Antenna Systems & Technology - Fall 2013 - (Page 16)

FEATURE ARTICLE Millimeter Wave Antenna Radome Systems for Satellite on the Move Applications By D.J. Kozakoff, Consultant and Chief Scientist - USDigiComm Corp. Spectrum crowding and the desire for ever increasing data rates are encouraging migration to higher millimeter wave (MMW) SATCOM frequency bands. Ka band SATCOM offers 24 times the bandwidth of C band systems or eight times the bandwidth of Ku band SATCOM [1]. In addition, SATCOM is the ideal technology to provide reliable beyond-line-of-sight (LOS) communications to platforms on the move. Supporting continuous broadband satellite on the move (SOTM) connectivity presents significant challenges including the need to compensate for shifting transmission paths and the use of high-performance high gain (small beamwidth) antennas, which must always be pointed toward the satellite. Many in the industry conclude that Ka-band capacity is a superior evolution of Ku-band capacity. For millimeter wave (MMW) SOTM applications, the design engineer encounters new challenges in achieving suitable antenna and antenna radome hardware not encountered in lower frequency SATCOM system design. MMW encompasses the frequency spectrum above 30 GHz and is sometimes called the extremely high frequency (EHF) wherein the wavelength (λ) is in the 1 mm to 10 mm range. Although in the MMW the atmospheric propagation (gaseous absorption) losses are greater than encountered than in the microwave, operation within the so-called atmospheric windows minimizes these losses. The Ka band SATCOM frequencies of interest meet these criteria. For the same antenna beamwidth (or gain) a MMW antenna is much smaller than its microwave counterpart. This allows a higher gain (smaller beamwidth) antenna to be used on the satellite. Figure 1. SATCOM on Hummer Vehicle The availability of increasing numbers of higher performance lower cost components permits one to innovate MMW communication transmitters and receivers which is also driving the long term migration of SATCOM to these higher frequencies where exceedingly large bandwidths are available [2]. A significant number of both commercial and military applications have emerged that employ Ka band SATCOM on platforms on the move. For instance, one commercial application is for Aeronautical Mobile SATCOM (SATCOM on aircraft), and one military application is for Communications on the Move (COTM), i.e. SATCOM on military vehicles. SOTM antennas currently available for SOTM may constitute the weak components of the system since they have to constantly track the satellite and compensate for the motion of the platform. On commercial boats, for instance, a specialized roll and pitch stabilized antenna pointing gimbal must be used to take out the effects of a ship’s motion. Phased arrays would benefit SOTM because the antenna beam could be steered rapidly to minimize antenna pointing-error. Alternatively, a multibeam phased array could be configured to operate in a monopulse mode for auto track capability. MMW Antenna Radome Considerations SATCOM radomes must provide simultaneous transparency at uplink and downlink frequency bands, which presents a difficulty to the radome designer when the uplink and downlink frequency bands are widely spaced apart in the frequency domain and are not a simple multiple of each other. To illustrate, for commercial Ku band operation (14 GHz uplink and 12 GHz downlink) the difference 16 Antenna Systems & Technology Fall 2013 www.AntennasOnline.com http://www.AntennasOnline.com

Table of Contents for the Digital Edition of Antenna Systems & Technology - Fall 2013

Editor’s Choice
Exponential M2M Market Growth Calls for Innovative RF and Antenna Solutions
Managing Distributed Antenna Systems Effectively and Efficiently
Millimeter Wave Antenna Radome Systems for Satellite on the Move Applications
Antennas
Components/Subsystems
Software/System Design
Test & Measurement
Antenna Systems 2013: Conference Preview
Marketplace
Industry News
Addressing Customer Requirements in Public Safety Antennas

Antenna Systems & Technology - Fall 2013