Figure 1 SA-7-8B006073 8 x 8 Butler matrix configuration.
A Butler matrix is a passive beamforming network used to feed a phased array of antenna elements. Compared to an active beamforming network, a Butler matrix has several advantages. It can have higher performance stability, repeatability, more reliable accuracy, a simpler configuration, smaller size and lower cost. However, there are also disadvantages. Limitations in component performance and manufacturing technology have historically made obtaining the required accuracy and frequency bandwidth a difficult challenge. MIcable is solving these challenges with cutting-edge design and advanced manufacturing to improve the accuracy and bandwidth of Butler matrices to new levels of performance. As an example, the SA-7-8B006073, a 0.6 to 7.25 GHz 8 × 8 Butler matrix, will be used to highlight these accuracy and bandwidth improvements.
8 × 8 BUTLER MATRIX FUNCTIONALITY
Figure 1 shows the SA-7-B006073 8 × 8 Butler matrix configuration, highlighting the layout and connections of the matrix. The diagram shows a reciprocal signal transfer between any of the eight input ports and any of the eight output ports. This enables simultaneous operation of the Butler matrix in both the transmit and receive path. This means that a signal on any A port will appear as outputs on the B1 to B8 ports simultaneously. These signals will have eight different phase values and this allows the system to enable as many as eight different sub-beams if the Butler matrix is connected to eight antennas. The Butler matrix is reciprocal, so a signal on any B port will appear as simultaneous outputs on ports A1 to A8. An SP8T switch can be used to select which of the A ports, from A1 to A8, will be the input or which of these ports will be supplying the output signal if the B ports are used as inputs.
The diagram of Figure 1 shows fixed phase shift stages in the Butler matrix configuration. These are used to change the relative phase of the signals. Table 1 shows the resulting phase relations among the eight output ports. The data in Table 1 shows how the Butler matrix architecture facilitates reciprocal signal transfer between any of the eight input ports and any of the eight output ports, enabling simultaneous operation as both a transmission and receiving system.
SPECIFICATIONS
Table 2 shows the RF performance specifications for the SA-7-8B006073 8 × 8 Butler matrix across four different frequency bands. These bands have been selected for their importance in 5G New Radio (NR) frequency range 1 (FR1) and Wi-Fi 6E/7E applications. Figure 2 shows representative amplitude balance and phase accuracy plots for port A1 as the input across the entire operating band of the device.
Figure 2 Amplitude balance and phase accuracy.
Some additional characteristics of the Butler matrix:
- Input Power (max.): 5 W CW (20 W CW available), 500 W peak
- Connector: SMA female
- Dimensions: 316 × 172.7 × 68.6 mm (L × W × H)
- Weight (max.): 5700 g
- Temperature: -40°C to +70°C (operating), -55°C to +85°C (storage)
- Environmental: Per MIL-STD-202F, Method 204D. Method 213B optional (contact supplier for detailed information).
The advantage of the SA-7-8B006073 8 × 8 Butler matrix is that it operates remarkably well over the entire 600 MHz to 7.25 GHz frequency range. As mentioned, Table 2 shows performance specifications over specific frequency ranges, emphasizing bands attractive to 5G NR FR1 and Wi-Fi 6E/7E applications. Measurements in the actual frequency bands yield much better performance. In 5G NR FR1 and Wi-Fi 6E/7E applications, the SA-7-8B006073 has the following typical performance:
- Phase Accuracy: ≤ ±6 degrees
- Amplitude Balance: ≤ ±1 dB
- Insertion Loss: 2 to 5.6 dB (above the 9 dB theoretical loss)
- VSWR: ≤ 1.3:1
- Isolation: ≥ 20 dB.
POTENTIAL APPLICATIONS
This performance, especially the phase accuracy and amplitude balance over such a broadband frequency range, differentiates the SA-7-8B006073 from competitive products and solutions. Compared to active phased array beamforming networks, the passive Butler matrix architecture boasts a straightforward across-matrix configuration that achieves the required phase shift in a smaller footprint. The passive architecture also helps ensure accurate and stable performance, higher power handling for each path and cost-effectiveness. The device is reciprocal, so the signals can be input from one port or multiple ports at the same time and used in a transmit or receive path. Operating frequencies from 600 MHz to 7.25 GHz, along with the performance characteristics, will enable beamforming and beam steering in a wide range of applications that include 5G, Wi-Fi, IoT, cellular phone/base station test, automotive electronics, communication, phased arrays and object detection.
MIcable Inc.
Fuzhou, China
en.micable.cn/index.php
