global military communications magazine how ka-band has

16 www.globalmilitarycommunications.com | March/April 2021

Global Military Communications Magazine

How Ka-band has become invaluableto the militarySatellite technology has long delivered vital capabilities todefence groups across the world, enabling secure andassured communications between forces at home andabroad. Satcom for military has a long and rich historywith frequent upgrades and advancements, culminatingin unparalleled efficiency.

Heidi Thelander, Vice President of Business Development,Comtech Xicom Technology

The introduction of Ka-band satellite communications(satcom) has changed military satcom forever – andtransformed commercial satcom as well! The changes continueas we transition toward full motion video imagery and real-timesensing data enabling global remote command and control whileproviding full-spectrum battlespace awareness to the warriors.These require massive:

• Data generation by new and innovative sensors;• High speed processing to transform raw sensor data into

critical usable information; and• Very high-capacity, low-latency global communications to

connect warfighters with data, processing and commandnetworks

Satcom plays a vital role in the global communications needsof current and future military structures, and the evolution ofmilitary satcom (milsatcom) is a story of ever-growing needs fordata transmission driving movement to higher frequencies, largerbandwidths, and increased spectral efficiencies. That story isundergirded by advances in technology along the way thatenable it to unfold.

A milsatcom historyMilsatcom has moved up in frequency consistently from L andS-bands through C, X, and Ku-bands to end up in Ka and Q-bands. This rise in frequency comes with an increase in availablespectrum and is driven by the need for higher throughput withsmaller antennas (Figure 1). The costs of moving higher infrequency are time and money to solve new technologychallenges and greater rain fade. But with Ka and Q-bands, themultiple-GHz-wide bands of spectrum allocated are highlyalluring. There is even potential on the horizon to use 5GHz ofuplink spectrum in the in Q/V-band.

For milsatcom, larger spectrum allocations at higherfrequencies are absolutely necessary to handle increasedsensor data transmission. Defense forces worldwide need bothcommercial and military satellites for their milsatcom needs.Special security, resilience, or guaranteed capabilityrequirements drove development of several key milsatcomsystems which are summarized in Figure 2.

Since the mid-1960s, the US military has used X-bandspectrum for Defense Satellite Communications System (DSCS)to provide up to 200Mbps capacity per satellite. This band hasmany constraints, including nearly adjacent transmit and receivebands that force integrators to ensure there are no RF leakageor passive intermodulation products that can wreak havoc inthe receive band. While X-band remains useful, it was notenough. As data transmission needs grew, military forces aroundthe world began relying heavily on commercial Ku-band.Expanding the Ku-band uplink from 500MHz to 750MHz barelymade a dent in the military’s additional needs.

Experimenting with Ka-band - Researchers predicted in the1970s that demand for geosynchronous (GEO) orbital slotswould exceed capacity for C and Ku-band satellites, which have2° separation requirements. As Ku-band orbital slots filled, theUS took steps toward Ka-band by launching the AdvancedCommunications Technology Satellite (ACTS) in 1993. ACTSwas the first high-speed, all-digital communications satellite with

Figure 1. Higher frequency satcom bands provide greater spectrum allocation. Photo courtesy of ComtechXicom Technology

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onboard baseband switching and operated in Ka-band. ACTS,along with Italsat, served a critical role in advancing satcomthrough experimentation with Ka-band RF technologies,propagation effects, and on-board switching. In 1997, a recorddata rate of 520Mbps TCP/IP throughput was achieved betweenlarge ground stations. In 1998, the Naval Research Lab usedACTS to achieve a Navy record 45Mbps uplink data rate for aship at sea using a Xicom TWTA on a one-meter trackingantenna aboard a 45ft yacht. These demonstrations proved high-speed Ka-band transmission capabilities, and they enabled thecommercial satcom industry to accept the technology risk ofbuilding a business at Ka-band. ACTS was decommissioned

after 10 years, but industry followed with new Ka satellitelaunches that now dominate total capacity.

Broadcasting at Ka-band - In 1998, the US Global BroadcastSystem (GBS) began broadcasting critical information to militaryusers globally over Ka payloads on two Ultra High FrequencyFollow-On (UFO) satellites. GBS now also broadcasts over theWideband Global Satcom (WGS) constellation at Ka-band. Over1,000 GBS receive suites deployed worldwide can subscribe tolarge-volume products like full-motion video from unmannedaerial vehicles (UAVs), digital maps, satellite imagery, and more.This critical distribution function couldn’t happen today withoutthe UFO and WGS Ka-band payloads.

Moving up to Q-band - The US identified a need to provide theUS President, Defense Secretary, and armed forces with reliablesatcom for strategic command and control, and the MilitaryStrategic and Tactical Relay (MILSTAR) program was born.MILSTAR incorporated adaptable anti-jam and low probability-of-intercept/detection (LPI/LPD) technologies with nuclearsurvivable designs to provide 2.4kbps peak speeds (Block I),and 1.5Mbps (Block II), for the most strategic commandcommunications. This author’s first project after college at TRWwas simulating and analyzing adaptive antenna-nullingalgorithms for the eventual MILSTAR antenna. When launchedin 1994, MILSTAR became the most sophisticated, secure,robust, protected satcom network in the world, but with 1.5Mbpspeak user data rate, there were limitations.

Advancing Protected Satcom - The US military worked withthe UK, Canada, Australia, and the Netherlands on the nextgeneration protected satcom, the Advanced Extremely HighFrequency (AEHF) satellite system, a joint service systemproviding survivable, global, secure, protected, jam-resistantcommunications for high-priority military assets. AEHF isbackward compatible with MILSTAR, operating at 44GHz uplink/20GHz downlink, but increases peak user data rates to 8.2Mbps.The sixth satellite launched in March 2020, completing globalcoverage from 65°N to 65°S. AEHF added to MILSTAR’s role byincreasing data rates and bandwidth, providing the US and alliesan advanced, highly-resilient protected satcom constellation.

Heidi Thelander, Vice President of BusinessDevelopment, Comtech Xicom Technology

Figure 2. Key Milsatcom systems from 1960s to present. Photo courtesy of Comtech Xicom Technology


19www.globalmilitarycommunications.com | March/April 2021


Military leads the way to Ka - While AEHF created protectedsatcom, military use of commercial Ku-band for bandwidth-hungry surveillance missions around the world was gobblingup capacity. The US began looking at Ka-band for relief. Availableuplink bands of 27.5-30GHz for commercial satcom and 30-31GHz for government/military use were very wide and largelyempty. Proposed high-throughput commercial Ka-band systemswere still experimental, and many weren’t proposing globalcoverage. The US decided on a military Ka-band solution. Useof 30-31GHz uplink and 20.2-21.2GHz downlink allocated forgovernment/military was one of the first real high data rate usesof Ka-band satcom besides direct broadcast.

Gap-filler goes global - The Wideband Gapfiller Satellite (WGS)system, later renamed Wideband Global Satcom system, firstlaunched in 2007, expanding capacity for the US and its allies.WGS was developed as an international network with usersincluding US military services, White House CommunicationsAgency, US State Department, and international partnersAustralia, Canada, Denmark, Luxembourg, New Zealand, theNetherlands, the Czech Republic and Norway. WGS providedX- and Ka-band capacity far beyond any the military had beforewith 2.4-3.6Gbps data transmission rate/satellite. The 1GHz ofspectrum available for military use at K/Ka-band, plus frequencyreuse with Ka spotbeams, yielded massive increases inmilsatcom transmission capacity. WGS-1 provided more capacitythan the entire DSCS constellation.

WGS keeps advancing - WGS Block I (satellites 1-3) provide2.4Gbps peak capacity/satellite and include Ka-band GBSaugmentation, adding new information broadcast capabilitiesand supporting two-way communications over GBS. Block II(4-6) incorporate RF bypass capability for airborne intelligence,surveillance, and reconnaissance (ISR) platforms requiring ultra-high bandwidth. WGS Block II Follow-On (7-10) add limitedprotected services for users with modems having anti-jamcapability. Two more satellites, (11/12), are under developmentwith narrower spotbeams for stronger connections, providingtwice the capability and enhanced security.

The start of commercial Ka-band - Commercial Ka-band’searly start was uneven, as companies launched small Ka-bandpayloads on Ku-band satellites to keep their slots. Severalcompanies began work on large Ka-band satellites for GEO

slots to cover the populated landmasses. Traditional satcom serviceproviders held back until they sawfuture revenue slipping away to upstartcompetitors with high capacity, lowcost/bit, and no legacy customers tosuppor t. Early Nor th Americansuccesses starting in 2005 using the29.5-30.0GHz uplink includedWildBlue’s competitively pricedconsumer internet access andDirecTV’s popular HD programming.These systems and others, likeEutelsat’s KaSat, Avanti’s Hylas, andThaicom’s IPSTAR, were commercialKa-band trailblazers.

The military starts to switch bands- With commercial Ka-band growing,military users became interested inswitching between the government/military band (30-31GHz uplink) andthe adjacent commercial band (29.5-30GHz or 29-30GHz uplink) duringoperations. If you’re on a congestednetwork, switching to another networkis a highly appealing option to military

users. The dual-band terminal must be real-time switchable, meetperformance requirements for both systems, and not grow toolarge, heavy, or costly. Broadband antennas can cover bothbands, and 1GHz-wide modems are available. Dual-bandswitchable frequency converters and broadband solid-statepower amplifiers (SSPAs) that meet gain flatness and linearoutput power across 2GHz are key technologies. Currentbroadband amplifier devices and programmable converter chipsenable design for very compact form factors like 16W WGS linearoutput power with field-commandable band-switching in rugged2kg packages (Figure 3).

GEO HTS widens Ka - Commercial Ka-band’s early years werefollowed by major industry investments in High ThroughputSatellites (HTS) for GEO orbits that push Ka-band on-orbitcapacity into the Tbps. HTS GEO capacity will keep growingthrough 2030, with quadrupling revenues. These HTS systemsuse the full 27.5-30.0GHz uplinks, but with varying frequencyplans such as a single 2.5GHz band with a new broadbandmodem, multiple overlapping 1GHz bands, and asymmetricalplans with varying sub-band bandwidth and spacing. Broadbandantennas and feeds are available that meet performance overthe wider band; the tougher challenge was custom multi-bandswitchable frequency converters for each system while meetingamplifier linearity and tight gain variation over 2.5GHz. Withmilitary users’ desire to add the 30-31GHz uplink, upconvertersmay need to have 4-5 sub-bands with 3.5GHz wide amplifiers.Flexible SSPA/BUC designs with programmable/adjustablebuilding blocks are critical to addressing the myriad frequencyplans. Changing frequency plans in multi-band switchable BUCsmust be simple and fast to meet short development timelines.

Ka-band LEO demands More - Recent industry focus is onnon-GEO systems, including low Earth orbit (LEO) and mediumEarth orbit (MEO) constellations that must launch 10s to 1000sof spacecraft to cover the globe with fast-moving satellitesorbiting much nearer Earth’s surface than GEOs. These LEOsystems cost more to launch and maintain than GEO with shorterlifetimes and many more gateways, but much lower latency. LEOsystems with intersatellite crosslinks (ISLs) have a big advantagein fewer ‘hops’ for low latency and higher network efficiency.They’re also advantaged for aero and marine mobility marketsand produce massive network capacity – 20+ Tbps by 2030.SpaceX’s Starlink, OneWeb, Telesat’s Lightspeed, Amazon’s

Figure 3. Switchable dual-band Ka SSPA/BUC for transportable terminals in2 kg package. Photo courtesy of Comtech Xicom Technology




Kuiper, and SES’s mPower are all proceeding with satelliteprocurement and ground terminal development, each pushingthe limits of possibility for an efficiency/cost edge. Complex,higher-order modulation and coding used to maximize spectralefficiency and drive down system cost/bit demand prettydramatic tightening of RF component requirements includinglower phase noise, phase jitter, error vector magnitude (EVM),and gain variation for SSPA/BUCs (Figure 4), all while radicallydriving down cost with high volume given the large number ofgateways and very large number of users.

Enhancing Ka-band for the military - Surveillance demandshave heightened since the US withdrew fromthe Open Skies Treaty in May 2020. UAVcapabilities continually increase, improvingimagery and monitoring for pre-emptivestrikes, surveillance, and remote real-timedecision-making. Defense departments andcontractors worldwide are investing heavily inISR capability, which just keeps driving uphigh-speed satcom requirements. The USNavy is outfitting the P-8A Poseidonsurveillance aircraft with high-speed satcomto support enhanced surveillance. AirborneISR platforms are looking beyond X-band, Ku-band, and standard Ka-band (27.5-31GHz) atalternative Ka-band spectrum to add capacityand enhance security. Non-standard Ka-bandfrequencies will require new terminal designs.New RF chipsets and output combiningstructures are needed for the amplifiers.Efficiency improvements are critical to enablethese higher data rates for extendedunmanned flights. Power amplifiers must bemore efficient and located very close to theantenna to minimize RF losses. Split boxdesigns, with the power amplifier mounted onthe antenna and multi-band block upconverterlocated elsewhere, reduce required SSPA

Figure 4. LEO Ka systems need SSPA/BUCs with better Phase Noise, Jitter and EVM performance to meetSpectral Efficiency Goals. Photo courtesy of Comtech Xicom Technology

linear output power, but demand operation in challenging cabin-external environments (Figure 5).

The impact of Ka-band satcom is accelerating, and militarysatcom users will benefit from both technology advances andnew system architectures coming online now and over the nextfew years. A lot of new capacity built at much lower cost/bit canbe applied to transmission of critical military communications ifgovernments can figure out how to work with commercialenterprises that build and operate these systems. Today’sgovernment/military users must seek flexibility and adaptabilityin networks and user terminals along with the performance andprotection they have always demanded.

Figure 5. Multiple-band Enhanced Ka SSPA/BUC for ISR platform is split toincrease EIRP and efficiency. Photo courtesy of Comtech Xicom Technology

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global military communications magazine how ka-band has

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