ALMA Band 1 Optics (35–50 GHz): Tolerance Analysis,Effect of Cryostat Infrared Filters and Cold Beam Measurements

The Atacama Large Millimeter/Sub-millimeter Array (ALMA) is currently the largest (sub-)mm wave telescope in the world and will be used for astronomical observations in all atmospheric windows from 35 to 950 GHz when completed. The ALMA band 1 (35–50 GHz) receiver will be used for the longest wavelength observations with ALMA. Because of the longer wavelength, the size of optics and waveguide components will be larger than for other ALMA bands. In addition, all components will be placed inside the ALMA cryostat in each antenna, which will impose severe mechanical constraints on the size and position of receiver optics components. Due to these constraints, the designs of the corrugated feed horn and lens optics are highly optimized to comply with the stringent ALMA optical requirements. In this paper, we perform several tolerance analyses to check the impact of fabrication errors in such an optimized design. Secondly, we analyze the effects of operating this optics inside the ALMA cryostat, in particular the effects of having the cryostat IR filters placed next to the band 1 feed horn aperture, with the consequent near-field effects. Finally, we report on beam measurements performed on the first three ALMA band 1 receivers inside test cryostats, which satisfy ALMA specifications. In these measurements, we can clearly observe the effects of fabrication tolerances and IR filter effects on prototype receiver performance.     

The Atacama Large Millimeter/Submillimeter Array

The Atacama Large Millimeter/Submillimeter Array (ALMA) is an international radio telescope under construction in the Atacama Desert of northern Chile. ALMA is situated on a dry site at 5000 m elevation, allowing excellent atmospheric transmission over the instrument wavelength range of 0.3-10 mm. ALMA will consist of two arrays of high-precision antennas. One, of up to 64 12-m-diameter antennas, is reconfigurable in multiple patterns ranging in size from 150 m up to ~ 15 km. A second array is composed of a set of four 12-m and 12 7-m antennas operating in one of two closely packed configurations ~ 50 m in diameter. The instrument will provide both interferometric and total-power astronomical information on atomic, molecular, and ionized gas and dust in the solar system, our galaxy, and the nearby to high-redshift universe. In this paper, we outline the scientific drivers, technical challenges, and planned progress of ALMA.     

ALMA North American Integration Center Front-End Test System

The Atacama Large Millimeter/submillimeter (ALMA) Array Front End (FE) system is the first element in a complex chain of signal receiving, conversion, processing and recording. 70 Front Ends will be required for the project. The Front End is designed to receive signals in ten different frequency bands. In the initial phase of operations, the antennas will be fully equipped with six bands. These are Band 3 (84–116 GHz), Band 4 (125–163 GHz), Band 6 (211–275 GHz), Band 7 (275–373 GHz), Band 8 (385–500 GHz) and Band 9 (602–720 GHz). It is planned to equip the antennas with the missing bands at a later stage of ALMA operations, with a few Band 5 (163–211 GHz) and Band 10 (787–950 GHz) receivers in use before the end of the construction project. The ALMA Front End is far superior to any existing receiver systems; spin-offs of the ALMA prototypes are leading to improved sensitivities in existing millimeter and submillimeter observatories. The Front End units are comprised of numerous elements, produced at different locations in Europe, North America and East Asia and are integrated at several Front End integration centers (FEIC) to insure timely delivery of all the units to Chile. The North American FEIC (NA FEIC) is at the National Radio Astronomy Observatory facility in Charlottesville, Virginia, USA. This paper describes the design and performance of the test set used at the NA FEIC to check the performance of the Front Ends, following integration and prior to shipment to Chile.     

Testing of electronic industries association land-mobile communication antenna gain standards at the national bureau of standards

The Electronic Industries Association has a published standard, EIA RS-329A, "Minimum Standards for Land-Mobile Communications Antennas," Dec. 1975. This standard details the minimum performance requirements and the test methods for evaluating the performance of fixed and base station antennas at frequencies from 25-1000 MHz. Also included in this standard are the specifications for a set of standard antennas for use in various frequency bands. The EIA Antenna Committee, TR8.11, requested the National Bureau of Standards to calibrate the gain of some of these antenna standards. Two antennas were calibrated in the 450-512-MHz band, and two antennas in the 800-900 MHz band. This paper describes in detail the techniques used throughout the measurement program, the results, and the measurement uncertainties. Two basic methods of measuring the gain of the EIA antennas were employed during this calibration. The three-antenna technique was used at some frequencies, and the standard field technique was used at other frequencies. Both techniques are described. The NBS antennas used for the measurements were standard-gain pyramidal horn antennas. The antenna range used for the measurement is described. This is a vertical range using nonmetallic towers and hardware, thus providing essentially free-space conditions in which reflections and multipath problems are minimized. The measurements were made in terms of absolute power gain, i.e., referenced to an isotropic radiator. These results are discussed and also compared to the gain figures listed in EIA standard RS-329A.     

A Low Noise 100 GHz Sideband-Separating Receiver

We have built a 100 GHz sideband-separating receiver. The receiver, a breadboard for the band 3 cartridges for ALMA, achieves a SSB noise temperature of 6hf/k with a 4–8 GHz IF. We show that it is possible to meet the ALMA specifications. The design of the receiver is reviewed and the relationships between the receiver noise temperature and properties of the components used in the receiver are discussed.     

Development of a Submillimeter Double-Ridged Waveguide Ortho-Mode Transducer (OMT) for the 385–500 GHz Band

We present design and evaluations of a submillimeter double-ridged waveguide ortho-mode transducer (OMT) for ALMA Band 8 (385–500 GHz) cartridge receiver. The measured transmission loss of the OMT at 4 K was 0.4–0.5 dB according to noise measurements with an SIS mixer. The polarization isolation was measured to be larger than 29 dB from quasioptical measurements. The OMT consists of a Bϕifot junction and a double-ridged guide. A robust design with allowable mechanical errors of 20 μm has been demonstrated.     

Design and Characterization of Purely Textile Patch Antennas

In this paper, we present four purely textile patch antennas for Bluetooth applications in wearable computing using the frequency range around 2.4 GHz. The textile materials and the planar antenna shape provide a smooth integration into clothing while preserving the typical properties of textiles. The four antennas differ in the deployed materials and in the antenna polarization, but all of them feature a microstrip line as antenna feed. We have developed a manufacturing process that guarantees unaffected electrical behavior of the individual materials when composed to an antenna. Thus, the conductive textiles possess a sheet resistance of less than 1Omega/squarein order to keep losses at a minimum. The process also satisfies our requirements in terms of accuracy meeting the Bluetooth specifications. Our investigations not only characterize the performance of the antennas in planar shape, but also under defined bending conditions that resemble those of a worn garment. We show that the antennas can withstand clothing bends down to a radius of 37.5 mm without violating specifications     

Short leaky-wave antennas of sum and difference patterns

A set of differential feed short (~0.7 λ₀) leaky-wave antennas with sum (Σ) and difference (Δ) patterns is presented. Rigorous field-theory analyses show that the radiation characteristics of these antennas agree well with the measurements. The performance of these antennas is well suited for direction finding applications     

Application versus network layer multicasting in ad hoc networks: the ALMA routing protocol

Application layer multicasting has emerged as an appealing alternative to network layer multicasting in wireline networks. Here, we examine the suitability of application layer multicast in ad hoc networks. To this effect, we propose a flexible receiver-driven overlay multicast protocol which we call Application Layer Multicast Algorithm (ALMA). ALMA constructs an overlay multicast tree in a dynamic, decentralized and incremental way. First, ALMA is receiver-driven: the member nodes find their connections according to their needs. Second, it is flexible, and thus, it can satisfy the performance goals and the needs of a wide range of applications. Third, it is highly adaptive: it reconfigures the tree in response to mobility or congestion. In addition, our protocol has the advantages of an application layer protocol: (a) simplicity of deployment, (b) independence from lower layer protocols, and (c) capability of exploiting features such as reliability and security that may be provided by the lower layers. Through extensive simulations, we show that ALMA performs favorably against the currently best application layer and network layer protocols. In more detail, we find that ALMA performs significantly better than ODMRP, a network layer, for small group sizes. We conclude that the application layer approach and ALMA seem very promising for ad hoc multicasting.     

High performance antenna systems for new VOA stations

Advancements in curtain-type high-frequency (HF) broadcast antennas are reviewed. Novel high-performance antennas for the Voice of America (VOA) are described, including vertical and horizontal beam selections, performance measurements, effects of finite ground and hills, radiation hazard zones, and transmission lines. Specifications for antennas to be installed at four new VOA stations are examined. The designs provide substantial flexibility in radiation-beam characteristics with four vertical beam modes and seven horizontal beam angles. it is believed that the technique of selecting the optimum radiation beam for ionospheric propagation to VOA target areas will provide a substantial improvement in the performance     

The temperture dependence of substrate parameters and their effecton microstrip antenna performance

In the common approach to the design of microstrip antennas, the designers rely on data provided in the manufacturers' specifications, even though such specifications are confined to standard environmental conditions. In practice, the electrical parameters of the substrates may deviate from the manufacturers' data, thus making the antenna designer adopt a deficient design strategy. In the study reported, microstrip substrates were exposed to large temperature variations and their temperature dependent properties were measured in a specialized laboratory for dielectric materials. The results include plots of the dielectric constant and dissipation factor for wide temperature ranges equivalent to those in airborne applications. On the basis of this experimental data, the substrates were divided into four categories according to their dielectric constant value and its temperature dependence. Using both manufacturers' data and the measured values, a series of microstrip dual-feed aperture-coupled patch antennas were designed for the four categories of substrates and the sensitivity of their electrical performance due to temperature variations was fully investigated     

Characterization of antennas for personal wireless communications applications

The advancement of antenna technology in personal wireless communication systems has been encouraged by the increasingly stringent demands placed upon these systems to provide low-power and highly reliable information transfer. The antenna designer must not only consider the cost, manufacturability, compactness, and system integrability of the radiator but also generate a product which satisfies rigid specifications concerning return loss, bandwidth, and gain while operating in a complex radiating environment. Successful, cost-effective approaches to the design of antennas for communication devices rely upon the implementation of sophisticated analysis tools, such as the finite-difference time-domain (FDTD) method, capable of predicting the electromagnetic behavior of complicated topologies. In this work, the behavior of planar inverted F, monopole, and loop antennas is investigated using tools based upon the FDTD approach. Such factors as the effects of the conducting chassis, plastic casing, and biological tissue on the antenna performance are investigated. Experimental measurements are used to validate the results obtained from computations and to provide further insight into the behavior of the different geometries. The use of antenna diversity to reduce the effects of multipath fading is discussed, and several examples of antenna diversity configurations are provided.     

Construction and Measurement of a 31.3–45 GHz Optimized Spline-profile Horn with Corrugations

A corrugated spline-profile horn has been designed to meet the stringent specifications and constraints of a receiver for Band 1 (31.3–45 GHz) of the Atacama Large Millimeter Array (ALMA). Given the physical restrictions of the receiver, the horn will be located behind a focusing lens placed 191 mm over its aperture. After this first focusing stage, the horn must have a reflection coefficient less than −20 dB and the cross-polarization not exceeding the −30 dB level in the entire frequency range. The side-lobes should be less than −25 dB at all frequencies and its half power beamwidth must be approximately 24° at 31.3 GHz and 16° at 45 GHz. The horn has been constructed using the split-block technique and characterized in a near-field scanner setup. The results show an excellent performance complying with all the requirements.     

Performance of the Production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA)

This paper presents the performance of production Band 3 receivers (84-116 GHz) for the Atacama Large Millimeter Array (ALMA) that operate in Chile at 5000 m altitude. The fabrication, and testing of a total of 73 receivers necessitated stringent quality control during assembly and custom designed automated test set for accurate and reproducible measurement results. Interfaces to the ALMA receiver system are described in details. The average single side band noise temperature of band 3 production receivers is 33.2 K, with a minimum of 24.4 K and a maximum of 45.5 K. As for image rejection, the average is 18 dB, with a minimum at 12 dB and a maximum of 21 dB. Other performances with test methodology are described such as gain variation within the IF band, the gain and phase stability, gain compression, and beam patterns. This paper also describes the interfaces to the ALMA front end system, the testing methodology used, and the test results.     

Influence of antenna configurations on performance of STBC in urban microcells

Based on urban microcell channel measurements, the bit error rate performance of a space-time block code with four transmit antennas using various dual-branch receive antenna configurations, is evaluated. It is demonstrated that with realistic handset antennas, it is possible to achieve performance very close to that of the theoretical uncorrelated Rayleigh case, although proximity of operator tissue (e.g. head) will result in several decibels performance degradation.     

Shaped dielectric lenses for wireless millimeter-wavecommunications

Dielectric-lens antennas are effective at producing highly shaped beams that can enhance the performance of wireless broadband communication systems. Beam shaping is used to reduce multipath interference, which causes fading and decay spread, and to enhance gain, so that the received power level is compatible with the requirements of high-data-rate transmission. This paper presents an overview of the design and measured performance of some examples of dielectric lenses that can be used in typical scenarios of wireless broadband communication systems. The paper also addresses the radio coverage produced by these antennas. The lenses are based on a single basic configuration where the feed is embedded in the lens body. This antenna configuration is flexible enough to accommodate different target beam-shaping specifications     

The First Candelabra for Circularly Polarized Broadcast Antennas

A study of a circularly polarized (CP) television multiple antenna installation shows that improved measurement and theoretical techniques are required to model the scattered horizontal pattern circularity and video response in a candelabra. Previously developed guidelines for horizontally polarized antennas in a candelabra are inadequate to describe the expected performance of CP antennas in the same configuration. Results of calculations and measurements of model CP antennas for a Columbus, Ohio candelabra are included.     

Antenna installed performance using diffraction theory

It is the performance of an antenna when installed in a complete system that is important. In situ measurements and measurements on scale models can be impractical or too costly. Computation of the performance of antennas on aircraft or spacecraft has considerable advantages, and may use the method of moments or diffraction theory. The paper concentrates on discussing the use of diffraction theory to compute the radiation patterns of low-gain antennas installed on conducting structures     

The characterization of a 34-meter beam-waveguide antenna at Kaband (32.0 GHz) and X band (8.4 GHz)

New antennas for the NASA Deep Space Network (DSN) have been built to replace the aging antennas of older designs for deep-space communications. These new antennas incorporate a new dual-shape design as well as a beam waveguide (BWG), which utilize a series of additional secondary mirrors to relocate the focal point into a stationary room below the main reflector. The advantages of using such a design include increased isolation of the feed package from outside environmental factors, such as moisture, wind, and temperature changes; and ease of access to the equipment for maintenance, troubleshooting and repair purposes. This article reports on the performance of a beam waveguide antenna at X-band and Ka-band microwave frequencies. The Ka-band antenna performance experiment (KaAP) antenna-efficiency measurements presented in this article were acquired at the Goldstone DSS-13 research and development (R&D) beam-waveguide antenna between December, 1993, and November, 1995. The measured antenna efficiency and ground-station figure-of-merit (gain divided by operating system noise temperature) as a function of elevation angle and their uncertainties are presented. Also described are the station configuration, the measurement technique, the modeling used in the analysis processing, and the historical evolution of the DSS-13 Ka-band antenna-efficiency measurements as progressive improvements and configuration changes were implemented