Input Reflection Coefficient Research Articles

A Two-Dimensional Beam-Steering Partially Reflective Surface (PRS) Antenna Using a Reconfigurable FSS Structure

A two-dimensional (2-D) (azimuth and elevation) beam-steering partially reflective surface (PRS) antenna is proposed in this letter. It consists of a probe-fed square patch antenna acting as the radiator and a reconfigurable PRS structure serving as the beam-steering superstrate. The reconfigurable superstrate employs 6 × 6 reconfigurable unit cells and is equally divided into four sections. By controlling the states of the PIN diodes inserted in each unit cell, four sections have diverse biasing combinations, which can generate ten different radiation models. As a result, the proposed antenna can radiate a boresight beam or a ±22° tilted beam in the plane of ϕ = 0°, 45°, 90°, and 135°. To verify the design feasibility, an antenna prototype operating at 5.5 GHz is fabricated and measured. The simulated and measured results for the input reflection coefficients and radiation patterns are in good agreement. The measured realized gains are around 10 dBi for all states. Moreover, the gain variation from the broadside direction to the tilted direction (22°) is less than 0.8 dBi. Compared with some reported 2-D beam-steering PRS antennas, the proposed design can achieve a much wider beam-tilting range with a more stable radiation performance and fewer tunable diodes.

Performance Analysis of X Band Horn Antennas using Additive Manufacturing Method Coated with Different Techniques

In this study, horn antennas operating in the X band (8 – 12 GHz), which were manufactured using the additive manufacturing method (AM) and coated with different conductive surfaces, are investigated. The construction of the antennas by the AM method involves fabrication of the antenna structure using acrylonitrile butadiene styrene (ABS) thermoplastic by a 3D printer; then, the antennas were coated with several conductive surfaces. Various conductive coatings used for the three antennas in this study are as follows: conductive silver paint for the first antenna, copper tape for the second, and copper plating for the third. In addition, the performance of these antennas was investigated in terms of input reflection coefficient, gain, radiation pattern, and weight, and the results were compared with those of the conventional aluminum horn antenna of same dimensions.

A Short-Ended Compact Metastructure Antenna with Interdigital Capacitor and U-shaped Strip

A compact metastructure (MTS) antenna utilizing zeroth order resonance (ZOR) techniques has been reported in this paper. The proposed coplanar waveguide (CPW) based MTS antenna has made up of interdigital capacitor (IDC), split ring resonator (SRR) and strips (rectangular and U-shaped). ZOR is a magnificent technique by which small dimensions of the antenna is attained. The presented structure exhibits compact size of 0.24λ0 × 0.27λ0 × 0.024λ0, where λ0 is the free space wavelength at ZOR frequency of 4.61 GHz. In the presented paper ZOR frequency is configured by series LC parameters as it follows short-ended boundary condition. The U-shaped strip is basically used to provide capacitance with the SRR which affects the resonance frequency by controlling the series inductance and capacitance of proposed short-ended structure. It is noticed that the presented antenna exhibits working band operation at 4.61 GHz (4.16–4.8 GHz) with input reflection coefficient of − 50.32 dB at ZOR frequency. The proposed antenna achieves properties such as omni-directional and dipolar radiation pattern in xz-plane and yz-plane respectively. Measured peak gain of 2.52 dB and simulated radiation efficiency of 94.27% permits the MTS antenna to be used widely in C-band applications. The designed antenna is fabricated and experimentally verified.

Slot-Loaded Microstrip Patch Sensor Antenna for High-Sensitivity Permittivity Characterization

A slot-loaded microstrip patch sensor antenna is proposed to enhance sensitivity in measuring the permittivity of planar materials. A thin rectangular slot was etched along the radiating edge of a rectangular patch antenna fed by a microstrip transmission line. Two resonant frequencies were created at a lower frequency compared to the single resonant frequency of a conventional ordinary patch antenna. The sensitivity of the proposed slot-loaded patch antenna was measured by the shift in the resonant frequency of the input reflection coefficient when the planar dielectric superstrate was placed above the patch, and was compared with that of a conventional patch antenna without the slot. The two antennas were designed and fabricated on a 0.76 mm-thick RF-35 substrate for the first resonant frequency to resonate at 2.5 GHz under unloaded conditions. Five different standard dielectric samples with dielectric constants ranging from 2.17 to 10.2 were tested for sensitivity comparison. The experiment results showed that the measured sensitivity of the proposed patch antenna were 3.54 to 4.53 times higher, compared to a conventional patch antenna, for the five samples.

60 GHz Single-Layer Slot-Array Antenna Fed by Groove Gap Waveguide

A V-band single-layer low-loss slot-array antenna is presented in this letter. Radiating slots are backed by coaxial cavities, which are fed through a groove gap waveguide E-plane corporate feed network. Cavity resonances are created by shortening nails with respect to the surrounding ones. This fact enables a compact single-layer architecture since coaxial cavities and feeding network can share the same bed of nails. A 16 × 16 array is designed, constructed, and measured to demonstrate the viability of this concept for high-gain single-layer slot-array antennas. In addition, this solution can be extended to circular polarization by seamlessly adding a polarizer above the slots without changing the feeding network piece. Measurements show a relative bandwidth of 10% with input reflection coefficient better than $-$ 10 dB and a mean antenna efficiency above 70% within the operating frequency band (57–66 GHz)

A 3–14 GHz, Self-Body Biased Common-Gate UWB LNA for Wireless Applications in 90 nm CMOS

Inspired from continuous growth in the field of low power and low noise wireless communication devices, a low noise amplifier (LNA) using self-body biased common-gate (CG) configuration is presented in this paper. The proposed LNA is designed for 3–14[Formula: see text]GHz ultra-wideband (UWB) frequency range using 90[Formula: see text]nm CMOS process. Common-gate configuration with self-body biasing has been used at the input stage to provide wideband input matching with low noise figure (NF) for the complete UWB frequency. An impedance matching network consisting of parallel to series RLC network has been used between common-gate and cascaded common source (CS) stages. Two stages of the CS configuration have been used for bandwidth enhancement and to increase the power gain (S[Formula: see text]) with acceptable NF. Buffer stage at the output has been used to achieve output reflection coefficient (S[Formula: see text]) less than [Formula: see text]10.8[Formula: see text]dB. The proposed LNA achieves an average S[Formula: see text] of 15.9[Formula: see text][Formula: see text][Formula: see text]0.7[Formula: see text]dB with a maximum of 16.7[Formula: see text]dB at 3.0[Formula: see text]GHz and NF of 1.68–2.7[Formula: see text]dB for 3.1–10.6[Formula: see text]GHz UWB frequency range. It provides input reflection coefficient (S[Formula: see text]) less than [Formula: see text]10.2[Formula: see text]dB, reverse isolation (S[Formula: see text]) less than [Formula: see text]75.8[Formula: see text]dB and a NF of 1.68–4.0[Formula: see text]dB throughout the proposed UWB frequency range. The proposed LNA provides input 1[Formula: see text]dB compression point (P1dB) of [Formula: see text]13[Formula: see text]dBm and input third-order intercept point (IIP3) of [Formula: see text]8[Formula: see text]dBm at 6[Formula: see text]GHz. It consumes 20.1[Formula: see text]mW of power from a 1.2[Formula: see text]V power supply.

A Microstrip Coupled Cylindrical Dielectric Resonator as a Displacement Sensor

This paper presents the numerical and experimental investigations on the use of a cylindrical dielectric resonator (DR) as a displacement sensor in the millimetre range, for the first time. The sensor principle is based on the sensitivity of the coupling between a resonator and a transmission line, which is a simple microstrip line in the present context, to positional changes (displacement) of the resonator. Corresponding change in the input reflection coefficient of the microstrip line can be used to quantify the displacement. It is demonstrated numerically that the sensitivity and the linearity of the displacement sensing are highly dependent on the dielectric constant of the DR, a feature that is absent in other resonator-based sensors. Experimental results for an available DR sample of dielectric constant 24, diameter 19.43 mm and height 7.3 mm, operating in the HEM11δ mode with a resonant frequency of 3.41 GHz are presented to validate the simulations. Analysis of the results shows that in the measurement range of 1–8 mm, the above arrangement gives a sensitivity of 2.01 dB/mm. Such displacement sensors may find application in strain or pressure measurement, as well as in diagnosing alignment or positional errors.

On the Fundamental Limitations of Ultra-Wideband Antennas

An electrodynamic limitation on the characteristics of antennas with a semi-infinite range as the limiting case of ultra-wideband (UWB) antennas is found. This limitation relates the directivity, the input reflection coefficient, the lowest operating frequency, and the overall size of the antenna and takes into account its geometric shape. An expression for estimating the lowest operating frequency of antennas with a given size and shape is obtained. Expressions for estimating the minimum achievable size and lowest operating frequency of rectangular printed UWB antennas with linear polarization are derived.

A High Gain Low Noise Figure Double Balanced Down Conversion Mixer for Band 1 of WiMedia System

Objective: To propose an improved double balanced down conversion mixer for band 1 of WiMedia system at RF frequency of 3.432 GHz and IF frequency of 264 MHz. Method/Analysis: The proposed mixer is based on the Gilbert cell architecture. It uses switch bias technique to improve the noise figure and resistive current injection technique to improve the conversion gain and linearity. A resonating inductor is used to cancel out the effects of parasitic capacitances. Moreover, T type impedance matching, LC impedance matching and output buffer are used at RF trans conductance stage, LO switching stage and load stage respectively for matching purpose. Mixer is simulated in 0.18 μm CMOS technology using keysight Advanced Design System (ADS) software. Findings: Simulation results show that mixer achieves maximum conversion gain of 8.057 dB, third order Input Intercept Point (IIP3) of -10.88 dBm, Double Sideband (DSB) noise figure of 3.515 dB and S11 of -22.926 dB at 1.8 V dc supply voltage. Novelty/Improvement: A high gain, low noise figure double balanced down conversion mixer with low value of input reflection coefficient and suitable linearity is proposed for band 1 of Wimedia system. Keywords: Current Injection Technique, Double Balanced, Down Conversion Mixer, L and T Type Matching Networks, Switch Bias Technique, Wimedia System

New design of UWB‐MIMO antenna with enhanced isolation and dual‐band rejection for WiMAX and WLAN systems

In this work, a new design of wide-band multiple-input multiple-output (MIMO) antenna with improved isolation and dual-band rejection is proposed for wireless systems operating over the entire ultra-wide-band (UWB), X-band, and Ku-band (3–18 GHz). The proposed four-element UWB-MIMO antenna is fabricated on Rogers RT/Duroid-5880 substrate with dimension of 73 × 73 × 0.79 mm 3 . It achieves high isolation (>20 dB) between antenna elements without using any decoupling structures. In order to prevent interference problems from nearby WiMAX (3.3–3.8 GHz) and WLAN (5.1–5.8 GHz) systems, a C-shaped stub is embedded in the radiating patch and a pair of U-shaped parasitic strips is inserted beside the feed line in the single element design. The effectiveness of the proposed design is demonstrated by investigating measurement and simulation results, and comparing them with other existing designs. The results show that the proposed design has an input reflection coefficient <−10 dB, a mutual coupling <−20 dB, and an omnidirectional radiation pattern across the bandwidth of interest (3–18 GHz) excluding the two rejected bands. Also, the proposed design exhibits high diversity performance in terms of envelope correlation coefficient (ECC <0.0015) and channel capacity loss (CCL < 0.3 bits/s/Hz). This reveals the effectiveness of the proposed design in wide-band wireless applications such as satellite communications and microwave medical imaging.

A W-band CMOS down-conversion mixer using CMOS-inverter-based RF GM stage for conversion gain and linearity enhancement

A W-band (75–110 GHz) down-conversion mixer with CMOS-inverter-based RF transconductance (GM) stage for 94 GHz image radar sensors in 90 nm CMOS is reported. Due to the current bleeding and GM contribution of the upper PMOS transistors of the RF GM stage, a larger load resistance can be adopted and a larger GM can be obtained while keeps the same linearity. This leads to a conversion gain (CG) enhancement. In addition, the second-order term GM (g2) and third-order term GM (g3) of the main NMOS transistors of the RF GM stage can be cancelled by those of the upper PMOS transistors and the auxiliary NMOS transistors of the RF GM stage. This leads to a better linearity. The mixer consumes 8.56 mW and achieves an excellent RF-port input reflection coefficient of − 10 to − 18 dB for frequencies of 88.4–103.4 GHz. In addition, for frequencies of 70–100 GHz, the mixer achieves CG of 13.9–17.5 dB and LO-RF isolation of 40.6–43.5 dB, one of the best CG and LO-RF isolation results ever reported for a down-conversion mixer with operation frequency around 94 GHz. Furthermore, the mixer achieves prominent NF of 16.4 dB and output third-order intercept point of 14.1 dBm at 94 GHz. These results demonstrate that the proposed down-conversion mixer architecture is very promising for 94 GHz image radar sensors.

Design of 5.2 GHz Low Noise Amplifier for Wireless LAN

Abstract A 5.2 GHz Low Noise Amplifier (LNA), intended for Wireless LAN. The input reflection coefficient and output reflection coefficient are both less than -10 dB. The amplifier provides a forward gain (S21) larger than 11dB, with a noise figure of 0.7dB. Another issue has been investigated concerning LNA having low power consumption. We have obtained a Pdc of 25 mW. The linearity of input third-order intercept point is 27dBm. Besides, we obtain 1dBm input compression of 8.8dBm. The chip area occupies for FR-4 Substrate is 5x2 cm2.

A 125-ps 8–18-GHz CMOS Integrated Delay Circuit

A wideband integrated delay chain chip with 5-bit main delay control, two error correction bits, maximum delay of 125- and 3.9-ps delay resolution, designed and fabricated in a 0.18- $\mu \text{m}$ CMOS technology is presented. This delay chain is a cascade of seven passive internal-switched delay blocks which the five main bits are based on novel delay structures. The proposed delay structures are similar to second-, fourth-, and sixth-order all-pass networks and are robust to mismatch effects of resistive parasitics of transistor switches. Measurement results of the fabricated delay chain show 15.2–23.3-dB insertion loss and less than 3.3-ps rms delay error over the intended frequency band from 8–18 GHz. Input and output reflection coefficients are better than −11 dB for the delay chain including the effect of RF bondwires and pads. The fabricated chip occupies an area of $2.0\times 1.0$ mm2 and has no dc power consumption.

1-D Electronic Beam-Steering Partially Reflective Surface Antenna

A 1-D electronic beam-steering partially reflective surface (PRS) antenna using a new reconfigurable PRS unit cell is proposed in this paper. The proposed work addresses the challenge to achieve a large beam steering angle with small gain variation and a small number of active/lumped elements by using a reconfigurable PRS superstrate only. The PRS unit cell consists of two back-to-back T-shaped strips with one PIN diode inserted between them and a pair of trapezoid patches (a rectangular patch and a pair of triangle parasitic patches). Beam steering is achieved by controlling the different states of PIN diodes. Thanks to the trapezoid patches, the proposed unit cell can generate a larger phase difference between different states, thereby leading to a larger beam steering angle. Furthermore, due to the addition of more degrees of freedom in the proposed unit cell, the phase difference can be easily manipulated. Moreover, since the T-shaped strips in each unit cell is connected with adjacent ones, the biasing network is very simple without needing a large number of lumped elements and dc biasing lines. The beam steering property is analyzed by using phased array theory. An antenna prototype with a main beam direction towards 0°, -18° and 18° operating at 5.5 GHz in the H-plane is fabricated and measured. Good agreement between the predicted simulation and measurement results for the input reflection coefficients and radiation patterns is achieved, which validates the feasibility of the design. The measured realized gains are over 11 dBi for all states with a 0.8 dBi gain variation.

Determination of Adulteration of Honey Syrup Using Open Ended Coaxial Probe Sensor at Microwave Frequency

Food quality assurance is becoming increasingly important in food processing industry as expectations from the consumers and competitions among food manufacturers continue to grow. For this singular reason, this research work is primarily aimed at studying the dielectric characteristics of pure honey and adulterated ones with a view to determine honey that has been adulterated. In this work, permittivity of pure honey, distilled water and honey—distilled water syrup mixtures with water content from 0% to 80% was studied from 1 to 20 GHz with open-ended coaxial-line sensor and a network analyzer at room temperature. The input reflection coefficient obtained from the vector network analyzer (Agilent 85,071) is then used to calculate and correlate the complex permittivity measured for the water and mixtures. Results showed that the die-lectric constants of all samples decreased with increasing frequency, while the pure honey had lower dielectric constant than distilled water but the mixture of water and honey increased with increases in water content. The maximum loss factor decreased with increasing water content.

&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$W$ &lt;/tex-math&gt; &lt;/inline-formula&gt;-Band Low-Profile Monopulse Slot Array Antenna Based on Gap Waveguide Corporate-Feed Network

This paper presents a gap waveguide-based compact monopulse array antenna, which is formed with four unconnected layers, for millimeter-wave tracking applications at W-band (85-105 GHz). Recently developed gap waveguide technology removes the need for galvanic contact among metallic layers of waveguide structures, and thereby, makes the proposed antenna suitable for easy and low-cost manufacturing. In this context, a low-loss planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The gap waveguide planar monopulse comparator network is integrated with a high-efficiency 16× 16 corporate-fed slot array antenna. The measured results of the comparator network show the amplitude and phase imbalance values to be less than 0.5 dB and 2°, respectively, over the frequency band of interest. The fabricated monopulse array antenna shows relative impedance bandwidths of 21% with input reflection coefficients better than -10 dB for the sum and difference ports. The null in the difference radiation pattern is measured to be 38 dB below the peak of the sum radiation pattern at 94 GHz. The measured gain is about 30 dBi for the same frequency. The low-loss performance of the comparator network and the feed network of the proposed array, together with the simple and easy manufacturing and mechanical assembly, makes it an excellent candidate for W-band compact direction-finding systems.

A Two-stages Microstrip Power Amplifier for WiMAX Applications

Amplification is one of the most basic and prevalent microwave analog circuit functions. Wherefore power amplifiers are the most important parts of electronic circuits. This is why the designing of power amplifiers is crucial in analog circuit designing. The intent of this work is to present an analysis and design of a microwave broadband power amplifier by using two stages topology. A two stages power amplifier using a distributed matching network for WiMAX applications is based on ATF-21170 (GaAs FET). The configuration aims to achieve high power gain amplifier with low return loss over a broad bandwidth. The proposed BPA is designed with a planar structure on an epoxy (FR4) substrate. The planar structure is also utilized for getting the good matching condition. The advanced design system (ADS) software is used for design, simulation, and optimization the proposed amplifier. The complete amplifier achieves an excellent power gain; is changed between 28.5 and 20dB with an output power of 12.45dBm at 1dB compression point. For the input reflection coefficient (S11) is varied between -20 and -42dB. While the output reflection coefficient (S22) is varied between -10 and - 49dB over the wide frequency band of 3.2-3.8GHz.

A 0.7 V, Ultra-Wideband Common Gate LNA with Feedback Body Bias Topology for Wireless Applications

An ultra-wideband (UWB) low noise amplifier (LNA) for 3.3–13.0 GHz wireless applications using 90 nm CMOS is proposed in this paper. The proposed LNA uses an improved common-gate (CG) topology utilizing feedback body biasing (FBB), which improves noise figure (NF) by a considerable amount. Parallel-series tuned LC network was used between the common-gate first stage and the cascoded common-source (CS) stage to achieve the maximum signal flow from CG to CS stage. Improved CS topology with a series inductor at the drain terminal in the second stage connected and cascoded CS third stage provides high power gain (S21) and bandwidth enhancement throughout the complete UWB. A common-drain buffer stage at the output provides high output reflection coefficient (S22). It achieves an average power gain (S21) of 14.7 ± 0.5 dB with a noise figure (NF) of 3.0–3.7 dB. It has an input reflection coefficient (S11) less than −11.7 dB for 3.3–13.0 GHz frequency and output reflection coefficient (S22) of less than −10.6 dB with a very high reversion isolation (S12) of less than −72.4 dB. It consumes only 5.2 mW from a 0.7 V power supply.

Safety of active catheters in MRI: Termination impedance versus RF-induced heating.

To investigate the effect of the termination impedance on the RF-induced heating of active catheters using analytical modeling. Interaction of an arbitrary electric (E) field and an isolated transmission line (TL) embedded in cascaded lossy media was analytically modeled. Termination impedances at the tip and the input sides were expressed as distinct parameters in the current and voltage distribution formulae that are obtained by solving the inhomogeneous wave equations using the Green's function approach. The tip specific absorption rate (SAR) was calculated for different E field configurations. The tip SAR was displayed on a color-coded Smith chart in terms of the normalized input reflection coefficient. Results of the analytical calculations were compared to transfer function (TF) measurements. An input impedance control unit that is integrated to the interface circuit was introduced. TFs from analytical model and measurements exhibited similar behaviors. Color-coded Smith charts shows that the analytical model and measured TF-based tip SAR depends strongly on the input reflection coefficient. Both for measured and analytical TFs, SAR can deviate up to 70% from the mean value for different input impedance values. This study shows that it is possible to change the RF-induced heating characteristics of an active catheter by adjusting the input impedance, and the presented analytical model is in good agreement with TF measurements.

Investigation on Different Forms of Circular Sectored-Dielectric Resonator Antenna for Improvement in Circular Polarization Performance

In this communication, some investigations have been performed on different forms of circular sectored-dielectric resonator antenna (CS-DRA) formed using different sector angles $(\beta)$ to improve the circularly polarized (CP) performance. The additional parameters of CS-DRA are aspect ratio ( $\alpha$ ) and sector angle ( $\beta $ ), which constitute a new optimization framework to analyze CP parameters. These compact structures (CS-DRAs) with simple coaxial probe feeding offer low-volume geometry with wide axial-ratio (AR) bandwidth as compared to conventional DRAs. Based on the results obtained in this investigation, it is found that appropriate values of “ $\alpha $ ” and “ $\beta $ ” could be chosen to improve the CP performance in terms of wide AR, and thus could not be avoided. In this communication, the fundamental mode $\text{TM}_{v,1,\delta }$ and next lower resonant mode $\text{TM}_{2v,1, \delta }$ have been excited to achieve the orthogonal polarizations. CS-DRA with the best performance has been fabricated to validate the simulation results. Simulated and measured AR bandwidths obtained are 15.2% (5.47–6.37 GHz) and 15.46% (5.43–6.34 GHz), respectively, whereas input reflection coefficient bandwidths are 58.5% (4.24–7.75 GHz) and 48.3% (4.65–7.6 GHz), respectively.