 dB up to 8.8 GHz, with only 0.03 dB extra pass-band loss.

In this paper, two high efficiency monolithic microwave integrated circuits (MMICs) are demonstrated using NANOTAM's in-house Ka-band fabrication technology. AlGaN/GaN HEMTs with 0.2 ${\rm \mu}$m gate lengths are characterized, and an output power density of 2.9 W/mm is achieved at 35 GHz. A three-stage driver amplifier MMIC is designed, which has a measured gain higher than 19.3 dB across the frequency band of 33–36 GHz. The driver amplifier exhibits 31.9 dB output power and 26.5% power-added efficiency (PAE) at 35 GHz using 20 V supply voltage with 30% duty cycle. Another two-stage MMIC is realized as a power amplifier with a total output gate periphery of 1.8 mm. The output power and PAE of the power amplifier are measured as 3.91 W and 26.3%, respectively, at 35 GHz using 20 V supply voltage with 30% duty cycle. The high efficiency MMICs presented in this paper exhibit the capabilities of NANOTAM's 0.2 $\rm\mu$m AlGaN/GaN on SiC technology.