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Roberto Rojas

Also published under: Roberto G. Rojas, R. G. Rojas, R. Rojas

Publications
99
Citations
837
Publications by Year
19852024
Co-Authors:
Show All Co-Authors (73)
Image of author Roberto Rojas

Roberto Rojas

Also published under: Roberto G. Rojas, R. G. Rojas, R. Rojas

Affiliation

MIT Lincoln Laboratory
Lexington
MA, USA

Publication Topics

Biography

Roberto G. Rojas (S'80–M'85–SM'90–F'01) received the B.S.E.E. degree from New Mexico State University, Las Cruces, in 1979, and the M.S. and Ph.D. degrees in electrical engineering from The Ohio State University (OSU), Columbus, in 1981 and 1985, respectively.,He is currently a Professor in the Department of Electrical and Computer Engineering, The Ohio State University. His current research interests include the analysis and design of conformal arrays, active integrated arrays, nonlinear microwave circuits, as well as the analysis of electromagnetic radiation and scattering phenomena in complex environments.,Dr. Rojas is an elected Member of the International Scientific Radio Union (URSI), Commission B. He won the 1988 R.W.P. King Prize Pa...
Publications
99
Citations
837
Publications by Year
19852024
Co-Authors:
Show All Co-Authors (73)
Author's Published Works

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Additive Manufacturing of Graded Dielectric Superstrate for Phased Arrays

Patrick Bluem;Roberto Rojas;Bradley Duncan;Devon Beck

2024 IEEE International Symposium on Phased Array Systems and Technology (ARRAY)
Year: 2024 | Conference Paper |
Additive manufacturing technologies have enabled a wide range of custom devices and advanced material fabrication. It is reported here an approach developed to provide dielectric graded RF metamaterials through an active mixing nozzle developed in prior work and novel low loss inks. By utilizing a active mixing nozzle, we can provide a continuous gradient across the z-stack of a material from a pe...Show More

Additive Manufacturing of Graded Dielectric Superstrate for Phased Arrays

Patrick Bluem;Roberto Rojas;Bradley Duncan;Devon Beck

Year: 2024 | Conference Paper |

Time Domain-Based Reflectometry Measurements for 3D Printed Graded Index Dielectrics

Patrick Bluem;Roberto G. Rojas;Bradley Duncan;Devon Beck

2022 IEEE/MTT-S International Microwave Symposium - IMS 2022
Year: 2022 | Conference Paper |
Cited by: Papers (2)
Advancements in additive manufacturing approaches and materials have created new possibilities for RF and microwave networks. However, these designs require different approaches to fully characterize the behavior of the network. The use of time domain methods can assist in providing understanding which is typically lost with conventional frequency domain methods. This paper highlights the use of a...Show More

Time Domain-Based Reflectometry Measurements for 3D Printed Graded Index Dielectrics

Patrick Bluem;Roberto G. Rojas;Bradley Duncan;Devon Beck

Year: 2022 | Conference Paper |

Graded Index Superstate Layer for Large Scan Angle Phased Arrays

Patrick Bluem;Roberto G. Rojas

2022 IEEE 22nd Annual Wireless and Microwave Technology Conference (WAMICON)
Year: 2022 | Conference Paper |
Cited by: Papers (1)
This paper discusses the use of a graded index superstrate scan layer to improve phased array scan performance. The graded index superstrate uses novel 3D printing techniques to develop an improved impedance matching layer to better match the antenna array to free-space. This superstrate layer is fabricated and tested using a waveguide technique to simulate an infinite array. These measurements ar...Show More

Graded Index Superstate Layer for Large Scan Angle Phased Arrays

Patrick Bluem;Roberto G. Rojas

Year: 2022 | Conference Paper |

Graded Index Dielectric Superstrate for Phased Array Scan Compensation

Roberto Rojas;Patrick Bluem

2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting
Year: 2020 | Conference Paper |
Cited by: Papers (1)
This paper presents the use of additively manufactured graded index materials to improve the scan impedance variation of phased arrays. Solvent-based extrusion permits the programmatically controlled printing of chosen material properties with relative permittivity ranging from 2 to 24.5. This low-loss material shows promise for improvement of scan impedance variation for high scan angles in a sma...Show More

Graded Index Dielectric Superstrate for Phased Array Scan Compensation

Roberto Rojas;Patrick Bluem

Year: 2020 | Conference Paper |

Antennas and RF Components Designed with Graded Index Composite Materials

Roberto Rojas;Patrick Bluem;Idahosa Osaretin;Bradley Duncan

2020 International Applied Computational Electromagnetics Society Symposium (ACES)
Year: 2020 | Conference Paper |
Cited by: Papers (1)
Antennas and RF components in general, can greatly benefit with the recent development of low-loss 3D print graded index materials. The additional degrees of freedom provided by graded index materials can result in the design of antennas and other RF components with superior performance than currently available designs based on conventional constant permittivity materials. Here we discuss our work...Show More

Antennas and RF Components Designed with Graded Index Composite Materials

Roberto Rojas;Patrick Bluem;Idahosa Osaretin;Bradley Duncan

Year: 2020 | Conference Paper |

Using Non-Foster Circuits and Characteristic Modes to Improve Small Half Loop Antenna Performance

Aseim M. Elfrgani;Keum-Su Song;Roberto G. Rojas

2019 International Workshop on Antenna Technology (iWAT)
Year: 2019 | Conference Paper |
Traditionally, electrically small wire antennas (ESAs) have a high-quality factor and low radiation resistance. This implies that ESAs are narrow band and have poorly realized gain. In this paper, we present an efficient way to improve the performance of an electrically small wire half loop antenna by loading it with a non-Foster circuit (NFC). The use of the theory of Characteristic Modes (CMs) p...Show More

Using Non-Foster Circuits and Characteristic Modes to Improve Small Half Loop Antenna Performance

Aseim M. Elfrgani;Keum-Su Song;Roberto G. Rojas

Year: 2019 | Conference Paper |

Interpretation of Antenna Scattering Phenomena with the Aid of Characteristic Mode Theory

Ezdeen A. Elghannai;Roberto G. Rojas

2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting
Year: 2018 | Conference Paper |
Cited by: Papers (5)
This article is a study of electromagnetic (EM) antenna scattering phenomena from the Characteristic Mode (CM) standpoint and aims to shed some light on scattering from antennas. Using CM theory, the modes can be classified to yield two different sets of modes. One set is orthogonal with the localized antenna's source field in the vicinity of the feed point and this set of modes are referred to as...Show More

Interpretation of Antenna Scattering Phenomena with the Aid of Characteristic Mode Theory

Ezdeen A. Elghannai;Roberto G. Rojas

Year: 2018 | Conference Paper |

Characteristic modal decomposition of reflection phase of a microstrip-patch reflectarray unit-cell

Abdul Maalik;Roberto G. Rojas;Robert J. Burkholder

2016 IEEE International Symposium on Antennas and Propagation (APSURSI)
Year: 2016 | Conference Paper |
Cited by: Papers (2)
This paper introduces the use of characteristic mode theory to the design of reflectarrays. Specifically, the phase of the total reflected field is decomposed into the phases of modal reflected fields associated with the unit-cell of the reflectarray. It then becomes possible to shape the reflection phase curve of the unit-cell by suppressing the undesired modes, thereby improving bandwidth perfor...Show More

Characteristic modal decomposition of reflection phase of a microstrip-patch reflectarray unit-cell

Abdul Maalik;Roberto G. Rojas;Robert J. Burkholder

Year: 2016 | Conference Paper |

Effect of inter-element spacing on scan-range of microstrip-patch, and microstrip-dipole reflectarrays

Abdul Maalik;Roberto G. Rojas;Robert J. Burkholder

2016 IEEE International Symposium on Antennas and Propagation (APSURSI)
Year: 2016 | Conference Paper |
In this work, we have demonstrated that a tight coupling between array elements can be used to realize wide-scanning reflectarrays. Furthermore, it has been shown that microstrip dipole is better than microstrip patch in terms of scan range for the same inter-element spacing.Show More

Effect of inter-element spacing on scan-range of microstrip-patch, and microstrip-dipole reflectarrays

Abdul Maalik;Roberto G. Rojas;Robert J. Burkholder

Year: 2016 | Conference Paper |

V-Band Integrated on-Chip Antenna Implemented With a Partially Reflective Surface in Standard 0.13- $\mu \text{m}$ BiCMOS Technology

Chuan-Chang Liu;Roberto G. Rojas

IEEE Transactions on Antennas and Propagation
Year: 2016 | Volume: 64, Issue: 12 | Journal Article |
Cited by: Papers (18)
A ${V}$ -band on-chip triangular planar monopole antenna implemented with a partially reflective surface (PRS) using standard 0.13- $\mu \text{m}$ BiCMOS technology is presented. The PRS, which is realized with a dual-layered gangbuster type-4 frequency selective surface structure, is designed to obtain 90% reflection of the incident power, thus reducing the power loss caused by the lossy silico...Show More

V-Band Integrated on-Chip Antenna Implemented With a Partially Reflective Surface in Standard 0.13- $\mu \text{m}$ BiCMOS Technology

Chuan-Chang Liu;Roberto G. Rojas

Year: 2016 | Volume: 64, Issue: 12 | Journal Article |

Biomimetic Antenna Array Using Non-Foster Network to Enhance Directional Sensitivity Over Broad Frequency Band

Aseim M. Elfrgani;Roberto G. Rojas

IEEE Transactions on Antennas and Propagation
Year: 2016 | Volume: 64, Issue: 10 | Journal Article |
Cited by: Papers (18)
Biologically inspired antenna arrays that mimic the hearing mechanism of insects are called biomimetic antenna arrays (BMAAs). They are attractive for microwave applications, such as compact direction finding systems. Earlier, the BMAAs were designed for narrow frequency band phase enhancement, whereas we now propose to design them for use with a non-Foster coupling network (NFC). As the NFCs are ...Show More

Biomimetic Antenna Array Using Non-Foster Network to Enhance Directional Sensitivity Over Broad Frequency Band

Aseim M. Elfrgani;Roberto G. Rojas

Year: 2016 | Volume: 64, Issue: 10 | Journal Article |

Computer-aided antenna feed design using Characteristic Modes

Bryan D. Raines;Ezdeen A. Elghannai;Roberto G. Rojas

2015 European Microwave Conference (EuMC)
Year: 2015 | Conference Paper |
Cited by: Papers (2)
A new design technique that provides practical feed designs for arbitrary PEC structures is introduced. The technique requires minimal guidance from a human operator Using the information provided by a modal analysis, known as Characteristic Modes, allows us to construct a feed arrangements solution(s). From this solution(s), we can obtain the number, locations, and excitation voltages of one or m...Show More

Computer-aided antenna feed design using Characteristic Modes

Bryan D. Raines;Ezdeen A. Elghannai;Roberto G. Rojas

Year: 2015 | Conference Paper |

Modal-based approach to tune and enhance the frequency and dielectric bandwidth of a UHF-RFID tag antenna mounted on a dielectric substrate

Ezdeen A. Elghannai;Roberto G. Rojas

2015 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting
Year: 2015 | Conference Paper |
Cited by: Papers (4) | Patents (1)
A methodology to design an RFID tag antenna is presented. The tag is explicitly designed to account for changes in the dielectric constant of a thin substrate supporting the antenna. The theory of Characteristic Modes (CM), a modal-based approach, is used to study the effect of the dielectric variation on the dominant modes. The outcome of the CM analysis provides valuable guidelines to design a t...Show More

Modal-based approach to tune and enhance the frequency and dielectric bandwidth of a UHF-RFID tag antenna mounted on a dielectric substrate

Ezdeen A. Elghannai;Roberto G. Rojas

Year: 2015 | Conference Paper |

V-band integrated on-chip antenna implemented with a partially reflective surface in standard 0.13-µm BiCMOS technology

Chuan-Chang Liu;Roberto G. Rojas

2015 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting
Year: 2015 | Conference Paper |
Cited by: Papers (2)
This paper presents a V-band on-chip triangular planar monopole antenna using IBM 0.13-µm BiCMOS technology. A partially reflective surface (PRS), which is realized with a dual-layered Gangbuster type-4 FSS structure, is exploited to increase the antenna frequency bandwidth, radiation efficiency and gain. The overall size of the antenna, including the PRS, is 0.86 mm2. The measured S11 is smaller ...Show More

V-band integrated on-chip antenna implemented with a partially reflective surface in standard 0.13-µm BiCMOS technology

Chuan-Chang Liu;Roberto G. Rojas

Year: 2015 | Conference Paper |

Design and evaluation of an antenna array for MIMO systems and handset wireless applications

A Eduardo Rodriguez;Ezdeen Elghannai;Roberto G. Rojas;Roberto Bustamante

2015 38th International Conference on Telecommunications and Signal Processing (TSP)
Year: 2015 | Conference Paper |
This paper presents a MIMO array platform to operates at 2.6 GHz LTE band for wireless communication systems. The array consists of four compact patch antennas on a dielectric substrate of 125 × 62.5 × 1.27 mm3. Modifications of the ground plane along with systematic placement and orientation of each antennas on top of the substrate plays a key role to reduce the mutual coupling which normally deg...Show More

Design and evaluation of an antenna array for MIMO systems and handset wireless applications

A Eduardo Rodriguez;Ezdeen Elghannai;Roberto G. Rojas;Roberto Bustamante

Year: 2015 | Conference Paper |

Antenna design via current control of antenna currents using theory of Characteristic Modes

Ezdeen.A. Elghannai;Roberto.G. Rojas

2015 9th European Conference on Antennas and Propagation (EuCAP)
Year: 2015 | Conference Paper |
An approach for designing antennas using the concept of current control and reactive loading is presented. This scheme is based on a modal analysis referred to as Characteristic Modes (CM) which is used to obtain physical insight about the antenna's behavior and to modify/improve the antenna's currents to achieve the desired goals. The scheme could be applied to obtain wideband impedance and radia...Show More

Antenna design via current control of antenna currents using theory of Characteristic Modes

Ezdeen.A. Elghannai;Roberto.G. Rojas

Year: 2015 | Conference Paper |

Successful realization of Non-Foster circuits for wide-band antenna applications

Aseim M. Elfrgani;Roberto G. Rojas

2015 IEEE MTT-S International Microwave Symposium
Year: 2015 | Conference Paper |
Cited by: Papers (11)
Non-Foster circuits (NFCs) are promising for numerous microwave and antenna applications because they are not limited by the gain-bandwidth product. Although NFCs can be very useful in many applications, successful realization of these circuits is difficult because they suffer from several issues, including losses, noise, and instability. As a consequence, an accurate and efficient design techniqu...Show More

Successful realization of Non-Foster circuits for wide-band antenna applications

Aseim M. Elfrgani;Roberto G. Rojas

Year: 2015 | Conference Paper |

Stability of non-Foster circuits for broadband impedance matching of electrically small antennas

Aseim M. Elfrgani;Roberto G. Rojas

2015 IEEE Radio and Wireless Symposium (RWS)
Year: 2015 | Conference Paper |
Cited by: Papers (5)
Non-Foster circuits are promising for numerous microwave and antenna applications because they are not limited by the gain-bandwidth product. However, the stability of these circuits is a key issue for their design. In this paper we introduce a three-step scheme to systematically stabilize a non-Foster circuit (NFC) topology that can be used in numerous applications. To demonstrate the stabilizati...Show More

Stability of non-Foster circuits for broadband impedance matching of electrically small antennas

Aseim M. Elfrgani;Roberto G. Rojas

Year: 2015 | Conference Paper |

Multiport Reactive Loading Matching Technique for Wide Band Antenna Applications Using the Theory of Characteristic Modes

Ezdeen A. Elghannai;Bryan D. Raines;Roberto G. Rojas

IEEE Transactions on Antennas and Propagation
Year: 2015 | Volume: 63, Issue: 1 | Journal Article |
Cited by: Papers (32)
A systematic framework is presented for designing an antenna with arbitrary shape and expanding its input impedance and pattern bandwidths using reactive loading. This method, unlike other design procedures, allows us to control the current distribution over the antenna structure with potentially fine granularity. This technique is applied to wire and microstrip antennas and it is shown to achieve...Show More

Multiport Reactive Loading Matching Technique for Wide Band Antenna Applications Using the Theory of Characteristic Modes

Ezdeen A. Elghannai;Bryan D. Raines;Roberto G. Rojas

Year: 2015 | Volume: 63, Issue: 1 | Journal Article |

A four-element antenna array for MIMO-LTE systems

Eduardo Rodríguez;Roberto Bustamante;Ezdeen Elghannai;Roberto G. Rojas

2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium)
Year: 2014 | Conference Paper |
Summary form only given. In this paper presents a compact MIMO array platform to operate at 2.6GHz Long Term Evolution (LTE) band for wireless communication systems. The array consists of four compact patch antennas on a dielectric substrate with total dimensions of 125×62.5×1.27mm3. Modifications of the ground plane along with systematic placement and orientation of each antenna on top of the sub...Show More

A four-element antenna array for MIMO-LTE systems

Eduardo Rodríguez;Roberto Bustamante;Ezdeen Elghannai;Roberto G. Rojas

Year: 2014 | Conference Paper |

Loop-type electrically small antenna loaded with non-foster circuit

Aseim Elfrgani;Roberto G. Rojas

2014 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)
Year: 2014 | Conference Paper |
Although electrically small antennas (ESAs) have gotten an increase attention because of their wide applications in wireless communications, they are not efficient radiators because of their high quality factor (Q). Therefore, matching networks are required to improve their input impedance and radiation characteristics. However, due to gain-bandwidth restrictions, wideband matching cannot be achie...Show More

Loop-type electrically small antenna loaded with non-foster circuit

Aseim Elfrgani;Roberto G. Rojas

Year: 2014 | Conference Paper |

Evaluation of total antenna (Q) in terms of the Qn of modes provided by theory of characteristic modes

Ezdeen A. Elghannai;Roberto G. Rojas

2014 United States National Committee of URSI National Radio Science Meeting (USNC-URSI NRSM)
Year: 2014 | Conference Paper |
Summary form only given. The study of the antenna Quality factor (Q) has been an active topic of research for a long time. Its importance is directly related to its connection to the antenna frequency bandwidth. Many authors have discussed the problem of formulating the Q of an antenna. Chu, Mclean, Wheeler, Gustafsson, Thal, Yaghjian, Harrington and Vandenbosch were among many whom studied the Q ...Show More

Evaluation of total antenna (Q) in terms of the Qn of modes provided by theory of characteristic modes

Ezdeen A. Elghannai;Roberto G. Rojas

Year: 2014 | Conference Paper |

Multiport antenna system matching using Network Characteristic Mode analysis

Ezdeen.A. Elghannai;Roberto.G. Rojas

2014 IEEE Antennas and Propagation Society International Symposium (APSURSI)
Year: 2014 | Conference Paper |
Cited by: Papers (1)
Antenna matching networks (MN) have been developed intensively over the past years. One purpose of antenna impedance matching is to maximize the transfer of power from source to load (antenna) by transforming a complex load to match a resistive or complex source impedance over a desired frequency band. However, in multi-antenna systems such as antenna arrays or MIMO systems, we need to consider di...Show More

Multiport antenna system matching using Network Characteristic Mode analysis

Ezdeen.A. Elghannai;Roberto.G. Rojas

Year: 2014 | Conference Paper |

Non-Foster circuit embedded within electrically small antenna

Aseim M. Elfrgani;Roberto G. Rojas

2014 IEEE Antennas and Propagation Society International Symposium (APSURSI)
Year: 2014 | Conference Paper |
Cited by: Papers (5)
Electrically small antennas (ESAs) have high quality factor and low radiation resistance. This implies that ESAs are narrow band and have poor realized gain. In this paper, we present an efficient way to improve the performance of an electrically small antenna by embedding a non-Foster circuit (NFC) inside the antenna structure instead of using matching network at the antenna feed. The antenna wit...Show More

Non-Foster circuit embedded within electrically small antenna

Aseim M. Elfrgani;Roberto G. Rojas

Year: 2014 | Conference Paper |

Stabilizing non-foster-based tuning circuits for electrically small antennas

Aseim M. Elfrgani;Roberto G. Rojas

2014 IEEE Antennas and Propagation Society International Symposium (APSURSI)
Year: 2014 | Conference Paper |
Cited by: Papers (6)
Although non-Foster circuits are very attractive for microwave and antenna applications because they are not restricted by the gain-bandwidth product, stability is a major issue with these circuits. This paper presents a systematic way to stabilize the widely used non-Foster circuit (NFC) topology originally introduced by Linvill [1]. As a case study, a NFC tuned electrically small antenna (ESA) i...Show More

Stabilizing non-foster-based tuning circuits for electrically small antennas

Aseim M. Elfrgani;Roberto G. Rojas

Year: 2014 | Conference Paper |

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