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.

This paper presents the design of frequency-tunable dual-band, tri-band and quad-band bandpass filters (BPFs). The proposed three BPFs can be independently tuned and individually switched by varying the capacitances of the varactors. In the designed tunable dual-band BPF (TD-BPF), common input/output feed lines are utilized for two tunable dual-mode resonators (TDRs). Further, three TDRs and four TDRs are employed to achieve tunable tri-band BPF (TT-BPF) and tunable quad-band BPF (TQ-BPF), respectively. Then, the TD-BPF and the TT-BPF are fabricated and measured to verify individual tunability and independent switchability. For the TD-BPF, the measurement results show that the center frequency (CF) of the first passband varies from 1.37 to 1.62 GHz, and the CF of the second passband varies from 2.3 to 2.64 GHz. In the measured TT-BPF, the tuning ranges of CFs of three passbands are 1.3–1.5 GHz, 2.36–2.6 GHz, and 3–3.54 GHz, respectively.

The purpose of this paper is to disclose improved crystal based frequency source system covering design techniques and experimental methodologies for the stabilization of phase noise performance of X-band phase-locked loop (PLL) at 10.6 GHz. Phase noise performance of PLL-based unit under test (UUT) is prone to disturbance occurred in random vibration profile frequency spectrum. UUT self-resonance plays vital role in occurrence of disturbance in random vibration profile. The stabilization of phase noise performance during dynamic (random) vibration condition is achieved by following methodologies, i.e. vibration-isolator compensation techniques, purification tactic for reference crystal of PLL, and spatial location analysis for finding out mounting position of reference crystal. Spatial analysis helps to filter out UUT self-resonance frequency from random vibration spectrum which leads to reduction of frequency resonance pickups during random vibration testing.

In this paper, a novel approach of high-accuracy calibration (HAC) method is employed to improve the resolution of tumor detection within a fibro-glandular breast model, and also an improved 3D back-projection approach to scan each focal point inside of the breast is presented. For these purposes, a simulated hemispherical setup of a multi-static array with a modified UWB bowtie antenna is applied around the breast. The superiority of the proposed HAC method is that all-time delays of multi-static channel paths are taken into account at preprocessing of reflected signals, and therefore the time location of tumor response can be estimated accurately in the late stage of recorded signals. As a result, stronger signals are obtained to detect the location of the tumor with higher spatial accuracy. By using the improved 3D back-projection method, a better approximation of transmission channel paths based on Fermat's principle is achieved. A realistic breast model is proposed with two cases of single and twin spherical tumors. Then, to validate the efficiency of the proposed HAC method to detect the time-dependent tumor location, several scenarios are studied in the mentioned model. Quantitative metrics of successfully reconstructed tumor (with a small radius of 7 mm) images prove the ability of the proposed imaging method for early-stage breast cancer detection.

This research involves a compact wideband circularly-polarized antenna array, which consists of a sequential rotating phase feed network, 2 × 2 mushroom-type metamaterial (MTM) unit, and so on. Each antenna array unit contains a microstrip feedline, an L-shaped slot antenna, and so on. The MTM-based antennas were incorporated with a sequential-phase network of sequentially rotated series-parallel feed to achieve wideband operation. The operational bandwidth and the radiation model in the high-frequency area were improved through the adjustment of spacing between the L-shaped slots while maintaining the size and structure of the MTM. The proposed design had dimensions of 80 mm × 80 mm × 3.5 mm (~1.64 λ0 × 1.64 λ0 × 0.072 λ0 at 6.15 GHz), and it was simulated, fabricated, and tested.

This paper presents a rollable metamaterial screen for high-efficiency wireless power transfer (WPT) system based on magnetic resonance coupling, which operates at 4.5 MHz. The rollable metamaterial screen with a fully expanded area of 750 mm × 750 mm is located in the middle between transmitter and receiver coils and focuses the magnetic field and, by such a way, significantly improves power transfer efficiency (PTE). The metamaterial screen can be rolled up, e.g. onto the ceiling when it is not used, and thus does not require any designated space for the screen saving space. A WPT system with the rollable metamaterial screen is designed, fabricated, and characterized. Improved PTE is qualitatively and quantitatively verified by light bulb experiments and vector network analyzer measurements. The PTE of the WPT system with the metamaterial screen increases from 36 to 58.52% and 10.24 to 31.36% for the distances between the transmitter and receiver coils 100 and 150 cm, respectively. The effects of lateral and angular misalignments on the PTE of the WPT system are also studied. Obtained results show that the rollable metamaterial screen improves the PTE even at the misaligned condition.

In this paper, a simple and efficient method to increase the gain and bandwidth of the wearable antennas used in several medical/communications systems is presented. To increase the gain and bandwidth simultaneously, the triple transmission lines (TTLs) method has been used. With this method, the frequency ranges of 1.7–2.5 and 5.4–5.95 GHz are covered with dual-band responses. Also, the simulated maximum gain at 2 and 5.8 GHz is equal to 8.26 and 9.86 dB, respectively. Using the TTLs method, the second frequency band (5.4–5.95 GHz) is achieved. Also, the gain improvement in operating frequencies is more than 4 dB compared to the conventional antenna. The dimensions of the proposed wearable high-gain antenna are 80 × 92 × 2 mm3 or 0.57 × 0.67 × 0.01 λg3 at 2 GHz. Finally, a dual-band sample antenna for use in medical systems was fabricated with a flexible felt substrate and its characteristics were measured. There is a good fit between the measurement and simulation results.

In this paper, a new printed triple-band planar antenna combing two different modified monopoles and an arc-shaped defected ground plane is proposed and studied. The used two simple monopoles consist of a rectangular ring and a rectangular patch attached a straight metal strip. And a compact arc-shaped defected ground structure is proposed and used to excite higher resonance frequency and improve the impedance matching of the antenna at lower and middle resonance frequencies. The main radiation element of the proposed antenna composed of only two simple monopoles can support three omnidirectional radiation modes at three desired bands. To indicate the working mechanism of the antenna, the design process is illustrated and the parametric studies are carried out. The experimental results of the fabricated prototype confirm that the triple-band antenna has better radiation efficiencies, appropriate gains, and stable omnidirectional radiation patterns. And the tested results also show that the antenna can provide enough bandwidths of 2.35–2.52, 3.2–4.16, and 5.13–5.87 GHz to cover all the desired 2.4/5.2/5.8 GHz WLAN and 3.5/5.5 GHz WiMAX operations. Moreover, the presented antenna has a very simple structure. Thus, the designed antenna has high practicality and broad prospects for WLAN and WiMAX applications.

One of the current trends in the integrated circuit (IC) development is the integration of antennas on-chip or in the package of the IC. This poses challenges in the production testing process of the packaged IC, as the antenna functionality has to be included and at least one of the signal ports cannot be accessed at a conducted manner. In order to measure the reflection coefficient of an integrated antenna, a contactless characterization method (CCM) can be used. In this paper, the practicality of a CCM is assessed, having the application of a cost-effective high-volume testing procedure for integrated antennas in mind. It is shown that the CCM yields accurate results for different imperfections in the measurement setup. Moreover, measurement results around 33 GHz using a connectorized patch antenna are shown, which experimentally verify the validity of using the CCM under near-field conditions.

Design of single-feed circularly polarized (CP) microstrip antenna is proposed in this article. The design employs the concept of E-shape patch with inclined fractal defected ground structure (IFDGS), which can improve the impedance bandwidth, gain, and axial ratio (AR) bandwidth. The excellent enhanced impedance bandwidth, axial ratio bandwidth, and gain are achieved by an inclined E-shaped fractal etched on the ground plane. The parameter studies of the E-shaped IFDGS are given to illustrate the way to obtain CP radiation. The third iterative IFDGS is fabricated on easily available FR4 substrate with a size of 0.494 λ0 × 0.494 λ0 × 0.019 λ0 (λ0 is the wavelength in free space at 3.624 GHz). The measured results verify the simulated results and show good agreement. The proposed antenna shows an impedance bandwidth of 12.7% at a centre frequency of 3.47 GHz and 3-dB AR bandwidth for this band is 2.39% at a centre frequency of 3.626 GHz. The measured peak gain for the proposed antenna is found as 8.1 dBi. The proposed antenna can be suitable for mobile WIMAX operation (IEEE 802.16e-2005 standard), wireless communication in CA-band and FCC.

A compact co-planar waveguide (CPW) fed planar elliptical antenna has been designed and presented for super wideband (SWB) characteristics. The designed antenna has an overall size of 30 × 30 × 1.57 mm3, and it consists of an elliptical patch radiator fed using a modified 50 Ω CPW-fed tapered microstrip feed line. By using a semi-ring shaped structure with a tapered feed line, an impedance bandwidth of 180.66% has been observed from 1.27 to 25 GHz with a ratio bandwidth of 19.68:1. To validate simulation results, the designed antenna has been fabricated and measured, and a reasonable agreement has been observed between simulated and measured results. It has also been observed that the designed antenna offers good radiation properties over the entire operating bandwidth. The simulated average gain and radiation efficiency of the proposed SWB antenna is noted to be 4.3 dBi and 95.77%, respectively; while the measured average gain and radiation efficiency is 3.8 dBi and 94.69%, respectively.