A Highly Miniaturized Active 90° Power Combiner MMIC Employing CE and CC Circuits

In this work, a highly miniaturized active 90° power combiner, employing InGaP/GaAs heterojuntion bipolar transistors (HBT), was fabricated on a GaAs substrate for MMIC applications. A novel composite structure employing common-emitter (CE) and common-collector (CC) circuits is proposed for 90° power combining. The size of the active 90° power combiner is approximately 2.2 percent of a conventional passive combiner. The active 90° power combiner showed good RF performance, comparable to a passive combiner at S-band. This work is the first 90° power combiner reported employing active devices.

From: Vol. 52 | No. 9 | September 2009 | Page 134

by Young-Bae Park, Young Yun, Suk-Youb Kang, In-Ho Kang, Ji-Won Jung and Kyu-Ho Park, Korea Maritime University, Busan, Korea; Kwang-Ho Anh, Korea Electronics Technology Institute Korea

A 90° power combiner has been used for signal mixing at the intermediate frequency (IF) output port of an image rejection mixer.^1,2 Until now, a passive branch-line coupler was mainly employed for 90° power combining.^1,3 However, the passive branch-line coupler occupies a very large circuit area.

For example, if the branch-line coupler is fabricated on a GaAs substrate with a thickness of 100 µm, for a signal mixing with an IF of 2.4 GHz, the size will be approximately 10.92 × 10.54 mm. Therefore, passive power combiners cannot be integrated on MMICs due to their very large size.⁴ To reduce the size of the 90° power combiner,⁶ it has to be fabricated using an active device. However, no study of a 90° power combiner employing an active device has been reported yet. In this work, for integration of the 90° power combiner on a MMIC, a highly miniaturized active 90° power combiner employing CE and CC circuits with InGaP/GaAs heterojunction bipolar transistors (HBT) is proposed.

Design of An Active 90° Power Combiner Employing CE and CC with InGaP/GaAs HBT

Figure 1 Schematic of the active 90° power combiner.

Figure 1 shows the schematic circuit of an active 90° power combiner employing CE and CC circuits. As shown, a novel composite structure employing common-emitter (CE) and common-collector (CC) circuits was used, with the output ports of the CE and CC circuits connected to each other. To compensate for the insertion loss of the active 90° power combiner, an amplifier was added at the output port.

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Design of An Active 90° Power Combiner Employing CE and CC with InGaP/GaAs HBT