In the WLAN network, due to the low power and high frequency of the technology, the coverage is limited, which results in most existing products having a relatively short communication range. Additionally, these systems often support only basic two-way transmission and reception. To address this, many transceivers now integrate power amplifiers, improving system integration and simplifying circuit design. However, the power output from these integrated amplifiers is often insufficient for long-distance communication, necessitating an external power module.
This paper focuses on the design and hardware implementation of a wireless power amplifier aimed at enhancing signal transmission power and improving receiver sensitivity. By boosting the transmit signal strength and amplifying the received signal, the system can support bidirectional communication over longer distances, particularly in 802.11b/g mode.
Figure 1 shows the system schematic diagram. A portion of the RF input power is directed to a detection circuit for processing. The detected RF envelope is compared with a fixed threshold level to control the transmit/receive status of the signal port. If the detected level exceeds the threshold, the RF switch is activated, enabling the transmit channel. Otherwise, it remains in receive mode.
### 1.1 Transmission Microstrip Line Design
The microstrip line plays a crucial role in RF circuit design, serving as part of the matching network and connecting various functional modules. It is used for signal input/output or circuit connection. Proper impedance matching between the front-end and back-end circuits minimizes power loss during transmission. The characteristic impedance of the microstrip line is typically set to 50Ω.
The characteristic impedance depends on factors such as the width (w) of the microstrip line, the dielectric constant (ε) of the PCB material, the board thickness (H), and the copper foil thickness (T). For FR4 material, the impedance is primarily determined by the line width. Using equation (1), we can calculate the required dimensions for optimal performance.
### 1.2 Power Amplifier Circuit Design
The power amplification circuit is responsible for boosting the transmitted signal to a higher power level. In this design, a double-tube balanced configuration is used, with two identical amplifier circuits connected in parallel to increase the output power. The selected chip, Anadigics’ AWL6153UM7P8, provides 25dBm output power at 5V DC voltage and 54Mb/s data rate in 802.11g mode. Simulation results in Agilent ADS2004 show that the insertion loss is less than 3dB at 2.4GHz, and the output power reaches 27dBm, equivalent to 500mW.
### 1.3 Low Noise Amplifier Receiver Circuit Design
The low noise amplifier improves the sensitivity of the received signal. The RFMD2373 chip was chosen for its high gain (up to 15dB), low noise figure (1.3dB), and low current consumption (10mA). It also features a P1dB of -3.5dBm and an IP3 of 9.5dBm at 2.4GHz. Adding a band-pass filter at the input helps reduce noise interference.
### 1.4 Detection Circuit Design
To prevent excessive voltage output from the power detector when receiving strong signals, a directional coupler is used to couple a small portion of the RF signal to the detection circuit. This avoids affecting the circuit's characteristic impedance. The output signal is then shaped and transformed to generate a switching control signal. The main channel attenuation is less than 1dB, with a coupling degree of 13dB. The simulation results using ADS software are shown in Figure 3.
### 1.5 Switching Control and Power Circuit Design
The detection circuit output cannot directly control the RF switch, so a transistor (MBT2222) is used as a driver to manage the RF switch and enable transmit/receive mode switching. A separate power supply circuit converts 9V to 5V to provide stable power to the amplifier module.
### 2. Wireless Power Amplifier Testing
#### 2.1 Port S-Parameter Test
Using the Agilent E5071B vector network analyzer, the S-parameters of the power amplifier were measured. The test results are presented in Figure 4.
#### 2.2 Communication Performance Test
An IQVIEW test instrument was used to emit a -30dBm RF signal as the input to the power amplifier. The received signal was analyzed using IQsignal Vector Signal Analyzer, showing successful reception at both 54Mb/s (802.11g) and 11Mb/s (802.11b) data rates. The test data is shown in Figure 5.
Due to limitations in the IQVIEW device, the transmitted signal was amplified using a self-made module (up to 13.44dBm) before being fed into the power amplifier’s transmit path. The resulting signal data is shown in Figure 6.
#### 2.3 Throughput Test
Throughput refers to the amount of data transferred or processed within a given time. After integrating the power amplifier into an existing WLAN network, the throughput was tested. The results showed that the average network throughput increased to over 20Mb/s, demonstrating the effectiveness of the power amplifier in extending network coverage and performance.
### 3. Conclusion
The 2.4GHz WLAN wireless power amplifier designed and implemented in this paper achieves a transmission power of 500mW and a receive gain of more than 10dB. It supports automatic transmit/receive switching and can be directly connected to major wireless APs. With an effective working range of up to 5km, this design is well-suited for use in extended WLAN networks.
Dongguan Pinji Electronic Technology Limited , https://www.iquaxusb4cable.com