Measured Radiation Patterns Research Articles

A Low-Cost SISL Differentially Fed Dual-Polarized Stacked Patch Antenna With Enhanced Common-Mode Suppression Using Characteristic Mode Analysis

A wideband differentially fed dual-polarized stacked patch antenna with high common-mode (CM) suppression is proposed in this article using the characteristic mode analysis (CMA) and the substrate integrated suspended line (SISL) technology. Based on the CMA, orthogonal slots are loaded within the stacked patch to enhance the directivity of the second-order degenerate modes and reallocate the resonating frequency of the fundamental degenerate modes. A crossed dipole is introduced within the driven patch to ensure polarization uniformity between the two paired degeneracies. The CM suppression level ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}_{\mathrm {CC}}11$ </tex-math></inline-formula> ) is enhanced from–10 to–1.30 dB within the frequency range of 4.0–7.0 GHz by embedding circular slots embedded within the stacked patch and controlling the slot radius. Measured results demonstrate a–10 dB differential impedance bandwidth of 28.4% (4.62–6.18 GHz) and high isolation of better than–39.5 dB between the differential ports. The antenna depicts stable measured radiation patterns with low cross-polarization (<–30 dB). The measured average antenna gain and efficiency are 9.55 dBi and 85.5% within the DM passband. In addition, a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{S}_{\mathrm {CC}}11$ </tex-math></inline-formula> better than–1.05 dB is measured within the desired DM band.

A Near-Field-Based Gain and Pattern Measurement Technique for Probe-Fed Millimeter-Wave Antennas [Measurements Corner

Driven by the perpetual demand for higher data rates, extensive research efforts have been devoted to millimeter-wave (mm-wave) 5G technologies in recent years. Highly integrated mm-wave antennas for 5G user equipment are considered one of the key components in the realization of mm-wave-based mobile networks. An accurate characterization of antennas is as important as antenna design. Despite great advances in measurement capabilities over the years, we are still facing many difficulties in probe-based mm-wave antenna measurements. This article presents a fast, simple, and accurate near-field (NF)-to-far-field (FF) technique for gain and radiation pattern measurements of probe-fed mm-wave antennas. A setup based on an electro-optical (EO) NF measurement system (NeoScan) is utilized to measure the NF of the antenna under test (AUT). The system uses a high-spatial-resolution nonintrusive probe to scan the NF in very close proximity to the antenna’s surface, which significantly alleviates multipath effects and reduces the required scan area. The radiation pattern of the AUT is computed using the NF-to-FF transformation. To obtain the gain of the AUT, a ground-backed dipole antenna is created and used as a gain standard. The absolute gain of the ground-backed dipole is characterized using the image method. Measurement accuracy is checked against the simulation. With the help of the standard gain antenna, the NF-to-FF method can be used to measure both the gain and radiation pattern of any type of probe-fed mm-wave antenna. For demonstration purposes, two test antennas, a horizontally polarized tapered slot antenna, and a dual-band vertically polarized hexagonal bridge antenna operating at 28 GHz are fabricated and characterized. Excellent agreement against full-wave simulation is achieved.

Measurement technique for increasing the allowable dimensions of antennas tested in a collimator installation

Large collimator setups are often in use for antenna radiation pattern measurements. Their quiet zone size limiting the allowable dimensions of the antenna under test, as a rule, do not exceed a half of the collimator’s profile. Retrieving ARP from measurements in a non-ideal environment can be a means to expand the working area. The subject of the article is such a technique based on of the representation of a real field by a converging cluster of plane waves. It turned out that at the stage of studying the field of the collimator, despite the requirements of the uniqueness theorem, measurements may be carry out on a certain limited area of the boundary surface. Acceptable results are obtained when the working area is up to 90% of the collimator cross section.

Antenna-coupled microbolometer based on VO2's non-linear properties across the metal–insulator transition region

This paper presents an antenna-coupled non-linear vanadium dioxide (VO2) microbolometer operating in the non-linear metal–insulator transition (MIT) region with an ultra-high responsivity of 6.55 × 104 V/W. Sputtered VO2 films used in this device exhibit 104 times change in resistivity between the dielectric and conductive states. The VO2 microbolometer is coupled to a wideband dipole antenna operating at 31–55 GHz and a coplanar waveguide for probed measurement. To enhance the sensitivity, the sensor is suspended in air by micro-electro-mechanical systems process. The large thermal coefficient of resistance of VO2 is utilized by DC biasing the device in the MIT region. Measurements for the fabricated sensor were performed, and a high responsivity was demonstrated, owing to non-linear conductivity change in the transition region. The measured sensitivity is &amp;gt;102 times higher than the state-of-the-art sensors. In addition, the concept of utilizing the proposed VO2 sensor in a mmWave imager was demonstrated by the radiation pattern measurement of a 4 × 4 (16 elements) antenna-coupled VO2 sensor array. The results presented in this work reveal the initial step to employ VO2's MIT for a hyper-sensitive sensor in future mmWave sensing and imaging applications.

T-Type Vertical Wall for Decoupling and Pattern Correction of Patch Antenna

The requirements of 5G/6G promote progress in the miniaturization of the antenna array, which promotes the development of a closely spaced decoupling technique. However, the present techniques face the common problem of beam tilt if the spacing is close. Thus, a pattern-corrected, closely-spaced technique is proposed in this paper for the two patch antennas with the λ0/20 edge-to-edge distance of the H-plane. The corresponding structure, which is inserted at the center of the spacing, consists of a vertical wall with a single substrate and two symmetrical T-type metals, and a slot at the center is reserved to adequately accommodate the vertical wall. The vertical strip at the other end of the T-type metal is connected to the ground of the patch antenna, while the parallel strip is placed exactly above the patch substrate. After an exact analysis, a prototype was fabricated and measured, and the results showed that the measurements agreed well with those of the simulations, the decoupling coefficients in the 5.8 GHz band were below −20 dB, and the measured radiation pattern at 5.81 GHz was corrected to the broadside from 28° and the maximum realized gain was 5.30 dB.

Bayesian Active Learning for Radiation Pattern Sampling Over Cylindrical Surfaces

In this article, a new motion-aware sampling strategy (MASS) is presented to speed up the measurement of radiation patterns around cylindrical surfaces. Differently from preexisting sampling techniques, the MASS directly chooses positions that reduce the overall travel time of the field antenna, rather than minimizing the total number of samples. The proposed strategy employs a Gaussian process model that is adapted to the field over a cylindrical surface. Moreover, a new acquisition function for Bayesian active learning is developed in order to efficiently search the peaks of the measured field and predict their values. Next, the proposed strategy is tested on the experimental data from a radiation pattern of a comb generator. Finally, the results are compared to standard grid sampling and Bayesian optimization strategies.

Reducing the Effects of the Superstrate on the Microstrip Omnidirectional Antenna With an Annular Ring

In this communication, a new method of embedding an annular ring into the superstrate is proposed and studied to reduce the negative effect of the superstrate on the microstrip omnidirectional antenna. The working mechanism of the annular ring is analyzed based on the E-field distributions and an equivalent model that can approximately determine the dimensions of the annular ring. The effect of the parameters of the superstrate and the annular ring on the antenna performance is analyzed to verify the equivalent model. With the help of the annular ring, the negative effect of deep ripples in the radiation pattern, the strong radiation at the lower hemisphere, and the sensitiveness of the radiation pattern to the ground size from the superstrate are mitigated. A fabricated prototype shows that the measured −10 dB impedance bandwidth is 0.7 GHz (12.9–13.6 GHz). Within the frequency range of 13–13.8 GHz, the measured radiation patterns have no deep ripples and the measured radiation at the lower hemisphere is weak. The proposed method of embedding an annular ring to the superstrate, which does not involve the optimization of superstrate’s parameters, can serve as a promising candidate in practical applications.

Conformal Folded Inverted-F Antenna With Quasi-Isotropic Radiation Pattern for Robust Communication in Capsule Endoscopy Applications

In this article, an antenna with quasi-isotropic radiation pattern is proposed in a 915 MHz industrial, scientific, and medical (ISM) band for robust communication with external devices. The overall structure of the proposed antenna is a folded inverted-F antenna (FIFA). In the simulation, the proposed antenna is integrated with dummy electronics to form a fully encapsulated capsule endoscope architecture. These dummy electronics are encapsulated in a copper cylindrical bucket used as the antenna ground to avoid electromagnetic (EM) interference between these dummy electronics and the antenna. The spherical phantom model is used in the initial design of the proposed antenna. Subsequently, an anatomical realistic phantom was used to evaluate the performance of the proposed antenna in a more realistic human environment. The simulated gain variation (GV) of the proposed antenna in the regular spherical phantom is about 8 dB, and the reflection and other factors caused by the irregular shape of the realistic human tissue environment lead to the GV of the antenna in the anatomically realistic phantom that is about 4 dB. The measurement of reflection coefficient and radiation pattern is carried out in a semisolid muscle-mimicking phantom using a fabricated prototype of the proposed antenna. The measured GV value is about 10.5 dB. Finally, the specific absorption ratio (SAR) was calculated to meet the human safety regulations and the communication link budget was calculated to evaluate the wireless biological telemetry performance of the proposed antenna.

Neural Network-Based Phase Estimation for Antenna Array Using Radiation Power Pattern

In this letter, a neural network-based interelement phase estimation method using radiation power pattern of the linear phased array is proposed. To validate the proposed method, a radiation pattern measured in an anechoic chamber is input to the neural network to estimate the initial phase errors, and to confirm practical estimation accuracy. The proposed method requires only single radiation pattern measurement and no additional measurements only for estimation. This indicates the proposed method is significantly more time-saving, compared to other conventional techniques. Furthermore, we propose a method to suppress the failure rate of estimation by recursively reinputting patterns into the neural network, and discuss its effectiveness. These results show that the proposed methods useful for phase estimation of the linear array in experiments.

Robust and Efficient Fault Diagnosis of mm-Wave Active Phased Arrays Using Baseband Signal

One key communication block in 5G and 6G radios is the active phased array (APA). To ensure reliable operation, efficient and timely fault diagnosis of APAs on-site is crucial. To date, fault diagnosis has relied on measurement of frequency domain radiation patterns using costly equipment and multiple strictly controlled measurement probes, which are time consuming, complex, and therefore infeasible for on-site deployment. This article proposes a novel method exploiting a deep neural network (DNN) tailored to extract the features hidden in the baseband in-phase and quadrature signals for classifying the different faults. It requires only a single probe in one measurement point for fast and accurate diagnosis of the faulty elements and components in APAs. Validation of the proposed method is done using a commercial 28 GHz APA. Accuracies of 99% and 80% have been demonstrated for single- and multi-element failure detection, respectively. Three different test scenarios are investigated: ON-OFF antenna elements, phase variations, and magnitude attenuation variations. In a low signal-to-noise ratio (SNR) of 4 dB, stable fault detection accuracy above 90% is maintained. This is all achieved with a detection time of milliseconds (e.g., 6 ms), showing a high potential for on-site deployment.

Cognitive Conformal Antenna Array Exploiting Deep Reinforcement Learning Method

A cognitive antenna array, which is designed by using deep reinforcement learning (DRL) is proposed in this article to adapt to the complex electromagnetic environment. Specifically, the phased array antenna is utilized as the manipulatable component to achieve the characteristic of beam steering with the help of the DRL algorithm. We begin by establishing a DRL-based framework, which is comprised of a microprogrammed control unit, power divider, digital phase shifter, and the patch antenna array. In the DRL algorithm, the desired beam steering is obtained through trial-and-error interactions with the environment, which is required to observe predefined rewards based on the current state and action. Next, the system is trained to perform beam steering, and a set of hyperparameters of the deep neural network are obtained and stored for practical usage. A good agreement is achieved between the simulated and measured radiation patterns of the planar phased array antenna, which validates the DRL-based phase distribution regulation algorithm. Finally, the algorithm is implemented in the design process of a conformal phased array antenna, and it is shown that the measured radiation performance of the array is satisfactory for different beam scan angles.

Microwave Diagnostics of Cold Atmospheric Pressure Plasma Jets Based on the Radiation Pattern Measurements

Microwave Diagnostics of Cold Atmospheric Pressure Plasma Jets Based on the Radiation Pattern Measurements

Three‐dimensional star antenna for wearable defense application

AbstractIn this letter, design and characterization of an antenna fabricated using the three‐dimensional star used in the epaulets of defense personnel are presented for its use in sub‐6 GHz 5G communication. Initially, the star antenna is designed and simulated using CST Microwave Studio by choosing its dimension in accordance with those in the epaulets. The star antenna is placed over a single‐sided copper‐clad substrate and is excited via a coaxial probe, where an attempt to achieve the optimum feed position is made via simulation. This is followed by simulation of a two‐star array antenna where the element separation commensurate with the arrangement as that on the epaulets. Subsequently, a single‐ and two‐star array antenna is fabricated and their return loss and free space radiation pattern measurements are carried out. Measured results reflect a good comparison with that of the simulated one.

Bandwidth enhancement of dual-band bi-directional microstrip antenna using complementary split ring resonator with defected structure for 3/5 GHz applications

&lt;span&gt;This paper presents a bandwidth enhancement of a dual-band bi-directional rectangular microstrip patch antenna. The novelty of this work lies in the modification of conventional rectangular microstip patch antenna by using the combination of two techniques: a complementary split ring resonator (CSRR) and a defected patch structure (DPS). The structure of antenna was studied and investigated via computer &lt;/span&gt;&lt;span&gt;simulation technology (CST). The dimension and position of CSRR on the ground plane was optimized to achieve dual bandwidth and bi-directional radiation pattern characteristics. In addition, the bandwidths were enhanced by defecting suitable shape incorporated in the microstrip patch. A prototype with overall dimension of 70.45×63.73 mm&lt;sup&gt;2&lt;/sup&gt; has been fabricated on FR-4 substrate. To verify the proposed design, the impedance bandwidth, gain, and radiation patterns were carried out in measurements. The measured impedance bandwidths were respectively 560 MHz (3.08-3.64 GHz) and 950 GHz (4.64-5.59 GHz) while the measured gains of each bandwidth were respectively 4.28 dBi and 4.63 dBi. The measured radiation patterns were in good agreement with simulated ones. The proposed antenna achieves wide dual bandwidth and bi-directional radiation patterns performances. Consequently, it is a promising candidate for Wi-Fi or 5G communications in specific areas such as tunnel, corridor, or transit and rail.&lt;/span&gt;

Wideband Slot Array Antenna Fed by Open-Ended Rectangular Waveguide at W-Band

A wideband slot array antenna at W-band with a single-layer corporate feeding network is presented in this letter. The radiating slots are fed by open-ended rectangular waveguides to widen the impedance bandwidth instead of a commonly used coupling mechanism. A subarray of two elements placed in the H-plane is designed. In order to fit the feeding network into one layer, a compact hybrid feeding network is used, which is a combination of ridge waveguides and E-plane hollow waveguides. An 8-by-8-elements array antenna is simulated and fabricated with brass. Two metal layers are assembled by the bottom edge of the ridge waveguide to minimize the power leakage through the gap. The measured prototype achieves a relative impedance bandwidth of 35.7% with a reflection coefficient below −10 dB from 77.5 to 111.2 GHz. A peak gain of 26.8 dBi with variations within 2.5 dB is obtained. The measured radiation patterns agree with the simulations quite well, and the gain reduction remains below 1 dB in the operating range.

Wideband Low-Sidelobe Slot Array Antenna With Compact Tapering Feeding Network for E-Band Wireless Communications

In this work, a wideband low-sidelobe slot array antenna for wireless communication system at E-band is presented. The slots are excited by a parallel feeding network where the Taylor distribution is applied. Two types of wideband unequal power divider with compact structures are designed for various output ratios to fit the limited feeding network space. One is integrated vertically inside a 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 1 elements subarray using a set of pins with asymmetrical offset. The other type is designed inside an E-plane T-junction with unbalance impedance at two output ports. To avoid main lobe tilt and asymmetrical radiation patterns, the feeding network is designed to be biaxially symmetrical, and the feed port is placed in the center of the back. A prototype is fabricated with brass and measured in an anechoic chamber. It achieves a peak gain of 25.8 dBi and a fractional impedance bandwidth of 19.2% with the reflection coefficient below −10 dB. The measured radiation patterns agree with the simulated patterns very well, and the sidelobe level (SLL) is lower than −21 dB.

Design of a Compact Omnidirectional Leaky-Wave Antenna Fed by Higher Order Mode

This article presents a novel leaky-wave antenna (LWA) based on a dielectric-filled rectangular waveguide (RWG) and fed by a higher order mode. The proposed quasi-uniform LWA has a compact configuration that is suitable for microwave applications, featuring the omnidirectional radiation patterns and low cross-polarization. In the frequency band of interest, the higher order mode, i.e., the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode, performs as a fast wave in the proposed quasi-uniform LWA, radiating via the transverse slots etched on the walls. The advantage of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode for LWA applications is analyzed and demonstrated. This higher order mode is excited via a mode convertor from an inline coaxial line to the dielectric-filled RWG. For the reduction in sidelobe levels at high frequencies, −25 dB Taylor amplitude distribution is applied to the etched slots. The dielectric-filled LWA with the inline coaxial feeding is fabricated and measured. The measurement is consistent with the simulation, showing frequency-driven beam-scanning capability with low cross-polarization in the elevation plane. The simulated and measured radiation patterns in the azimuth plane illustrate the omnidirectional radiation patterns and thus confirm the radiating performance of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode in the proposed LWA. The advantages of the scanned beams and omnidirectional radiations are promising for radar systems.

A Broadband Low-Profile Transmitarray Antenna by Using Differentially Driven Transmission Polarizer With True-Time Delay

A broadband low-profile folded transmitarray (FTA) is proposed and investigated, in which a novel wideband transmission polarizer (TP) is used to realize low-profile design. The proposed TP, mainly consisting of a differential-fed grid-slotted patch antenna, can realize high-efficiency transmission and polarization selection simultaneously within a wideband frequency range. Moreover, the proposed TP can realize linear transmission phase because of the true-time delay (TTD) technique. Owing to the function of polarization selection and linear transmission phase, the TP can be used as antenna element for a FTA. A 140-element FTA is designed and fabricated by combining the TP with a broadband polarization rotation reflecting surface (PRRS). The measured radiation patterns agree well with the simulated results, and a peak gain of 24 dBi and maximum aperture efficiency of 44.7% are achieved. Furthermore, −1 and −3 dB gain bandwidth with 25.9% and 33.3% are also experimentally demonstrated in the proposed FTA, respectively.

Slot loaded folded half-mode substrate integrated waveguide antenna for wideband applications

In this work, a new folded half-mode substrate integrated waveguide (HMSIW) cavity has been conceived to design a wideband high gain slot antenna. Initially, a rectangular (90 mm × 10 mm) HMSIW, loaded with two identical slots at two ends, is designed to operate in the X-band. Thereafter, it has been folded to form a U-shape considering the possibilities of staggering between the closely spaced operating bands to realize a true wideband printed antenna with a higher gain. The proposed antenna, thanks to the excitation of the staggered higher-order modes in the folded slot-loaded rectangular HMSIW, exhibits an excellent wideband performance of 48.44% (9.15–15 GHz) with a maximum peak gain of 9.25 dBi. This low profile structure with an overall dimension of 0.91λ0 × 0.91λ0 × 0.047λ0 is printed on a single layer double-sided RT/duroid® 5880 substrates with a circular shaped ground plane. The design concept has been validated through impedance and radiation pattern measurement of the fabricated prototype revealing a good agreement with the simulated results.

Compact Broadband Antenna with Vicsek Fractal Slots for WLAN and WiMAX Applications

This paper aims to design a compact broadband antenna for wireless local area network (WLAN) and worldwide interoperability for microwave access (WIMAX) applications. The suggested antenna consists of an octagonal radiator with Vicsek fractal slots and a partial ground plane, it is printed on FR-4 dielectric substrate, and its global dimension is 50 × 50 × 1.6 mm3. The antenna is designed and constructed using both CST MICROWAVE STUDIO® and CADFEKO electromagnetic solver, and in order to validate the acquired simulation results, the antenna is manufactured and tested using vector network analyzer E5071C. The measurement results show that the designed antenna attains a broadband bandwidth (S11 &lt; −10 dB) from 2.48 to 6.7 GHz resonating at 3.6 and 5.3 GHz, respectively. The broadband bandwidth covers the two required bands: WiMAX at the frequencies 2.3/2.5/3.3/3.5/5/5.5 GHz and WLAN at the frequencies 3.6/2.4–2.5/4.9–5.9 GHz. In addition, the suggested antenna provides good gains of 2.78 dBi and 5.32 dBi, omnidirectional measured radiation patterns in the E-plane and the H-plane and high efficiencies of 88.5% and 84.6% at the resonant frequencies. A close agreement of about 90% between simulation and measurement results is noticed.