DESIGN OF WIDEBAND WAVEGUIDE-FED PLANAR ANTENNA ARRAY IN THE KU-BAND

Ph.DDOCTOR OF PHILOSOPH

Realizing a 140\ua0GHz Gap Waveguide–Based Array Antenna by Low-Cost Injection Molding and Micromachining

This paper presents a novel micromachining process to fabricate a 140\ua0GHz planar antenna based on gap waveguide technology to be used in the next-generation backhauling links. The 140\ua0GHz planar array antenna consists of three layers, all of which have been fabricated using polymer-based microfabrication and injection molding. The 140\ua0GHz antenna has the potential to be used as an element in a bigger 3D array in a line-of-sight (LOS) multiple input multiple output (MIMO) configuration to boost the network capacity. In this work, we focus on the fabrication of a single antenna array element based on gap waveguide technology. Depending on the complexity of each antenna layer’s design, three different micromachining techniques, SU8 fabrication, polydimethylsiloxane (PDMS) molding, and injection molding of the polymer (OSTEMER), together with gold (Au) coating, have been utilized to fabricate a single 140\ua0GHz planar array antenna. The input reflection coefficient was measured to be below − 11\ua0dB over a 14% bandwidth from 132 to 152\ua0GHz, and the antenna gain was measured to be 31 dBi at 140\ua0GHz, both of which are in good agreement with the simulations

W-Band Low-Profile Monopulse Slot Array Antenna Based on Gap Waveguide Corporate-Feed Network

This paper presents a gap waveguide-based compact monopulse array antenna, which is formed with four unconnected layers, for millimeter-wave tracking applications at W-band (85–105 GHz). Recently developed gap waveguide technology removes the need for galvanic contact among metallic layers of waveguide structures, and thereby, makes the proposed antenna suitable for easy and low-cost manufacturing. In this context, a low-loss planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The gap waveguide planar monopulse comparator network is integrated with a high-efficiency 16x16 corporate-fed slot array antenna. The measured results of the comparator network show the amplitude and phase imbalance values to be less than 0.5 dB and 2\ub0, respectively, over the frequency band of interest. The fabricated monopulse array antenna shows relative impedance bandwidths of 21% with input reflection coefficients better than −10 dB for the sum and difference ports. The null in the difference radiation pattern is measured to be 38 dB below the peak of the sum radiation pattern at 94 GHz. The measured gain is about 30 dBi for the same frequency. The low-loss performance of the comparator network and the feed network of the proposed array, together with the simple and easy manufacturing and mechanical assembly, makes it an excellent candidate for W -band compact direction-finding systems

A STUDY ON SERIES SLOT ARRAY ANTENNA DESIGN METHODOLOGY AND ITS APPLICATION TO DUAL LINEAR POLARIZATION

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 2. 남상욱.본 논문에서는 임의의 선형편파 발생을 위한 직렬 슬롯 배열안테나 설계 방법을 제시하였다. 45도 기울어진 선형편파 발생이 가능하고 동시에 임피던스 정합, 균일전장 분포를 형성할 수 있도록 '교차 리액턴스 슬롯 쌍'을 기본 방사체로 제안하였다. 이 기본 방사체를 이용하면 개별 방사 슬롯 간의 간격이 관내 파장의 반 파장 간격으로 위치시킬 수 있기 때문에 grating lobe를 억제할 수 있다. 또한, 제안한 안테나 설계 기법은 기판 집적 도파관 기술 (substrate integrated waveguide, SIW)을 통해 구현하였고 전장 시뮬레이터 및 제작, 측정을 통해 설계 기법의 적합성을 검증하였다. 먼저, Ka-밴드 용 선형 및 평면 배열안테나를 설계하였다. 45도 선형편파를 발생시키기 위해 적층의 SIW 구조로 배열안테나를 구현하였으며 균일 전장이 발생되는 원리를 등가회로 및 임피던스, 전류 순환 방정식을 이용하여 검증하였다. 나아가, 전자장 시뮬레이터를 통한 결과와 비교•분석하였다. 두 번째로, 낮은 부엽레벨을 가지도록 개별 방사체의 전장 계수 조절 방법을 제안하였다. 각 직렬 방사 슬롯을 흐르는 모드 전류의 크기를 조절하기 위해 개별 방사체의 위치를 중심선을 따라 이동시킬 수 있다. 이러한 옵셋 조절 방법을 이용하여 ‒20 dB 및 ‒26 dB Dolph-Chebyshev 계수를 가지는 선형 배열안테나를 설계하였고 제안한 방법의 효용성을 제작 및 측정을 통해 검증하였다. 마지막으로, ±45도 이중 선형편파 발생을 위한 설계 기법을 제안하였다. 동일한 개구면을 공유하는 두 선형편파 간의 격리도를 최대화하기 위해 교차 슬롯 간에 수직 조건을 만족할 수 있도록 기판의 유전율 및 방사 SIW의 폭을 결정하였다. 나아가 제안한 설계 기법을 8 × 8 이중 평면 모노펄스 안테나 설계에 응용하였다. 모노펄스 동작을 위해 기존의 금속 도파관 전송선로를 이용해 제작된 비교기를 결합하였으며 반사손실, 방사패턴, 이득 등의 전기적인 결과를 확인하였다.1. Introduction 1 1.1 Conventional Slot Array Antennas for Linear Polarization 3 1.2 Substrated Integrated Waveguide (SIW) Technology 5 2. Linear Slot Array Antenna for 45º-Inclined Linear Polarization 9 2.1 Introduction 9 2.2 Proposed Antenna Configuration 10 2.2.1 Single Slot Module and Impedance Extraction 11 2.2.2 Alternating Reactance Slot Pair 14 2.2.3 Equivalent Circuit Analysis using Recursive Formulas 17 2.2.4 Centered-Inclined Series-to-Series Coupling Slot 20 2.3 Simulation and Measurement 22 2.4 Summary 25 3. Planar Slot Array Antenna for 45º-Inclined Linear Polarization 30 3.1 Introduction 30 3.2 Proposed Antenna Configuration 33 3.3 Feeding Network Design and Analysis 35 3.4 Coupling and Radiating Slot Arrangement for In-Phase Excitation 41 3.5 Wideband Coax-to-SIW Transition Design and Analysis 42 3.6 Simulation and Measurement 48 3.6.1 Uniform Electric Field Distribution 48 3.6.2 Back-to-Back Coax-to-SIW Transition 52 3.6.3 Reflection Coefficient, Gain, and Radiation Patterns 54 3.7 Summary 57 4. Excitation Control Method for Low Sidelobe Level 63 4.1 Introduction 63 4.2 Axial Displacements for Excitation Control 66 4.3 Design Procedure for Excitation Control 73 4.4 Simulation and Measurement 77 4.5 Summary 82 5. Dual Linear Polarized SIW Monopulse Antenna for Tracking Radar 85 5.1 Introduction 85 5.2 Design Considerations for Dual LP Radiating SIWs 88 5.3 The Proposed Dual LP 8 by 8 SIW Monopulse Protptype Antenna 92 5.3.1 Folded Short-Circuited Stubs 95 5.3.2 Shunt-to-Series Coupling Slots 96 5.3.3 Series-to-Series Coupling Slots 97 5.4 RWG Comparator for Monopulse Operation 98 5.5 Experimental Results 103 5.5.1 Dual LP SIW Sub-Array Antenna 103 5.5.2 Dual LP SIW Monopulse Antenna 107 5.6 Summary 109 6. Conclusion 116Docto

Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz

The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks

Compact RF Integration and Packaging Solutions Based on Metasurfaces for Millimeter-Wave Applications

The millimeter-wave frequency range has got a lot of attention over the past few years because it contains unused frequency spectrum resources that are suitable for delivering Gbit/s end-user access in areas with high user density. Due to the limited output power that the current RF active components can deliver in millimeter-wave frequencies, antennas with the features of low profile, high gain, high efficiency and low cost are needed to compensate free space path loss and increase the communication distance for the emerging high data rate wireless systems. Moreover, it is desired to have a compact system by integration of the antenna with passive and active components at high frequencies.In order to move towards millimeter-wave frequencies we need to face significant hardware challenges, such as active and passive components integration, packaging problems, and cost-effective manufacturing techniques. The gap waveguide technology shows interesting characteristics as a new waveguide structure. The main goal of this thesis is to demonstrate the advantages of gap waveguide technology as an alternative to the traditional guiding structures to overcome the problem of good electrical contact due to mechanical assembly with low loss. This thesis mainly focuses on high-gain planar array antenna design, integration with passive and active components, and packaging based on gap waveguide technology. \ua0We introduce several low-profile multilayer corporate-fed slot array antennas with high gain, high efficiency and wide impedance bandwidth operating at the millimeter-wave frequency band. A system demonstration consisting of two compact integrated antenna-diplexer and Tx/Rx MMICs for Frequency-division duplex (FDD) low latency wireless backhaul links at E-band is presented to show the advantages of gap waveguide technology in building a complete radio front-end. Moreover, the use of several new manufacturing methods, such as die-sink Electric Discharge Machining (EDM), direct metal 3-D printing, and micro-molding are evaluated to fabricate gap waveguide components in a more effective way.Furthermore, a novel air-filled transmission line, so-called multi-layer waveguide (MLW), that exhibits great advantages such as low-cost, simple fabrication, and low loss, even for frequencies beyond 100 GHz, is presented for the first time. To constitute an MLW structure, a rectangular waveguide transmission line is formed by stacking several thin metal layers without any electrical and galvanic contact requirement among the layers. The proposed concept could become a suitable approach to design millimeter-wave high-performance passive waveguide components, and to be used in active and passive components integration ensuring mass production at the same time

An Overview of Recent Development of the Gap-Waveguide Technology for mmWave and Sub-THz Applications

The millimeter-wave (mmWave) and sub-terahertz (sub-THz) bands have received much attention in recent years for wireless communication and high-resolution imaging radar applications. The objective of this paper is to provide an overview of recent developments in the design and technical implementation of GW-based antenna systems and components. This paper begins by comparing the GW-transmission line to other widely used transmission lines for the mmWave and sub-THz bands. Furthermore, the basic operating principle and possible implementation technique of the GW-technology are briefly discussed. In addition, various antennas and passive components have been developed based on the GW-technology. Despite its advantages in controlling electromagnetic wave propagation, it is also widely used for the packaging of electronic components such as transceivers and power amplifiers. This article also provided an overview of the current manufacturing technologies that are commonly used for the fabrication of GW-components. Finally, the practical applications and industry interest in GW technology developments for mmWave and sub-THz applications have been scrutinized.Funding Agencies|European Union - Marie Sklodowska-Curie [766231WAVECOMBEH2020-MSCA-ITN-2017]</p

Dry film photoresist-based microfabrication: a new method to fabricate millimeter-wave waveguide components

This paper presents a novel fabrication method based on dry film photoresists to realize waveguides and waveguide-based passive components operating at the millimeter-wave frequency (30–300 GHz). We demonstrate that the proposed fabrication method has a high potential as an alternative to other microfabrication technologies, such as silicon-based and SU8-based micromachining for realizing millimeter-wave waveguide components. Along with the nearly identical transfer of geometrical structures, the dry film photoresist offers other advantages such as fewer processing steps, lower production cost, and shorter prototyping time over the conventional micromachining technologies. To demonstrate the feasibility of the fabrication process, we use SUEX dry film to fabricate a ridge gap waveguide resonator. The resonator is designed to exhibit two resonances at 234.6 and 284 GHz. The measured attenuation at 234 GHz is 0.032 dB/mm and at 283 GHz is 0.033 dB/mm for the fabricated prototype. A comparative study among different existing technologies indicates that the reported method can give a better unloaded Q-value than other conventional processes. The measured unloaded Q-values are in good agreement with the simulated unloaded Q-values. The signal attenuation indicates that SUEX dry film photoresists can be used to fabricate passive devices operating at millimeter-wave frequencies. Moreover, this new fabrication method can offer fast and low-cost prototyping

Mode Theory of Multi-Armed Spiral Antennas and Its Application to Electronic Warfare Antennas

Since their invention about 55 years ago, spiral antennas have earned a reputation for providing stable impedance and far-field patterns over multi-decade frequency ranges. For the first few decades these antennas were researched for electronic warfare receiving applications, primarily in the 2-18 GHz range. This research was often done under conditions of secrecy, and often by private contractors who did not readily share their research, and now have been defunct for decades. Even so, the body of literature on the two-armed variant of these antennas is rich, often leading non-specialists to the misconception that these antennas are completely understood. Furthermore, early work was highly experimental in nature, and was conducted before modern data collection and postprocessing capabilities were widespread, which limited the range of the studies. Recent research efforts have focused on extending the application of spirals into new areas, as well as applying exotic materials to `improve\u27 their performance and reduce their size. While interesting results have been obtained, in most instances these were incomplete, often compromising the frequency independent nature of these antennas. This thesis expands the role of the multi-armed spiral outside of its traditional niche of receive-only monopulse direction finding. As a first step, careful study of the spiral-antenna mode theory is undertaken with particular attention paid to the concepts of mode filtering and modal decomposition. A technique for reducing the modal impedance of high arm-count spirals is introduced. The insights gained through this theoretical study are first used to improve the far-field performance of the coiled-arm spiral antenna. Specifically, expanding the number of arms on a coiled arm spiral from two to four while providing proper excitation enables dramatically improved broadside axial ratio and azimuthal pattern uniformity. The multiarming technique is then applied to the design of an antenna with exceptionally stable and clean radiation patterns without use of an absorbing cavity. The multiarming technique allows the spiral to retain its pattern integrity at frequencies well below those of comparable two-armed spiral antennas. A quadrifilar helix-type of end-loading is applied to the end of the spiral, resulting in dramatically-improved low-frequency gain. Careful application of resistive end-loading allows good impedance matching at frequencies as low as one-half of the Mode 1 cutoff frequency, while providing acceptable radiation efficiency due to effective use of the available antenna volume. A novel dual-layering technique for reducing the spiral\u27s modal impedance is presented, allowing the antenna to present a good impedance match to a 50 ohm system. The third application of mode theory has been to exploit the wideband multi-mode capability of the multi-armed spiral antenna to implement a simple wide-band radiation pattern nulling technique on a multi-armed spiral antenna. It is shown that wideband nulling is possible and that, in contrast to traditional array antennas, grating lobes do not appear even over extremely wide bandwidths. Simple techniques for addressing the phenomenon of null rotation with frequency are discussed. Finally, mode theory has been used to analyze beamformer non-idealities. This has led to the revelation that the spectral distribution of beamformer errors is at least as important as the magnitude of those errors. Proper choice of beamformer topology can result in noticeable improvement in the antenna performance