This paper presents for the first time high-efficiency W-band power amplifiers (PAs), the design of which follows the digital PA (DPA) design concept. Two DPAs with different output networks have been realized: a single-band version (S-DPA) for 95 GHz and a dual-band design (D-DPA) for signal frequencies fS of 68 GHz (first band) and 76 GHz (second band), respectively. The PAs are realized as monolithic microwave-integrated circuits (MMICs) in a 0.8 μm InP DHBT transferred-substrate process. They utilize a double-emitter-finger DHBT unit cell with an emitter area of 2 × 0.8 × 6 μm3 each. In contrast to the usual W-band PAs, the proposed single-stage amplifier MMICs do not apply any special reactive matching for the transistor, which leads to very compact chip sizes of 0.27 mm2 (S-DPA) and 0.39 mm2(D-DPA). The S-DPA includes one band-pass filter (BPF) at the output with 0.6 dB insertion loss (IL) and 24 dB input return loss (RL) at the signal frequency of 95 GHz. The dual-band BPF shows 0.7 dB IL in both bands with a RL of more than 21 dB each. Applying an overdriven sinusoidal input signal to emulate digital operation the DPAs achieve a maximum output power of 14.4 dBm and power-added efficiency of 31% when using the single-band configuration. Collector efficiencies of more than 80% and the flexible multi-band operation demonstrated prove the great potential of the digital PA concept for future high-speed communications.

Novel impedance transforming directional couplers are proposed in which the achievable impedance transformation ratio is increased above the previously reported limit related to coupling of the coupled-line sections. The proposed couplers consist of two coupled-line sections between which uncoupled sections of left-handed lines are connected. The presented concept has been verified by circuit simulations as well as by measurements of the manufactured 3-dB coupled-line impedance transforming directional coupler operating at f0 = 1.2 GHz and featuring twofold increased impedance transformation ratio R = 4.

This paper presents a review of filtering methods to eliminate echo in antenna measurements. Two different methods, fast Fourier transform and Matrix Pencil, are explained, compared, and simulated in a planar near field where other effects, such as aliasing, can and will be present if the simulation is not appropriately made and the parameters are not carefully chosen. Finally both methods are applied to real measurements of a dipole in a Microwave Vision Group multiprobe system and of a horn in a single-cut measurement. Other effects, such as window shift, may appear depending on the geometry of the system where the measurement is taken. These effects must be taken into consideration and carefully corrected.

The development of compact radio frequency identification (RFID) tag is the key requirement for wireless tracking of precious small size goods/packages in transport. A design of compact meander line tag antenna having inductive coupling feed is presented for RFID system operating at ultra high frequency band of 865–867 MHz. The size of the proposed tag antenna is 43 mm × 10 mm, and is designed using Higgs 4 IC chip (made Alien Technology, USA) having impedance of 20.55 − j191.45 Ω at centre frequency 866 MHz. The antenna characteristics such as impedance, radiation pattern, bandwidth, and effect of ground on gain and tag size are analyzed and found to closely match with the simulated values. The observed value of reading range varies from 87.5 to 35 cms depending on mounting on non-metal and metal packages, respectively.

Continuous-wave (CW) radars have been recently investigated in healthcare aiming at contactless health monitoring. However, a major problem in monostatic CW architectures is represented by the unwanted leakage produced by poor isolation between transmitter and receiver, which can drastically decrease the receiver's sensitivity reducing therefore the radar dynamic range. Although this situation can be easily controlled in case of narrowband CW radar by an appropriate passive microwave design, it becomes much more complicated in case of stepped-frequency CW and frequency-modulated CW architectures that present an ultra-wideband nature. In this paper, a monostatic CW radar integrating a tunable wideband leakage canceler aiming at indoor tagless localization is presented and discussed. The use of the feedforward canceler allows a strong reduction of the unwanted leakage over the whole radar bandwidth. Experimental results demonstrate the feasibility of this approach, showing an outstanding improvement of the radar dynamic range.

As a recently proposed concept, multiple-input multiple-output (MIMO) radars exhibit much higher spatial resolution than traditional transmitter based radars because of the synthesized virtual array. In this paper, the problem of minimum redundancy (MR)-MIMO array synthesis is addressed, which seeks to maximize the virtual array aperture of MIMO radars for a given number of transmitting and receiving elements. A hybrid method combining autocorrelation property of cyclic difference sets (CDSs) and global search characteristics of ant colony optimization (ACO) is proposed for a rapid and numerically-effective exploration of MR-MIMO array configurations. Numerical experiments validate the proposed method, showing improvements in convergence rate and computational cost with respect to bare ACO-based search as well as improvements in the generality and configuration variety with respect to the CDS-based method.

This paper presents a novel ultra-low-loss high-pass filter with 3 dB cutoff frequency of 890 MHz for astronomical receiver radio frequency interference mitigation application. The filter consists of three series capacitors, four shunt inductors, and microstrip circuit board. Specially, 4 shunt inductors are actualized by fabricating air-core short-circuit coaxial cable inductors in the filter box body, and the quality factor of these cable inductors is up to 762.2 and 1046, respectively, at 1.4 GHz. In the expected passband of 1.1–1.9 GHz, S parameters measurement show that insertion loss is lower than 0.16 dB and two-port return loss is larger than 20 dB; noise measurement show that filter noise temperature is lower than 8 at 300 K ambient temperature. Noise sources of this filter are analyzed by simulation and measurement.

In this paper a high gain aperture-coupled membrane antenna with a frequency selective surface (FSS) on a superstrate layer has been investigated. The base membrane antenna consists of a microstrip patch on the top of Roger RT-5580 substrate, supported by FR4 and is excited through an aperture fed by substrate-integrated waveguide (SIW). The CST Microwave Studio simulation results show that the proposed membrane structure has an impedance bandwidth (BW) of 8.85% from 75.97 to 82.96 GHz with a gain of 6.29 dBi at 79 GHz. To improve the gain, a superstrate layer is loaded above the membrane antenna, which increases the gain by 9.11 dB at 79 GHz. Furthermore by using FSS under superstrate layer, the gain is again increased by 2.5 dB. The total antenna structure provides a gain of 17.9 dBi at 79 GHz by keeping the same BW. The measured results are provided for the input matching (S11) only, the simulated results for the antenna gain and radiation patterns are obtained with the use of CST and are validated by using HFSS. The measured S11 BW of the total antenna is from 75.57 to 84.18 GHz (10.89%), which is in agreement with the simulated results.

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.

Step-impedance resonators and step-impedance capacitor coupling pads are introduced to microstrip band-pass filters to suppress spurious stop-band responses up to the ninth order, thereby providing a very wide stop band. Combined with improvements in existing suppression techniques, the overall suppression in one of the filters, with 1 GHz center frequency and 42% bandwidth, is −54 dB, up to 8.9 GHz. By also using suitably placed resistors, spurious levels are now depressed to −67 dB up to 8.8 GHz, with only 0.03 dB extra pass-band loss.

In this paper, an ultra-wideband (UWB) filter with a notch band using T-shaped step impedance resonator loaded with cross-shaped open stubs has been presented. The notch band is formed by utilizing intrinsic zero. The characteristics of the new quad-mode resonator have been analyzed using odd-even mode analysis method. It can be shown that it is the intrinsic zero that generates the notch band. In addition, wide tunable notch band form 5–9.3 GHz can be achieved. A UWB filter with a notch band centered at 6.25 GHz using the proposed quad-mode resonator has been designed, fabricated, and tested. Experiment results show that the attenuation in notch frequency is >22 dB while the return loss of the simulation and measurement results are 22 dB/20 dB and 14.5 dB/11.2 dB in the lower and upper passband, respectively, which illustrate that the simulation and measurement results are in agreement.

A compact multi-layer N-way power-dividing structure with good isolation and output return loss performance is proposed. The isolation network is circularly distributed that constitutes a closed ring-shaped architecture. The equivalent circuit model is given and the [S] matrix is developed to analyse and design the power-dividing structure. Finally, a six-way power divider centered at 2.1 GHz is designed and fabricated. The measured and simulated results agree well with each other. The total size of the power divider is 0.13λg × 0.19λg.

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.

This paper presents, a dual-band bandpass filter using asymmetric stepped impedance stub loaded open loop resonator (OLR) for WLAN and WiMAX application. The outer OLR is realized to operate at lower passband of 2.45 GHz which is directly coupled to input and output ports whereas the asymmetric stepped impedance stub that loads the outer resonator contributes to 3.5 GHz passband. The introduction of asymmetric stepped impedance stub provides further control of improving the upper passband edge selectivity of second passband and in shifting the spurious modes away from second band thereby contributing to the wide upper stopband. The insertion loss is within 1.5 dB for each passband with 10 dB passband bandwidth of 250 MHz at both bands. A stopband up to 10 GHz is also obtained. A prototype is developed and the s-parameters obtained from electromagnetic simulation, equivalent transmission line model and measurement are in close agreement. The overall dimension of the filter is 25.45 × 15.89 mm2 which renders it a compact size.

Design and realisation of a compact power divider based on half mode substrate integrated waveguide (HMSIW) with an arbitrary power dividing ratio is presented. This design consists of a substrate integrated waveguide (SIW) transition, two bisected HMSIW transitions by a gap, an SIW-to-microstrip transition, and two microstrip feed lines. In addition, a resistor is attached between two HMSIW transitions. To adjust the power division ratio, four parameters are introduced. Furthermore, four graphs are plotted using a three-dimensional electronmagnetic (3D EM) simulator to graphically determine the introduced parameters. In this study, three circuits with power division ratios of 1:1, 1:4, and 1:8 are simulated using the 3D EM simulator and fabricated on a Rogers RO4003C substrate. The results show a good agreement between the simulated and measured results. The measured results display these circuits (1:1, 1:4, and 1:8) have the bandwidths of 70, 36, and 40%, respectively. Moreover, the proposed structures (1:1, 1:4, and 1:8) are compact and their overall sizes are $1.13 \times 1.04\lambda _g^2 $, $0.96 \times 0.91\lambda _g^2 $, and $0.81 \times 0.78\lambda _g^2 $, respectively. These structures have the advantages of the compactness in size, wide bandwidth, high power division ratio (from 1:1 to 1:16), and compatibility with planar circuits.

A tunable radiator for space application has been developed to meet stringent requirements in terms of electrical and environmental specifications but also low mass, simple manufacturing and low cost. The element is based on the folded planar inverted F-antenna, with size of one quarter of wavelength. It is mechanically tunable to adjust input impedance for any various positions on the satellite body and possible obstacles and protrusions. Results in terms of radiation pattern, S parameters, shock and vibration tests are presented. The antenna operates in ultra-high frequency band (400 MHz) in linear polarization. It has been designed to act as the basic element for miniaturized multi-function antenna systems on board of small satellites that can operate in three different radiating modes and in both left and right hand circular polarizations.

In this paper, a novel two-stage fish spear-shaped multimode resonator (MMR)-based ultra wideband (UWB) bandpass filter (BPF) is presented. The fish spear-shaped MMR is loaded with stepped impedance resonator in order to improve the out-of-band performance of the proposed filter. The proposed UWB BPF filter has fractional bandwidth better than 110%. In order to validate the present design approach, the filter is fabricated on RT/Duroid 5880 having dielectric constant 2.2, thickness 0.787 mm and loss tangent of 0.0009. The measured passband bandwidth of the filter is from 3.3 to 11.85 GHz, with insertion loss of 1.5 dB and return loss better than 12 dB in the passband. The proposed filter has sharp selectivity and upper stopband with 20 dB attenuation from 12 to 24 GHz.

Use of frequency-selective surfaces (FSSs) is proposed to shield rooms against electromagnetic fields in order to achieve secure indoor communications and reduce human exposure to external fields. The secure room is designed using two-layer FSSs with an FR4 substrate to cover 10–12 GHz frequency band. Different elements in each layer and shift in the position of elements are the reasons for more than 3 GHz bandwidths in X band. The performance of the structure is also stable versus the misaligned position of layers. An equivalent circuit model is proposed for the structure and results show −20 dB isolation between inside and outside of the room in the desired frequency band. Bio tissue is located inside the cubic structure with FSS walls and the results of the specific absorption rate are demonstrated and compared in two rooms with FSS cover on concrete walls and a room with concrete walls. The 17 × 17 cm2 two-layer FSS is fabricated for the measurement and the results are presented. The designed FSS can be used in the construction of wave-isolated room for any application.

This paper reports on a microwave heater at 20 GHz for digital microfluidics. It allows rapid heating of nanoliter fluid samples and simultaneous temperature monitoring by correlating the reflection coefficient of the heater with the temperature dependency of the relative permittivity of the lossy fluid under consideration, in this case demineralized water. Microwave heating was performed with power levels of 20 and 23 dBm at the on-wafer probe tips on samples of 500 nL. Temperature measurements were carried out with a miniaturized type K thermocouple, and a platinum resistor to monitor the reference temperature. Microwave and thermal performances have been characterized using multi-physics software, and measurements obtained with a large signal vector network analyzer showed good agreement with simulated data. An average heating rate of 20 °C/s was observed during the first 4 s of the heating process.

This paper presents for the first time a wavetable-based coding scheme to generate a high-speed binary input signal for digital RF power amplifiers. The approach maximizes the utilization of the time domain handling capabilities of the pulse forming circuit. Key features are a greatly improved output spectrum purity in comparison with common digital modulators, the ability to adjust the modulator to any given pulse forming hardware and a built-in signal correction option that comes without additional computational cost. To give a first impression on the modulators behavior and its possibilities to adapt to different hardware constraints, simulations are carried out for different parameter variations and for different baseband bandwidths. Furthermore, the proposed concept is emulated with an arbitrary waveform generator to gather additional measurement data. For a 5 MHz wideband code division multiple access (WCDMA) signal (6.5 dB peak-to-average power ratio) at 900 MHz, an error vector magnitude (EVM) of 0.26% and better than >58 dB adjacent channel leakage ratio (ACLR) were recorded. To the authors’ knowledge, these are the best values achieved so far for a single-bit coding scheme without digital predistortion that still maintains maximum power coding efficiency.