A 245 GHz sensor system for gas spectroscopy is presented, which includes a SiGe receiver (RX), a SiGe transmitter (TX), and a 0.6 m long gas absorption cell between the TX and RX. The integrated local oscillators of the RX and the TX are controlled by two external phase locked loops (PLLs), whose reference frequencies are swept with constant frequency offset for a low IF of the RX. The RX consists of a differential low noise amplifier (LNA), an integrated 122 GHz local oscillator (LO) with 1/64 divider, a 90° differential hybrid, and active subharmonic mixer. The TX consists of an integrated 122 GHz LO with 1/64 divider, and a frequency doubler. The RX and TX are fabricated in 0.13 µm SiGe BiCMOS with ft/fmax of 300/500 GHz. Using external dielectric lenses for the TX and RX, the absorption spectrum of gaseous methanol has been measured. The reference frequency of the TX-PLL is modulated for frequency-modulation spectroscopy. The performance of the sensor system is demonstrated by measuring the 2f absorption spectrum (second harmonic detection) of gaseous methanol.

In this paper, a vase-shaped monopole antenna is presented for dual band notch (WiMAX IEEE802.16 3.30–3.80 GHz with C-band 3.80–4.20 GHz and WLAN IEEE802.11a/h/j/n 5.15–5.35 GHz, 5.25–5.35 GHz, 5.47–5.725 GHz, 5.725–5.825 GHz) UWB and other wireless services (close range radar: 8–12 GHz in X-band & satellite communication: 12–18 GHz in Ku-band). Measured VSWR of proposed antenna shows a high band-rejection for WiMAX along with C-band with VSWR = 25.33 at 3.77 GHz and WLAN with VSWR = 6.0 at 5.64 GHz is achieved by cutting two C-shaped slots on the radiating patch. Designed antenna covers a wide usable fractional bandwidth 160% (2.58–20.39 GHz). Furthermore, the measured gain of antenna is relatively stable across the impedance bandwidth except band-notched. In addition, antenna offers omni-directional pattern, reasonably small 20 × 20 × 0.787 mm3 and easy to construct structure.

A compact antenna module with a single band notch at wireless local area network (WLAN) (5.725–5.825 GHz) for ultra-wideband (UWB) multiple input multiple output (MIMO) applications is proposed. Proposed antenna which acquires size of 0.299 λ × 0.413 λ × 0.005 λ mm3 at 3.1 GHz consists of two symmetrical radiators placed side by side on global merchandise link (GML) 1000 substrate (εr = 3.2, tan δ = 0.004). Isolation between the antenna elements is >18 dB in the whole UWB band, which is achieved by introducing the vertical stub and H-slot between the monopole radiators in the ground plane. The simulated and measured results of the antenna system are in good agreement. The proposed antenna covers entire UWB with impedance bandwidth (|S11| < −15 dB) from 3.1 to 11 GHz except at WLAN notched band. The designed antenna module bears low envelope correlation coefficient and minimal multiplexing efficiency hence fulfilling criteria suitable for various wireless MIMO applications.

This paper introduces a new maritime search and rescue system based on S-band illumination harmonic radar (HR). Passive and active tags have been developed and tested while attached to life jackets and a small boat. In this demonstration test carried out on the Baltic Sea, the system was able to detect and range the active tags up to a distance of 5800 m using an illumination signal transmit-power of 100 W. Special attention is given to the development, performance, and conceptual differences between passive and active tags used in the system. Guidelines for achieving a high HR dynamic range, including a system components description, are given and a comparison with other HR systems is performed. System integration with a commercial maritime X-band navigation radar is shown to demonstrate a solution for rapid search and rescue response and quick localization.

In this paper, a fractal-based complementary split-ring resonator (CSRR) has been introduced as a defected ground structure (DGS) in the ground plane of a dual-mode microstrip bandpass filter to produce a new compact filter with dual-band response. The conventional double square ring resonator structure is modified such that its inner ring is made with a fractal shape instead of a square. Measured and simulation results show that the resulting filter offers a dual passband response; the higher passband is attributed to the dual-mode microstrip ring structure, whereas the lower passband is as a result of the embedded CSRR DGS structure. In addition, the results show that the position of the lower passband could be varied, to a certain extent, without affecting the position of the higher passband by applying higher fractal iteration levels to the inner split ring. These features, together with the compact size the proposed filter offers, make it suitable for use in a wide variety of dual-band communication applications. Measured results, carried out on filter prototypes, have been found in agreement with those theoretically predicted.

In this paper, a complete design procedure, together with robust system validation approaches, is presented for implementing a high-performance re-configurable digital predistortion (DPD) test platform for compensating for nonlinear distortion and memory effects induced by radio frequency (RF) power amplifiers (PAs) in the transmitters of modern wireless communication systems. This hardware and software co-operated test system not only enables effective validation for DPD algorithm development, but also provides a high-performance and reliable hardware-based linearization test platform. The experimental test was applied on a medium power Doherty amplifier, which was designed for 3 G/4 G wireless communication base stations. By applying our DPD algorithms on the proposed platform, more than 30 dB improvements in adjacent channel power ratio can be achieved for Universal Mobile Telecommunications System and long-term evolution signal excitations.

In this paper, a differential microfluidic sensor and comparator based on a pair of microstrip lines loaded with dumbbell-shaped defected ground structure resonators is applied to the characterization of electrolyte concentration in samples of horse urine. Since variations in the total electrolyte content in urine may be indicative of certain pathologies, the interest is to use the device as a comparator, in order to determine changes in the electrolyte concentration as compared to a reference level. To validate the approach, we have made differential measurements of a set of urine samples with different electrolyte concentrations (which have been previously obtained by means of electrochemical methods). The obtained results correlate with the nominal electrolyte concentrations of the samples, thereby pointing out the potential of the approach as a low-cost pre-screening method (or complementary diagnosis system) to detect potential pathologies or diseases in horses and other animals.

This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments

We review the main results of the development of whispering gallery mode (WGM) resonators and their unique applications due to their quasi-optical functionality. Several types of advanced WGM resonators are proposed by the authors. The theoretical results are described for the resonators with an analytical solution of the electromagnetic problems. Special emphasis is given to the interaction of moving charged particles and waves of cylindrical resonators. Important aspects are described concerning the developed sapphire resonators, for which an exact solution can only be found by using specially designed computer program products. A separate section of the paper is devoted to application aspects of the WGM resonators. In particular, it describes advanced solutions for overcoming the problems of measuring the small microwave (MW) surface impedance of unconventional superconductors in the form of large-area thin films and small samples under study. In addition, a demonstration of accurate complex permittivity measurements of small volumes of lossy liquids is provided. Special emphasis is given to highly stable MW signal sources, namely Ka-band transistor-based feedback oscillator and solid-state maser WGM oscillators. Recently obtained results are presented of experimental studies of the auto-oscillatory system developed on the basis of the WGM resonator with relativistic electron beam.

A large-signal model and a simulation technique based on non-sinusoidal voltage excitation are used to obtain the electric field snapshots from which the series resistance and related high-frequency properties of a 35 GHz Silicon Single-Drift Region (SDR) Impact Avalanche Transit Time (IMPATT) device have been estimated for different bias current densities. A novel method is proposed in this paper to determine the parasitic series resistance of a millimeter-wave IMPATT device from large-signal electric field snapshots at different phase angles of a full cycle of steady-state oscillation. The method is based on the depletion width modulation of the device under a large-signal condition. The series resistance of the device is also obtained from the large-signal admittance characteristics at threshold frequency. The values of series resistance of a 35 GHz SDR IMPATT diode obtained from the proposed method and the large-signal admittance method are compared with experimentally reported values. The results show that the proposed method provides better and closer agreement with the experimental value.

This article addresses the analysis and digital signal processing (DSP)-based mitigation of phase noise and sampling clock jitter in orthogonal frequency division multiplexing (OFDM) radios. In the phase noise studies, the basic direct-conversion receiver architecture case is assumed with noisy downconverting oscillator. In the sampling jitter case, on the other hand, the so-called direct-radio-frequency-sampling receiver architecture is deployed utilizing bandpass sub-sampling principle. The basis for the DSP-based impairment mitigation techniques is first formed using analytical receiver modeling with incoming OFDM waveform, where the effects of both oscillator phase noise and sampling clock jitter are mapped to certain type subcarrier cross-talk and distortion compared to ideal receiver case. Then iterative detection principles and interpolation techniques are developed to essentially estimate and cancel the subcarrier distortion. Also some related practical aspects, like channel estimation, are addressed. The performance of the proposed mitigation techniques is analyzed and verified with extensive computer simulations. In the simulations, realistic phase-locked-loop-based oscillator models are used for phase noise and sampling clock jitter. In addition, different received signal conditions like plain additive white Gaussian noise channel and extended ITU-R Vehicular A multipath channel are considered for practical purposes. Altogether the obtained results indicate that the effects of oscillator and sampling clock instabilities can be efficiently reduced using the developed signal processing techniques.

A novel compact multiple-input–multiple-output (MIMO) antenna system operating from 5 to 7.3 GHz is proposed for wireless applications. It comprises of two similar antennas with microstrip feeding and radiating patches developed on a reduced ground plane. The developed antenna system resonates at a dual-band of 5.4 and 6.8 GHz frequencies, giving an impedance bandwidth of 38% (based on S11 < −10 dB). The unique structure of the proposed MIMO system gives a reduced mutual coupling of −27 dB at 5.4 GHz resonant frequency and −19 dB at 6.8 GHz resonant frequency and in the entire operating band the coupling is maintained well below −16 dB. The envelope correlation coefficient of the proposed MIMO system is calculated and is found to be less than 0.05 in the operating band. The measured and simulation results are found in good agreement.

This paper presents the results of Doppler-polarimetric radar signal analysis, computer modeling, and real data processing that show the correlation between differential Doppler velocity (DDV), which is a difference between mean Doppler velocities measured at orthogonal polarizations of electromagnetic waves, and parameters of rain including both rain microstructure (parameters of drop-size distribution) and turbulence intensity in resolution volume. The reasonability to use DDV as one of the informative parameters in the recognition neural network system is checked.

This paper deals with the numerical dosimetry for adult and children models exposed to CW signals of several wireless communication systems (UMTS, WiMax, and Bluetooth) within a partly shielded environment represented by a realistic car model. More than 20 mono- and multi-source exposure scenarios are considered. Computational results demonstrate that, for all considered exposure scenarios, the specific absorption rate (SAR) is at least 40 times (whole-body average) and 10 times (local SAR) lower than the exposure limits fixed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The whole-body average SAR values for children are found to be typically 1.1–1.3 times higher than those of adults. Under several exposure scenarios, the local SAR in the limbs of children models is 2–3 times higher than corresponding values in adult models. The power density distributions within the car have been also analyzed for one, two, and three simultaneously emitting devices. The results show that the homogeneity of the power density distribution increases with increasing number of simultaneously operating transmitters. These data suggest that the use of several wireless communication devices within a car leads to exposure levels that are several orders of magnitude below international exposure limits, even for the multi-exposure scenarios for both adult and children models.

A design of annular ring microstrip antenna with finite ground structure is proposed in this paper. The proposed geometry offers impedance bandwidth of 2.362 GHz and has stable radiation patterns for all resonant frequencies in the operational band. It is also found that shape and dimension of the finite ground plane is a key factor in improving the bandwidth of the proposed geometry. The geometry is low profile and has simple structure, therefore can be used for lower band of ultra-wideband applications.

This paper introduces a symmetric bar chart-shape (SBCS) microwave sensor for measuring permittivity of fluidic samples. For designing purposes, the introduced sensor was used based on the field changes between the SBCS and rectangular loop microstrip (RLM) structure. When a sample is placed on the sensing location, interaction between SBCS and RLM varies the field intensity. The vinegar samples were combined with water and then they are placed on the sensor. The change in field intensity changes the resonance frequency. However, there is a relationship between the permittivity of samples and the resonance frequencies. The proposed sensor is implemented on the substrate of RO4003C. The relative permittivity of samples changed from 59 to 77 and the resonance frequencies changed from 2.3 to 1.4 GHz. The quality factor is 3544 and the sensitivity is 2.2%.

Piezoelectric thin films have existing and promising new applications in microwave filter technologies. The final performance depends on many parameters, and very specifically on the materials properties of each involved material. In this article, materials and properties for thin-film bulk acoustic wave resonators are discussed on some selected issues: the piezoelectric coefficients and acoustic losses of AlN, the relation of the first one with microstructural parameters, the inclusion of parasitic elements, and the merits of and problems with ferroelectric materials.

This paper presents an efficient approach for the design of a non-uniform single ring circular antenna array (CAA) for the synthesis of the optimal far-field radiation pattern. A recently proposed meta-heuristic-based optimization technique known as ant lion optimization (ALO) is applied in this paper to determine the optimum set of current amplitude excitation weights and the inter-element distance among the array elements to reduce the side lobe level (SLL) and 3-dB beam width considering the mutual coupling effect. The results achieved by employing the ALO algorithm are compared with the uniform radiation pattern and with those of the recently reported literature containing equal sets of elements to prove the superiority of ALO algorithm. Three different design examples of 8, 10, and 12 elements CAA are presented, and their performances are compared to illustrate the capability of the ALO algorithm-based approach over those of the recently reported literature.

This paper presents a compact microstrip tri-band bandpass filter (BPF) using two multimode stepped-impedance resonators (SIRs) with a 0° feed structure. The fundamental odd-mode and even-mode resonant frequencies and the third resonant frequency are utilized to determine the center frequencies of the tri-band filter. The mode-splitting technique is used by combining two SIRs with electrical coupling. Therefore, two modes generate one passband and the bandwidths can be controlled by the electrical coupling strength. The 0° feed network is applied to create one pair of transmission zeros at each side of all the triple passbands, resulting in high selectivity. Finally, a tri-band BPF with the central frequencies of 1.8, 2.4, and 5.8 GHz, and respective fractional bandwidths of 8.9, 12.5, and 5.3% are designed and fabricated. The simulated and measured results show a good agreement.

ADS-B provides convenient means of air traffic control (ATC) for its low cost and simple ground station hardware. In a low percentage of cases, aircraft positions transmitted via ADS-B are error prone due to e.g. faulty wiring with onboard navigation systems. In the proposed approach, direction of arrival (DOA) estimation is used to verify ADS-B airborne positions. The potential positioning error of ADS-B is thereby evaluated by comparing DOA estimates to DOA values calculated from ADS-B references and the sensor position and orientation. To prove the accuracy of the applied DOA estimation sensor, an additional measurement campaign using a dedicated measurement aircraft has been conducted.