A LOW-NOISE MMIC AMPLIFIER AS A MICROWAVE-TO-OPTICS LINK Ertan Zencir, Ercument Arvas, Richard Michalak * Department of Electrical Engineering and Computer Science, Syracuse University Syracuse, New York 13210, United States of America * Air Force Research Laboratory, AFRL-SNDR 25 Electronic Pkwy, Rome, New York 13441, United States of America Email: ezencir@syr.edu , earvas@syr.edu , michalakr@rl.af.mil ABSTRACT A low-noise MMIC distributed amplifier was designed to operate as a microwave-to-optics link in certain radar applications. It was designed to have a small signal gain of 12 dB in the frequency band of 3.1 to 3.5 GHz. In addition to the flat gain requirement, good input and output return losses with a noise figure less than 5 dB were to be realized. The amplifier has 50 Ω input and output impedances. Test measurements on the first built prototype show that amplifier has an average small signal gain of 6.2 dB in the band under the bias conditions V ds =3.5 V, and V gs =0.56 V. Input return loss is –5.47 dB, output return loss is –9.49 dB and the average isolation is –29.51 dB. Noise figure of the amplifier changes between 5.48 and 6.46 dB in the band. A gain ripple of ±0.50 dB is obtained. I. INTRODUCTION Air Force Space-based Radar applications require a broadband, linear, low-noise, large dynamic range, very light- weight, low-loss, EMI-immune microwave transmission bus or analog link to connect the sensor elements to the centrally-located space time adaptive processor. Currently deployed analog links use narrowband, heavy and lossy coaxial cables for transmission. The stressing link broadband requirements can be met, launch and on-orbit costs will be greatly reduced, and mission performance enhanced by using integrated microwave and fiber-optical technologies for the microwave link subsystem. Optics is inherently more broadband and EMI-immune than traditional coax-based technology. Demonstrated fiber-optical links to-date have consisted of separate amplifier, optical source, modulator, modules connected together to form complete transmitter and receiver systems. The monolithic integration of high- speed electronics in the form of MMIC circuitry has reduced costs and improved electronics performance, and hence the integration of optics with MMIC driver circuits will further improve performance of link applications [1]. This proposed system involves the design and fabrication of a link transmitter, to modulate RF from a receiving antenna onto a 1.3µ carrier in optical fiber. Figure 1 shows a future monolithically integrated opto-electronic MMIC link transmitter chip. In this chip, radar signals are carried via a microwave coaxial connection under the chip to a low-noise distributed amplifier, which is impedance matched to drive the integrated laser. The optical signal with microwave modulation imposed exits via the optical fiber to the left. This fiber connects, meters away, with a similar receiver chip that converts the optical signal to microwave. The signal is then mixed and down-converted, digitized, and processed by the onboard radar signal processing electronics. Target link specifications of this link transmitter include 3.1-3.5 GHz RF, 50 Ω antenna patch microwave input, GaAs MMIC 3-stage distributed low-noise amplifier with 20 dB gain and 3 dB maximum noise figure, 5 mW directly modulated 1.3µ DFB laser diode, and 70-96 dB link dynamic range. The planned research approach involved the demonstration of a first generation hybrid amplifier circuit built in Syracuse University RF/Microwave Lab (http://surf.syr.edu). The next step involved was the design and manufacturing of a preliminary MMIC GaAs amplifier (reported here) with 50 Ω input and output matching. Then the design of a GaAs MMIC amplifier driving an externally mounted laser and meeting full specifications will be the continuation of the work reported here. Finally a flip-chip bonded version of a link transmitter will be realized.