Frequency Scanning Capability Research Articles

Sub-THz Broadband Transmitting Metasurfaces With Enhanced Frequency-Scanning Capability

Sub-THz Broadband Transmitting Metasurfaces With Enhanced Frequency-Scanning Capability

Single‐layer dipole antenna with large angle beam deflection and frequency scanning capability

In this paper, a printed single-layer dipole antenna with beam deflection and frequency scanning capability by loading a co-planar metamaterial array is investigated. The metamaterial array consists of 6 × 3 U- and inverse-U-shaped unit cells and performs as a two-dimensional gradient refractive index medium. Beam deflection can be achieved by utilizing the phase shift property resulting from the interaction of the EM wave emanating from the antenna with medium that exhibit different refractive indices. Utilizing the Refractive index-Size (n-S) response of the U- and inverse-U-shaped structure, beam-tilting with large angle of 38° at the fixed frequency is obtained. The gain is enhanced by 2.5 dBi. At same time, as the Refractive index-Frequency (n-F) response of the proposed structure, the main beam of the proposed antenna can achieve considerable frequency scanning range within the −10 dB bandwidth. The main beam scanning of 42° in the E-plane over the frequency range of 2.06–2.61 GHz with the gain is enhanced by at least 2.5 dBi. A prototype of the proposed antenna has been fabricated and measured to verify the simulation results.

Surface Plasmon Polariton Leaky-Wave Antennas With Wideband Arbitrary Multibeam Radiation

A simple method to synthesize multibeam radiation patterns with modulated linear spoof surface plasmon polariton (SSPP) leaky-wave antennas (LWAs) is proposed. We analytically proved that, for this specific type of LWA, the superposition of modulated antenna shapes can lead to a direct superposition in its radiation pattern. To validate this method, several simulations are performed, and two antennas are fabricated and tested. These results show that various types of radiation pattern, e.g., single-beam, dual-beam, or multibeam at various directions, can be achieved with little need for design efforts. The proposed antennas have features of the highly diverse radiation pattern, high gain (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 14.6$ </tex-math></inline-formula> dBi, measured), wideband, large frequency scanning capability ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 120$ </tex-math></inline-formula> ° with ignorable open stopband effect at broadside), and have very simple structures that are easy to design and fabricate.

A High-Gain Leaky-Wave Antenna Using Resonant Cavity Structure With Unidirectional Frequency Scanning Capability for 5G Applications

This paper presents a high-gain leaky-wave antenna based on a resonant cavity (RC) structure with the capability of unidirectional beam scanning over predefined frequencies and desired beam angles. Frequency scanning is achieved by implementing a properly-designed single-layer partially reflective surface (PRS) based on a simple ray tracing-based design procedure. In the proposed structure, two techniques are combined to make the beam scanning unidirectional. First, a metallic wall is placed at a proper distance from the radiator to suppress the antenna propagation at undesired directions. Second, a feed antenna with a tilted beam is designed as the main radiating element inside the cavity to radiate over desired beam angles. A prototype of the proposed antenna is fabricated and measured demonstrating a beam scanning from $12^{o}$ to $46^{o}$ over the frequency band from 25 to 31 GHz. Moreover, a maximum gain of 15.4 dBi is achieved at 26 GHz on the elevation plane with tilted angle of $22^{o}$ . The proposed leaky-wave antenna is suitable for various wireless applications, in particular the $5^{th}$ generation of cellular networks and small cell base station antenna (BSA) applications.

Analytical Study of Open-Stopband Suppression in Leaky-Wave Antennas

In the majority of leaky-wave antennas (LWAs), the lack of broadside radiation is due to the existence of an open-stopband (OSB) at broadside. In this letter, we present a study on the OSB suppression in LWAs. In particular, we start from a simple unit cell comprising a planar waveguide having alternating open and short sidewalls. The analytical and simulated band structures testify consistently that OSB suppression can indeed be realized by proper design, analytically studied using mode-matching, and further supported by full-wave simulations. An LWA is then implemented using the substrate integrated waveguide (SIW) technology, which provides interesting features such as a high directive beam with frequency scanning capabilities, and a simple feeding network, making it well suited for microwave applications. Phase and leakage constants are adjusted to yield a directive beam with beam scanning over a wide range of angles (from -30˚ to 30˚). The presented 25-cell LWA has a wide impedance bandwidth of 20% around 15 GHz with high efficiency and operates with peak gains of about 9 dBi throughout the frequency scan range of 13.5–16.5 GHz. A prototype is fabricated using standard substrates, and measured results show an excellent agreement with the simulated results, validating the proposed concepts.

Improving directional radiation quality based on a gradient amplitude acoustic leaky wave antenna

In this work, we show how to modify radiation amplitude with a leaky wave antenna to improve the quality of sound radiation. The designed gradient amplitude leaky wave antenna consists of a straight pipe with periodically loaded membranes, open channels and Helmholtz resonators. An equivalent acoustic composite right/left-hand transmission line that considers the effects of viscous-thermal and viscous-elastic losses is utilized to steer the radiation angle continually from backward to forward as a function of the incident frequency. The numerical results show that by appropriately selecting the structural parameters of the channel and Helmholtz resonator cavity, the quality of the directional radiation is improved based on the gradient distribution of the radiation amplitude and the near unitary phase. Compared with traditional antennas, the proposed gradient amplitude antenna incorporates a frequency scanning capability with gradient amplitude, which improves the directivity quality of the acoustic waves among the operated frequency band, and provides a new design method for acoustic leaky wave antennas.

Multiple-frequency measurement based on a Fourier domain mode-locked optoelectronic oscillator operating around oscillation threshold.

We propose and experimentally demonstrate a photonic-assisted approach to microwave frequency measurement based on frequency-to-time mapping using a Fourier domain mode-locked optoelectronic oscillator (FDML OEO) operating around oscillation threshold. A relationship between the frequency of the unknown input microwave signals and the time difference of the output pulses is established with the help of the frequency scanning capability of the FDML OEO and, thus, can be used for microwave frequency measurement. The proposed scheme is characterized as having broad bandwidth, high resolution, multiple-frequency detection capability, and tunable measurement range. Microwave frequency measurement with a measurement range up to 16GHz and a low measurement error of 0.07GHz is realized.

Microwave photonics frequency-to-time mapping based on a Fourier domain mode locked optoelectronic oscillator.

An approach to microwave photonics frequency-to-time mapping (MWP FTM) is proposed based on a Fourier domain mode locked optoelectronic oscillator (FDML OEO). In this approach, a relationship between the frequency of the input microwave signal and the time difference of the output pulses is established with the help of the fast frequency scanning capability of the FDML OEO. The ability to measure the microwave spectral information in the time domain using the proposed system has the potential to enable new metrology and signal processing schemes with a superior performance in terms of real-time bandwidth and operation speed compare with traditional approaches. As an application example, single and multi-tone microwave frequency measurement are experimentally demonstrated based on the proposed MWP FTM system.

A Compact Beam-Scanning Leaky-Wave Antenna With Improved Performance

A compact microstrip leaky-wave antenna (MLWA) with reduced sidelobe level and increased linear frequency-scanning capability is proposed in this letter. Symmetric Yagi-like elements are introduced, which reduce the sidelobe level by radiating the remaining power at the physical end of MLWA, and make the radiation plane ( xz plane) symmetric. Defected ground plane is used to optimize the working of Yagi-like elements. Measured results show that the sidelobe is suppressed about 16 dB at 4.8 GHz. To further reduce the sidelobe level, improve frequency-scanning capability, and increase the gain, the leaky section of the antenna is tapered, and two slots of equal dimensions are introduced. The frequency beam scanning is improved compared with the conventional MLWAs by achieving a total beam scan of 78° (from broadside [12°] to endfire [90°]). The measurements performed on the fabricated prototype exhibit good agreement with simulations.

Low-Cost and High-Efficiency Antenna for Millimeter-Wave Frequency-Scanning Applications

This letter presents the design, optimization, fabrication, and measurements of a new dielectric grating antenna for millimeter-wave frequency-scanning applications. The proposed antenna is made of high-resistivity silicon, and the structure is essentially a dielectric image guide with the rectangular grating on its sides. This simplifies the fabrication process and introduces flexibility in the grating profile. The radiation mechanism is extensively studied using two different commercial full-wave solvers as well as the measured data from the fabricated samples. The optimized antenna achieves a radiation efficiency of 84% and a gain of 18 dB at 100 GHz. It provides a frequency-scanning capability up to 20° covering the frequency range between 97-103 GHz. The antenna return loss is better than - 10 dB in this range. The measured return loss and radiation pattern show a good agreement with the simulation results.

Measurement Setup for Imaging Applications Using Frequency Scanning Illumination

A measurement setup for imaging applications is presented. The idea is to reuse an existing antenna measurement setup to develop the imaging system by using a frequency scanning antenna array that focuses the incident field on the object under test (OUT) at different angular positions by means of a frequency sweep. From the measured total field data, an inverse technique based on source reconstruction is proposed to recover the OUT profile. In order to check the feasibility of the proposed setup and for the sake of simplicity, the OUTs to be dealt with present translation symmetry along one dimension (2-D problems). Measurement results and full-wave method-of-moment simulations are presented to test the proposed setup as well as to point out the frequency scanning capabilities.

A leaky-wave antenna using double-layered metamaterial transmission line

A novel leaky-wave antenna (LWA) is proposed using a double-layered resonant-type metamaterial (MTM) transmission line (TL). The MTM TL is composed of periodically arranged complementary split ring resonators (CSRRs), capacitive gaps, and metal caps. By introducing the extra metal cap in additional layer of the basic artificial MTM TL element, an increased left handed capacitor by 36 % with respect to that using none cap is engineered, which is necessary to implement a balanced condition, and thus a continuous beam steering property of the resultant LWA in terms of providing phase constants from negative to positive values. For verification, a 20-cells LWA sample is fabricated and measured. Consistent numerical and experimental results have both validated the continuous frequency-scanning capabilities of the antenna from backward −29° to forward 72° (including the broadside). The proposed prescription opens a way toward new types of MTM LWAs with easily engineered broadside radiation.

Design of a metamaterial-inspired size-reduced wideband loop antenna with frequency scanning characteristic

A novel metamaterial-inspired loop antenna is proposed towards wideband operation, size reduction and frequency scanning capabilities. The high permeability characteristic of split rings resonators (SRRs) is utilised to reduce the size of a loop antenna. The SRRs also improve the impedance matching of the loop antenna, and thus significantly increase the bandwidth. Moreover, the proposed antenna has a frequency scanning capability because of the existence of SRRs. According to the measured results, the proposed antenna has a 10 dB operating band from 2.3 to 3.8 GHz with the absolute bandwidth of 1.5 GHz and the fractional bandwidth of 50%. Owing to SRRs, the first-order resonant frequency of the antenna shifts from 3.5 to 2.4 GHz, leading to an effective size reduction of 32% against the original loop antenna. The proposed antenna exhibits a continuous frequency scanning capability with the total scanning angle of 135°, sweeping from 75 to −60°.

Initial assessment of a waveguide with dielectric-filled corrugations as a technology for slot antennas with backward-to-forward scanning capabilities

The frequency-scanning capabilities of continuous-type leaky-wave antennas have usually been restricted to main-beam pointing angles within the forward quadrant. With the appearance of metamaterial concepts, wave propagation with negative and zero phase constant has made it possible to spread the scanning directions, allowing main-beam angles into the backward quadrant, as well as the broadside direction. In this paper, a straight long slot antenna, implemented in a rectangular waveguide with dielectric-filled corrugations, is analyzed, constructed and measured, and an analysis method, based on an equivalent homogeneized waveguide, is proposed. Some features of the antenna, such as losses, radiation pattern and gain are studied, in order to assess the performance and suitability of the composite right/left-handed waveguide technology used. The obtained results highlight the limiting factors for the applicability of the corrugated waveguide in antenna applications, while confirm the validity of the analysis technique proposed.