National defense has taken on new meaning in a terrorist- filled world. The United States Department of Homeland Security (DHS), tasked with that defense, must be alert to a wide range of threats, from biological to vehicular. RF and microwave technologies play a major part in their efforts, representing tools as well as threats. In the hands of terrorists, even the most seemingly benign RF device, such as a cell phone, can be deadly.

The market for high-frequency electronics in DHS-related applications is growing rapidly, as tracked by such organizations as Homeland Security Research, which researches and reports on different segments of the homeland security market. For example, the firm's "Global Counter IEDMarkets and Technologies Forecast2008- 2112" looks at an aggregate market approaching $30 billion worldwide for defense against improvised explosive devices (IEDs). Counter-IED equipment includes a wide range of RF/microwave devices, from amplifiers to frequency synthesizers. Although IEDs are largely a component of overseas battlegrounds, the DHS concern is that these devices may become more prevalent on domestic soil.

Countering an IED involves the use of RF technology: for detection and firing prevention. Ground-penetrating radar (GPR) systems are typically used for detection, using one or more antennas to transmit pulses into the ground and receive the radar returns, processing the returns for information on different items buried in the ground, such as land mines or IEDs. The list of companies supplying systems or components for GPRs is long, and includes Aeroflex, BAE Systems, 3D-Radar, NIITEK, Inc., and Thales.

Last year, NIITEK, for example, launched its VISOR MINI-HMDS system, an ultrawideband (UWB) vehicleintegrated GPR based on the Husky- Mounted Detection System (HMDS). It is designed for transport on a light patrol vehicle and, with robot and detection equipment, is about one-tenth the size of a full-sized HMDS system.

Since some of these IEDs are triggered remotely by RF transmitters, including cellular telephones, various manufacturers have developed different types of jammers to disrupt the link between the transmitter and the bomb. Manufacturers such as Security Intelligence Technologies and directory listings such as Armed Forces International can provide information on different types of RF jammers.

Cellular jammers are typically used in prisons or government installations to prevent unauthorized communications. The MS2POR series of RF jammers from Security Intelligence Technologies, for example, is directional, with controlled RF transmit levels. Bomb Jammer offers its VIP 200 Bomb Jammer IED jammer in a briefcase. Designed to block receivers at cellular and satellitetelephone frequencies, it can prevent a remote-controlled IED (RCIED) from receiving a detonation signal.

Of course, for any jammer to be effective, it must be activated, and this usually requires the concurrent use of a detection system to locate a signal of interest (to be jammed). Netline Communications Technologies, for example, has developed a system called CellTrack comprised of multiple sensitive cellular telephone detectors connected to a central computer running the firm's software. Each cellular phone detector is a small covert device that can detect a variety of cellular standards simultaneously.

But DHS concerns are far greater than countering IEDs. The organization was initially tasked with ensuring the interoperability of communications during domestic disasters, such as a terrorist attack, as well as establishing a "virtual fence" around any entry points into the country. DHS communications solutions are following the trend of tactical military radios, with an increasing use of software-defined-radio (SDR) architectures for programmable interoperability between different frequency bands and modulation formats. One of the leading tactical/public-safety radio suppliers, Harris Corp., supports federal, state, and local agencies with its SDR-based Unity XG-100 multiband radio. The handheld radio provides digital APCO P25 secure and analog FM communications across VHF, UHF, 700-MHz, and 800-MHz public safety bands. It also integrates a Global Positioning System (GPS) receiver for position information.

For first responders and other public-safety applications, Motorola, offers the APX 7000 Multi-Band Portable Radio. The hand-held radio is based on the firm's fourth-generation Project 25 (P25) standards- based-communications-network technology and can operate in any two of the following bands: 700/800 MHz, VHF, and UHF Range 1. ITT's Aerospace/Communications Division has developed its RF Blade as a complete wireless network for first responders and border patrols. The hybrid wireless system can operate with little or no infrastructure.

With the increasing use of drones and unmanned aerial vehicles (UAVs) in DHS applications, such as surveillance and border patrol, communications to and from the drone becomes critical. AValon RF is one of many companies supplying lightweight transmitters and receivers for secure UAV communications from 390 MHz to 2.7 GHz. The firm employs coded-orthogonal frequency-division multiplex (OFDM) technology for robust digital video/data transmission in hostile environments. The company's wireless links provide a range to 40 miles in airborne applications.

Numerous DHS applications involve millimeter-wave signals. Terahertz frequencies from 0.1 to 10 THz are of interest for DHS applications because of their capability of detecting the particular rotational signatures of gas-phase molecules. For example, Argonne National Laboratories has devoted much effort to the detection of chemicals, gases, and radiation by means of millimeter-wave radar. Its system, based on a backward-wave oscillator (BWO), has successfully detected 12 PPM methyl chloride at 60 m. The system has also been used to detect different types of explosives as well as propane tank leaks at a distance of 720 m.