dB Gain Variation Research Articles

H-plane gap-RGW horn antenna with very low side lobe level

This paper presents and applies a new concept of gap-RGW to develop a new configuration for RGW H-plane horn antennas. The proposed antenna is fully metallic and can generate a very low side-lobe level along with a flat gain response over a reasonable bandwidth, which is one of the advantages of this antenna. A prototype of the presented structure is designed and fabricated which provides the impedance bandwidth (S11 < − 10 dB) of about 25% with SLL < − 20 dB and 2 dB gain variation over the operating bandwidth.

A 23–29.5 GHz three‐stage mm‐wave GaN power amplifier using arbitrary two‐port complex‐impedance matching method

SummaryThis paper presents a broadband monolithic millimeter‐wave integrated circuit GaN power amplifier (PA) with arbitrary two‐port complex‐impedance matching method. The proposed matching topology has been applied to interstage matching network design by modifying traditional coupling matrix and synthesizing a desired network. The optimum load traction technique is introduced to provide some more suitable Zopts. After continuous‐wave test, the three‐stage MMIC PA achieves a peak PAE of 39.1% with a 34.9 dBm output power from 23 to 29.5 GHz and the measured S21 is 32.5 dB with a ±2.5 dB gain variation. When driven by a 400 MHz OFDM modulation signal with a PAPR of 8.5 dB, the measured ACPR is improved to −40.6/−40.7 dBc with DPD. In this case, the PA achieves an average PAE of 11.7% and a 26.7 dBm average output power.

Analysis of Doherty Power Amplifier Matching Assisted by Physics-Based Device Modelling

The Doherty Power Amplifier represents one of the most promising solutions for the design of high-efficiency power stages. In the widely adopted ABC scheme, the Doherty Amplifier design critically depends on the accuracy of the device model in different operating conditions, ranging from class AB to class C. For the class C case, library models are often inaccurate, while experimental characterization is difficult since it must be carried out in large signal conditions and with varying gate bias. In this paper, we propose an alternative approach, based on physics-based Technological CAD (TCAD) simulations of the complete Doherty amplifier along with the analysis of its individual MAIN (class AB) and AUXILIARY (class C) stages. TCAD simulations seamlessly provide an accurate modelling of the device behavior in all operation classes, including the device turn-on and the nonlinear capacitances, and easily account for the cross-loading effects of the MAIN and AUXILIARY devices through the output network and the effect of the device feedback (gate-drain) capacitance on the input matching. Analyzing a GaAs Doherty stage at 12 GHz, we show that the input phase of the auxiliary stage can be exploited for the Doherty power amplifier optimization in terms of gain, linearity and efficiency, showing a 9 dB gain with less than 1 dB gain variation from back-off to peak power with a power-added efficiency exceeding 45% over a Doherty region extending to a more than 6 dB output power back-off.

Millimeter-Wave 1-D Wide-Angle Scanning Pseudo-Curved Surface Conformal Phased Array Antennas Based on Elongated Planar Aperture Element

To perform wide-angle scanning while maintaining a planar low profile, we propose a new kind of millimeter-wave (mmWave) planar phased array antenna using inclined beam elements to imitate a curved surface conformal (CSC) array, called a pseudo-curved surface conformal (PCSC) phased array antenna. We present the concept of our PCSC phased array and then design an elongated planar aperture antenna (EPAA) element, achieving stable high broadside gain and wide beam on the scanning plane within a wide bandwidth. Then, by introducing asymmetries to the EPAA element, the beam inclination of the EPAA element can be adjusted. Accordingly, we use EPAA elements with different beam inclinations to form a 1 × 4-element 1-D wide-angle scanning PCSC phased array antenna. We design, fabricate, and measure a prototype of our proposal, with measured results showing that the proposed design has a 3 dB gain variation across a scanning range of more than ±62° (and as high as ±68°) within the 5G mmWave band (24.25 to 29.5 GHz), which is about ±10° better than its traditional counterpart.

W-Band Low-Profile Transmit Array Based on Wideband Partially Reflecting Surface

This communication presents a wideband low profile transmit array (TA) with a small height-to-diameter (H/D) ratio of 0.285 working at a center frequency of 100 GHz, which consists of a waveguide feed source, a metal ground plane, a partially reflective surface (PRS), and a transmission surface (TS). A PRS with not only a positive reflection phase gradient, but also a negative transverse reflection magnitude gradient is designed above the ground plane to reduce the height as well as to broaden the bandwidth of the TA. The proposed TS is composed of eight unit cells (UCs) with a high transmission magnitude and phase differences of 45° in a broadband range. Four passive antenna prototypes with different beam directions are fabricated to validate the design concepts, and good agreements are obtained between the radiation patterns, gain curves, and return losses. The measured peak gain is 20.7 dBi with aperture efficiency (AE) of 10.5% at 99.5 GHz. A relative bandwidth of 15.2% is obtained within 3 dB gain variations, making it a promising candidate for sixth-generation (6G) wireless communication applications.

A 16–24-GHz SiGe Decibel-Linear Low-Gain-Error Digitally Controlled High-Efficiency Variable Gain Amplifier

This letter presents a 16–24-GHz decibel-linear low-gain-error variable gain amplifier (VGA) in 130-nm SiGe technology. Negative feedback resistor is used in current source to expand the gain variation range and improve decibel-linearity. The nonproportion metal-oxide-semiconductor (MOS) array is introduced to reduce the gain variation error. This design achieves a 15–0 dB gain variation range at 1-dB gain step with root mean square (rms) gain-error less than 0.3 dB. The measured OP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1dB</sub> is greater than 9.5 dBm between the 1-dB bandwidth of 16–24 GHz and this VGA consumes 8.8 mA from a 1.6-V supply.

Wideband Isotropic Antenna With Miniaturized Ground for Enhanced 3 dB Coverage Ratio

In this letter, a wideband three-dimensional (3-D) isotropic antenna is proposed with improved 3 dB coverage ratio. Based on the investigation about the effect of the metallic ground size on isotropic radiation, a compact sequential-phase feeding network made of lumped components with miniaturized ground is elaborately designed for wide operating bandwidth and enhanced 3 dB coverage ratio in 3-D space. In the measurement, the antenna prototype is with the size of 70 × 70 × 0.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (0.23 × 0.23 × 0.0017 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ). The measured result shows that the proposed antenna provides the 6 dB gain variation fractional bandwidth of 4% and the 3 dB coverage ratio of more than 80%, leading to promising usage for wideband isotropic radiation applications.

Wideband Circularly Polarized Stacked Patch Antenna Based on TM₁₁ and TM₁₀

A wideband circularly polarized (CP) stacked patch antenna based on TM₁₁ and TM₁₀ is proposed in this article. This four-port antenna consists of a circular patch and a square patch, where the square patch is located above the circular patch. Taking into account the mutual coupling between four ports, the active reflection coefficient (ARC) is adopted to describe the impedance matching of the antenna, and a simplified form of ARC is derived. The abnormal electric field distribution generated in the square patch is attributed to the superposition of the electric fields of two orthogonal TM₁₀ modes, which is theoretically verified. Due to the coupling between TM₁₁ mode and TM₁₀ mode, a new resonance mode appears in a square patch, where the abnormal electric fields on the two diagonals are generated simultaneously. The effect of the square patch on the circular patch is equivalent to a capacitor at the lower frequency end and the higher frequency end of &#x2212;10 dB impedance bandwidth, while it acts as an inductor at the middle frequency band. Besides the horizontal patch of <inline-formula> <tex-math notation="LaTeX">$\lceil $ </tex-math></inline-formula>-shaped feed is sandwiched between two radiators to enhance coupling. Finally, a wideband feed network composed of Wilkinson power divider and phase shifter is devised to provide four signals of equal magnitude and quadrature phase for proposed antenna. To verify the design concept, a prototype is fabricated and measured. The results show that left-hand circularly polarized (LHCP) radiation is achieved. The 3 dB gain variation bandwidth is 44.6&#x0025;, ranging from 1.48 to 2.33 GHz, in which VSWR &#x003C; 1.5 and AR &#x003C; 1.5 dB. Besides the peak gain is 9.5 dBic and antenna efficiency is not less than 64&#x0025;.

Single Waveguide Feed Omnidirectional and Circularly Polarized Transceiver Waveguide Slot Antenna for Satellite Communication Applications

In this study, an omnidirectional and circularly polarized transceiver antenna, which can be used in simultaneous operations over transmit (TX) and receive (RX) channels for telemetry, tracking, and command (TTC) applications on the space segment of satellite communication, is proposed. The radiation and feed parts of the antenna consist of waveguide structures for high power necessity in transmit (telemetry) section. The radiation part includes two different sections of rotationally symmetric slotted arrays on circular waveguide, and radially outward metallic disks to improve omnidirectionality and circular polarization. The feed part contains a dual-band mod converter from rectangular TE10 mode to circular TM01 mode for symmetric field excitation over slots where the input of the converter is the standard rectangular waveguide. The design, simulation, and measurement results of the antenna are shown over a 3D printed prototype at Ku-band with center frequencies of 12 GHz and 14.25 GHz for TX and RX, respectively. With thin slots in telemetry section and thick slots in telecommand section, measured bandwidths for TX and RX frequencies are obtained approximately as 200 and 450 MHz, respectively. While TX band with maximum 3 dB gain variation over azimuth, maximum 3 dB axial ratio and minimum −3 dBi gain over 70° elevation beamwidth has relatively better performances at the expense of narrow bandwidth, RX band has maximum 3.5 dB gain variation over azimuth, maximum 4 dB axial ratio and minimum −6 dBi gain over 55° elevation beamwidth at the expense of wide bandwidth.

Pattern Reconfigurable Dual-Polarized Dipole Antenna With Staggered Parasitic Elements

This paper presents a pattern reconfigurable dual-polarized dipole antenna with staggered parasitic elements operating in 3.5 GHz band. The proposed antenna is designed by assembling two linearly polarized antennas to be orthogonally polarized, and each antenna includes two parasitic elements and a single dipole element. A circuit including a varactor is inserted into each parasitic element, and the current phase of the parasitic element changes according to the capacitance of the varactor. Each antenna has a beam steering range of about ±30° in the E-plane, and the beamwidth and gain are maintained uniformly regardless of the steering angle due to the angled parasitic element. Also, because of the continuously changing characteristic of the varactor, the beam of the proposed antenna is steered continuously, and only four varactors are used. The size of the fabricated dual-polarized antenna is 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.40λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.47λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , and the measured results confirm that the antenna has an average gain of around 6 dB with 0.3 dB gain variation.

Low-Profile Ultrawideband Circularly Polarized Metasurface Antenna Array

A compact low-profile ultrawideband circularly polarized (CP) metasurface antenna (MSA) array is presented in this letter. The array consists of 2 × 2 sequentially rotated symmetric MSA elements and a wideband four-way feeding network providing stable phases of 0°, 90°, 180°, and 270°. By using the constructed feeding network and MSA element, the CP array can achieve an ultrawideband CP performance with a low profile of 0.05λ L . The measured results show that the proposed MSA array achieves the 10 dB impedance bandwidth of 97.2%, 3 dB axial ratio bandwidth of 83.2%, and 3 dB gain variation bandwidth of 73.8%. Compared with the other designs in published literatures, the proposed CP MSA array owns the advantages of low profile with a simple structure and good CP performance without any air gap, thus indicating a promising candidate in compact wideband wireless systems.

Gain-control technique in double-pass parallel hybrid fiber amplifier

In this paper, the effect of gain control technique in double pass parallel hybrid fiber amplifier in terms of gain level as well as pump powers optimization are simulated using Optisystem and experimentally validated. An average gain level of 22.8 dB and overall gain variation of 3 dB within C and L band regions are achieved. The gain flatness bandwidth of 60 nm from 1530 to 1590 nm are obtained. A comparison with a single pass parallel hybrid fiber amplifier is presented. This comparison showed an average gain level of 38.5% higher than single pass-structure utilizing only 650 mW of Raman pump which is 18.7% lower.

Dirac leaky wave antenna for millimetre‐wave applications

Dirac dispersion cones enable remarkable wave phenomena in electronics as well as electromagnetic systems. In this work, the authors experimentally demonstrate for the first time the Dirac leaky wave antennas (DLWAs) at millimetre-wave (mm-wave) frequencies. The demonstrated DLWAs are implemented in the substrate integrated waveguide technology, delivering unprecedented features at high frequencies such as radiation at, and continuous beam scanning through broadside, with ease of fabrication, making these designs well suited for mm-wave applications such as emerging fifth generation and Internet of Things, radar and imaging. It is shown that a planar Dirac photonic crystal can be realised composed of air columns inside a host SIW waveguide, exhibiting a closed bandgap and linear dispersion around broadside. Phase and attenuation constants are controlled to obtain directive beam and scanning in a wide range of angles (from −30° to 20°). The presented DLWAs have a wide impedance bandwidth around 28 GHz with high efficiency, and operate with peak gains of about 16 dBi with <1 dB gain variation throughout the frequency range from 25 to 31 GHz. Several designs have been proposed, and their prototypes were fabricated using standard substrates. Measured results show excellent agreement with the simulated results, validating the proposed concepts.

Analysis and Design of Reflectarray Antennas Based on Delay Lines: A Filter Perspective

The analysis and design of reflectarray (RA) antennas based in delay lines is introduced for the first time from a filter perspective. To this purpose, each unit-cell of the RA is considered as a network composed of two ports, one being the delay line and the other one the free-space. This approach allows to borrow the coupling matrix formalism from filter theory and apply it to design unit-cells exhibiting broadband operation together with very sharp frequency responses. The concept is demonstrated with the aid of planar printed unit-cells coupled to substrate integrated waveguides (SIWs) through slots, a configuration that offers significant advantages to shape its frequency response while providing relatively low loss. With the aim of validation, a third order filter structure integrated in SIW-based unit-cells has been experimentally tested using the waveguide simulator technique, at a center frequency of 9 GHz. Measurements demonstrate a high-quality linear phase variation and range, and large frequency selectivity together with broadband response for the element of about 18%. The experimental results show the feasibility of this approach for the design of broadband reflectarray antennas exhibiting sharp gain responses. To illustrate the concept, a medium size reflectarray has been theoretically designed using the proposed unit cell at 9 GHz, showing a directive beam with 35.8 dB gain, sharp gain selectivity over 18 dB, and confirms the wide band operation with 20.3% bandwidth for a 3 dB gain variation.

A Fully Integrated K-Band Dual Down-Conversion Receiver for Radar Applications in 90 nm CMOS

A fully integrated K-band dual down-conversion receiver for phased array radar applications in 90 nm CMOS is presented. The receiver utilizes the dual down-conversion architecture to achieve superior performance. The integrated 1.15 GHz image-rejection filter (IRF) provides enough wideband (22 MHz) image rejection ratio at 140 MHz offset before the second down-conversion by utilizing the Q-enhancing and frequency staggering techniques to compensate the component loss. The low noise amplifier realizes the single-to-differential-ended conversion at the input with a transformer and achieves good common-mode rejection. The 70 MHz intermediate frequency baseband consists of two cascaded 3rd-order band-pass active RC filters (BPFs) and one automatic gain control (AGC) loop, with the integrator frequency compensation technique to lower down the requirements on the embedded Op-Amps. Two phase-locked loop (PLL) frequency synthesizers are integrated to provide the local oscillation (LO) signals for the down-conversions, where the matching of the charge-pump is improved by adding one extra current compensation branch. The measurements of the prototype show that the receiver converts the targeted mm-wave signal to 70 MHz intermediate frequency while achieving 8.3 dB noise figure (NF), 51-95 dB variable gain range and >45 dB image rejection ratio at 140 MHz offset with >22 MHz signal bandwidth. The receiver draws 74 mA current (excluding 2 PLLs) from the 1.2 V power supplies and occupies a core area of 4.58 × 0.53mm 2 (excluding 2 PLLs).

Wideband Omnidirectional Slotted-Waveguide Antenna Array Based on Trapezoidal Slots

This manuscript presents a novel approach for designing wideband omnidirectional slotted-waveguide antenna arrays, which is based on trapezoidal-shaped slots with two different electrical lengths, as well as a twisted distribution of slot groups along the array longitudinal axis. The trapezoidal section is formed by gradually increasing the slot length between the waveguide interior and exterior surfaces. In this way, a smoother impedance transition between waveguide and air is provided in order to enhance the array operating bandwidth. In addition, we propose a twisting technique, responsible to improve the omnidirectional pattern, by means of reducing the gain ripple in the azimuth plane. Experimental results demonstrate 1.09 GHz bandwidth centered at 24 GHz (4.54% fractional bandwidth), gain up to 14.71 dBi over the operating bandwidth, and only 2.7 dB gain variation in the azimuth plane. The proposed antenna array and its enabling techniques present themselves as promising solutions for mm-wave application, including 5G enhanced mobile broadband (eMBB) communications.

Wide Angle Beam Steerable High Gain Flat Top Beam Antenna Using Graded Index Metasurface Lens

This paper presents a beam steerable low-profile lens antenna with a flat top wide beam and a high gain operating at 10.10 GHz. It consists of a graded index metasurface (GIMS) lens placed on the top of a microstrip patch antenna (MPA) radiator. An ultrathin linear graded index metasurface (LGIMS) and a radial graded index metasurface (RGIMS) lens were designed for the magnitude and phase transformation of the radiated beam from the microwave radiator. First, an LGIMS lens antenna was designed by placing an LGIMS on the top of an MPA radiator at an optimum height. A maximum measured gain of 16.37 dBi indicating a maximum gain enhancement of 11.50 dB with beam steering in a conical plane with a vertex angle of 84° was observed. Next, a flat top beam (FTB) antenna with a stable gain band was designed by placing an RGIMS on top of an LGIMS lens antenna. The measured peak gain of 14.82 dBi with an FTB pattern having a 1 dB gain variation range of about 96° is observed. Furthermore, the movement of the LGIMS and the RGIMS on top of the radiator results in continuous beam scanning with a maximum gain variation of 1 dB in a conical plane with a vertex angle of about 100°. A maximum gain of 14.82 dBi with a maximum gain enhancement of 10.30 dB at 10.15 GHz was obtained due to the linear and angular movement of the LGIMS and the RGIMS in the FTB antenna. The simulated and measured results are in good agreement.

Two-Dimensional Pattern-Reconfigurable Cross-Slot Antenna With Inductive Reflector for Electromagnetic Torso Imaging

A wideband and low-profile cross-slot pattern reconfigurable antenna for electromagnetic imaging systems is proposed. The antenna is designed to cover the human chest area with steerable unidirectional radiation patterns at 0.7–0.9 GHz. The antenna is comprised of a corrugated cross-slot as the main radiator, and four parasitic slots with four p–i–n diodes operating as reflectors. An embedded feeding network with six p–i–n diodes is used to feed the main slot and switch the feeding path to modify the direction of the radiated beam (vertical/horizontal). In addition, an inductive mesh-grid surface is used to reduce the back lobe and enhance the operating frequency bandwidth. The antenna dimensions are ${0.8} {\lambda }_{0} {\times 0.} {8} {\lambda }_{0} {\times 0.18} {\lambda }_{0}$ (where ${\lambda }_{0}$ is the wavelength of the lowest frequency operation). By turning the parasitic slot p–i–n diodes to ON/OFF modes, the main beam can be steered along five distinctive positions at 0°, and at ±30° in two perpendicular planes. The antenna achieves a peak gain of 9 dBi at 0.8 GHz with 1 dB gain variations over the band of operation with a peak front-to-back ratio of 20 dB.

A Low-Profile Wideband CP End-Fire Magnetoelectric Antenna Using Dual-Mode Resonances

A low-profile wideband circularly polarized (CP) magnetoelectric (ME) antenna with high-gain and an end-fire radiation beam is proposed in this paper. It consists of a magnetic dipole (M-dipole) and two pairs of printed crossed strips to produce vertically and horizontally polarized E-field components, respectively. With the appropriate combination, the proposed ME antenna exhibits an inherent 90°-phase difference at endfire for these two field components. CP end-fire radiation, therefore, can be achieved. Two techniques using the L-probe coupled feeding structure to excite the M-dipole operating at both the basic ( $0.5\lambda $ -) and higher ( $1.5\lambda $ -) modes for the dual-mode resonances and using two pairs of printed strips with different dimensions for the dual-frequency resonances are introduced to realize the wideband operation. The measurement results show that the wide impedance bandwidth (IMBW) of 2.40–4.24 GHz (1.84 GHz, 55.4%) and 3 dB axial-ratio bandwidth (ARBW) of 2.36–3.86 GHz (1.5 GHz, 48.2%) are achieved. In addition, the stable end-fire radiation patterns with a peak gain of 7.57 dBi are observed over the operating band. The bandwidth for 3 dB gain variation is 2.34–3.97 GHz. Hence, the proposed antenna with its main beam in parallel with the substrate shows the potential for some point-to-point communications such as the radio-frequency identification (RFID) system.

Flat Reflectarray That Generates Adjacent Beams by Discriminating in Dual Circular Polarization

One planar $18 \times 18$ cm2 reflectarray prototype, capable of generating adjacent pencil beams with the orthogonal circular polarizations (CPs) in the Ka-band (19.2–20.2 GHz), has been designed, manufactured, and measured as a proof-of-concept to demonstrate the possibility of beam separation in the dual-CP applications. The prototype exhibits main beams pointing at elevation angles of 16.7° and 21.3° for left-hand CP and right-hand CP, respectively. A 1.5 dB gain variation and 66% of efficiency are achieved in the frequency band 19.2–20.2 GHz for a design center frequency of 19.7 GHz. These results will be useful for the future work, involving the design of multispot dual-CP and dual-band planar reflectarrays.