888 IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 50, NO. 3, MARCH 2002 HF, VHF, and UHF Systems and Technology Frederick H. Raab, Senior Member, IEEE, Robert Caverly, Senior Member, IEEE, Richard Campbell, Member, IEEE, Murat Eron, Member, IEEE, James B. Hecht, Senior Member, IEEE, Arturo Mediano, Member, IEEE, Daniel P. Myer, Member, IEEE, and John L. B. Walker, Senior Member, IEEE Invited Paper Abstract—A wide variety of unique systems and components inhabits the HF, VHF, and UHF bands. Many communication systems (ionospheric, meteor-burst, and troposcatter) provide be- yond-line-of-sight coverage and operate independently of external infrastructure. Broadcasting and over-the-horizon radar also operate in these bands. Magnetic-resonance imaging uses HF/VHF signals to see the interior of a human body, and RF heating is used in a variety of medical and industrial applications. Receivers typically employ a mix of analog and digital-signal-processing techniques. Systems for these frequencies make use of RF-power MOSFETs, p-i-n diodes, and ferrite-loaded transmission-line transformers. Index Terms—Broadcasting, communication, HF, high fre- quency, ionosphere, magnetic-resonance imaging, meteor burst, MOSFET, p-i-n diode, radar, receiver, RF heating, transmis- sion-line transformer, troposphere, UHF, ultra-high frequency, VHF, very high frequency. I. INTRODUCTION I N THE early days of wireless, it was generally accepted that lower frequencies were better for long-range communica- tion, and this principle was indeed true for ground-wave prop- agation. Radio amateurs were thus relegated to the “useless” wavebands of “200 meters and down” (1.5 MHz and above). The amateurs, however, soon (late 1921) discovered the capabil- ities of high frequencies (HFs) (2–30 MHz) for long-range com- munication via the ionosphere using only modest transmitters and antennas. Communication at VHF (30–300 MHz) and UHF (300 MHz–1 GHz) was originally thought to be limited to line of sight (LOS) distances. Circa World War II, however,a number of scattering modes (e.g., meteor, troposphere) were discovered that could reliably provide beyond-LOS (BLOS) communica- Manuscript received July 16, 2001. F. H. Raab is with Green Mountain Radio Research (GMRR), Colchester, VT 05446 USA. R. Caverly is with the Department of Electrical and Computer Engineering, Villanova University, Villanova, PA 19085-1478 USA. R. Campbell is with TriQuint Semiconductor, Hillsboro, OR 97124-5300 USA. M. Eron is with Ericsson Amplifier Technologies, Hauppauge, NY 11788-3935 USA. J. B. Hecht is with the Cedar Rapids Design Center, RF Micro Devices, Cedar Rapids, MI 52498-0001 USA. A. Mediano is with OMB Sistemas Electronicos, Universidad de Zaragoza, Zaragoza E-50015, Spain. D. P. Myer is with Communication Power, Brentwood, NY 11717-1265 USA. J. L. B. Walker is with Semelab plc, Lutterworth, Leics. LE17 4JB, U.K. Publisher Item Identifier S 0018-9480(02)01969-5. tion. Today, a variety of LOS and BLOS communication and radar systems operate at HF/VHF/UHF. At HF/VHF/UHF, the effects of line length and component layout are significant design issues. However, the wavelengths remain large enough that lumped elements are generally pre- ferred to or used in conjunction with transmission lines for fil- tering and matching. The needs for high power and large band- widths favor the use of components such as RF-power MOS- FETs, p-i-n diodes with large time constants, and ferrite-loaded transmission-line transformers. II. HF COMMUNICATION HFs (2–30 MHz) offer long-range and even worldwide com- munication via the ionosphere. Since HF systems require only modest transmitters and antennas, and do not require external infrastructure, HF links can be easily established from remote locations, or following a natural disaster. Terminals are often connected to the local PSTN or Internet to allow remote access. HF is widely used for voice and data communication by military, diplomatic, aeronautical, marine, and amateur-radio services. However, the variable and dispersive nature of the ionosphere imposes some unique requirements on both hardware and com- munication protocols. A. HF Communication Systems The transmitting station consists of a transmitter, matching network, and antenna. The receiving station includes an antenna, matching network or active preamplifier, and re- ceiver. Most HF equipment is operable over all or most of the 2–30-MHz range, and each group of users is typically assigned a number of frequencies or bands. HF systems employ a wide variety of transmitting antennas [1]. Low-angle radiation is needed for long-range communi- cation, while high-angle radiation is needed for shorter range “near-vertical-incidence-skywave” (NVIS) communication. It is not necessary to match the polarizations of the transmitting and receiving antennas because the ionosphere generally pro- duces elliptical polarization. Low-angle directional transmission is usually accomplished by a mechanically rotated “beam” such as a Yagi (specific fre- quency) or log-periodic dipole array (band of frequencies). The gains are typically in the range of 3–10 dB. Low-angle om- nidirectional transmissions typically use monopoles. Conical 0018–9480/02$17.00 © 2002 IEEE