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).

1. The CMX90A705 medium-power amplifier from CML Microcircuits targets satcom applications in the 27.5- to 31-GHz part of the Ka-band.

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.

2. The datasheet shows an evaluation board for the PA and includes the BOM and a schematic as well.

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).

3. At these Ka-band frequencies, PCB substrate and stackups are critical design considerations.

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.