Ka-band GaN Power Amplifier Delivers 5.5 W for SATCOM Terminals
Small low- and medium-earth orbit (LEO and MEO) satellites are getting considerable, well-deserved attention, but their complementary and lower-profile ground stations also merit design consideration. Addressing this arena, CML Microcircuits Ltd. (UK) introduced the CMX90A705, a Ka-band power amplifier (PA) that’s a cost-effective building block for commercial high-volume satellite-communication (SATCOM) terminals (Fig. 1).
The CMX90A705 is a two-stage gallium-nitride-on-silicon carbide (GaN-on-SiC) linear PA that delivers +37.4 dBm (5.5 W) of saturated power over a frequency range of 27.5 to 31 GHz, with 16.5 dB of small signal gain. It can be used as both a driver and as the final stage of power amplification in satcom terminals.
Adjacent channel power ratio (ACPR) is better than −28 dBc @ 30 dBm (average), while power-added efficiency (PAE) is 22% at saturated power. The dual-side biasing eases layout issues; DC bias is 100 mA at +27.5 V for this nominal 28-V DC device. The PA’s RF input and output ports include integrated DC-blocking capacitors and are nominally matched to 50 Ω to simplify design-in.
Rugged Power-Amplifier Eval Board
The detailed 16-page datasheet has over 40 figures characterizing many critical aspects of performance and capabilities versus relevant parameters. In addition, it details the 26- × 50-mm EV90A705 evaluation board with a schematic, bill of materials (BOM), and layout (Fig. 2). The evaluation board also includes drain and gate-feed decoupling capacitors suitable for QPSK-type modulation.
Don’t even think of using the standard “workhorse” FR4 PCB laminate for this evaluation board. The EV90A705 PCB uses a single layer of Isola I-TERA MT40, 8-mil thickness with ½-oz copper, mounted to an aluminum carrier (via a thermal compound), which provides rigidity and thermal dissipation (Fig. 3).
Note that the I-Tera MT40 features a dielectric constant (Dk) that’s stable between −55 and +125°C up to W-band frequencies. It also offers a lower dissipation factor (Df) of 0.0031 compared to PTFE and other commercial microwave and high-speed laminate materials.
The CMX90A705 comes in small-form-factor, 4- × 4-mm, thermally enhanced, air-cavity quad flat no-lead (QFN) packaging and is available now.
Reference
“I-Tera® MT40 Very Low-Loss Laminate and Prepreg,” Isola Group.
About the Author
Bill Schweber
Contributing Editor
Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple topic-specific sites for EE Times, as well as both the Executive Editor and Analog Editor at EDN.
At Analog Devices Inc., Bill was in marketing communications (public relations). As a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these.
Prior to the MarCom role at Analog, Bill was associate editor of their respected technical journal and worked in their product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls.
Bill has an MSEE (Univ. of Mass) and BSEE (Columbia Univ.), is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.