Application Notes

Papers

“Fiber Optic RF Distribution (RF)”
[Scott McLaughlin, Jeff Wells, Tim Wurth]

Abstract: The use of fiber optics is considered herein as means to distribute Radio Frequency (RF) signals across Printed Circuit Boards (PCB). The use of fiber optics is studied with an emphasis on reducing inter-board Electromagnetic Interference (EMI). High performance RF circuits are especially sensitive to EMI and other Radio Frequency Interference (RFI), resulting in poor circuit-to-circuit isolation, spurious signals, additional filtering requirements, and increased shielding constraints. Fiber optic cable has the beneficial characteristics of extremely low cross-coupling and is not conductive along its length; this equates to tremendous promise as a means for distributing RF signals with limited EMI/RFI. The innovative concept is applicable to PCBs which have high level of RF signals traversing near multiple sensitive RF circuits.

“L and S Band Tunable Filters Provide Dramatic Improvements in Telemetry Systems”
[Tim Wurth, et al]

Abstract: Meeting the filtering requirements for telemetry transmitters and receivers can be challenging. Telemetry systems use filters to eliminate unwanted spurious or mixing products. The use of tunable microwave filters for both L and S Band can improve filter selectivity and provide low insertion losses in the filter passband. Along with meeting specifications, these microwave filters with the ability to tune an octave, reduce size and cost by the reduction of multiple, fixed-frequency filters. As size, weight and power are often a concern with aeronautical telemetry systems, this paper will demonstrate that microstrip tunable filters can be small in size and use minimal power. Telemetry transmitters are subject to difficult spurious emission and interference specifications and require selective filters to eliminate spurious signals before the final amplification. Telemetry receivers on the other hand are subject to intense Image and Local Oscillator (LO) rejection requirements and demand low insertion loss for front-end filtering. Low insertion loss filtering before the Low Noise Amplifier (LNA) circuit limits degradation to the system noise figure (NF). By using different filter topologies and state-of-the-art, high-Q varactor diodes, tunable microwave filters can be optimized for two different functions. The two functions emphasize either low insertion loss or selectivity. An important design consideration with tunable filters, when compared to typical fixed frequency filters, is the degraded intermodulation performance. This is largely due to the non-linear behavior of the varactor diodes. This paper describes the benefits and limitations of microwave tunable filter architectures suitable for both aeronautical telemetry transmitters and telemetry receivers. Information on the computer modeling of varactor diodes will be covered as a critical part of the design. Potential design considerations for microwave tunable filters will also be covered. Through the use of simulation software and filter prototypes, this paper presents dramatically improved filter performance applicable to telemetry transmitters and receivers.

“Telemetry System Sustainment”
[Mike Trimble, Tim Wurth, et al]

Abstract: Tactical training ranges provide an opportunity for all of the armed forces to assess operational readiness. To perform this task the various training ranges have deployed numerous telemetry systems. The current design efforts in place to upgrade the capabilities and unify the ranges under one telemetry system do not address the training ranges’ need to maintain their training capability with the legacy systems that have been deployed until the new systems are ready. The purpose of this paper is to present two successful system sustainment efforts with different approaches to serve as models for preserving the current level of training range capabilities until the next generation of telemetry systems are deployed. While the two programs illustrated here deal primarily with the transponder components of the systems, these same methods can be applied to the other aspects of legacy telemetry system sustainment efforts.

“A Global Positioning System (GPS) Interference Electronics Support Measure (ESM) Payload System for Unmanned Aerial Vehicles (UAVs)”

[Tim Wurth, Jeff Wells]

Abstract: Modern battlefields depend on GPS for precision navigation and timing. Unfortunately, GPS signals are very-low level and GPS interference, both intentional and unintentional, can severely degrade GPS performance. Unmanned Aerial Vehicles (UAV), which have proven their value on the battlefield, rely heavily on GPS for navigation and flight integrity. Key to continued mission success for UAVs is enhanced anti-jamming capabilities. A revealing test of anti-jamming performance for a UAV is to maintain GPS synchronization, while accurately locating a GPS jammer. A small, modular ESM payload is needed to supply anti-jamming performance for the UAV and secondarily, to use DF techniques to locate the GPS jammer. This paper investigates a small, low-power, low-cost, modular solution to reducing the vulnerability to jamming of UAVs by leveraging commercial off-the-shelf technology. A miniaturized GPS antenna configuration that both lowers susceptibility to GPS jamming, and also allows accurate determination of the GPS jammer’s location, is presented. This GPS antenna arrangement consists of two GPS antenna arrays, one positioned on the top of the UAV (facing skyward) and one positioned on the underside of the UAV (facing the ground). The top antenna array acquires and tracks a minimum of 4 GPS satellites for accurate positioning and timing. The bottom antenna array is used to detect and locate GPS interference, and in coordination with the top array, limits susceptibility to GPS interference. The first action upon detecting GPS interference is to alter the reception pattern of the top GPS antenna array to reduce the amount of interference processed by the GPS receiver. Simultaneously, sampled data from both antenna arrays are used to monitor the effect of the interference and calculate the position of the jammer.

“Employing a Communications Payload on an Unmanned Underwater Vehicle (UUV) for Harbor Monitoring and Homeland Defense”
[Jeff Wells, Mark Manning, Tim Wurth]

Abstract: The Homeland Defense community is increasing its focus on port security and harbor protection. Rising to the challenge, the U.S. Coast Guard is tasked with monitoring and protecting our harbors where commercial container ships enter. Tracking of the onboard containers is of great concern to the protectors of the waterfront. A system capable of identifying the number of containers onboard the vessel, when the containers are added or removed, contents of the containers, etc., will significantly reduce the potential for a security problem by providing essential information to the Coast Guard or other port security so that they can decide whether or not pre-boarding is necessary. That is, boarding the ship and inspecting the cargo while still at a safe distance from the harbor. This paper presents a system that utilizes transmitters embedded on the containers which incorporate unique ID codes identifying the container, its history, and other information. A Communication/Navigation Aid (C/NA) type vehicle/buoy concept, presently being developed by Sippican (under contract to the Office of Naval Research (ONR) as part of the Autonomous Operations – Future Naval Capabilities (AO-FNC) program), positioned at sea, would include a payload of NuWaves’ communication transceivers able to receive the cargo container’s transmitted ID and forward this information by RF link to a ground station. The Port Authority and/or the Coast Guard would then utilize the information to make an assessment of the vessel prior to port entry. Although, this paper illustrates a scenario applicable to the cargo shipping industry, it is also applicable to other homeland defense areas such as unattended open ocean force protection, drug and law enforcement, and environmental monitoring.

“Shielding Effectiveness: Principles and Calculations”
[Jeff Wells]

Abstract: Components and printed circuit boards are dramatically being reduced in size. The smaller size incorporates new design challenges to RF engineers induced from radiating elements located near, and adjacent to, sensitive devices and low noise circuits (i.e. synthesizer PLL and LNA circuitry) Understanding the principles of effective shielding will mitigate the interference and significantly reduce desensitization issues of critical RF circuitry.

“A Survey of COTS Wireless Transceiver Solutions for Unmanned / Unattended Homeland Defense Systems”
[Tim Wurth, Jeff Wells, Mike Trimble]

Abstract: As the war on terrorism continues abroad, the need to maintain security at home remains a major concern. Every aspect of the security effort can benefit from rapid information transfer. Advances in Commercial-Off-the-Shelf (COTS) radios make them valuable in applications ranging from deployed sensors on unsecured borders, to organizing an emergency response team. Additionally, the reduced cost and availability of these transceivers make them a viable alternative to custom developments. As an example, COTS radios can serve as the communication element in Unattended Ground Sensor (UGS) and munitions systems. Other applications include networked sonobuoys and networked RFID tracking. An additional advantage of COTS solutions is that they are available in a small form factor. They have extremely small mechanical outlines and are easily installed in systems requiring miniature designs and light payloads such as man-pack emplaced radios for the Army’s Future Combat System (FCS), as well as missions carried out by Unmanned Aerial Vehicles (UAV). The availability of the COTS radios result in a low-cost alternative for communication links that are applicable to military and Homeland Defense projects. They provide an easily obtainable, low-cost radio alternative enabling quick design cycles to meet mission timeliness. COTS solutions eliminate months from a typical design cycle and have many features already implemented such as ad-hoc routing and encryption. This enables robust hardware to be fielded quickly when a new need arises. The focus of this paper is to identify different COTS modules that can efficiently and cost effectively be applied to these and other various applications.

“A Miniature Disposable Radio (MiDR) for Unattended Ground Sensor Systems (UGSS) and Munitions”
[Jeff Wells, Tim Wurth]

Abstract: Unattended and tactical sensors are used by the U.S. Army’s Future Combat Systems (FCS) and Objective Force Warrior (OFW) to detect and identify enemy targets on the battlefield. The radios being developed as part of the Networked Sensors for the Objective Force (NSOF) are too costly and too large to deploy in missions requiring throw-away hardware. A low-cost miniature radio is required to satisfy the communication needs for unmanned sensor and munitions systems that are deployed in a disposable manner. A low cost miniature disposable communications suite is leveraged using the commercial off-the-shelf market and employing miniature universal frequency conversion architecture. Employing the technology of universal frequency architecture in a commercially available communication unit delivers a robust disposable transceiver that can operate at virtually any frequency. A low-cost RF communication radio has applicability in the commercial, homeland defense, military, and other government markets. Specific uses include perimeter monitoring, infrastructure defense, unattended ground sensors, tactical sensors, and border patrol. This paper describes a low-cost radio architecture to meet the requirements of throw-away radios that can be easily modified or tuned to virtually any operating frequency required for the specific mission.

“Successful Project Management – Being a Member of the Team”
[Jeff Wells]

Abstract: Project Managers are required to pull together personnel to form a team but quite often fail to perform as a team member themselves. Team forming rituals fail at the hand of one individual, the project manager himself. Although schooling, certification, and other educational attributes contribute to the knowledge base of a project manger it does not necessarily breed successful project managers. Triumphant project mangers have inherent skill sets that provide team members with the required corridor for them to be successful and thrive in the project’s environment. This paper looks at what being a true member of the project team represents and the inherent skill sets of victorious project managers.

“Power Amplifier Design: Exploiting Today’s Technology”
[Jeff Wells]

Abstract: Typical VHF/UHF power amplifier designs are limited in operational bandwidth and efficiency. The inefficiency causes an excessive use of costly prime power, which equates to significant heat dissipation, and in turn results in unsatisfactory size and weight form factors. By exploiting present state-of-the-art interrelated technology such as broadband impedance matching, semiconductor properties, amplifier design techniques, etc., a realistic high power RF Amplifier design can be optimized to include both attributes of high efficiency and very broadband capability.

“Power Amplifier Requirements for Next Generation Radios”
[Jeff Wells]

Abstract: The Armed Services is moving to software capable radios, which allow the radio operation to be changed via software. This dramatic increase in flexibility can only be realized if the RF power amplifiers are also flexible. Present power amplifier technology does not satisfy the needs of the evolving military requirements. Specifically, power amplifier designs are limited in operational bandwidth. This equates to numerous fielded amplifiers and unsatisfactory implementation and maintenance requirements. Recent initiatives target innovative wide band and flexible power amplifier techniques to support next generation radios. Innovative techniques are required to develop wide band dynamically controlled power amplifiers that are scalable within the 2MHz to 2GHz spectrum that ultimately increase communications capabilities.

Attenuator Designs

PI Attenuators for RF and Wireless Engineering: PI Attenuator Designs
T Attenuators for RF and Wireless Engineering: T Attenuator Designs

Other RF Design Information

RF Power Conversion Chart: dBm to mW power conversion
Return Loss to VSWR Conversion: VSWR Effects on TX Power

Standard Frequency Designations