A review on SIW and its applications to microwave components

Substrate-integrated waveguide (SIW) is a modern day (21st century) transmission line that has recently been developed. This technology has introduced new possibilities to the design of efficient circuits and components operating in the radio frequency (RF) and microwave frequency spectrum. Microstrip components are very good for low frequency applications but are ineffective at extreme frequencies, and involve rigorous fabrication concessions in the implementation of RF, microwave, and millimeter-wave components. This is due to wavelengths being short at higher frequencies. Waveguide devices, on the other hand, are ideal for higher frequency systems, but are very costly, hard to fabricate, and challenging to integrate with planar components in the neighborhood. SIW connects the gap that existed between conventional air-filled rectangular waveguide and planar transmission line technologies including the microstrip. This study explores the current advancements and new opportunities in SIW implementation of RF and microwave devices including filters, multiplexers (diplexers and triplexers), power dividers/combiners, antennas, and sensors for modern communication systems

Compact, Low-Profile, Linearly and Circularly Polarized Filtennas Enabled with Custom-Designed Feed-Probe Structures

© 1963-2012 IEEE. Compact, low-profile, linearly polarized (LP), and circularly polarized (CP) patch-based filtennas are realized with a custom-designed coupling probe. It introduces a deep null at both the lower and upper band edges of the filter response. These two nulls facilitate a quasi-elliptic bandpass behavior and can be independently controlled to achieve sharp band-edge skirts and high out-of-band suppression levels. The CP version evolves from the LP design by introducing a T-shaped near-field resonant parasitic (NFRP) element near the probe to create two transmission paths with an inherent 90° phase difference. Its presence facilitates the simultaneous excitation of the TM10 and TM01 modes of the patch without the need for any power divider or phase delay line, reducing the design complexity and lowering the insertion loss. Prototypes were fabricated, assembled, and tested. The measured results agree well with their simulated values. They are low profile (0.03 \lambda _{0} height) and compact in size ( 0.04~\lambda _{0}^{2} footprint). The LP and CP prototypes exhibit, respectively, a -10-dB fractional impedance bandwidth of 7% and an overlapping axial ratio fractional bandwidth of 4.5%. Excellent measured performance characteristics are demonstrated, including flat passband realized gain values and filter responses with sharp roll-off rates and high out-of-band suppression levels

Inverted microstrip Gap Waveguide filtering antenna based on coplanar EBG resonators

This article belongs to the Collection RF and Microwave CommunicationsA new simple design of an inverted microstrip Gap Waveguide filtering antenna integrated with two stopband filters is proposed in this work. In order to simultaneously provide filtering and radiating functions, we use the direct integration approach to cascade two periodic sets of coplanar coupled EBG resonators with a slot antenna. The analysis shows that the filters can be easily adjusted in the same feeding layer of the antenna, without extra circuitry and without modifying the lines. EBG-filters are compact and offer great flexibility in determining the frequency, width and selectivity of the rejected bands. Experimental results for an X-band filtering antenna prototype are provided showing a 7.3% transmission band centered at 10.2 GHz and a realized gain peak of 2.1 dBi. The measurements demonstrate the filtering capability of the proposed antenna, achieving rejection levels greater than 12 dB and 20 dB for the bands below and above the operation band. The proposed low-complexity design offers good performance as a filter and as an antenna, showing the essential advantages of the Gap Waveguide Technology, including low losses, self-packaging and limited cost. This work demonstrates the possibility of integrating the new coplanar EBG-filters into future Gap Waveguide antenna designs to avoid unwanted radiation, to reduce interfering signals or to provide high isolation in multiband systems.This research was funded by the Spanish Ministerio de Ciencia, Innovación y Universidades grant numbers [Agencia Estatal de Investigación PID2019-107688RB-C21 and TEC2016-79700-C2-R]

A Wideband Low-Profile All-Metal Cavity Slot Antenna With Filtering Performance for Space-Borne SAR Applications

This letter presents a wideband all-metal cavity slot antenna with a filtering performance for space-borne synthetic aperture radar applications. The proposed antenna element consists of a metal cavity and several radiation slots. It is fabricated by aluminium through milling and welding process, the techniques of which are reliable for the space environment. Benefiting from multiresonances of the cavity and slots, the antenna is able to obtain a wide operating bandwidth. Additionally, the cavity has a very low profile of 2.8 mm, equivalent to 0.093 wavelength at the central operating frequency. An 8 × 12 antenna array is designed, fabricated, and measured for performance verification. The measured impedance bandwidth with S 11 <;-10 dB is achieved from 7.2 to 12.2 GHz, giving a relative bandwidth of 51%. Furthermore, it shows good filtering characteristic with more than 20 dB out-of-band rejections, which is capable to suppress unwanted interferences and contribute to a good electromagnetic compatibility desig

Reconfigurable and multiband antennas with resonant and reactive loads

Reactive and resonant loads have been used from the very beginning of antenna design to improve impedance matching, bandwidth, and current distributions on antennas, and to create multiband and reconfigurable antennas.Trap loaded dipoles are one of the simplest resonator-loaded antennas and are traditionally loaded with either an inductor-capacitor pair or a quarter wavelength stub integrated into a dipole or monopole to create a second operating frequency at the trap resonant frequency. Adding resonant loads to antennas will only increase in popularity and practicality as filtennas are more often used for their SWaP improvements, better noise performance, and potential for additional degrees of reconfigurability. In this dissertation, I demonstrate that resonant loads can introduce lossy modes, and I significantly revise and expand the theory of the basic trap dipole antenna, which is a valuable aid in designing resonator loaded antennas with higher degrees of complexity. Based on the new analysis, I demonstrate novel series LC trap dipoles, dual-band inductor loaded trap dipoles, and parallel and series LC trap slots. The newly developed design process also allows for the integration of any kind of resonator or reactive load to be used to create trap style antennas. A reconfigurable load is also used to demonstrate novel tunable trap antennas. The design procedure is ultimately adaptable to any resonators that can be practically fabricated and physically incorporated into the antenna structure

Advanced direct metal 3D printed passive components for wireless communications and satellite applications

This thesis presents the design of advanced microwave passive filters, antennas, and antenna arrays using direct metal 3D printing technology. These work all incorporate the printing technology into the RF component design process, demonstrating the potential possibilities of direct metal 3D printing in the investigation and fabrication of passive microwave components with irregular shapes but attractive features. This thesis's works involved an extensive frequency range that starts with investigating S-band filters and then extends to C-band and Ku-band filters and antennas design. It is well known that in S- and C- band radio frequency (RF) applications that miniaturization is a critical factor for RF devices besides high performances. For this reason, the first project in this thesis proposed a novel compact waveguide loaded air slots resonator for designing inline bandpass filters. As a result, the designed filters not only have a smaller size than coaxial ones but also have controllable transmission zeros with inline structures. Since the air slots resonator is loaded inside the cavity, it is difficult to fabricate by conventional methods, but accessible by 3D printing technique with appropriate self-support structures. The fabrication quality was reflected by the mechanical and RF property measurements, which first demonstrated the advantage of using 3D printing technique to fabricate components with complex structures. The second project presents a compact high-Q fan-shaped folded waveguide resonator, which is applied to successfully design one C-band filter and filtering antenna. High performance RF properties and easy-to-print structures are always considered together. Accordingly, this work proposed and validated novel slots cross negative coupling topology of the filter and novel filtering antenna theory. Also, each of the designed components has better self-supported structures that can be printed with only two pieces, which highly reduced assembly processes and errors. Furthermore, the RF properties from measurement results further demonstrated that the reliability of the metal 3D printing technology for C-band RF applications. The concepts of the third project are extended from the second project but replaces the folded waveguide resonator with a metal strong coupling resonator (MSCR). The MSCR allows for even further compact dimensions while maintaining a high Q value of over 1000. It also allows producing mixed electrical-magnetic coupling by the curving coupling metal pairs intentionally. Except for the desired RF properties, the designed filter based on the MSCR can be printed as a whole even with complex inner circuits structures. Furthermore, the MSCR was integrated with the helical antenna using the proposed theory presented in the second project. Although the helical antenna belongs to the electrical-small antenna, the designed filtering antenna still has a high transmission efficiency of more than 95% and a 6 dBi realized gain concerning its less than quarter-wavelength. In addition, the filtering antenna has five helical radiation elements and one filter prototype but was printed with only three pieces, which showed the advantages of the direct metal 3D printing technology again. The fourth and the last project introduces a Ku-band slots antenna array application based on the sine corrugated waveguide resonator. Similar to previous projects, advanced RF performances were pursued in this project, in addition to demonstrating the use of 3D printing technology to fabricate compact and specific structures. The designed antenna array achieved a higher gain, wider band, and more simple feeding networks. The mode analysis method based on the EM software CST was applied to guide the design since no related formulas were available. The designed model was printed with two pieces and was measured thoroughly. The measured surface roughness, in-band responses, and radiation patterns showed promising results for the sine corrugated waveguide and 3D printing technology in satellite applications. In general, this thesis researched and proved the reliability and advantages of direct metal 3D printing technology in designing and fabricating advanced microwave passive components below the Ku-band. It should be mentioned that the designed passive components in this thesis can be easily re-designed/re-configured and applied on the 5G wireless base station and satellite communication systems

Analysis and design of new electronically reconfigurable periodic leaky-wave antennas

[SPA] El principal objetivo de la tesis es el estudio de nuevas tecnologías en el campo de las antenas reconfigurables. En particular, la tesis se centra en explorar y explotar el potencial que presentan un tipo de antenas denominadas como ¿Antenas basadas en Modos de Fuga¿ para controlar electrónicamente su diagrama de radiación. La tesis desarrolla el análisis, diseño y fabricación de tres novedosas antenas basadas en modos de fuga capaces de variar mediante unas pocas señales de control y de forma continua su ángulo de apuntamiento. El mecanismo de reconfiguración electrónica principalmente se basa en el control de la dispersión de los modos de fuga excitados en dichas estructuras, mediante un control electrónico introducido empleando estructuras periódicas resonantes combinadas con elementos activos tales como diodos varactores. La tesis demuestra claramente la utilidad de estas antenas en el campo de la reconfiguración electrónica, proponiendo estas nuevas estructuras como alternativas a otras soluciones más clásicas (como antenas en array de fase reconfigurables o reflectores parabólicos mecánicamente re-orientables mecánicamente) y otras de actualidad (como reflectarrays, transmitarrays, antenas metamateriales o antenas pixeladas), las cuales todas ellas presentan otros problemas en términos de coste, complejidad de diseño o limitaciones de escalabilidad en frecuencia, aportando así esta tesis novedosos conceptos de reconfiguración electrónica.[ENG] The thesis aims the design of novel reconfigurable antennas with electronic beam-scanning. In particular, the antennas analyzed are known as Fabry-Perot Antennas (FPA) and are currently of high interest in the scientific community because of their high-directivity, low-profile and structure simplicity, what allow them to be an interesting alternative to other technologies (e.g. parabolic reflectors, phased arrays, etc.) which require of complex power distribution networks, bulky external sources or costly techniques to achieve reconfigurable capabilities. In this thesis, the integration of active components, such as varactor diodes, with FPRA structures, is exploited to achieve electronic control of their aperture illumination, which in turn results in the electronic steering of the radiation-pattern main beam. A modal analysis based on the leaky-wave theory has allowed to understand and predict the behavior of these structures. An equivalent circuit model was developed to design and optimize the dimensions of theses complex structures, saving computational cost and time. The antennas are based on the control of the frequency dispersion response and the electromagnetic band-gap (EBG) properties of periodic structures, employing specially designed Frequency-Selective Surfaces (FSS) loaded with varactor diodes. Three novel antenna prototypes were manufactured to demonstrate electronic steering capability operating at 5.5GHz. Continuous scanning in elevation (1D scanning) and also in elevation and azimuth simultaneously (2D scanning) have been achieved employing just a few control signals (between 1 and 4 signals). The antenna structures have been implemented in a low-cost technology based on parallel plate waveguides and printed circuit boards which have allowed to design antennas with a reduced profile. Theoretical, simulated and experimental results are shown for each prototype to demonstrate the concepts. Also, some future lines related to novel planar reconfigurable antennas in development are also outlined. One of the main potential advantages of the reconfiguring principles presented for future applications is their frequency scalability. This would allow to apply these concepts to other technologies, such as MEMS or graphene, to build new reconfigurable antennas able to operate at higher frequency bands (e.g. mm-bands) for future applications.Universidad Politécnica de Cartagen

Horn Antennas and Dual-Polarized Circuits in Substrate Integrated Waveguide (SIW) Technology

The Substrate Integrated Waveguide (SIW) technology is a very promising candidate to provide widespread commercial solutions for modern communications systems. Its main advantage is the possibility to integrate passive/active components and antennas in the same substrate by using standard manufacturing processes, such as the Printed Circuits Board (PCB) processing technique. Nevertheless, the production of low-cost SIW devices is inherently linked to commercially available substrates and fabrication methods. In particular, these constraints usually limit (a) the frequency range of operation of certain SIW antennas and (b) the possibility of creating multimode structures dealing with orthogonal polarizations. The motivation of this PhD thesis is to overcome these two limitations by proposing innovative SIW components based on PCBs in order to favour the compatibility with existing systems and to lower their cost. Hence, the usage of the SIW technology would be extended towards new applications and scenarios. One type of antenna strongly affected by the limitation (a) is the H-plane SIW horn antenna. While standard horns are employed in many applications and in a wide range of frequencies, their counterparts in SIW technology are restricted to the Ka-band and above. At lower frequencies, commercial substrates are electrically thin and the performances of these end-fire antennas severely diminish. To solve this problem, a novel low-profile SIW horn antenna has been designed to be used at the Ku-band and below, while offering wideband characteristics. In addition, the horn shape has been further optimized to reduce the antenna footprint for a given directivity. In order to overcome the limitation (b), a substrate integrated guide able to simultaneously carry orthogonally polarized modes has been developed: the so called Extended Substrate Integrated Waveguide (ESIW). An ESIW dual-polarized system composed of an Orthomode Transducer (OMT) feeding a dual-polarized horn antenna has been designed and experimentally verified. The overall combination of concepts and ideas proposed in this thesis opens the door towards new SIW components that can increase the capacity, robustness and compactness ofmodern communication systems

Direct Antenna Modulation using Frequency Selective Surfaces

In the coming years, the number of connected wireless devices will increase dramatically, expanding the Internet of Things (IoT). It is likely that much of this capacity will come from network densification. However, base stations are inefficient and expensive, particularly the downlink transmitters. The main cause of this is the power amplifier (PA), which must amplify complex signals, so are expensive and often only 30% efficient. As such, the cost of densifying cellular networks is high. This thesis aims to overcome this problem through codesign of a low complexity, energy efficient transmitter through electromagnetic design; and a waveform which leverages the advantages and mitigates the disadvantages of the new technology, while being suitable for supporting IoT devices. Direct Antenna Modulation (DAM) is a low complexity transmitter architecture, where modulation occurs at the antenna at transmit power. This means a non-linear PA can efficiently amplify the carrier wave without added distortion. Frequency Selective Surfaces (FSS) are presented here as potential phase modulators for DAM transmitters. The theory of operation is discussed, and a prototype DAM for QPSK modulation is simulated, designed and tested. Next, the design process for a continuous phase modulating antenna is explored. Simulations and measurement are used to fully characterise a prototype, and it is implemented in a line-of-sight end-to-end communications system, demonstrating BPSK, QPSK and 8-PSK. Due to the favourable effects of spread spectrum signalling on FSS DAM performance, Cyclic Prefix Direct Sequence Spread Spectrum (CPDSSS) is developed. Conventional spreading techniques are extended using a cyclic prefix, making multipath interference entirely defined by the periodic autocorrelation of the sequence used. This is demonstrated analytically, through simulation and with experiments. Finally, CPDSSS is implemented using FSS DAM, demonstrating the potential of this new low cost, low complexity transmitter with CPDSSS as a scalable solution to IoT connectivity