Antennas

In addition to chip antennas on various USB attached wireless devices, three types of external antennas are attached to various RF devices on the nodes.

WiFi Antennas

Most of the internal WiFi devices are attached to dual band (2.4/5 GHz), blade style omni-directional antennas shown in Figure 1. These are mounted at the end of the two rods extending at the 45 degree angle downwards from the node harness as shown in Figure 2 with the distance between the two antenna rods (i.e. the two internal WiFi devices) of 26 inches.

These antennas have a typical donut-shaped shape radiation pattern​ with an average gain of 2 dBi (@ 2.4 GHz) and 4 dBi (@ 5GHz).

Multi-standard Antennas

A number of SDR units in the grid have multi-band (i.e. multi-standard) antennas​ covering most of the WiFi and 4G bands. They are mounted on a square plate 12 inches apart (in the horizontal plane) as shown in Figure 4. To minimize antenna correlation, the corner positions are used with the TX (and RX) of each RF chain on opposite diagonal corners.

Top-down view of multi-band antenna panel:

Front of USRP
RFB RX2	RFA TX/RX
RFB TX/RX	RFA RX2

Massive-MIMO Antennas

The top of each Massive-MIMO mini-rack is populated with a horizontal array of 32 antennas​. They are mounted on a rectangular plate with a 2 inch spaced grid pattern. The antenna locations correspond to the locations of the USRPs to which they are attached (see table below).

Example antenna configuration (top-down view) for node23-1 through node23-8:

Back of Massive-MIMO mini-rack
23-7 RF A RX2	23-7 RF A TX/RX	23-7 RF B RX2	23-7 RF B TX/RX	23-8 RF A RX2	23-8 RF A TX/RX	23-8 RF B RX2	23-8 RF B TX/RX
23-5 RF A TX/RX	23-5 RF A RX2	23-5 RF B TX/RX	23-5 RF B RX2	23-6 RF A TX/RX	23-6 RF A RX2	23-6 RF B TX/RX	23-6 RF B RX2
23-3 RF A RX2	23-3 RF A TX/RX	23-3 RF B RX2	23-3 RF B TX/RX	23-4 RF A RX2	23-4 RF A TX/RX	23-4 RF B RX2	23-4 RF B TX/RX
23-1 RF A TX/RX	23-1 RF A RX2	23-1 RF B TX/RX	23-1 RF B RX2	23-2 RF A TX/RX	23-2 RF A RX2	23-2 RF B TX/RX	23-2 RF B RX2
Front of Massive-MIMO mini-rack

Electronically Steerable Antennas

4 nodes with USRP X310 devices in addition to standard antennas (WiFI for two internal devices and multi-standard paddle antennas) are equipped with a electronically steerable antenna and a block of RF switches facilitating antenna selection.

The 2.4-2.5 GHz ​Fidelity Comtech FCI-3740 Phased Array device actually comprises of:

• Directional antenna with 14.5 dBi of gain and 49 electronically selectable antenna patterns
• Omni-directional 9 dBi antenna
• Embedded GPS

The antenna is managed either directly by the USRP via a fast GPIO-to-RS485 link or through OMF services which facilitate the selection of power state and pattern selection.

Antenna Switching Hardware

The antenna switching hardware is shown in Figure 6. It consists of: bank of RF switches, RS-485 drivers and Raspberry PI as an embedded controlled. This hardware enables remote antenna selection and steering.

The bank of switches is used to route both nodal WiFi and X310 antenna feeds to either regular antennas or to directional or omni-directional antennas on FCI-3740. The table below shows switch states and corresponding antenna selections (blanks indicate the particular switch state does not matter for the particular configuration).

Configuration	SW 1	SW 2	SW 3	SW 4
Node Wifi 0 → standard antenna	RF 1
Node Wifi 0 → directional (FCI antenna)	RF 2	RF 1
USRP RF A → standard antenna			RF 1
USRP RF A → directional (FCI antenna)		RF 2	RF 2
USRP RF B → standard antenna				RF 1
USRP RF B → omni (FCI antenna)				RF 2

The embedded controller is used to provide IP/HTTP based remote management. Directional Antenna AM Service is used by experimenters to manage the antenna selection and steering.