Co-Design of Integrated Microwave Amplifier and Phase Shifter Using Reflection-Type Input Matching Networks for Compact MIMO Systems  
[PERSON]  
1 Division of Electronics and Information Engineering, Jeonbuk National University, Jeonju-si 54896, Jeonbuku-do, Republic of Korea; [EMAIL_ADDRESS]  
[PERSON]  
2 JIANT-IT Human Resource Development Center, Jeonbuk National University, Jeonju-si 54896, Jeonbuku-do, Republic of Korea; [EMAIL_ADDRESS]  
[PERSON]  
3 Jennbuk HEC Intelligent Innovation Research Center, Jeonbuk National University, Jeonju-si 54896, Jeonbuku-do, Republic of Korea; [EMAIL_ADDRESS]  
[PERSON]  
1 Division of Electronics and Information Engineering, Jeonbuk National University, Jeonju-si 54896, Jeonbuku-do, Republic of Korea; [EMAIL_ADDRESS]  
Footnote 1: email: {john.john. are important circuits in radio frequency (RF) front-end systems. Microwave amplifiers are typically used to amplify the power level of a signal for long-distance transmission. Conversely, a phase shifter is an essential circuit used for controlling the phase of a signal without significantly affecting its amplitude. By adjusting the phase, the propagating signal can be controlled in order to steer and transmit in specific direction, which is crucial for applications such as phased array antennas, multiple input and multiple output (MIMO) systems, and beamforming networks [7; 8; 9; 10]. The microwave frequency typically ranges from 300 MHz to 300 GHz, which is divided into several sub-bands, such as L-band (1-2 GHz), S-band (2-4 GHz), C-band (4-8 GHz), X-band (8-12 GHz), Ku-band (12-18 GHz), K-band (18-27 GHz), Ka-band (27-40 GHz), and millimeter bands above 30 GHz. This work chooses a center frequency (\(f_{0}\)) of 2.45 GHz, which is in the S-band. More specifically, this frequency is part of the industrial, science, and medical (ISM) radio bands. The 2.45 GHz ISM band is license-free and has been standardized around the world, making it popular for a wide range of uses, including Bluetooth, Wi-Fi, microwave heating, and biomedical telemetry. Figure 1a shows the typical structure of an RF front-end transmitting system where phase shifters and microwave amplifiers are individually designed with termination impedances equal to a system impedance (\(Z_{0}\)) of 50 \(\Omega\). In this conventional approach, if the return loss (RL) characteristics of individual circuits are not good, then cascading two circuits may cause signal reflection due to the impedance mismatch. Furthermore, the conventional cascading topology may lead to increases in circuit size, cost, and degrade overall electrical performances, resulting from the increasing insertion loss (IL) by mismatching and additional devices such as adaptor and cable. To mitigate these disadvantages, Figure 1b illustrates a co-design approach, where the phase shifter is matched directly to the optimum source impedance (\(Z_{S}\)) of the microwave transistor, eliminating the need for additional input matching networks. Therefore, the co-designed approach can allow the circuit miniaturization and performances improvement of the RF front-end by eliminating a number of components (such as additional matching networks, connecting cables, and adapters) and their corresponding ILs. In recent years, various configurations of phase shifters have been investigated. Based on their circuit topologies, these phase shifters can be classified as transmission types [11; 12] and reflection types [13; 14; 15; 16; 17; 18; 19; 20]. Compared to transmission-type configurations, reflection-type phase shifters can provide good RL by using identical reflection loads connected at the through and coupled ports of the 3 dB branch-line hybrid. Recently, numerous  
Figure 1: RF front-end transmitter of a wireless communication system: (**a**) conventional cascading design topology and (**b**) proposed co-designed microwave amplifier phase shifter (CPS: conventional phase shifter; CIMN: conventional input matching network; COMN: conventional output matching network; AMN: antenna matching network).