In this paper, dual-band and tri-band bandpass filters (BPFs) with fully independent and controllable passbands based on multipath-embedded resonators are presented. The dual-band BPF consists of two double open-ended stub-loaded terminal-shorted resonators (DOESL-TSRs) with a common via-hole connected along the symmetric plane of the filter. Based on DOESL-TSRs, a triple open-ended stub-loaded terminal-shorted resonator (TOESL-TSR) is proposed in the design of tri-band BPFs. The resonant characteristics of DOESL-TSR/TOESL-TSR are analyzed by the numerical calculation method. The measured results of the dual-band BPF show that the center frequencies (CFs) are located at 2.595 and 5.75 GHz, respectively, with 3 dB fraction bandwidth (FBWs) of 15 and 12.8%. The measured CFs of the tri-band BPF are located at 2.545, 3.775, and 5.95 GHz, respectively, with 3 dB FBWs of 9.8, 9.3, and 5.5%. Both of the filters exhibit the merits of fully independent and controllable passbands, high selectivity, and compact size.

In this paper, the main nonidealities appearing in polar transmitters will be addressed, together with several implementation considerations. Special attention will be paid to the role of AM modulation nonlinearity and parasitic AM-to-PM conversion, once architecture mechanisms such as time-delay mismatch between branches or limited bandwidth in the amplitude path are controlled. The device limiting factors for a highly efficient switched mode operation and a linear amplitude modulation will be identified. Some circuit design and implementation guidelines for the RF modulating stage and the envelope amplifier will be discussed, to finish with system-level analysis considerations under two-tone and real communication signal excitations.

In this paper, a simple and compact coplanar waveguide (CPW)-fed four coexisting inverted-L-shaped radiating elements based wideband (ILW) multi-input and multi-output (MIMO) antenna has been presented for wearable wireless applications. The 50 Ω CPW feed structure has been used to excite the four inverted-L-shaped radiators in a wide square slot of the proposed four-port wearable MIMO antenna. The four diagonal strips are extended from the corners of the wide square slot to form a square split ring structure in the center, which suppresses the coupling of electromagnetic waves among coexisting compact quad inverted-L-shaped radiators. The proposed ILW wearable MIMO antenna achieves a wide −10 dB simulated impedance bandwidth of 58.18% (3.9–7.1 GHz) and more than 30 dB isolation along with much reduced envelope correlation coefficient (<0.0002), high diversity gain (>9.9 dB), and specific absorption rate lower than 1 W/kg in the entire operational band. The simulated results are in good agreement with the measured ones. This ensures its utility for several wearable wireless applications in the C-band that comprises WLAN (5 and 5.2 GHz), Wi-MAX (5.5 GHz), and ISM band (5.8 GHz) applications.

A 16-element coplanar waveguide series fed hexagonal array antenna is proposed at millimeter-wave frequency range. In this paper, the analysis is initiated from a single-element hexagonal patch then extended to 1×2 array, 1×4 array, and 4×4 series fed hexagonal patch array antennas. The idea behind this design is to improve fractional bandwidth stage-wise with improved gain maintaining constant efficiency with all the structures. The 16-element array antenna is fabricated on Rogers RT Duriod 5880™ substrate with ɛr = 2.2 and 0.508 mm thickness. This array antenna exhibits low return loss at 28 GHz with a reflection coefficient value of −31.02 dB including almost 102% radiation efficiency and attained a maximum gain value of 8.98 dBi. The results are quite comparable with simulated 4×4 array antenna using the HFSS tool. The size of the proposed antenna is quite small which will be best suited for 5 G Femtobase stations to provide indoor communications at millimeter-wave frequencies.

In this paper, triple-band stacked microstrip patch antennas (MPAs) are presented with wide impedance bandwidth and suppressed cross-polarization level. Triangular and circular shaped slots are embedded in the patch of antenna. Slot-loaded microstrip patches are fed with meandered microstrip line supported by a semi-ground plane structure. Triangular shaped slot-loaded MPA shows triple resonance at frequencies 2.2, 4.45, and 5.3 GHz having bandwidth of 45.9, 19.23, and 15.67%, respectively. Circular shaped slot-loaded MPA also shows triple resonance at frequencies 2.2, 4.42, and 5.38 GHz having bandwidth of 50.24, 33.21, and 13.43%, respectively. Using circular slot in place of triangular; bandwidth of the first and the second band is improved by 4.34 and 13.98%, respectively. Both the proposed antennas show an omnidirectional radiation pattern at all three resonance frequencies in the xz-plane with almost 0 dBi gain. Both the proposed antennas are fabricated on a FR-4 epoxy substrate and show a minimum level of cross-polarization radiations.

The major component for the effective functioning of airborne unmanned aerial vehicles (UAVs) is an antenna. The unified integration of an antenna with UAVs without disturbing the other components of UAVs, compact size, thin, and wideband antennas are preferred. Based on these prerequisites, a low-profile and a wideband antenna is presented for autonomous UAVs for C-band applications. The antenna is designed on an extremely thin substrate of size 0.01λ0 without compromising the antenna's broad bandwidth. The antenna structure comprises a corrugated U-shaped patch, a few parasitic patches along with the partial ground. Initially, only a single mode was excited using a U-shaped patch, then further on introducing a few more parasitic patches along with corrugations in a U-shaped patch other modes were also coupled leading to enhancement in the bandwidth of the antenna. The proposed antenna along with a 2 × 2 quad-port multiple input, multiple output (MIMO) antenna is designed and fabricated. The measured results are found to be in good agreement with the simulated results. A broad bandwidth of 74.5% (4.1–9.0 GHz) with 5.02 dBi peak gain at 6.6 GHz is exhibited by the fabricated MIMO antenna. Thus, the designed antenna proves to be an effective candidate for UAV-based C-band applications.

This paper presents a technique that enables both efficiency and linearity enhancements of power amplifiers (PA) used in communication systems. It consists in the implementation of a dynamic bias control combined with digital base-band predistortion. The aim of this paper is to describe a methodology and successive steps of the design procedure to reach optimum performances in terms of power added efficiency (PAE) and linearity. It is here applied to a 100 W wide-band lateral diffused metal oxide semiconductor (LDMOS) push–pull amplifier (50–500 MHz) driven by orthogonal frequency division multiplexing (OFDM) signals. When the amplifier is driven by a continuous wave (CW) signal and operates at a constant 28 V drain bias voltage, it exhibits 100 W output power and 60% PAE. When it is driven by an OFDM signal, a 10 dB output power back-off is necessary to have a −25 dBc adjacent channel power ratio (ACPR) and PAE decreases down to 10%. By properly implementing an envelope tracking bias system, 40 W output power along with 38% PAE and −27 dBc ACPR have been reached. Applying base-band digital predistortion provides additional linearity improvements at high PAE (for only one point PAE lost, a 5 dB improvement is obtained for ACPR).

A high-gain microstrip patch-type WiMAX antenna operating at 3.5 GHz has been designed with a parasitic radiator and a raised ground plane. Antenna design has been carried out through extensive three-dimensional electromagnetic simulations. The patch antenna itself provides a realized gain of about 3.6 dB at 3.5 GHz. When a parasitic radiator is placed on top of the patch antenna, the gain increases from about 3.6 dB to about 7.4 dB. The raised ground plane further enhances the gain by about 1.5 dB. Hence the overall gain improvement is about 5.3 dB without the need of a radio-frequency amplifier.

We report investigations on the fabrication and characterization of graphene nanoribbon (GNR) field-effect transistors. Graphene layers are obtained from the thermal decomposition of a Si-face 4H-SiC substrate. To achieve high dynamic performance, a structure with an array of GNR connected in parallel was fabricated by e-beam lithography. The best intrinsic current gain cut-off frequency of 60 GHz and maximum oscillation frequency of 28 GHz were achieved. This study demonstrates the exciting potential of GNR in high-frequency electronics.

This paper describes some key points in the history and development of the European Microwave Conference, the European Microwave Week, and the European Microwave Association, starting from 1969. It captures the way in which the conference since the earliest days has sought to create a successful blend of scientific and industry interests and has adapted itself to and indeed shaped the many existing technical changes that have characterized and continue to be at the core of the field of microwave engineering.

We present a method to realize a low-power and high-speed digital-to-analog converter (DAC) for system-on-chip applications. The new method is a combination of binary-weighted current cells and R-2R ladder and is specially suited for modern BiCMOS technologies. A prototype 5 GS/s DAC is implemented in 0.13 μm SiGe BiCMOS technology. The DAC dissipates 26 mW and provides an SFDR higher than 48 dB for output frequencies up to 1 GHz.

In this paper characterization of dielectric materials in liquid and powder phase using concentric closed and split ring resonators of length λ, λ/2, and λ/4 is reported. Experimental results have been validated by simulations and theoretically modeling. Sensitivity of the resonator with closed rings was maximum. Experimentally extracted values of dielectric constant of ferrite ranged from 14.05 to 15.1 with closed ring resonators and from 13.6 to 14.02 with split ring resonator, respectively. For spirulina platensis the dielectric constant was lying in the range 1.78–1.93 and 1.74–2.04 with closed ring and split ring resonators, respectively. The values extracted experimentally are in good agreement with simulation and theoretically found values. However, the values obtained from closed ring resonator were in agreement with the dielectric constant values of ferrite and spirulina platensis.

A wideband staircase pattern defected ground monopole antenna integrated with an artificial magnetic conductor (AMC) reflector has been proposed for C-band (4–8 GHz) and ITU band (8.01–8.5 GHz) applications. The integrated antenna consists of a staircase antenna at top, a 2 × 2 AMC reflector at the bottom and an air substrate as gap between them. The AMC offers 18.5% ± 90° reflection phase bandwidth from 6.10 to 7.32 GHz. The AMC layer has achieved mu-negative properties in the designated band. The AMC proffers polarization independent behavior in the respective frequency band depicting robustness in AMC reflection phase characteristics. The integrated antenna has offered a wide impedance bandwidth of 2.78 GHz (42.8% at 6.5 GHz and 34.1% at 8.15 GHz) due to the defected ground monopole. The integration of wideband AMC beneath the staircase monopole antenna alters the out of phase radiation to in-phase planer pattern which enhances the peak gain up to 9.7 dB. It reduces the 1-g averaged specific absorption rate to 0.223 and 0.324 W/kg at the two designated bands. The structure maintains almost similar bandwidth and gain due to artificial human body loading.

This contribution deals with a frontend for interleaved receive (Rx)-/transmit (Tx)-integrated phased arrays at K-/Ka-band. The circuit is realized in printed circuit board technology and feeds dual-band Rx/Tx- and single-band Tx-antenna elements. The dual-band element feed is composed of a substrate-integrated waveguide (SIW) diplexer with low insertion loss, a low-noise amplifier (LNA), a bandpass filter, and several passive transitions. The compression properties of the LNA are identified through two-tone measurements. The results dictate the maximum allowable output power of the power amplifier. The single band feed consists of a SIW with several transitions. Simulation and measurement results of the individual components are presented. The frontend is assembled and measured. It exhibits an Rx noise figure of 2 dB, a Tx insertion loss of ~ 2.9 dB, and an Rx/Tx-isolation of 70 dB. The setup represents the unit cell of a full array and thus complies with the required half-wave spacing at both Rx and Tx.

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.

Fresnel Zone Plate lens (FZPL) antennas working in the V and W band are reported in this paper with half and quarter phase correction respectively. A low cost and straightforward technological process is used to manufacture the dielectric lenses using only one foam material where the dielectric constant is controlled. Simulation and measurement results are in good agreement that confirms the viability of such a process to fabricate inhomogeneous structures. Good loss efficiency of 73 and 55% are obtained at 60 and 85 GHz respectively with the two different FZPL designs.

The paper describes the design and development of a low profile wide scanned conformal active 1 × 32 phased array antenna for Ku-band SATCOM applications. The realized antenna is diagonally polarized and covers full transmit frequency band (i.e. 13.75–14.5 GHz) of Ku band SATCOM. All the developed sub-systems of the antenna, i.e. conformal radiating array, conformal transmit module, manifold network, and beam steering unit are described. The VSWR of the antenna is better than 1.65 over the complete transmit frequency band. The antenna has the beam steering capability of ±60° in the array plane. Designed antenna is best suited for airborne applications, where antenna profile contributes considerable aero drag and RCS to the host platform.

Precise characterization of concealed person-worn objects will speed up the passenger screening process by reducing the rate of nuisance alarms, while also enhancing the airport security imaging systems. This paper presents an automatic, real-time method for wideband millimeter-wave radar identification of the nominal surface contours of the human body – even with affixed foreign objects or when a segment of the body cross-section is not captured by the radar – without relying on the body's bilateral symmetry. The developed method is verified experimentally when applied to the actual images generated by a laboratory airport scanning prototype developed recently by the US Department of Homeland Security (DHS). Our method uses the noisy collection of radar cross-section reflectivity data to extract the main contours and estimates the nominal body surface cross-sections through fitting a small-term Fourier series of circumferential variation. This is a necessary step for accurate characterizing of concealed terrorist threat objects affixed to the body.

A compact dual ports antenna with high isolation is proposed for handheld radio frequency identification (RFID) reader which is rarely reported in open literatures. Different with conventional handheld RFID reader antennas with single port, the proposed antenna transmits and receives signal separately. The proposed antenna operating with full duplex mode can enhance effectively sensitivity of reader, since the strong transmitting signal of reader with single port is usually highly coupled with weak receiving backscatter signal of tag. The antenna utilizes E-shaped aperture-coupled patch structure that occupies less volume and provides further space-saving efficiency. The height of the proposed antenna is only 6.8 mm and the volume of that is 80 mm × 80 mm × 6.8 mm, which is easy to integrate in handheld RFID readers. The antenna uses two E-shaped coupling apertures to excite two orthogonal modes for dual-polarized operation. High isolation of around −30 dB is obtained by proper arrangement of the length of coupling apertures and the position of the stubs. The measured results show −10 dB matching band and −25 dB isolation band from 2.32 to 2.6 GHz and from 2.3 to 2.55 GHz, respectively. The antenna is suitable for applications in handheld RFID readers.

A new time reversal (TR) method for target imaging is proposed in this paper. Through single measurement by the antenna array, the received signals are utilized to form the space–frequency–frequency multistatic data matrix (MDM). Singular value decomposition is applied to the matrix to obtain the left singular vectors which span the signal subspace. The obtained vectors are divided into multiple subvectors by two different schemes and used to provide target signatures in the form of coarse frequency dependence and relative phase shifts that can be exploited to construct the imaging function. The performance of the proposed method is investigated through numerical simulations for both single and multiple targets, and the results are compared with the traditional TR method using the frequency–frequency MDM. It turned out that the proposed method is able to achieve high resolution with limited array aperture and shows satisfactory robustness in noise environment. Furthermore, experimental results are provided to show the availability of the method in practical applications.