We present the realization of an frequency-modulated continuous-wave radar target simulator, based on a modulated-reflector radar system. The simulator, designed for the 24 GHz frequency band, uses low-cost modulated-reflector nodes and is capable to simultaneously generate multiple targets in a real-time environment. The realization is based on a modular approach and thus provides a high scalability of the whole system. It is demonstrated that the concept is able to simulate multiple artificial targets, located at user-selectable ranges and even velocities, utilized within a completely static setup. The characterization of the developed hardware shows that the proposed concept allows to dynamically and precisely adjust the radar cross-section of each single target within a dynamic range of 50 dB. Additionally, the provided range-proportional target frequency bandwidth makes the system perfectly suitable for fast and reliable intermediate frequency-chain calibration of multi-channel radar systems. Within this paper we demonstrate the application of the concept for a linear sweeped frequency-modulated continuous-wave radar. The presented approach is applicable to any microwave-based measurement system using frequency differences between transmit- and receive signals for range- and velocity evaluation, such as (non-)linear sweeped as well as pure Doppler radar systems.

This manuscript deals with the development of a novel configuration of a wide-band single-layer frequency selective surface (FSS) for wide-band rejection applications. The established unit cell is composed of a simple circular ring on the top side of the substrate and a combined conductive element on the backside. Such an inclusion of conductive elements and accurate tuning of their dimensions ends in the rejection of a wide frequency band extended from 6.3 to 16.3 GHz. Moreover, the proposed structure exhibits a stable response against different angles of incidence for both TE and TM polarizations. Detailed simulation and measurement studies are carried out to investigate the performance of the proposed FSS. The obtained results are discussed in depth.

Microwave and millimeter-wave reflectometry is one of the potential techniques for the diagnosis and detection of biological abnormalities, such as subcutaneous masses or cancerous tumors in human body. In this paper, a high-quality microwave sensor based on planar misrostrip resonator is designed, fabricated, and successfully tested with different kinds of biological samples. The proposed sensor has unique properties such as small size, simple fabrication, non-contact with a sample, excellent de-coupling from surroundings, and high microwave power is directly coupled into the tissue. Two experiments are performed for the detection of visible and hidden “lipoma” (fat masses), and minimum size of “lipoma” that is diagnosed by the sensor is obtained as well. In this regard, a two-dimensional image of hidden “lipomas” with amplitude contrast about 30 dB and frequency shifts contrast about 60 MHz at a λ/10 (at 13.5 GHz) stand-off distance is provided. Finally, a measurement scenario for the detection of skin cancer based on the artificial model using different layers of raw chicken with different water content is described. Results show that the proposed microscope is easy to fabricate and provide a low-cost solution for fast and accurate skin cancer detection.

The Misell algorithm is one of the most widely used phase retrieval holography methods for large reflector antennas to measure surface deformation. However, it usually locks in a local minimum because it heads downhill from an initial estimation without any consideration whether it heads for a global minimum or not. The core problem of the Misell algorithm is to find an initial estimation near the global minimum to avoid local stagnation. To cope with the problem, we construct a hybrid Misell algorithm, named modified very fast simulated annealing (MVFSA)-Misell algorithm, to search for the global minimum with a high efficiency. The algorithm is based on the combination of the MVFSA algorithm and Misell algorithm. Firstly, the MVFSA is utilized to obtain a rough position near the global minimum in limited steps. Then, the Misell algorithm starts from the rough position to converge to the global minimum with high speed and accuracy. The convergence characteristic of the proposed algorithm was discussed in detail through digital simulation. Simulation results show that the algorithm can reach global minimum in a very short time. Unlike the traditional Misell algorithm, the hybrid algorithm is not influenced by initial phase estimation.

This paper presents a fully-integrated direct-conversion fundamentally-operated mixer-first quadrature receiver module with a tunable LO in the 219–266 GHz band. It has been implemented in a 0.13-μm SiGe heterojunction bipolar transistor technology. It includes an on-chip LO path driven externally from the printed circuit board (PCB) connector level at 13.6–16.7 GHz. A hybrid coupler generates the quadrature LO signal, which drives a pair of double-balanced fundamentally-operated down-conversion mixers, whose RF ports are connected to a wideband lens-integrated on-chip ring antenna. The chip-on-lens assembly is placed in the recess of a high-speed PCB and wire-bonded. To compensate the inductive behavior of the wire-bond interconnection between the chip and the PCB at the high-speed IF outputs, an on-board 8-section step-impedance low-pass filter has been implemented. The module shows a 47 GHz 3-dB radio frequency/local oscillator operation bandwidth (BW), a peak conversion gain of 7.8 dB, a single-side-band noise figure of 11.3 dB, and a 3-dB IF BW of 13 GHz. The in-phase and quadrature amplitude imbalance stays below 1.58 dB for the 210–280 GHz band. The down-conversion and the baseband stages consume together 75.5 mW, while the LO path 378 mW. The maximum data-rate achieved with this receiver in combination with the transmitter presented in [1–3] is 60 Gbps for quadrature phase shift keying modulation.

This paper presents a novel asymmetric coplanar waveguide-fed quad-band hybrid antenna for wireless applications. The proposed hybrid antenna combines a conventional monopole antenna and a zeroth-order resonator antenna to perform a dual-mode operation. The first mode is generated by a slotted monopole antenna, supporting the two higher resonances at about 3.5 and 5.8 GHz. The second mode is supported by loading a composite right-/left-handed transmission line unit cell near the slotted monopole, contributing to the two lower resonances at about 1.6 and 2.5 GHz. It is printed on an FR4 substrate with the overall dimensions of 40 mm × 24 mm × 1.6 mm. Experimental results demonstrate that it can cover the global positioning system (1.57–1.59 GHz), wireless local area network (2.4–2.485, 5.15–5.35, and 5.725–5.825 GHz), and worldwide interoperability for microwave access (2.5–2.69, 3.3–3.7, and 5.25–5.85 GHz) applications with monopole-like radiation patterns and acceptable gains.

A novel Scarecrow-shaped patch antenna has been presented for broadband applications. The proposed antenna composed of an elliptical shape radiating patch, partial ground plane, and 50 Ω microstrip line which is Boolean added with the radiating patch. To achieve wide impedance bandwidth, an elliptical notch and two rectangular-shaped parasitic slots have incorporated on the ground plane. This antenna has printed on FR-4 substrate (tan(δ) = 0.02, εr = 4.3) with the thickness of 1.6 mm. It is energized by coaxial feed which is connected with a microstrip line through via. The proposed configuration has examined numerically with the help of CST Microwave Studio and experimentally also. The broadband property of this antenna has been achieved by adjusting the dimensions of an elliptical notch. The antenna exhibits the bandwidth of 116.32% from 1.23 to 4.65 GHz for S11 <−10 dB. Current distribution and far-field pattern at resonating frequencies 1.29, 1.77, 2.28, 2.94, and 3.72 GHz have been studied. It has been found that the far-field pattern is distorted at frequency 3.72 GHz due to higher order modes. Effect of parameters on frequency response of the antenna has also been investigated to know the behavior of the antenna.

In this paper, we present a novel dual-band wearable compact flexible antenna for body-centric wireless communications (BCWCs). The design is based on a modified planar dipole with parasitic elements, meandered lines, and a rectangular reflector embedded into a hydrophobic rubber-textile multilayer substrate in order to get both good antenna performance and mechanical properties. The antenna's structure is analyzed and optimized in free space (FS), on a numerical and an experimental homogeneous flat phantom. The overall dimensions of the antenna are 50 mm × 40 mm × 4.6 mm and a prototype mass of 11 g, which makes it suitable for practical applications in BCWCs. The built prototype resonated at 2.47 GHz with a |S11|−26.90 dB and at 5.42 GHz with a |S11|−24.60 dB in the FS. The measured bandwidths are 500 MHz (2.2–2.7 GHz) and 1000 MHz (4.65–5.75 GHz) at lower and higher bands, respectively. The antenna exhibits a measured maximum gain of 1.17 dBi at 2.66 GHz and a radiation efficiency of 28.44% in FS. The 10 g average maximum specific absorption rate is 0.165 W/kg at 2.70 GHz and 0.520 W/kg at 5.24 GHz when the antenna is placed on the numerical phantom at net input power 0.1 W.

This paper presents a wideband, low-cost, high-performance, and continuous phase shifter for millimeter-wave (mm-wave) phased array systems. Its operational principle is based on modifying the propagation mode of a grounded coplanar waveguide (GCPW) line by placing a high dielectric constant slab over the GCPW line. The propagation constant and hence the phase shift is varied by changing the air gap height between the GCPW line and the dielectric slab. As a proof of concept, a piezoelectric transducer is used to precisely control this air gap height. A printed circuit board-based phase shifter prototype has been designed, fabricated, and tested at two different frequency bands (19–21 and 28.5–30.5 GHz), which are the downlink and uplink bands, respectively, of the Ka-band two-way satellite communication system. A continuous and almost linear phase–voltage characteristic has been achieved experimentally with average phase shift variations 170° and 260° over the two bands, respectively. The footprint of the proposed phase shifter is 2.1 mm×3 mm, which is quite small and suitable for low-profile mm-wave applications. The average insertion losses over the two bands are <0.53 and 2.35 dB with very low variations±0.22 and ±0.35 dB, respectively.

The benefit of cryogenic cooling on the performance of millimeter-wave GaAs Schottky-barrier varactor-based frequency multipliers has been studied. For this purpose, a dedicated compact model of a GaAs Schottky-barrier varactor using a triple-anode diode stack has been developed for use with a commercial RF and microwave CAD tool. The model implements critical physical phenomena such as thermionic-field emission current transport at cryogenic temperatures, temperature dependent mobility, reverse breakdown, self-heating, and high-field velocity saturation effects. A parallel conduction model is employed in order to include the effect of barrier inhomogeneities which is known to cause deviation from the expected I--V characteristics at cryogenic temperatures. The developed model is shown to accurately fit the I--V --T dataset from 25 to 295 K measured on the varactor diode stack. Harmonic balance simulations using the model are used to predict the efficiency of a millimeter-wave balanced doubler from room to cryogenic temperatures. The estimation is verified experimentally using a 188 GHz balanced doubler cooled down to 77 K. The model has been further verified down to 14 K using a 78 GHz balanced doubler.

In this paper, an ultra-wideband (UWB) band-pass filter (BPF) with a sharp notch band is presented. The UWB BPF consists of modified elliptical-ring and multi-mode stub-loaded resonator (MM-SLR). By adding the asymmetric tight coupled lines resonator via input/output (I/O) lines, it can be achieved UWB band-pass response. With adding two bends to the middle resonator, a notch band at 6.86 GHz is created, so that it can be controlled using the mathematical formulas (MF). In the meantime, the equivalent circuit of the middle resonator is obtained using L–C analysis. Measured results of fabricated filter have the advantage such as ultra-wide pass band (fl and fH of the defined UWB pass band are 3.776 and 10.42 GHz, which satisfy the requirements of FCC-specified UWB limits), compact size, low insertion loss <0.65 dB and the stop band of the proposed filter is from 11.1 to 16.32 GHz with attenuation of −39.8 to −42.14 dB, respectively. The proposed UWB filter is realized using the substrate with dielectric constant of 2.2 and substrate height of 0.787 mm. Experimental verification is provided and good agreement has been found between simulation and measurement results.

A novel concept of using fractal antenna with metamaterial and slot to achieve multiband operation is investigated. The antenna consists of an L-shaped slot, Sierpinski triangle (used as fractal) as the radiating part and metamaterial circular split ring resonator (SRR) as the ground plane. The introduction of metamaterial in the ground plane makes the antenna operate at 3.3 GHz (middle WiMAX). The etching of Sierpinski triangle and L-shaped slot in the radiating monopole perturbs the surface current distribution; thereby increasing the total current path length which tends the antenna to further operate at 5.5 (upper WiMAX), 7.3 (satellite TV) and 9.9 GHz (X-band), respectively. The extraction of medium parameter of a circular SRR through waveguide medium is discussed in detail. The antenna has a compact dimension of 0.33λ0 × 0.27λ0 × 0.01λ0 = 30 mm × 24.8 mm × 1.6 mm, at a lower frequency of 3.3 GHz. Under simulation, antenna operates at 3.3, 5.5, 7.3 and 9.9 GHz with S11 < −10 dB bandwidth of about 5.9% (3.24–3.44 GHz), 5.6% (5.31–5.62 GHz), 7.3% (6.99–7.52 GHz) and 3.02% (9.78–10.08 GHz), respectively. In measurement, antenna exhibit resonances at 3.1, 5.52, 7.31, 9.72 GHz with S11 < −10 dB bandwidth of about 3.5% (3.04–3.15 GHz), 5.01% (5.44–5.72 GHz), 13.2% (6.76–7.72 GHz) and 5.77% (9.42–9.98 GHz), respectively. Good impedance matching and stable radiation characteristics are observed across the operational bandwidth of the proposed configuration.

This paper presents the design and characterization of a D-band (110–170 GHz) monolithic microwave integrated direct carrier quadrature modulator and demodulator circuits with on-chip quadrature local oscillator (LO) phase shifter and radio frequency (RF) balun fabricated in a 130 nm SiGe BiCMOS process with ft/fmax of 250 GHz/400 GHz. These circuits are suitable for low-power ultra-high-speed wireless communication and can be used in both homodyne and heterodyne architectures. In single-sideband operation, the modulator demonstrates a maximum conversion gain of 9.8 dB with 3-dB RF bandwidth of 33 GHz (from 119 GHz to 152 GHz). The measured image rejection ratio (IRR) and LO suppression are 19 dB and 31 dB, respectively. The output P1dB is −4 dBm at 140 GHz RF and 1 GHz intermediate frequency (IF) and the chip consumes 53 mW dc power. The demodulator, characterized as an image reject mixer, exhibits 10 dB conversion gain with 23-dB IRR. The measured 3-dB RF bandwidth is 36 GHz and the IF bandwidth is 18 GHz. The active area of both the chips is 620 µm × 480 µm including the RF and LO baluns. A 12-Gbit/s QPSK data transmission using 131-GHz carrier signal is demonstrated on modulator with measured modulator-to-receiver error vector magnitude of 21%.

Design and fabrication of a microstrip feedline-based Vivaldi antenna in the frequency range of 6.0–8.0 GHz have been presented. The Vivaldi antenna is a planar antenna, fabricated at the microstrip feedline by having an exponentially tapered slot profile on it. An optimized computer-aided design has been developed and simulated for the desired radiation parameters like voltage standing wave ratio, bandwidth, directionality, beam-width, etc. The optimized design has been fabricated and tested. Wherever the results are not found as desired; problem has been comprehensively investigated and analyzed. This is found associated with a discontinuity at feed line, fabrication tolerance constraints and parasitic capacitance at the edges or the bent of the microstrip feedline which introduce the parasitic reactance in antenna design. Here, the presented work explores a generalized theoretical procedure for the compensation of associated problem by incorporating the reactive patch on the feedline. The developed theory is applied in fabrication and tested for the desired results.

An integrated reconfigurable antenna capable of spectrum sensing along with various reconfiguration features such as polarization, frequency, bandwidth, and radiation pattern is proposed here. The proposed antenna senses the spectrum by UWB antenna from 2 to 11 GHz to identify the spectrum conditions. After identifying the direction of maximum traffic or interference, the proposed antenna accordingly reconfigures its radiation pattern in order to mitigate the interference using switchable shorting posts. The antenna can reconfigure its polarization state using a switchable slot in the circular antenna. Frequency reconfigurability is obtained by using a varactor diode from 2 to 4 GHz. The antenna can reconfigure its bandwidth from UWB to NB by switching the active ports state. Measured and simulated results of the proposed antenna shows very good agreement, hence, validating the proposed design.

This paper presents a technique to increase the bandwidth in substrate integrated waveguide (SIW) cavity-backed antennas, inspired by the design of cavity filters. The proposed structure consists of a slot antenna backed by two cavities, located one on top of the other and coupled through a slot. To demonstrate the bandwidth increase, a standard cavity-backed SIW antenna, with a rectangular slot etched in the top metal plane, has been designed, manufactured, and measured. Subsequently, a similar antenna was developed, by doubling the substrate thickness with the aim to improve the bandwidth. Finally, the new topology of two-cavity SIW antenna has been implemented and compared with the two previous ones. Simulation and experimental results show that the proposed two-cavity antenna exhibits a bandwidth twice as large as the standard SIW cavity-backed antenna.

Frequency- and time-domain characteristics as well as indoor propagation channel impulse response of a compact dual band-notched ultra-wideband (UWB) slot antenna are investigated in this paper. The antenna consists of a narrow rectangular radiation patch and a rectangular wide slot in the modified ground plane. A pair of L-shaped stubs are connected to the radiation patch to obtain band-notched property in WLAN band and a narrow straight stub is placed on the back side of the substrate to create band-notched characteristics in X-band downlink satellite communication system. Moreover, two small parasitic strips are added to the radiation patch to enhance the bandwidth (BW) of the antenna up to 14 GHz. A comprehensive study on time-domain and indoor propagation channel characteristics of the proposed antenna is also presented throughout the paper. A ray-tracing approach based on geometrical optics is applied to analyze the indoor channel characteristics. The designed antenna not only has a wide BW and compact size but also has appropriate radiation and time-domain characteristics over the antenna operating BW. The measured and simulated results are in good agreement. These advantages make the proposed antenna as a desirable option for UWB impulse radio applications.

A passive evanescent mode half-mode substrate integrated waveguide (HMSIW) resonator loaded with a complementary split ring resonator (CSRR) is designed and fabricated for humidity sensing applications. The use of the CSRR which is etched on the top plane of the HMSIW can significantly reduce the size of the device. Without any sensing material, the sensor which has a compact size of 0.17λg × 0.17λg can provide high humidity sensitivity up to 5.82 MHz/%relative humidity (RH) at high RH region (>84.3%). The results indicate that the proposed structure is a promising candidate for radio and microwave humidity sensing applications.

A compact printed quadrant shaped monopole antenna is introduced in this paper as a good prospect for ultra wideband- multiple-input multiple-output (UWB-MIMO) system. The proposed MIMO antenna comprises two perpendicularly oriented monopoles to employ polarization diversity. An open circuit folded stub is extended from the ground plane of each radiating element to enhance the impedance bandwidth satisfying the UWB criteria. Two ‘L’ shaped slots are further etched on the radiator to provide good isolation performance between two radiators. The desirable radiator performances and diversity performances are ensured by simulation and/or measurement of the reflection coefficient, radiation pattern, realized peak gain, envelope correlation coefficient (ECC), diversity gain, mean effective gain (MEG) ratio and channel capacity loss (CCL). Results indicate that the proposed antenna exhibits 2.9–11 GHz 10 dB return loss bandwidth, mutual coupling <−20 dB, ECC < 0.003, MEG ratio ≈ 1, and CCL < 0.038 Bpsec/Hz, making it a good candidate for UWB and MIMO diversity application.

A simple multiple-input-multiple-output (MIMO) antenna with quad-band-notched characteristics for ultra-wideband (UWB) system is proposed and tested in the article. Based on two similar radiators, the UWB-MIMO system only occupies 22 mm × 28 mm. By etching an inverted L-like meander slot, two inverted L-shaped slots, and adding a C-shaped stub beside the feeding line, four notched bands are realized (3.25–3.6, 5.05–5.48, 5.6–6, and 7.8–8.4 GHz) to suppress interference from WiMAX, lower WLAN, upper WLAN, and uplink of X-band satellite communication system. With a T-like stub extruding from the ground plane, port isolation is effectively improved. The results show that the antenna covers 3.1–10.6 GHz UWB frequency band except four rejected bands and has high isolation of better than −20 dB over most of the frequency band. Moreover, envelope correlation coefficient and good radiation patterns also prove that the introduced antenna is suitable for UWB applications.