This paper presents a simple reconfigurable bandpass filter switching from 2.4 to 5 GHz based on PIN diodes. The proposed filter is intended to add frequency-tunability to antenna systems used in cognitive radio applications. It consists of a bent connecting stub with two open-circuited quarter-wave stubs grounded via PIN diodes. By controlling the didoes states, the electrical length of the stubs can be switched from quarter-wave to half-wave and vice versa, so as to tune the filter center frequency. The proposed design approach consists of ensuring communication at 2.4 GHz while blocking the 5 GHz band in the ON state, whereas in the OFF state, the filter is intended to reject the 2.4 GHz band and passing the 5 GHz band. A prototype of the proposed filter is fabricated and measured to validate the proposed concept. Both simulated and measured results show a two-state filter with a wide tuning range from 2.4 to 5 GHz and a good stopband rejection level better than 40 dB. Moreover, a flat group delay of about 0.55–0.7 ns is achieved within the operating bandwidth in both states. The proposed filter is able to achieve simultaneous bandwidth and frequency control, showing an important tool to meet modern system requirements.

In this paper, a new compact hybrid fractal antenna with ultrawideband (UWB) behavior is proposed. Two merged fractals shapes, i.e. Sierpinski carpet and Sierpinski Gasket fed with coplanar waveguide (CPW) feed make patch as multiband and broadband antenna. The antenna is optimized using particle swarm optimization for side length of Sierpenski Gasket fractal and bandwidth. The overall width of the patch is taken as a parameter for optimizing bandwidth. The total size of presented antenna is 59 × 29 mm2. The antenna resonates at 2–5.2 GHz, so that wideband operation is observed. Antenna with this type of characteristics can be used when UWB response at lower frequencies is required. Sierpenski Gasket performs two functions in the proposed design, i.e. to radiate as well as impedance transformer to Sierpenski carpet. The proposed design presents novelty in design to achieve proper impedance matching to edge of Sierpenski carpet design with CPW feed by making Sierpenski Gasket as impedance transformer.

In this paper, a uniplanar RF-MEMS second-order bandpass filter with reconfigurable center frequency is presented. It is based on quarter-wavelength slotline resonators and coplanar waveguide (CPW)-to-slotline multimodal immitance inverters (MIIs), which are reconfigured using RF-MEMS switchable CPW air-bridges (SABs). The filter can be adequately explained and designed using multimodal theory and circuit models. A surface micromachining process on high-resistivity silicon substrate was used to fabricate the filter. Experimental results show frequency reconfiguration from 12 to 13 GHz, maintaining the same relative bandwidth, and insertion losses of 4.6 and 4.7 dB, respectively.

The rate of signal transmission on or between monolithic integrated circuits is limited by the cross-talk and the dispersion due to the wired interconnects. The bandwidth limitations can be overcome by wireless chip-to-chip and on-chip interconnects via integrated antennas. In this work the utilization of the electronic circuit ground planes as radiating elements for the integrated antennas has been proposed. This allows for optimal usage of chip area, as the antennas share the same metallization structure as the circuits. By exciting the interconnects between the patch areas in transmission line modes as well as in antenna modes, the interference between signals from circuit to circuit and antenna excitation signals is minimized. This has been achieved by inserting a transformer in the antenna feeding network. Examples of possible antenna and feeding structures have been investigated numerically. Scaled prototypes of the integrated antennas have been manufactured and measured.

Nature inspired optimization algorithms, namely artificial bee colony (ABC) optimization and firefly algorithm (FA), have been applied to synthesize beam patterns of a hexagonal planar array of isotropic elements. Two different cases, comprising two different beam patterns of a pencil beam and a square footprint pattern over a bounded region with lower peak sidelobe levels are presented. The pencil beam is generated by thinning the uniformly excited array and the square footprint pattern is generated by imposing optimum amplitudes, phases, and their corresponding states (“on”/“off”) to the array elements. The optimum values of the parameters for both the cases are computed using ABC and FA individually, and the superiority of FA over ABC for the proposed problem in terms of computing solutions for both the cases is established.

A compact CPW-fed printed monopole slot antenna is presented for ultra-wideband (UWB) applications. The antenna comprises of a dome-shaped radiating element in which embedded is an open-loop inverted triangular-shaped slot (TSS). The antenna is fed through a coplanar waveguide to provide an ultra-wide impedance bandwidth of 8.95 GHz (2.58–11.53 GHz) which corresponds to a bandwidth ratio of 1:4.46 for VSWR <2. The antenna possesses a notch band functionality to filter out interfering C-band signals like wireless local-area network (WLAN). The notch band frequency is determined by physical parameters defining the TSS that allows fine control of the notch's location. The proposed antenna also possesses a flat gain response expect at the notched band and occupies a relatively small volume of 25 × 25 × 0.8 mm3 for ease of system integration.

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.

A novel miniaturized dual-mode bandpass filter (BPF) using hexagonal loop resonator is presented. In order to reduce the circuit size, capacitive loading structure is applied to enhance the self-capacitance and electrical length of the hexagonal loop resonator. The frequency selectivity and out-of-band rejection of the proposed BPF can be improved by the two inherent transmission zeros in each side of the passband. Compared with the conventional hexagonal loop resonator without capacitive loading structure, the size of the proposed resonator is reduced by 46.6%. The simulated and measured results are presented and show good agreement.

A broadband circularly polarized (CP) beam-steering antenna array is presented. CP antenna is composed of four identical CP slot elements with 2 × 2 configuration and a 4 × 4 feeding network. CP slot element is utilized in array form to improve impedance bandwidth and sequentially rotation method is used to increase axial-ratio bandwidth. Moreover, uni-planer compact electromagnetic band-gap structure is applied to enhance the overall performance of antenna array. Measured results depict that the array has impedance bandwidth over a frequency range of 4.1–7 GHz (~53%) for S11 ≤ −10 dB and 3 dB axial-ratio bandwidth of 1.95 GHz that is between 4.6 and 6.55 GHz (~35%). The antenna array has peak gain of 11 dBi at 5.5 GHz.

A mode converter design using the concept of periodic substrates loading in a circular waveguide, to convert TM01 mode to TE11 mode is presented in this paper. The detailed design principle, simulation, and measurement results are included in this study. Simulation results show that the purity of output fundamental TE11 mode of the converter approaches 99.2% for an operating frequency of 3.2 GHz. The mode conversion efficiency is more than 90% over 3.07–3.25 GHz band and the relative bandwidth is 5.6% (180 MHz). The proposed TM01–TE11 mode converter has advantages, such as the compact, lightweight structure, high conversion efficiency, and proper bandwidth. The fabrication cost is relatively low and the structure is easy to fabricate. The power-handling capability is limited to 10 MW due to dielectric-based design. The compactness and portability of the system (e.g. Space applications, Accelerators, High Power Microwave) can be improved significantly using the proposed mode converter.

The next generation mobile communication systems impose challenging performance, size, and cost requirements on the power amplifiers (PAs). This paper presents novel DC-biasing circuits, which are compact and yet can control the harmonics almost arbitrarily. The proposed circuit consists of a composite right-/left-handed (CRLH) transmission line (TL) stub, of which the size and harmonics-control function can be tuned by modifying the dispersion diagram of the stub line. As a proof of concept, a compact 2-GHz 7-W GaN HEMT class-F PA using the versatile CRLH-TL stubs was fabricated, demonstrating 85.8% drain efficiency and 77.3% power-added efficiency.

In this paper, we designed and developed a novel internal compact printed loop antenna for WWAN/WLAN/ISM/LTE smartphone applications. The proposed antenna is composed of a meander loop antenna and a capacitively coupled feeding line. It has a planar structure, with an overall dimension of 120 × 60 mm2, the antenna portion occupying a size of 20 × 60 mm2, which makes it suitable for practical smartphone applications. The results of our measurement reveal that the prototype antenna can provide two wide frequency bands of 712–1078 and 1757–2930 MHz, which cover multi-band for GSM850/GSM900/DCS1800/PCS1900/UMTS2100/IMT2000/WLAN2400/ISM2450/LTE700/LTE2300/ LTE2500. The antenna also shows good radiation characteristics and gain peaks for frequencies over the desired operating bands. We also studied the specific absorption rate (SAR) of the proposed antenna placed at the bottom of a mobile phone. The obtained SAR values are all below the SAR limit of 1.6 W/kg for the 1 g head tissue and 2.0 W/kg for the 10 g head tissue. We used CST Microwave Studio and Ansoft HFSS for the simulation and the design of the antenna and present in this paper the details of the design considerations, as well as the results on the reflection coefficient, the surface current distributions, the radiation characteristics, and the gain of the proposed antenna.

A circularly polarized stub-matched inverted L-shaped antenna for C-band applications is presented in this communication. Antenna parameters of inverted L-shape on the radiating patch and slits, notch, square strips and stub on the ground plane and the effect of these are analyzed. The proposed optimized antenna (A5: 0.54λ0 × 0.54λ0 × 0.02λ0 mm3) is selected among antennas (A1 – A5) with 5.1 GHz design frequency after simulation through high-frequency structure simulator (HFSS). Circular polarization is obtained by introducing stub/perturbation on the ground plane. By introducing stub, the highest measured (S11 < − 10 dB) impedance bandwidth of 50.9% (3.48 – 5.86 GHz) is observed amongst the reported and compared bandwidths. Peak gain of 5.32 dBi and 3 dB axial ratio bandwidth of 16.2% (4.71 – 5.54 GHz) is reported in the present work. An antenna is useful in the entire downlink frequency (3.7 – 4.2 GHz) of the C band.

In this paper, the use of regularization methods to solve the location problem in multilateration systems, using Mode-S signals, is studied, evaluated, and developed. The Tikhonov method has been implemented as a first application to solve the classical system of hyperbolic equations in multilateration systems. Some simulations are obtained and the results are compared with those obtained by the well-established Taylor linearization and with the Cramér–Rao lower bound analysis. Significant improvements, for the accuracy, convergence, and the probability of location, are found for the application of the Tikhonov method.

This paper presents a feasibility study for the implementation of a concurrent dual-band power amplifier (PA) design suitable for 1.98 GHz WCDMA and 3.42 GHz WiMAX digital systems. The proposed PA design was compared with a test bed based on a pair of dedicated single-frequency band PAs. The dual-band PA exhibited simultaneous peak output power levels of 24 and 17 dBm in the lower and in the higher bands to maintain ACPR and EVM requirements below 33 dBc and 5%, respectively. The conclusions drawn in the paper justify the design effort of this innovative solution, which is capable of increasing the PAE for concurrent dual-band operation maintaining the performance of more conventional solutions.

A recently developed material based on carbon nanotubes is used here for the realization of single- and double-layered frequency-selective surfaces (FSSs) with relevant absorbing properties. The peculiar characteristics of carbon nanotubes are exploited to devise high-loss resonant ring structures periodically arranged to build the FSS. By introducing two layers of rings, an absorber with stable characteristics over a wide frequency band and over a wide range for the incident wave angle is achieved.

The demanding tasks for automotive radar systems in multitarget scenarios require an increased target separation performance and new sensor concepts. In this contribution, a highly integrated 77 GHz time domain multiplex (TDM) MIMO radar is presented. The sensor is feasible for advanced direction of arrival (DOA) estimation in azimuth and elevation. For efficient and high-quality measurements a fractional-n phased locked loop (PLL) with integrated waveform generator, enabling chirp and frequency modulated continous waveform (FMCW) modulations, is implemented. Spatial beamforming is done with series feed array patch antennas in combination with a dielectric cylindrical lens. For the improvement of the direction of arrival (DOA) estimation performance a new lens-based MIMO radar approach is introduced. Therefore the classical MIMO approach is combined with the advantages of an optical beamforming concept. Due to the usage of these techniques the sensor performance in accuracy, ambiguity suppression, and angular resolution can be significantly increased.

A new planar microstrip-fed monopole ultra-wideband (UWB) antenna with dual notched bands has been presented. By employing a simple dual-mode resonator with two symmetrical outer high-impedance lines beside the microstrip feed line of the proposed UWB antenna, two controllable rejection bands with high-frequency selectivity are created. The parametric studies of the proposed structure are explored for the dual band-notched operating mechanism. Finally, the experimental results, including return losses, radiation patterns, and peak gains are shown, declaring that the proposed antenna has good impedance matching performance and radiation pattern properties.

In this paper a monostatic frequency-modulated continuous-wave (FMCW) radar system around a center frequency of 24 GHz with a wide tuning range of 8 GHz (≈33%) is presented. It is based on a fully integrated single-channel SiGe transceiver chip. The chip architecture consists of a fundamental VCO, a receive mixer, a divider chain, and coupling/matching networks. All circuits, except for the divider, are designed with the extensive use of on-chip monolithic integrated spiral inductors. The chip is fabricated in a SiGe bipolar production technology which offers an fT of 170 GHz and fmax of 250 GHz. The phase noise at 1 MHz offset is better than −100 dBc/Hz over the full-tuning range of 8 GHz and a phase noise of better than −111 dBc/Hz is achieved at 27 GHz. The peak output power of the chip is −1 dBm while the receive mixer offers a 1 dBm input referred compression point to keep it from being saturated. The chip has a power consumption of 245 mW and uses an area of 1.51 mm2. The FMCW radar system achieves a power consumption below 1.6 W. Owing to the high stability of the sensor, high accuracy mesaurements with a range error <±250 µm were achieved. The standard deviation between repeated measurements of the same target is 0.6 µm and the spatial resolution is 28 mm.

In this paper, a self-actuated frequency-selective radome is presented and applied to a microstrip antenna. The radome acts as a self-triggered switchable screen to achieve adaptive electromagnetic protection in the L band. A prototype of the radome is fabricated to measure its transmission performance. The switchable characteristic is verified by a high-power radiation experiment carried out in a waveguide system. Besides, the antenna is placed under the radome to realize integration analysis, and the radiation performance of the composite antenna radome is measured in the anechoic chamber.