Foundations For Microwave Engineering

In this communication, we propose a high scanning rate leaky-wave antenna (LWA) based on a slow-wave substrate integrated waveguide (SIW) structure. The slow-wave effect is introduced by etching periodical slots on the top surface of SIW. The LWA radiation is subsequently realized by introducing sinusoidal modulation to the slots profile. Such a structure significantly improves the scanning rate of LWA due to the small group velocity at the slow-wave region. Simulation and measured results indicate that the proposed LWA scans a wide angle in a narrow bandwidth near the cutoff frequency of surface plasmon polariton. Within the frequency band 13.5–13.9 GHz (3% relative bandwidth), the measured scanning angle is from 2° to 37° with the measured gain all above 9.2 dBi.

Scanning Rate Enhancement of Leaky-Wave Antennas Using Slow-Wave Substrate Integrated Waveguide Structure

This paper presents a general overview of substrate integrated transmission lines, from the perspective of historical background and progress of guided-wave structures and their impacts on the development of microwave circuits and integration solutions. This is highlighted through a technology roadmap involving the categorized five generations of microwave circuits. In particular, the substrate integration technologies are reviewed and discussed with focus on technical features, design highlights, component developments, structures evolution, and systems integration. A number of examples are presented to showcase some of the selected milestone research and development activities and accomplishments in connection with substrate integrated transmission line technologies, with particular focus on substrate integrated waveguide (SIW) techniques. Practical applications and industrial interests are also presented with key references and technical results, which show more and more product developments in the end-user sectors. It can be found that the popularity of SIW techniques is closely related to the achieved seamless integration of planar and non-planar structures into a unified design space, thereby allowing the possibility of combining major advantages of all the structures while alleviating their potential drawbacks. The future perspectives of the substrate integration technology are discussed through five major research directions, which suggest potential impacts in the development of future generations of circuits and systems such as system-on-substrate (SoS).

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Substrate Integrated Transmission Lines: Review and Applications

A dual-mode composite microstrip line (DMC-MSL) is reported in this paper for the purpose of designing dual-band antennas and devices with a large frequency ratio. The metallic strip of the conventional MSL is replaced with a substrate integrated waveguide (SIW) arranged into a thin dielectric laminate, which leads to that two modes operating in different frequency bands, i.e., the quasi-TEM mode and the TE10-like mode, can propagate along the transmission line structure simultaneously. The DMC-MSL with a dual-layered planar configuration combines the merits of the MSL and the SIW. In addition, by adjusting the permittivity of the dielectric laminate used for realizing the thin SIW, the frequency ratio of the two operating modes can be varied flexibly. Based on the DMC-MSL structure, a novel dual-band leaky-wave antenna is presented. Periodic parasitic microstrip patches and the transverse slot array etched on the SIW are introduced in order to generate the required spatial harmonics. A feed structure that can excite the two operating modes of the DMC-MSL separately is designed as well. The fabricated prototype verifies that backward and forward frequency-scanning radiation beams are achieved within the low-frequency band from 5.75 to 8.5 GHz and the high-frequency band from 35 to 41.5 GHz, respectively. The proposed DMS-MSL structure and the leaky-wave antenna offer a new mean to implement antennas and devices for microwave and millimeter-wave dual-band applications.

Dual-Band Leaky-Wave Antenna Based on Dual- Mode Composite Microstrip Line for Microwave and Millimeter-Wave Applications

In this paper, we propose a novel slow-wave half-mode substrate integrated waveguide (HMSIW) combined with spoof surface plasmon polariton (SPP) structure. In this design, subwavelength corrugated grooves are etched on the up metal layer of HMSIW to support an SPP mode. The dispersion and transmission characteristics of the proposed hybrid HMSIW-SPP structure are analyzed and compared with the classic HMSIW. To experimentally validate this design, a prototype is fabricated and measured. A slow-wave effect is clearly observed in the proposed hybrid transmission line, and its wavelength is reduced by over 50% without sacrificing its transmission performance. This structure features a simple architecture and excellent slow-wave effect.

Slow-Wave Half-Mode Substrate Integrated Waveguide Using Spoof Surface Plasmon Polariton Structure

A class of slow-wave substrate integrated waveguide (SIW) structures patterned with microstrip polyline is presented, theoretically studied, and experimentally validated, which demonstrates some interesting slow-wave propagation effects. The slow-wave SIW (SW-SIW) enables the size reduction of a physically large circuit without sacrificing its performance. A size reduction of 40% of the lateral dimension is achieved with reference to that of the conventional SIW counterpart at the same cutoff frequency. Meanwhile, the phase velocity of the waveguide is also reduced by 40%, resulting in a smaller longitudinal dimension for a given electrical length. Both lateral and longitudinal effects give rise to a total size reduction, largely extending the operation range of SIW structures in the low-frequency region, which has often been restrained by a physical dimension-related cutoff frequency. Also, a transmission line-based two-dimensional (2-D) equivalent-circuit model is proposed and deployed for the modeling and analysis of the slow-wave mechanism. The results from the equivalent-circuit model agrees very well with that from the full-wave simulations. Furthermore, a broadband microstrip to SW-SIW taper with good return loss is designed for measurement verification. Using the proposed SW-SIW structure, the size of conventional SIW-based microwave circuits such as power splitters, couplers, and filters can be further reduced in addition to the existing size-reduction techniques.

Slow-Wave Effect of Substrate Integrated Waveguide Patterned With Microstrip Polyline

In this paper, mode composite waveguide (MCW) is proposed, which consists of inner and outer wave-guiding duo structures. The outer structure acts as a rectangular coaxial line suitable for lower frequency operation for its compact size, while the inner structure works as a rectangular waveguide suitable for higher frequency operation thanks to its simple structure and low loss. The MCW can propagate signals in the inner waveguide with TE10 mode and/or the outer waveguide with TEM mode depending on frequency to achieve optimal performance for both low- and high-frequency operations. In this paper, the fundamental waveguide parameters and higher order modes of the duo waveguides are examined. The proposed MCW prototypes are fabricated on a triple-layer PCB structure using the emerging substrate integration techniques. The MCW is fabricated and measured through the proposed microstrip line to the inner and outer waveguide transitions, and an MCW simultaneous feeding circuit is also presented. For this simultaneous feeding circuit, the good matching is achieved from 7.5 to 10.5 GHz for the low-frequency operation and from 25 to 39 GHz for the high-frequency operation, respectively.

Mode Composite Waveguide

In this paper, a guided-wave structure, the half-mode composite waveguide (HMCW) is proposed and presented. Similar to the conventional mode composite wave- guide (MCW), the HMCW also has an inner and outer waveguides, each working in its half-mode operation, respectively. In the HMCW structure, the signal propagates in the inner waveguide with quasi- $\text{TE}_{0.5-0}$ mode and along the outer waveguide with the quasi-TEM mode. The HMCW’s half-mode operation principle, impedance, loss, and propagation characteristics including higher order modes are analyzed. Compared to its full-size counterpart, the HMCW only occupies half the space, when operating within the same frequency band. Simulation results show that the transmission loss of the HMCW is comparable to that of the full-size MCW. Thus, it is also suitable for both low- and high-frequency design and applications. To measure and integrate the HMCW with other planar circuits, a joint feeding network for the HMCW is also proposed. Its circuit prototype is fabricated on three layers of substrate using a multilayer substrate integration technique. This joint feeding network can simultaneously excite the inner and outer waveguides, respectively, in an independent manner. In measurements, both the inner and outer waveguides are transitioned to microtrip lines, and a good matching is achieved from 4.4 to 11.2 GHz with a relative bandwidth of 87.2% for the outer waveguide at low frequency and from 18.6 to 32.6 GHz with a relative bandwidth of 54.7% for the inner waveguide at high frequency, respectively.

Half-Mode Composite Waveguide

In this paper, a joint feeding network within a triple layer topology is described and studied for mode composite waveguide (MCW). MCW consists of inner and outer dual wave-guides, and this feeding network can independently excite the outer waveguide from the top and bottom layers, and the inner waveguide from the middle layer. The outer waveguide feeding structure consists of a multilayer power divider in series with a dual taper structure while the inner waveguide feeding structure consists of a right angle bend in series with a taper. This joint feeding scheme completely isolates the inner and outer waveguide feeding structures from each other, thus allowing an independent design and optimization of each feeding structure. Furthermore, due to its suppressing nature of higher order modes, this feeding network can be used with any operation frequency combination in connection with the inner and outer waveguides. The prototyped feeding network experimentally exhibits good matching within its operation bands from 6.9 to 11.8 GHz for the outer waveguide, and from 13.5 to 24.1 GHz for the inner waveguide.

Joint feeding network for mode composite waveguide

In this work, a mode composite waveguide (MCW) based dual-mode filter is proposed and studied. This filter uses the inner waveguide of MCW as the input and output feedings, and the outer waveguide of MCW as the dual-mode resonator. The two degenerate modes in the outer waveguide resonator are used for the dual-mode filter operation, which generates two transmission poles and one finite transmission zero. The two transmission poles are used to control the filter bandwidth, and the finite transmission zero is used to improve the out of band selectivity. The generated finite transmission zero can be placed at either the left or right vicinity of the passband by adjusting the input and output feeding parameters. Two types of dual-mode filter are designed at 10 GHz with 2% fractional bandwidth. Type I filter exhibits a transmission zero at the left vicinity of the passband while type II filter exhibits one at the right. The type I dual-mode filter is fabricated and its measurement results agree with its simulations.

Jiapin Guo

Papers

Slow-Wave Effect of Substrate Integrated Waveguide Patterned With Microstrip Polyline

Mode Composite Waveguide

Half-Mode Composite Waveguide

Joint feeding network for mode composite waveguide

Mode composite waveguide filter with dual-mode operation