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 article, an extremely wideband, isolation-enhanced, low-profile “Multiple-Input-Multiple-Output” (MIMO) antenna along with dual-band-notched features has been investigated. The antenna proposed herein, possesses two mutually orthogonal staircase-etched radiators for achieving a wide bandwidth. The radiating elements are placed mutually perpendicular in order to achieve polarization diversity and high isolation, i.e. for minimization of mutual coupling effect between adjacent radiating elements. The antenna exhibits an extremely wide frequency bandwidth covering 1.2–19.4 GHz except two frequency band notches centered at 3.5 and 5.5 GHz, respectively, originated due to the incorporation of a “Rectangular Complementary Split Ring Resonator (RCSRR)” structure and by etching dual “L-shaped” slits in the ground plane. The center frequency of the notched bands is adjusted by fine tuning of the dimensions of the incorporated band-notching structures. Isolation level (S21) better than −20 dB has been obtained due to the insertion of a “T-shaped” parasitic element as a decoupling structure. A prototype of the proposed antenna having dimension of 20 mm × 20 mm (0.08 λo × 0.08 λo) is fabricated and the antenna responses have been measured. Obtained results show that the miniaturized MIMO diversity antenna is undoubtedly a capable contender for communications supporting an extremely wide impedance bandwidth along with band-notched features for WLAN and WiMAX.

A proximity-fed complementary Sierpinski gasket fractal with equilateral triangular shape resonator in multilayer structure to achieve dual-band behavior for WiMAX and WLAN applications has been proposed. An electromagnetic coupled stacked structure of two different patches operating at two frequencies (3.5 GHz WiMAX and 5.8 GHz wireless LAN) has been designed for dual-band wireless applications. Proposed antenna was simulated using CST Microwave Studio based on the finite integration technique (FIT) with perfect boundary approximation (PBA). Finally, the proposed antenna was fabricated and some performance parameters were measured to validate against simulation results. The design procedures and employed tuning techniques to achieve the desired performance are presented.

A simple design for triple-band circularly polarized (CP) wide slot antennas is proposed and experimentally investigated. The proposed antenna having a microstrip-fed rectangular patch with T-shaped notch for triple-band operation and a modified wide square slot on ground plane for CP operation. The measured 10 dB reflection bandwidths are 1.24% (≈340 MHz from 2.56 to 2.9 GHz), 9.63% (≈430 MHz from 4.25 to 4.68 GHz), and 5.34% (≈490 MHz from 8.93 to 9.42 GHz). The generated 3 dB axial ratio bandwidths of the proposed antenna are 7.54, 8.98, and 1.65% at operating frequencies around 2.65, 4.45, and 9.09 GHz, respectively. The measured peak gains within the 3 dB axial ratio bands are 3.03, 3.5, and 5.64 dBi. The simulated and measured results for the return loss, axial ratio, and antenna gain show a good agreement, which validate the antenna design.

The paper is a joint work between the LEAT (France) and the ENRI (Japan) in the framework of a Sakura project supported by the JSPS and the French Ministry of Foreign Affairs. The purpose is the study of a FOD (Foreign Object Debris) detection system on airport runways. An FM-CW mm-wave radar working between 76.25 and 76.75 GHz is used together with a high directivity printed reflectarray. In addition, a second measurement campaign has been conducted with a 73.8–79.8 GHz (6 GHz band) radar. Measurement results show detection capabilities of a −20 dBsm cylinder up to 35 m that is 10 m less than the FAA recommendations. Antenna improvements are discussed for reaching the requirements and system performance as well as the use of calibration objects.

A reconfigurable band-pass filter with switchable bandwidth, for wireless applications is demonstrated using a dual-mode microstrip square-loop resonator. The proposed filter has been designed on Rogers RO4003C and achieves switchable bandwidth by changing the length of two tuning stubs with the implementation of two strategically placed p-i-n diodes as switching elements. The filter was designed with a center frequency of 2.4 GHz and the two distinct operation states have bandwidths, 113 MHz (4.8%) with an insertion loss of 1.2 dB and 35 MHz (1.5%) with an insertion loss of 1.5 dB. The physical size of the fabricated reconfigurable filter including the implementation of the DC bias lines is comparable to the size of a conventional filter.

A compact dual-band bandpass filter using stub-loaded stepped impedance resonator (SLSIR) with cross-slots is presented. The symmetric SLSIR is analyzed using even- and odd-mode techniques. Design equations are derived and they are used to guide the design of the circuits. Two passbands can be easily tuned by cross-slots and open stubs. Transmission zeros among each passbands are created, resulting in high isolation and frequency selectivity. An experimental circuit is fabricated and evaluated to validate the design concept. The fabricated filter is compact with 19.76 × 12.7 mm2. The measurement results are in good agreement with the full-wave simulation results.

In this paper, we present a novel flexible moon-shaped slot implantable antenna for neural recording systems and head implants. It covers both medical Industrial, Scientific and Medical band (2.45 GHz) and impulse ratio ultra-wideband (IR-UWB) frequency range (3.1–10.6 GHz) for forward and backward telemetry applications. It has a simple and miniaturized structure in comparison with the antennas reported in the other researches. Furthermore, for adapting with natural curvature of human head, a flexible substrate is chosen with a good antenna performance under the bending. The proposed antenna is analyzed in a multi-layer box model of head tissues to speed up the antenna design procedures. On the basis of the simulation results, we achieved the good impedance matching over the desired frequency range (S11 below −10 dB). Far-field characteristics are considered, as well. The directivity is in suitable range for UWB short-range communications and its mean value is 3.84 dBi. Finally, to take into account patents’ safety regulations and the effective isotropic radiated power restriction in the desired frequency range, the maximum power of transmitter has been calculated. A phantom containing a mixture of sugar and water is used to test the fabricated antenna. The measured parameters are well matched to the full-wave simulation results.

Burst mode operation is proposed as an efficiency improving technique for power amplifiers. The core idea is to modulate the amplitude of the envelope signal into a series of square-wave pulses such that the width of the signal burst or the total amount of pulses are varied according to the envelope. The phase information is still contained by the timing of the pulses. This work presents the efficiency and linearity analysis of burst mode radio frequency (RF)/power amplifier (PA). In addition, the efficiency performance is compared when the burst mode RF power amplifiers (PA) is connected to a wideband load or a narrowband filter. It is shown that burst mode PAs are more efficient than the conventional Class B PAs. To achieve an even more favorable efficiency, a transmission line is inserted between the output of the switching RF PA and the filter to improve the filter's impedance characteristic. Additionally, the efficiency and linearity of the burst mode PA with and without transmission line has been studied and simulated thoroughly. To demonstrate the validity of the efficiency formulas and linearity considerations, a printed circuit board (PCB)-mounted burst mode PA using a laterally diffused metal oxide semiconductor (LDMOS) transistor was fabricated. Measurements show a peak efficiency of 78% and 28.8 dBm of output power.

In this paper, the first reported waterproof inkjet-printed dual-band monopole antenna on the flexible organic paper substrate is presented. The antenna, which operates at 900 MHz and 2.4 GHz, is inkjet-printed on commercially available photopaper using conductive silver nano-particle ink. To protect it from ambient humidity, a 1 µm thick Parylene-C layer was deposited on top of the antenna. To verify its waterproof capability, the Parylene-C coated antennas were submerged in distilled water for 48 days, and no significant performance degradation was observed in its performance.

A compact circularly polarized (CP) patch antenna is presented for modern communication systems. The prospective antenna consists of a microstrip-line inset-fed rectangular patch and a defected ground plane. A rotated rectangular slot and a modified electric-inductive-capacitive (m-ELC) resonator are introduced in the patch and the ground plane to achieve multiband behaviour. A corner of the radiating patch is truncated and an arrow-shaped stub is introduced for generating circular polarization. The physical area of the substrate is 0.26λ0 × 0.22λ0, and the radiator size is 0.16λ0 × 0.14λ0, where λ0 is the free-space wavelength estimated at the lowest frequency. The measured (S11≤-10 dB) bandwidths of the antenna are 80 MHz (3.58%) at 2.23 GHz, 75 MHz (2.64%) at 2.84 GHz, 80 MHz (2.50%) at 3.19 GHz, and 70 MHz (1.82%) at 3.83 GHz. The measured 3-dB axial ratio bandwidths are 40 MHz (1.41%), 100 MHz (3.12%), and 60 MHz (1.57%) at 2.84, 3.20 and 3.82 GHz, respectively. The proposed planar antenna design does not need dual-feed or multi-layered patches for achieving multiple CP bands. It offers easy integration with the printed circuits of the communication systems.

This article introduces a cylindrical dielectric resonator antenna (CDRA) fed with a rhombic ring-shaped tapered feed for Multiple-Input-Multiple-Output (MIMO) applications. The proposed hybrid MIMO CDRA resonates at four frequency bands 2.5, 5.09, 6.8, and 9.0 GHz with isolation levels of 22, 34.22, 30.55, and 18.55 dB. Isolation enhancements are achieved by introducing “L” shaped slots on the partial ground plane. Parametric analysis is performed to validate the optimized dimensions of the tapered feed without and with DRA and defected ground structure. Diversity performance is examined by using envelope correlation coefficient and diversity gain. The proposed antenna operates in the S, C, and X-bands and is suitable for RF communication mobile broadband services, Wi-Fi, radar, and satellite applications. Good agreement is observed between simulated and measured results.

In this paper, a microstrip diplexer is designed based on a novel structure consisting of the meandrous and patch cells. It operates at 0.8 and 0.9 GHz for global system for mobile communications applications. The proposed diplexer is well miniaturized with an overall size of 0.01 λg2. It has the narrowband channels making it appropriate for the modern long-range communication systems, which are widely accepted by the industry. The introduced diplexer has the other advantages of low insertion and return losses and the good isolation between channels better than −30 dB. Moreover, there is a good upper stopband rejection so that the first and second harmonics are suppressed with a maximum level of −30 dB. The designing method is based on finding the effective parameters to control the resonance frequency, miniaturization and harmonic attenuation simultaneously. To validate the designing method and simulation results, the proposed diplexer is fabricated and measured. There is a good agreement between the simulated and measured results.

Most non-linear behavioral models of amplifiers are based on functions that are analytic at the origin and thus can be replaced by their Taylor series development around this point, e.g. polynomials of the input signal. Chebyshev Transforms can be used to compute the harmonic response of the model to a sine input signal. These responses are polynomials of the input signal amplitude. A second application of the Chebyshev transform to the first harmonic response or radio frequency (RF) characteristic will lend the carriers and intermodulation (IM) products for a two-carrier input signal, again polynomials. An important class of non-analytic non-linear behavior encountered in practice, such as hard limiters and detectors are either empirically treated or only approximated by an analytic function such as the hyperbolic tangent. This work proposes to generalize the polynomial non-linearity theory by adding non-analytic at the origin functions that, like polynomials, are invariant elements of the Chebyshev Transform. Devices modeled with these non-analytic at the origin functions exhibit intermodulation behavior significantly different from that of classical polynomial models, giving theoretical foundation to a number of important unexplained practical measurement observations.

In this work, we propose a broadband, polarization-insensitive and wide incident angle stable metamaterial absorber (MA) based on the resistive film. The absorber consists of a three-layer structure with each layer of dielectric substrate printed with different shapes of resistive film. The multilayer structure not only extends the absorption bandwidth but also maintains high absorption under large wave incident angles. Numerical simulation shows that the absorptivity of a normal incident wave is above 90% in the frequency range 2.34–18.95 GHz, corresponding to a relative absorption bandwidth of 156%. Moreover, the whole MA structure has a total thickness of 11.3 mm, corresponding to 0.09 λ0 at its lowest absorption frequency. Due to the high symmetry of the structure, the absorber has good polarization insensitivity. In addition, for both transverse electric and transverse magnetic incidence, the proposed absorber achieves an absorptivity of more than 80% at incident angles of up to 45° and thus has good stability for wide incident angles. The absorption principle of the absorber is analyzed by the surface current and power loss density distribution. Parameter analysis is also performed for bandwidth optimization. Due to its advantages of wideband absorption with high efficiency, the proposed absorber has the potential to be applied to the energy-harvesting and electromagnetic stealth fields.

A compact asymmetric coplanar strip fed Sinc shaped monopole antenna suitable for multifrequency operations is proposed for portable wireless devices. The proposed Sinc shaped monopole antenna with truncated half ground plane operates at three frequency bands, 2110–2380, 4180–4600, and 5200–5678 MHz, showing fractional impedance bandwidths of 12, 9, and 8.8%, respectively, suitable for Universal Mobile Telecommunications System, Long Term Evolution handheld devices, Worldwide Interoperability for Microwave Access, Wireless Local Area Network, Hyperlan-2, and aeronautical navigation applications. Proposed antenna shows a dual mode of polarization. Finally a prototype model is developed for a typical configuration and the simulated results are validated experimentally.

Two different topologies of radio frequency micro-electro-mechanical system (RF MEMS) series ohmic switches (cantilever and clamped–clamped beams) in coplanar waveguide (CPW) configuration have been characterized by means of DC, environmental, and RF measurements. In particular, on-wafer checks have been followed by RF test after vibration, thermal shocks, and temperature cycles. The devices have been manufactured on high resistivity silicon substrates, as building blocks to be implemented in different single-pole 4-throw (SP4 T), double-pole double-throw (DPDT) configurations, and then integrated in Low Temperature Co-fired Ceramics (LTCC) technology for the realization of large-order Clos 3D networks.

In through the wall imaging systems, wall parameters like its thickness and dielectric constant play an important role in the true and correct image formation of an object behind the wall made of various materials like brick cement, wood, plastic, etc. Incorrect estimation of these parameters leads to dislocation of the object and smearing or blurriness of the image too. A new autofocusing technique for a stepped frequency continuous wave -based radar at the frequency of 1–3 Ghz has been developed that corrects the wall's parameters like its thickness and dielectric constant and provides a better focused image of the target. For this purpose, a peak signal to noise ratio -based autofocusing technique has been developed by using curve fitting and the genetic algorithm. It is observed that the proposed technique has capability to focus the image up to good extent.

A 240-GHz monostatic circular polarized SiGe frequency-modulated continuous wave radar system based on a transceiver chip with a single on-chip antenna is presented. The radar transceiver front-end is implemented in a low-cost 0.13 µm SiGe HBT technology version with cut-off frequencies fT/fmax of 300/450 GHz. The transmit block comprises a wideband ×16 frequency multiplier chain, a three-stage PA, while the receive block consists of a low-noise amplifier, a fundamental quadrature down-conversion mixer, and a three-stage PA to drive the mixer. A differential branch-line coupler and a differential dual-polarized on-chip antenna are added on-chip to realize a fully integrated radar transceiver. All building blocks are implemented fully differential. The use of a single antenna in the circular polarized radar transceiver leads to compact size and high sensitivity. The measured peak-radiated power from the Si-lens equipped radar module is +11 dBm (equivalent isotropically radiated power) at 246 GHz and noise figure is 21 dB. The characterization bandwidth of the radar transceiver is 60 GHz around the center frequency of 240 GHz, and the simulated Tx-to-Rx leakage is below −20 dB from 230 to 260 GHz. After system calibration the resolution of the system to distinguish between two targets at different distance of 3.65 mm is achieved, which is only 21% above the theoretical limit.

In this paper, a flexible single fed planar circular polarized slot antenna is proposed for Internet of Things wideband applications. The antenna flexibility is achieved by employing a mechanically bendable liquid crystalline polymer substrate. The overall antenna volume is 50 mm × 42 mm × 0.1 mm. The antenna design uses 45° rotated elliptical ground structure for generating circular polarized radiation over wideband spectrum. Two parametrical analyses targeting the slot ground are introduced in order to achieve the most efficient design. The final antenna design demonstrates a good matching in terms of reflection coefficient (<−10 dB), semi-omnidirectional radiation patterns, average gain of 4 dB, and <3 dB axial ratio over entire frequency band of operation. All antenna parameters are studied in both straight and bent antenna setup scenarios. Good agreement between simulation and measurement results of the antenna parameters are achieved. For both straight and bent antenna scenarios, the antenna receiving functionality in time domain is confirmed by retrieving highly correlated impulse responses.