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.

A novel microstrip low-pass filter (LPF) using radial patched resonator and modified T-shaped resonators is designed to achieve ultra-wide stop-band. Also, the designed LPF has successfully addressed the problems of compactness and insertion loss, simultaneously. LC equivalent circuit of the proposed filter is calculated and equation for the sharpness in transition band is obtained based on LC equivalent circuit and transfer function. The proposed filter not only exhibits a very wide stop-band of 168%, but also is able to suppress the 11th-harmonic response in conjunction with a small size of 0.147 × 0.052λg, where λg is the guided wavelength at 1.47 GHz. It is shown that the simulated results are highly consistent with the measured data.

An envelope tracking (ET) radio frequency (RF) power amplifier (PA) is described intended for handsets and applications where a large number of PAs are needed. Instead of the usual split frequency architecture, a linear tracking charge pump structure is proposed. This allows the supply voltage of an RF PA to increase during the peaks of a high peak-to-average power ratio signal. When combined with an LDMOS RF PA, 42.9% efficiency was achieved at 31.3 dBm output power (POUT) when amplifying a 5 MHz bandwidth 8 dB PAPR 3rd Generation Partnership Project (3GPP) long term evolution signal. The first channel adjacent power ratio (ACPR) without digital pre-distortion was −30.4 dBc, meeting the 3GPP handset emission mask. The ACPR could be improved to −32.5 dBc by adopting a curved envelope shaping function at a reduced efficiency of 38.9%.

This paper presents possible configurations of dual band filters based on transverse magnetic (TM) Dual mode cavities. The concept is to use TM dual-mode cavities in order to design compact dual band filters. High flexibility is obtained in terms of transmission zero (TZ) positioning. By using this approach a number of TZs up to the number of poles is attainable. Zeros can be placed in both the lower and upper stop-bands as well as between the two pass-bands to increase their insulation. The use of TM cavities allows a dramatic reduction of the filter length without significantly reducing the RF performances. Two three-cavity TM dual-band filters with six symmetric and asymmetric TZs have been designed and manufactured to validate the proposed geometry.

In this paper, a novel compact ultra-wideband (UWB) bandpass filter (BPF) without and with one sharply notched band is presented. The UWB bandpass characteristic is achieved using slotted resonators (SR) and a notch is obtained by spiral defected ground structure (SDGS) without any change in SR structure. Center frequency of the notched band can be easily changed (from 5 to 9 GHz) by tuning the dimensions of SDGS. To verify the feasibility of the proposed filter, two UWB BPFs, one without the notched band and the other with a notched band, at 8.0 GHz are developed and fabricated, there by suppressing the spurious satellite-communication signal within passband. Measured results of two fabricated filters have the advantages of wide −3 dB bandwidth from 3.1 to 10.6 GHz (which satisfies the requirements of US Federal Communication Commission -specified UWB limits), compact size, low insertion loss (<0.6 dB), and a wide upper stopband with high attenuation (−20 to −50 dB).

Through-the-Wall Imaging is an ever-expanding area in which processing time, scanning time, vertical, and horizontal resolutions have been tried to improve. In this study, several methods are investigated to obtain efficient reconstruction of through-the-wall imaging radar signals with high resolution. Microwave radar signals, which are produced in YTU Microwave Laboratory, are processed by compressive sensing (CS). B and C scanned reflection data samples collected between 1 and 7 GHz frequency band are taken randomly at 1/4, 1/2 of whole amount and reconstructed by CS method. Considering the signal structure, 10 and 20 compressible Fourier coefficients are taken through CS to analyze the difference between them. In addition, we applied synthetic aperture radar (SAR) processing, also combined with SAR-Multiple Signal Classification over raw data. Experimental performance results are given and shown in the figures with high quality.

In this paper, a novel microwave oscillator incorporating miniaturized nested split-ring resonators is proposed. The high-quality (Q) factor and wide spurious-free band of the NSRR contribute to low-phase noise and high-harmonic suppression of the proposed oscillator circuits. In addition, the NSRR is featured by compact size of 0.12λg × 0.12λg, where λg is the guided wavelength of resonance frequency. The fabricated 2.4 GHz oscillator has an output power of 11.7 dBm with 5 V DC supply and 10 mA current consumption. The second harmonic suppression is −45.49 dBc, the phase noise is −110 dBc/Hz @100 kHz, and the DC–RF conversion efficiency is measured as 30%.

This paper proposes a technique to design wide band switched-line (SL) true-time-delay (TTD) networks, commonly used for phased array antenna (PAA) applications. This study investigates the constant-delay behavior of switched-line phase shifters based on single-pole double-throw (SPDT) switches. Circuit sizing starts by considering the effective S-parameters of the switches, to use their non-idealities as an integral part of the phase shift linearly dependent to the frequency and by considering, from the beginning, the possible spatial positioning of elements that allows the circuit feasibility as a design target. The aim of this study is to provide a technique suitable for the design of well-matched TTD networks with a flat delay in wide bandwidth. In this paper, we propose new design formulas for which we show a single-frequency implementation. A computational strategy is used to obtain numerical solutions of the derived equations with this study. Finally, a monolithic X-band TTD circuit example is shown.

This paper describes the development of an L-Band (f0 = 1.575 GHz) high power and efficient solid state power amplifier (SSPA) designed for the European satellite navigation system (i.e. Galileo). The amplifier, developed in the framework of the European Project named SLOGAN, exploits the GH50-10 GaN technology available at United Monolithic Semiconductor foundry. The aim of the project is to offer, using as much as possible European technologies, a valid alternative to replace traveling wave tube amplifiers with more compact and reliable systems. All the SSPA functionalities, i.e. power supply, power conditioning and radio frequency amplification, are integrated in the developed architecture and accommodated in a single box with limited volume and mass. The required output power level is achieved by parallelizing several GaN die power bars of 12 and/or 25.6 mm. In continuous wave operating mode, the overall SSPA delivers an output power higher than 250 W at less than 2 dB of gain compression in the whole E1-band. Moreover, the registered gain and efficiency are higher than 67 dB and 54%, respectively.

This paper proposes a compact, low-loss, and low-cost phase shifter for millimeter-wave/sub-THz applications. The basic idea is to perturb the propagation constant of a high resistivity silicon image guide by high-dielectric constant barium lanthanide tetratitanates (BLT) ceramic loading. Three different BLT ceramic samples have been tested. The measured maximum phase-shift variation reaches 150° at 100 GHz with an average insertion loss of 2.85 dB and an insertion loss variation <0.7 dB for a sample of a 5-mm length. The proposed phase shifter has a bandwidth from 95 to 105 GHz. A low-cost fabrication technology has been developed and used to realize this phase shifter.

Continuous wave radars usually use separate transmit and receive antennas that are close to each other. In such a configuration, the antenna crosstalk is the strongest echo acquired by the radar surveillance channel. Sidelobes of the strongest echo are spread over all range cells, limiting the dynamic range of the radar. In this paper, a mismatched filter approach is presented that substitutes classic correlation in order to suppress correlation sidelobes. Both simulations and measurements are presented.

The paper experimentally investigates indoor visible light communication (VLC) channels. The disturbances come from the light bulbs and other VLC systems. The paper demonstrates that the noisiest light bulbs are the fluorescent lamps which emit high frequency disturbances. Different light bulbs are examined to make an optimal carrier choice for the transmitted signal. In the next part of the paper several modulation schemes and two kinds of detector systems are compared. The paper represents also the advantages and disadvantages of receiver constructions with and without a lens. The optimum modulation for different application is investigated.

A novel ultra-wideband Microstrip bandpass filter using Radial Stub Loaded Resonator (RSLR) and interdigital coupled Lines is presented in this paper. The RSLR and decagonal patch form a resonator named M to create tuneable multiple notches in the passband for the suppression of Wireless Local Area Network systems’ interference. To realize sharp roll-off, two adjustable transmission nulls are located at the lower and upper frequencies out of the passband. Even and odd-mode analysis is presented to calculate modal resonance frequencies contributing to create the ultra-wide passband. Bessel function is employed to estimate the input impedance of the radial stub which is used in formulation of even and odd mode admittances. Simulated and measured results show a passband from 3.4 to 12 GHz (135% bandwidth around 6.39 GHz) with a rejection notch at 4.99 GHz is achieved with return losses better than 14 and 12 dB in the first and second passbands, respectively. The insertion loss is lower than 0.9 dB in the 90% of passband and rejection level is greater than 19 dB from 12.25 to 17.45 GHz.

A broadband six-way out-of-phase substrate-integrated waveguide (SIW) power divider was designed, analyzed, and fabricated for low loss and out of phase dividing applications. The SIW technology was used to realize the power divider; where it consists of a central dual-disc probe connected with coaxial outer-conductor impedance matching transformer and six SIW-to-microstrip transitions as output probes. Three of the SIW-to-microstrip transitions are located at the top plane, whereas the other three are at the bottom plane of the power divider to achieve the out-of-phase dividing functioning. These transitions are all the same in size and shape for symmetry reason. Good transmissions from coaxial input port to six-way SIW power divider were also achieved. There is a reasonable agreement between measured and simulated results.

The recent developments in electronic cards such as the network equipment are characterized by the miniaturization of the board size and the increasing complexity of the layout. Because of these requirements, multi-layered printed circuit boards are commonly used and vias connecting signal lines on different layers, or integrated circuit devices to power and ground planes, are frequently used and often essential. However, a via is not an ideal transmission line. Besides, it creates discontinuities at high frequencies leading to high insertion loss degradation of signal which limits the performances of integrated circuit and systems. In this paper, the impacts of coupling between via and parallel-plates cavity on the response of microwave integrated devices are highlighted in the first part. Then, to describe the intrinsic interaction between the via transition and parallel-plate modes, the notion of parallel-plates matrix impedances is presented and new boundary conditions like open or plated through holes shielded boundaries of the cavities are introduced. Then, using this physics-based model, an intuitive equivalent circuit has been developed. Finally, the proposed approach and the equivalent circuits were validated by using comparisons with electromagnetic simulations and measurements in different scenarios.

In this paper, a new asymmetric structure is proposed for the dual-band unequal application, in which both open- and short-ended stubs are applied. Closed-form design equations are obtained for the proposed power divider using the modified even- and odd-mode analysis method. It is observed that the proposed power divider can operate at high frequency ratio from 2.3 to 3.7 and has a wide operating band. Besides, this proposed circuit can offer flexibility in fabrication. For verification, two power dividers operate at 1/2.5 GHz with different values of line impedance are fabricated and tested. There is good agreement between simulation and experimental results, validating the proposed design concepts.

This paper describes a linear-polarized reflector that reflects incident wave almost parallel to its surface at 60 GHz, when illuminated by an impinging plane wave with normal incidence. This structure is designed as a simple and low-cost passive repeater with both a quasi-endfire radiation and a flat profile. Working as a transmission relay, it is a quite potential and possible solution to improve the radio-coverage in the T-shaped corridor, which is a typical scenario of non-light-of-sight (NLOS) environment for 60 GHz indoor communications. The proposed repeater consists of an array of parallel grooves with appropriate depths, drilled in a metallic plate. Full-wave simulations and theoretical investigations are carried out to demonstrate the working principle and to optimize the performance. Then, an 80-groove breadboard in the size of 200 mm × 200 mm is fabricated and measured to explore the feasibility of the concept. In a practical measurement, when the distance from the repeater to transmitting antenna (Tx) is 2 m, and to the receiving antenna (Rx) is 1.5 m, the repeater exhibits a main beam at ±75° with gain up to 22.7 dB. The communication between Tx and Rx in NLOS areas is thus successfully recovered.

In this paper, a novel multi-mode resonator is presented, which is formed by cascading several open-circuited transmission line sections with a coupled-line section. Owing to its symmetry, even- and odd-mode analysis methods are applied to analyze its resonance characteristic. Based on this resonator, a microstrip ultra-wide bandwidth (UWB) bandpass filter is designed, fabricated, and measured. The simulated and measured results show that its bandwidth can cover the desired UWB. Return loss in passband is better than −14 dB. This filter is featured by good selectivity and wide stopband. Stopband suppression as low as −40 dB can be achieved within frequency range from 12 to 16 GHz.

The backscatter from radar object carries Doppler information of scatterers on the object determined by the radial velocity of scattering points and the radar transmitted frequency. For a rotating object this information is contained in the frequency characteristics over varying aspect angle. Frequency characteristics are used to create projections for Doppler radar tomographic imaging. This paper presents a method for high resolution imaging of a rotating target using a time-frequency transform of a returned signal as tomographic projections. The resolution of a tomographic image depends not only on radar system parameters but also depends on the resolution of input projections. The reassigned spectrogram is proposed for building of tomographic projections, due to its possibility of squeezing of frequency spread. The reassigned spectrogram is sensitive to noise so the denoising procedure in the time-frequency domain must be performed before the reassignment procedure. The denoising is performed by removing Short Time Fourier Transform (STFT) noise coefficients below the appropriate threshold. The STFT is a linear time-frequency transform and coefficients, which belong to the signal and coefficients which belong to noise can be analyzed separately. The efficiency of the proposed idea of imaging is supported by results of numerical experiments.

This paper presents an analytical model to characterize the radiation pattern of focused aperture antennas. The model is based on the classic parabolic on pedestal distribution for amplitude, but in this work the focusing phase term is considered and applied in the Fresnel region. The model is useful for millimeter and submillimeter wave imaging radar systems that usually work in the Fresnel region of the antenna. Analytical closed expressions are developed to predict the available resolution (transversal beamwidth) and operating range (axial beamwidth) of such systems. The effects of the first- and second-order phase distributions on the aperture have also been also studied in order to show the scanning effect, the axial refocusing, and the astigmatic beam degradation.