A compact substrate integrated waveguide CRLH leaky-wave antenna for S-band applications

Fixed-frequency beam scanning leaky-wave antennas (LWAs) that can scan their main beam over a specific frequency band are highly desired for future wireless communication systems. A composite right-/left-handed (CRLH) LWA is developed in this article that facilitates fixed-frequency continuous beam scanning over a wide operational frequency band. A variation of a simple single-layer nonreconfigurable frequency-based continuous beam scanning CRLH LWA is considered first. Its dispersion properties are approximately investigated using an equivalent circuit model. It is reported how two groups of varactor diodes can be incorporated into its basic circuit model to electronically control its dispersion behavior. An optimized reconfigurable CRLH LWA with practical dc biasing lines is then realized from this nonreconfigurable design. Fixed-frequency continuous beam scanning, from backward to forward directions through broadside, is reported over a wide operational frequency band. Simulations predict that the antenna can operate from 4.75 to 5.25 GHz with the main beam being continuously scannable at each frequency point. A prototype was fabricated, assembled, and tested. The measured results confirm its simulated performance characteristics.

In this paper, novel composite right/left-handed (CRLH) leaky-wave antennas based on folded substrate-integrated-waveguide (FSIW) structures are proposed. The proposed leaky-wave antennas were realized by periodically loading the radiating slots on the top metallization of the FSIW-based CRLH transmission lines. The structural advantages of the FSIW combined with the unique dispersion characteristics of the CRLH transmission line enable the proposed leaky-wave antennas to present continuous beam-scanning capability from backflre to endflre directions, occupy smaller footprint size, and provide more design ∞exibility than the conventional CRLH leaky-wave antennas. Two of such CRLH leaky-wave antennas were developed. In addition to the continuous beam scanning, it is found that the radiation e-ciency and polarization of the FSIW-based leaky- wave antennas can be easily tuned by means of the slot size and slot orientation, respectively, indicating their potential for versatile applications. Calculated and experimental results are presented and compared. A good agreement is obtained. To the best of our knowledge, it is the flrst time that the leaky-wave antenna exploits both of the dispersion behavior of the CRLH transmission lines and the structural beneflts of the FSIW conflguration.

A compact single-radiator circularly polarized (CP) leaky-wave antenna (LWA) based on composite right/left-handed (CRLH) transmission line is presented. The proposed antenna is based on substrate-integrated waveguide (SIW), and its unit cell consists of a T-shaped interdigital slot, which provides a CRLH property, a proper CP, and also effective compactness for the full-length LWA. The proposed LWA provides beam scanning from -19° to +84° over the frequency range of 7.35-10.15 GHz, while maintaining a good CP. By providing the balanced condition for the CRLH unit cell, a continuous backward-to-forward scanning including broadside is achieved. The maximum gain of the LWA is 8.95 dB which is satisfactory, considering the compactness of the antenna. Moreover, the radiation efficiency has an average of 85.7% over the operating frequency band. The measurement results are in good agreement with the simulation ones and show considerable advantages over the SIW-based CP LWAs proposed in the recent literature.

An electronic tunable composite right/left-handed (CRLH) transmission line (TL) leaky-wave antenna (LWA) with horizontal scanning properties based on liquid crystal is presented. The advantages of the proposed antenna are: 1) Convenient to fabricate; 2) Scanning range from negative angle to positive angle; 3) Scanning in a horizontal plane; 4) Convenient to constitute an array. The transmission and radiation characteristics of the CRLH LWA are theoretically analyzed and simulated.

In this paper, new approaches for predicting the radiation patterns of composite right/left-handed (CRLH) leaky-wave antenna (LWA) are proposed and compared with the conventional approaches. The conventional approach for fast calculating the scanning angle of main beam, as well as the conventional array factor (AF) approach based on isotropic point sources for calculating the radiation pattern, has low accuracy when the scanning angle or observing angle approaches to the axial directions. To solve this problem, an improved AF approach is proposed, which has taken into account the influence of non-isotropic point source in each period of the CRLH structure. In addition, a traveling-wave line-source approach is also presented, which is very simple but efficient and accurate for the computation of the radiation patterns of CRLH LWAs.

A different parameter extraction approach based on zero immittances for composite right/left-handed (CRLH) structure is presented. For lossless unit cell equivalent circuit model, LC parameters of series and parallel branches are extracted according to series resonance frequency and parallel resonance frequency, respectively. This approach can be applied to symmetric and unbalanced CRLH structures. The parameter extraction procedure is provided and validated by T-type unit cell model. The responses of distributed prototype and extracted equivalent LC circuit model are in good agreement. The equivalent circuit modeling can improve the degree of freedom in the CRLH TLs design. This parameter extraction method provides an effective and straightforward way in CRLH metamaterials design and applications in telecommunication systems.

We report the fundamental design guideline for a metamaterial (MTM) leaky-wave antenna with continuous tuning capability of radiation directions without causing band gaps. The proposed design is the composite right–left hand (CRLH) type MTM, and each cell has a slot that could be in the open- or close-state with indicating as 0 and 1 states. With the MTM-based design, a leaky-wave antenna consisting of eight MTM units can be controlled by states of periodical MTM units such as coding states 0000–0000, 1010–1010, …, 1111–1111, rather than by frequency tuning, thereby realizing continuously beam scanning without any stopband from −30° to +30° in the fixed frequencies from 9 to 9.2 GHz. The proof-of-concept level tuning capability is confirmed by experiments using the closed- or open-patches that emulate the electrical short- or open-state of individual switch. The measured results show that the MTM-based leaky-wave antenna can obtain state-dependent and continuous beam scanning at the fixed frequencies of 9–9.2 GHz. It can be applied for radar sensing with requiring continuous and state-dependent beam scanning properties.

In this paper, we formulate and experimentally demonstrate direction of arrival (DoA) estimation with a two-port composite right/left handed (CRLH) leaky-wave antenna (LWA) using the multiple signal classification (MUSIC) algorithm. The CRLH LWA consists of a cascade of metamaterial unit cells, periodically modulated using varactor diodes. By changing the voltages across series and shunt varactors, the antenna is able to uniformly steer its radiation pattern. The proposed modified MUSIC algorithm, uses both antenna's input ports to estimate the DoA. Conventionally, the MUSIC algorithm needs to calculate the correlation matrix from the output vector of an array of antenna elements. In this work, we show in detail how the correlation matrix can be computed when using leaky-wave antennas. The algorithm is demonstrated using LWA in an anechoic chamber and the estimated DoA results are in good agreement with the predicted angles.

We designed a leaky wave antenna based on X-type composite right/left handed (CRLH) transmission line. Due to the wide-band nature of X-type CRLH transmission line, the antenna can provide a wide impedance bandwidth. The antenna can provide 5dB scanning pattern from 5.6GHz to 7.6GHz. The presented antenna shows a significantly low level of cross-polarized patterns using the balanced symmetric.

A novel analog real-time spectrum analyzer (RTSA) for the analysis of complex nonstationary signals (such as radar, security and instrumentation, and electromagnetic interference/compatibility signals) is presented, demonstrated, and characterized. This RTSA exploits the space-frequency mapping (spectral-spatial decomposition) property of the composite right/left-handed (CRLH) leaky-wave antenna (LWA) to generate the real-time spectrograms of arbitrary testing signals. Compared to digital RTSAs, it exhibits the advantages of instantaneous acquisition, low computational cost, frequency scalability, and broadband or ultra-wideband operation. The system is demonstrated both theoretically by a commercial full-wave simulator and an efficient Green's function approach and experimentally by a parallel-waveguide prototype including a metal-insulator-metal CRLH LWA, 16 patch antenna probe detectors circularly arranged around the LWA, and a digital oscilloscope performing analog/digital conversion and time-domain acquisition before the postprocessing and displaying of the spectrogram. The system is tested for a large diversity of nonstationary signals and generates, in all cases, spectrograms that are in excellent agreement with theoretical predictions. The fundamental tradeoff between time and frequency resolutions inherent to all RTSA systems is also discussed, and an interchangeable multi-CRLH LWA solution is proposed to handle signals with different time durations.

In this article, a multilayered circularly polarized (CP) leaky-wave antenna (LWA) is proposed, based on the composite right/left-handed (CRLH) transmission line concept. The proposed design is composed of a substrate integrated waveguide (SIW) structure and its multilayered unit cell consists of H-shaped interdigital (ID) slots on the top with a truncated patch, sandwiched between the two substrates. Circular slots are introduced periodically on the ground plane to achieve wideband circular polarization. Proposed CRLH SIW-based LWA shows the capability of continuous beam scanning from −38° to +71° within the frequency range of 7.6–10.6 GHz while maintaining good circular polarization in the frequency range of 8.3–10.6 GHz. The peak gain of the proposed LWA is 10 dB and the average radiation efficiency is 86.1% over the complete impedance bandwidth. The measured results of the fabricated prototype are in good agreement with the simulated ones. The proposed antenna can be used for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$X$ </tex-math></inline-formula> -band radar and satellite applications.

A new type of broadband circularly polarized leaky-wave antenna (LWA) with high-gain based on a corrugated substrate integrated waveguide (CSIW) structure is proposed and investigated. The CSIW structure that employs open-circuit stubs to replace metallic vias has the advantages of low-cost and easy fabrication as compared to conventional substrate integrated waveguides. Each unit-cell of the proposed LWA consists of two quarter-wavelength microstrip lines and a half-mode CSIW cell with three open-circuit stubs. Two M-shaped slots etched on the half-mode CSIW cell enables the generation of circularly polarized (CP) radiation. The full LWA, which consists of thirteen matched unit-cells cascaded along the direction of propagation enables continuous backward to forward beam scanning. The properties of the CSIW structure, including impedance matching and phase constant, are analyzed by Bloch impedance and dispersion simulations and the influence of the dimensions of the open-circuit stubs on the CP LWA performance is also investigated. A protype of the proposed LWA is fabricated and characterized. The measured results indicate that the proposed CSIW LWA has a high peak gain (9.3-12.5 dBi) throughout a large beam-scanning angle range from -28° to +25°, and the impedance bandwidth and 3-dB axial ratio (AR) bandwidth are over 40% covering the full $\textit {Ka}$ -band.

This paper presents the results and investigation of substrate integrated waveguide (SIW) leaky-wave antenna (LWA) based on the composite right/left-handed (CRLH) structure designed for X band applications. The interest is given to two antenna types: uniform CRLH antenna, non-uniform CRLH antenna where three balanced CRLH unit cells are used in the design. Results of both structures show that a wide scanning range over the frequency bandwidth from 9 to 13.4 GHz is obtained. The side lobe level is remarkably decreased in the non-uniform structure especially around the broadside area which is suitable for many scanning applications.

In this paper, an active integrated circularly polarized leaky wave antenna (AICPLWA) is proposed. The proposed design works in X-band. The leaky wave antenna is designed using half-mode substrate integrated waveguide technique, that provides circularly polarized beam. The proposed active integrated antenna consists of a leaky wave antenna section which is cascaded with active device to make a self-oscillating radiating structure. The leaky wave antenna has beam scanning ability by varying the input signal frequency and hence the oscillator section is modified using an active tunable reactance to provide a voltage tunable oscillation frequency to the leaky wave antenna section to achieve automatic beam scanning ability. The proposed active tunable reactance provides wider tuning range than commercial varactor for a small range of variation of tuning voltage. The proposed leaky wave antenna has a wide operating range covering the whole X-band and has axial ratio of better than −4.5 dB throughout the frequency range of interest. The oscillation frequency range provided by the active section is 10.5-10.95 GHz with the variation of tuning voltage from −4 V to −1.1 V. The AICPLWA covers an automated beam scanning range from 34°-40° for the 10.5-10.95 band. The proposed AICPLWA can be used in various applications such as microwave imaging, sensing radars requiring automotive beam scanning module.

A 3D space-to-frequency mapping array comprised of a composite right/left-hand (CRLH) feed network and CRLH leaky-wave antennas (LWAs) is presented for microwave frequencies. Highly directive pencil beams can be scanned by varying frequency in a small footprint network with only passive CRLH structures. Simulation results are provided as demonstration.