Fig 2 - uploaded by Kagan Topalli
Content may be subject to copyright.
Butter fl y antenna structure: (a) physical dimensions and (b) two-port representation of the antenna.
Source publication
We develop a simple and robust impedance characterization method for planar THz antennas with micron- and submicron-size port geometries. Such antennas are often encountered in THz sensing applications where an ultrafast electronic device, such as a Schottky junction or a heterostructure backward diode, is integrated with a planar antenna structure...
Context in source publication
Context 1
... note here that this antenna geometry can be represented as a two-port structure where the DC-out pad region and the diode location are the first and second ports, respectively [as illustrated in Fig. 2(b)] [4], [5]. With its larger dimensions, compared to the diode port, the DC-out pad is a more accessible location for contact-probe measurements. Using this two-port model, one can analytically show that the reflection coefficient (impedance) at the diode location (second port) can be extracted using three measurements taken at the ...
Citations
... In terms of characterization methods of THz photoconductive antennas, Topalli et al. 183 presented an indirect impedance characterization method for planar THz antennas monolithically integrated with electronic sensor devices. This method is based on coplanar contact-probe measurements taken at an accessible location (e.g., a readout pad), which provides crucial experimental data to verify the impedance seen by the integrated device. ...
... However, the effect of buffer layer thickness in reduction of R s is not significant [17] and increasing the doping levels deteriorates other device characteristics like breakdown voltage and ideality factor [18]. By taking these factors into consideration, there is an apparent need for an accurate modeling of THz planar Schottky diodes in order to improve the device structure for enhanced Schottky diode-based detector performance, where an antenna and a diode are integrated monolithically [19,20]. ...
In this paper, we present the electromagnetic modeling of a performance-enhanced planar Schottky diode for applications in terahertz (THz) frequencies. We provide a systematic simulation approach for analyzing our Schottky diode based on finite element method and lumped equivalent circuit parameter extraction. Afterward, we use the developed model to investigate the effect of design parameters of the Schottky diode on parasitic capacitive and resistive elements. Based on this model, device design has been improved by deep-trench formation in the substrate and using a closed-loop junction to reduce the amount of parasitic capacitance and spreading resistance, respectively. The results indicate that cut-off frequency can be improved from 4.1 to 14.1 THz. Finally, a scaled version of the diode is designed, fabricated, and well characterized to verify the validity of this modeling approach.
... The integrated diodes can be reliably produced with cutoff frequencies beyond 1 THz [5], [6] and are fabricated in a standard 50Ω on-chip coplanar waveguide environment. Butterfly antennas [7] are used to couple the THz signal onto the diode under test for 2-port S-parameter measurements. The quasi-optical system of the non-contact probe stations is illustrated in Fig. 1. ...
... As it was studied in [19], for an electrically large hemispherical lens, multiple reflections do not have a significant effect on the antenna performance. Additionally, in a previous work the impedance of a scaled version of the butterfly antenna has been characterized using an indirect measurement method [20]. The results exhibit very good agreement with the computed impedance. ...
We present a novel THz computed tomography system that enables fast 3-dimensional imaging and spectroscopy in the 0.6-1.2 THz band. The system is based on a new real-time broadband THz camera that enables rapid acquisition of multiple cross-sectional images required in computed tomography. Tomographic reconstruction is achieved using digital images from the densely-packed large-format (80×64) focal plane array sensor located behind a hyper-hemispherical silicon lens. Each pixel of the sensor array consists of an 85 μm × 92 μm lithographically fabricated wideband dual-slot antenna, monolithically integrated with an ultra-fast diode tuned to operate in the 0.6-1.2 THz regime. Concurrently, optimum impedance matching was implemented for maximum pixel sensitivity, enabling 5 frames-per-second image acquisition speed. As such, the THz computed tomography system generates diffraction-limited resolution cross-section images as well as the three-dimensional models of various opaque and partially transparent objects. As an example, an over-the-counter vitamin supplement pill is imaged and its material composition is reconstructed. The new THz camera enables, for the first time, a practical application of THz computed tomography for non-destructive evaluation and biomedical imaging.
... As it was studied in [19], for an electrically large hemispherical lens, multiple reflections do not have a significant effect on the antenna performance. Additionally, in a previous work the impedance of a scaled version of the butterfly antenna has been characterized using an indirect measurement method [20]. The results exhibit very good agreement with the computed impedance. ...
We present a large-format, sub-millimeter-resolution, focal plane array sensor for THz imaging. Each pixel in the sensor array consists of broadband THz antennas monolithically integrated with ultra-fast heterostructure backward diodes for THz sensing. With the aid of in-house hybrid electromagnetic modeling tools, the focal plane array is optimized for diffraction limited image resolution and conjugate impedance matching for highest THz sensitivity. The camera is designed to operate in the 0.6-1.2 THz band with 5 frames-per-second image acquisition speeds, making it ideal for THz imaging applications, such as security screening, non-destructive evaluation and chemical, pharmaceutical, and medical imaging. The simulation results are validated by measurements to demonstrate sub-millimeter resolution with a pixel optical responsivity of 600 V/W at 0.7 THz.
... For example, focal plane array antennas feature very small details that do not allow direct probe contact for input impedance characterization. Alternatively, indirect methods have been developed in order to characterize THz antennas [5]. However, these methods cannot be readily applied to a wide range of THz devices. ...
We propose a contactless characterization approach for evaluating semiconductor devices and integrated circuits that operate in the THz regime (0.1-3 THz). The non-contact probe consists of on-chip receiving and transmitting THz antennas in a co-planar waveguide environment. Commercially available frequency extension modules with horn antennas are used in conjunction with microwave vector network analyzers to excite the proposed non-contact probe. A hemispherical lens couples the signals into device under test using the on-chip antennas. We discuss the calibration process and present the numerical evaluation of two non-contact probe schemes.
In this work, a graphene-based Photoconductive bowtie dipole antenna on a photonic crystal substrate is investigated for Terahertz radiation. Basic graphene radiator involving uniform substrate operates at dual bands of 1.4THz and 1.9THz with an efficiency of 80% and directivity of 3.3 dBi. Photonic crystal structure is created by implanting periodic arrangement of cylindrical air holes in the Gallium Arsenide (GaAs) substrate to enhance the performance of the basic antenna design. Due to the suppression of surface wave modes by the photonic crystals, additional resonance is created at 2.1THz, making the antenna to operate at triple bands of 1.4 THz, 1.9 THz and 2.1 THz. Opto-electronic simulation is carried out and emission intensity spectrum is also determined for the first time, in a graphene-based terahertz bowtie dipole antenna involving photonic crystals in it. The directivity of the proposed antenna with photonic crystal is found to be 13.7dBi, which is 10 dB improvement over the conventional design and efficiency of 95% is achieved.
The imperative development in the wireless technology leads to the enormous research in least discovered range of terahertz (THz) frequencies. The spectrum for newer 5G technology and earlier generations of wireless communication is positioned in millimeter/microwave regime. However, regular escalating demand of high data speed requires the devices to work on higher frequencies. The nonionizing nature, low attenuation windows, and higher penetration properties makes THz regime as the prominent candidate for future wireless communication. The THz frequencies lie between microwave and photonic region in electromagnetic spectrum. The regular increasing demand of THz technology in various applications like military, medical, spectroscopy, imaging, sensing, material characterization, and communication makes it more attentive among THz research group. Most of the application needs a means of wireless data transmission and reception, which is possible through the integration of antennas in the devices. The performance of wireless systems depends on the optimal design of the antenna. In THz regime, high path loss necessitates the designing of antenna with high-gain characteristic. In last decade, numerous THz antennas are proposed even though many challenges like suitable material selection, cost-effective design, precise fabrication, integration with existing device are still persist in this domain. The microstrip technology is a better candidate for THz antennas due to its features like easier integration, simple fabrication, low cost and light weight. Initially, this work provides a survey on recent literatures on THz antennas, challenges, fabrication techniques and measurement methods. Further, a microstrip antenna is presented for THz application. The proposed antenna is designed and simulated using electromagnetic simulation software HFSS. Finally, the chapter concludes the result of designed antenna and future research possibilities for THz antennas.
This chapter labels the recent advances of terahertz (THz or 10¹² Hz) technology-based image processing and its applications. In short, the sandwiched regime between infrared and microwaves, bridging the gap amid optics and electronics is renowned as the THz. THz image processing deals with the interaction of matters in the sub-millimetre wavelength band (ca. 300 GHz to 3 THz) of a distinct electromagnetic spectrum indistinguishable from the other spectroscopic techniques. The THz regime also known as the “THz gap” for a long time as neither microwave nor optical devices could entirely subjugator this mysterious realm with its countless unseen scientific assets. Thus, the discovery of THz imaging techniques becomes successful to fill the gap. In general, the traditional THz technology can simultaneously acquire both image and spectral information to address various fields such as security, aerospace industries, medicine, materials science, biomedical imaging and others. The development and commercialization of THz imaging systems are now broadly accepted as the accessible alternative roots, such as electron lasers, Smith-Pur-cell emitters, backward wave oscillators, synchrotrons, are relatively expensive components. Therefore, THz image processing tries to find the solution through its generation, manipulation and detection of THz radiation to expand its usability as check-up tool for various imaging applications. For example, higher sensitivity of THz wave is convenient to investigate the specific behaviour of bio-molecules. In addition, advanced digital image processing algorithms in association with THz pulsed imaging (TPI) are effective for screening, diagnosis and treatment to examine the 3D structures of biological samples like cancer tumours. Apart from that, THz spectrum might not only impact wireless network architectures (e.g. WLAN/WPAN/D2D) or security screening but also in aerospace industries using diode detectors through non-ionizing radiation. In contrast to X-rays, THz wave is completely harmless that can pass through clothing, objects and packages to recognize the inside materials and substances. At a glance, THz imaging along with detection technology contributes to identify opaque objects with clear borders, shaping this book a must-read for anybody in the arena of digital imaging and biomedical engineering.
In this letter, we experimentally validate the concept of bespoke lenses for the specific design of a log-spiral feed. Bespoke lenses are designed using the concept of quasi-conformal transformation optics to enhance the radiation properties for a given feeding. Our experimental results demonstrate that the antenna with its bespoke lens has higher gain, lower cross polarization, lower side lobes and lower axial ratio than with a conventional hyper-hemispherical lens.
