Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
Issue link: https://electronicsmilitarydefense.epubxp.com/i/78772
Technology Embedded Antennas For Tactical Military Applications While today's military radios are highly adapted to the battlefield environment, they have not kept pace with consumer wireless in one key area — antenna design. by James O'Keeffe, Ph.D., P.E. oday's military radios are challenged to keep pace with the rapidly evolving world of con- sumer wireless technology — to meet users' increasing demand for higher bandwidth. The battlefield is becoming a more information-rich envi- ronment, with increased emphasis on multiplatform radio communication between soldiers, unmanned aerial vehicles (UAVs), satel- lites, and command centers. Information goes far beyond voice communications to now include imagery, video to the front lines, data, and even Internet access. In recent years, programs such as Advanced Wireless Networks for the Soldier (AWNS) and the Joint Battle Command-Platform (JBC-P) handheld have aimed to equip soldiers with high- er-bandwidth, smartphone-like capabili- ties. One challenge these programs face in providing higher bandwidth to mili- tary radios is, in most cases, the absence of a network of base stations, coupled with environments ranging from deserts to cluttered urban environments. To adapt to this range of operating conditions, software-defined military radios employ multiple radio waveforms, frequency hopping, and transmit powers in the range of 50 W. While today's military radios are highly adapted to the battlefield environment, one element that has not kept pace with consumer wireless is antenna design. Soldier- or vehicle-mounted radios often use waveform-specific narrowband monopole and dipole antennas. The observ- ability of the antenna presents a challenge. Not only do the antennas reveal the presence of a radio, they can also give clues to the communications ability of the radio. The other obvious disadvantage is the need to carry multiple antennas and change them as needed. T The Rise Of Embedded Antennas Until the early 2000s, cell phones used external quarter- wave monopole and helical antennas, similar to many of 14 Electronic Military & Defense ■ www.vertmarkets.com/electronics Figure 1: Embedded antennas, already well advanced in consumer handsets, are poised for widespread deployment in military radios (photo courtesy of TE Connectivity). today's military radios. Because the antennas protruded beyond the main profile of the phone's case, they were prone to damage and were ergonomically inconvenient. Even short, stubby antennas snagged easily on clothing and detracted from the convenience of a compact hand- held device. Whip antennas were narrowband with iso- tropic radiation patterns and poor per- formance compared to today's devices. By comparison, the antennas in today's laptops, tablets, and smartphones are vir- tually invisible. The latest generations of phones have embedded antennas for mul- tiple uses, including 3G, 4G, GPS, Wi-Fi, Bluetooth, and near field communication (NFC). Initially, embedded antennas strug- gled to offer similar antenna efficiency to monopole antennas. However, through innovative designs — such as meandered lines — the latest embedded antennas offer efficiency greater than 50%, even at lower frequency bands such as LTE in the 698 to 787 MHz range. The improvement is exemplified by the ability of newer phones to operate in elevators and crowded multipath urban environments. Molded Interconnect Devices (MIDs) Antennas can now be integrated directly onto radio enclo- sures using a process called molded interconnect device (MID) technology. In its most basic form, MID technology integrates functionality into molded parts using selective metal plating. This technology is most often used in three basic ways: 1) to reduce part counts in electromechanical assemblies by integrating electrical functionality, 2) to replace wiring, and 3) to embed antennas. Techniques used to manu- facture MID parts include two-shot molding and laser direct structuring (LDS). The two-shot molding process employs two distinct thermoplastic polymers and an electroless plating process. In order to achieve the selectivity during plating, a catalyst- doped "plateable" resin is molded in conjunction with a