This paper summarizes the results of recent monolithic millimeter-wave circuits (MMICs) developed at TRW using the most advanced MMIC technologies, including GaAs-based power high electron mobility transistor (HEMT) on 2-mil thick substrate, InP-based HEMT and hetero-junction bipolar transistor (HBT) MMICs. For power applications, the 2-mil GaAs MMIC power amplifiers (PAs) demonstrated state-of-the-art output power performance at Ka- (35 GHz) and W-band (94 GHz). For InP HEMT MMIC, a 155-GHz low noise amplifier (LNA) was demonstrated, while for InP HBT MMIC, a 94-GHz fundamental mode voltage controlled oscillator (VCO) exhibited output signal at 94.7 GHz. The 155-GHz LNA and 94-GHz VCO are the highest frequency three-terminal device amplifier and bipolar device fundamental-mode oscillator ever built, respectively. Moreover, the HEMT and HBT devices have been successfully integrated on the same InP substrate and a 24-GHz frequency source consisting an HBT VCO and a HEMT buffer amplifier as well as an HBT-regulated 94-GHz HEMT LNA on a single chip using selective epitaxy technique was demonstrated. These results represent state-of-the-art development status of MMICs and the technologies can be greatly beneficial to the next generation millimeter-wave (MMW) wireless communication systems.

Broadband wireless millimeter wavelength services provided from a high altitude long operation (HALO^TM) aircraft are now feasible. Our talk emphasizes the conceptual design of a 'bandwidth-on-demand' wireless network whose data rates to and from the subscriber will measure in the multi-megabit per second range. A variety of metropolitan area spectrum bands offer the needed bandwidth. An attractive choice is the LMDS band near 28 GHz and system characteristics at this frequency are described. The HALO^TM Aircraft fuselage will house packet switching circuitry and fast digital network functions. The communications antenna and related components will be located in a pod suspended below the aircraft fuselage. To offer 'ubiquitous' service throughout a large region, the HALO^TM antenna will utilize multiple beams arranged in a typical cellular pattern. Broadband channels to subscribers in adjacent cells will be separated in frequency. As the beams traverse over a user location, the virtual path through the packet switch will be changed to perform a beam-to-beam handoff. Overviews of the system architecture and the network elements are presented along with descriptions of the frequency plan and equipment. The utilization of components under development for terrestrial LMDS products is described.

Radio wave attenuation for space vehicles during atmospheric re-entry is discussed. Attenuation as a function of frequency and altitude are shown. Attractive millimeterwave regions are discussed. An equation for attenuation during re-entry is listed.

Millimeter wave communications systems experience variation in propagation due to rain and other causes. This paper describes a 7.25 km experimental link at 28 GHz in Dallas, Texas used for studying propagation effects. Received signal data was collected at 30 second intervals over a five month period. The data shows the effects of clear air variation and rain fade loss. Weather data including rain rate was also collected at 1 minute intervals at the transmit and receive sites. During the observation period, rain rates greater than 38 mm/hr and fades greater than 44 dB occurred less than 0.01% of the time. During rain fades, the received signal varied at a maximum rate of 0.3 dB/sec. Rain fades of 20 dB or less extended for duration of 40 minutes. During clear days, signal variations of up to 7 dB occurred including enhancement and attenuation. The standard deviation of clear air fading was about 1 dB.

Channelized receivers are useful in communications systems that use frequency division multiplexing, and in wideband radar and electronic warfare receivers. In present wideband communications equipment, the channelization function is done typically with discrete elements such as mixers and surface acoustic wave (SAW) bandpass filters on a single channel basis. Recently much activity has been directed to using digital techniques and devices to make smaller, cheaper receivers. Following this trend, this paper exploits the 'Timeline' 0.18 micron CMOS technology recently announced by Texas Instruments and show the bandwidths, levels of system integration, and package sizes that become possible with the Timeline technology. The design example shown is a digital channelizer for a system with 150 MHz total bandwidth including 60 channels on 2.5 MHz channel centers. A polyphase filter bank algorithm with 6x oversampling compared to the channel spacing is used. The design is suitable for a burst communication receiver. With the Timeline technology, an ASIC that implements two maximally decimated filter banks at the above bandwidths is shown. The ASIC fits onto a 20 mm by 20 mm die and consumes about 7 watts. Three such ASICs are then needed to implement the complete 6x oversampled filter bank, which will output 60 complex channels at 15 MSPS for about 20 watts.

Angel Technologies Corporation ('Angel') and its partners are creating a wireless broadband metropolitan area network to interconnect tens to hundreds of thousands of users each at multi-megabit per second data rates for multi-media file transfers and interactive discourse. A high altitude long operation (HALO^TM) aircraft will circle above commercial airline traffic to serve as the hub of the broadband network for providing ubiquitous signal coverage and dedicated point- to-point connections throughout a footprint encompassing a typical metropolitan center, its suburbs, and beyond. Broadband wireless services will be delivered to diverse enterprises to promote new forms of collaborative work and information exchange, thus creating a virtual 'Cone of Commerce^TM' with the HALO^TM aircraft at its apex. This presentation introduces the HALO^TM Network and describes the flow of messages within and beyond the signal footprint in terms of the basic network elements. The aircraft design is described and its payload attributes are highlighted. The concept of operations and key operational factors are addressed. Types of services are described. The advantages of the HALO^TM Network relative to terrestrial and space layers are summarized for broadband services. Near term actions are stated.

In this paper we summarize the effects of modulation and channel coding on the design of wide angle scan, broadband, phased array antennas. In the paper we perform several trade studies. First, we investigate the amplifier back-off requirement as a function of variability of modulation envelope. Specifically, we contrast constant and non-constant envelope modulations, as well as single and multiple carrier schemes. Additionally, we address the issues and concerns of using pulse shaping filters with the above modulation types. Second, we quantify the effects of beam steering on the quality of data recovery using selected modulation techniques. In particular, we show that the frequency response of the array introduces intersymbol interference for broadband signals and that the mode of operation for the beam steering controller may introduce additional burst or random errors. Finally, we show that the encoder/modulator design must be performed in conjunction with the phased array antenna design.

The theoretical analysis and designing results of bandpass millimeter wave band filters based on partially filled waveguide-dielectric resonators are presented. Both narrow- and wide-band filters with a widened region of suppression up to a doubled working frequency and higher, with low losses in the limits of a maximally flat characteristic (0.2 - 0.5 dB), have been designed. The computer modeling results are in good agreement with the experimental data.

AstroTerra's TerraLink^TM 8-155 laser communications equipment is designed for a clear weather range of 8 km and a data rate of 230 Mb/s, and TerraLink 4-155 is designed for a 2 km range. The TerraLink equipment achieves a reduction in scintillation-induced intensity fluctuations by using large receive apertures and multiple transmit apertures. We present measurements of received intensity fluctuations at different ranges through 4 inch and 8 inch receive apertures. We also present link margin data, with its implications for use of lasercom equipment in various weather conditions. Scintillation measurements were made while a communications link was operating by placing a second receive telescope with a PIN photodiode next to one of the lasercom transceivers. By plotting the probability of intensity vs. intensity, the necessary link margin to achieve a desired burst error rate can be calculated. At the longest ranges, the TerraLink equipment requires a scintillation fade margin of about 10 dB to achieve a 10^-9 bit error rate. The equipment is designed with an additional margin of 4 - 5 dB for atmospheric attenuation.

Never before has the opportunity for terrestrial optical wireless communications links been so great. The high data rates attainable, up to OC-24, make it a very attractive and cost effective alternative to traditional fiber optic and microwave links. With today's demand for interactive multimedia-based applications, such as video conferencing and telemedicine, optical wireless products are the only ones that can provide the needed bandwidth in situations when it is too costly or impossible to install fiber optic cable. Recent developments in laser and optics technologies, in addition to auto beam tracking, permit transmission units to achieve excellent performance rates in all weather conditions.

We describe four measurement techniques to characterize the performance of an optical wireless channel. The characteristics of each technique are illustrated through experimental measurements. These four techniques include: (1) bit-error rate measurements, (2) measurements of the mean and variance of the received optical power from which the bit- error rate can be estimated, (3) measurements of the fade rate and fade duration histograms of the optical carrier, (4) measurements of the intensity and phase distributions of atmospheric propagated laser beams using a Shack-Hartmann wavefront sensor.

Lasers provide a means for transmitting larger quantities of data at higher rates than conventional radio frequency devices and can be utilized during radio silent operations on the battle field. A forward scout needs to be able to observe the positions of various targets and relay that information back to a tactical operations command center in a covert manner. The BiCom device built by Trex Communications provides laser ranging, azimuth and elevation angle to a target, GPS position information, data storage and transmit capability, and full duplex audio transmission capability, all in a 3 kg hand held package. The communication channel utilizes an eye safe lasercom transceiver for covert voice or data transfer at 100 kbps at distances of up to 5 km. The information gathered electronically by the unit is sufficient to calculate the actual GPS positions or military grid coordinates of the observed targets. Several dozen targets can be stored in memory for later transmission via lasercom. Field tests were conducted by US Army personnel to evaluate these units and compare the results with conventional means of target position determination and data transfer. A description of the system and results of these tests are presented.

The simulation and realization of a miniaturized optical terminal with direct acquisition, direct and homodyne tracking modes and homodyne data transmission are presented. The miniaturized receiver head and the frontend electronics, with its sophisticated signal processing capabilities, combine the tasks of partner-terminal acquisition, direct tracking, homodyne tracking and homodyne data detection. Various pointing, acquisition and tracking (PAT) strategies have been experimentally verified in an optical free space test-bed. A complex link-simulation was developed enabling performance evaluation of the receiver head. Simulation results for direct spatial acquisition and pseudo 4-quadrant tracking are shown. Our technique eliminates the need for additional acquisition hardware like beacon laser and CCD camera.

Laser and LED-based wireless communication systems provide license-free interconnection for voice, data. And video transport with high bandwidth and high data rate capabilities. These systems allow for the immediate, reliable and low-cost extension of copper and fiber-based networks to any end user, providing efficient bypass access to high data rate backbone networks and interconnection among voice and data network components operating at speeds ranging from T-1 voice to full throughput ATM at 155 Mbps. The wireless optical beams constitute a 'Virtual Fiber^TM' in the air, providing the capabilities of fiber in situations where wired connectivity is unavailable, impractical, expensive or slow-to-implement, while achieving a combination of cost, bandwidth, speed and reliability that cannot be matched by microwave, spread spectrum or other competing wireless technologies. The use of optical beams in the air eliminates the rf bottleneck by providing bypass access and building-to-building links with transport connectivity at and above 155 Mbps. Future generations are already under development which will accommodate emerging technologies including gigabit ethernet. This paper addresses the following issues: (1) Trade-offs between rf and optical wireless technologies and products. (2) The effects of weather and the achievement of all-weather operations to distances of 1 km. (3) The achievement of reliable operations with examples and case studies.

A maximal-ratio angle-diversity receiver is composed of multiple sectors with relatively small field-of-views. Each sector estimates the signal-to-noise ratio (SNR) of the collected signal and its gain made proportional to the relation i/(sigma) ², where i and (sigma) represent the average signal and the shot noise root mean square (rms) values, respectively. The output signals of all sectors are then combined through an adder circuit. This paper presents the design and implementation of a maximal-ratio receiver using discrete components. A major challenge is the design of the variable gain amplifier (VGA) which requires a large dynamic range because of the large fluctuations of both signal and noise in a typical office room environment. This problem was overcome through the utilization of a cascade of two VGAs where the assignment of gains to each VGA minimizes dynamic range requirements through an innovative topology. The first one provides a gain inversely proportional to the rms shot noise and the second one a gain proportional to the SNR referred to the input of the front-end. Measurements on an implemented prototype show results close to the ideal gain of a maximal-ratio receiver making the proposed techniques suitable for maximal-ratio angle-diversity receivers.

Emerging wireless telecommunication systems, including the terrestrial LMDS (Local Multipoint Distribution System) and next-generation communication satellite systems (e.g., Spaceway^SM, et al.) are driven by economics to require a burst-transmission protocol for their return links (i.e., subscriber-to-hub or subscriber-to-satellite links). Limited spectral bandwidth to support these return links demands that they achieve high spectrum efficiency, measured in terms of bps/Hz (bits-per-second-per-Hertz). High-order modulations offer practical spectrum-efficient solutions for continuous links, but technical difficulties associated with phase- coherent demodulation of high-order burst signals have previously precluded these modulations as a viable option. In fact, state-of-art burst signal demodulation is currently limited to differentially-detected QPSK (DQPSK). Although so- called block-coherent demodulators generate acceptable symbol- error rates, they introduce such strong symbol-to symbol correlation as to preclude efficient soft-decision decoding. In summary, new wireless links demand burst modems with bandwidth-efficiency and power-efficiency superior to currently available technology. SiCOM research has developed a practical burst demodulator compatible with both high-order modulations and soft-decision maximum-likelihood decoding. This paper describes the capabilities and characterizes the performance of this revolutionary demodulator. In particular, detailed performance comparisons are provided between the current state-of-art burst demodulator/decoder, using DQPSK and Reed-Solomon FEC (forward error correction), and SiCOM's new burst demodulator using 8PSK with concatenated TCM (trellis-coded modulation) and Reed-Solomon FEC. For ATM (asynchronous transfer mode) cell transfer, with identical link constraints, (i.e., signal-to-noise ratio, bandwidth, and bit-error rate), the new modem supports fully 25% higher information transfer rates. For message traffic with less- critical latency constraints, message-specific interleaving easily provides orders-of-magnitude improvement in data quality over the DQPSK/RS approach, with identical bandwidth and SNR (signal-to-noise ratio).

Wideband digital data transmissions supporting the 51.82 Mbps (STS-3), 155.52 Mbps (STS-3) and higher data transmission formats are contemplated for future terrestrial point-to-point and point-to multipoint microwave systems as exemplified by the MMDS, LMCS/LMDS and MVDS services, as well as for satellite systems. The traditional approach of using QPSK modulation with powerful error correcting codes will face a significant challenge in overcoming the technical difficulty of supporting the clock/symbol rates required at these data rates using cost effective CMOS processes, the wide bandwidth required for these data rates using QPSK. SiCOM has developed an ASIC chip set, that, in addition to shaped QPSK, will support 8-PSK and 16-QAM modulation formats on in-phase and quadrature channels with transmission rates to 155.52 Mbps (STS-3).