Final Design

Fig.1 CAD model of the final antenna range design

The final design consisted of four major components: a rectangular anechoic chamber, a 2-axis gantry system, a cooling system for the transmitting antenna, and a control board for the gantry system and the cooling system

Rectangular Anechoic Chamber

Fig.2 Final design of the rectangular anechoic chamber

The final design of the rectangular anechoic chamber consists of the following components:

• • Sandwich Panel

Designed to meet the functional requirement on reflectivity while providing protection to the antennas and other components, the sandwich panels functionally served as the walls and the door of the anechoic chamber. The sandwich panels consisted of three layers: a piece of Laird HR-25 microwave absorber, a layer of heavy duty aluminum foil, and a layer of clear polycarbonate sheet. The microwave absorber was chosen such that its reflectivity satisfies the reflectivity requirement at the operating frequency of the antenna under test, and the aluminum foil was required by the manufacturer for optimal performance. In addition, the clear polycarbonate sheet is impact-resist, protecting the microwave absorbers and aluminum foils. Moreover, all three layers were bonded together using 3M Super 77 spray adhesive.

• PVC T-slots

    T-slots made of polyvinyl chloride (PVC) provide structural rigidity to the anechoic chamber while minimizing the weight.

• Anechoic Chamber Door

A sliding door made of a piece of sandwich panel was designed to prevent interference and electronic eavesdropping during the experiments while providing ease of replacing the antenna under test. The sliding door features four roller wheels that fit into the t-slots and a magnetic door latch that can lock the door firmly when it is fully closed.

2-axis Gantry System

Fig.3 Final design of the gantry system

Fig.4 Schematic illustration of the gantry system layout

The final design of the gantry system consists of the following sub-groups:

• Mechanical

Fig.3 provides a schematic illustration of the layout of the gantry system. The timing belts and pulleys were driven by two NEMA-17 stepper motors for precise position control. In addition, three fiberglass rods and two custom designed linear bearings with 3D Printed housing and dry-running nylon sleeve bearing were used to provide smooth movement of the receiving antenna with minimum cost. Moreover, a 3D Printed receiving antenna holder with timing belt clamps was designed and manufactured to hold the receiving antenna and keep the timing belts in tension.

Fig.5 3D printed linear bearing, exploded view

Fig.6 Idler pulley, exploded view

• Electronics

An Arduino MEGA 2650 board and a RAMPS (RepRap Arduino Mega Pololu Shield) 1.6 were used to control the gantry system and operate all stepper motors. The Arduino MEGA platform and the RAMPS board were capable of accommodating two Texas Instruments DRV8825 stepper motor drivers, two optical endstops for sensing the home position. 

Fig.7 RAMPS 1.6 board

• Software

An open source firmware Marlin was used with the Arduino MEGA 2650 board and the RAMPS 1.6 shield to control the gantry system. The Marilin firmware featured G-code with more than 150 commands and a motion system with lookahead, interrupt-based movement, and linear acceleration. In addition, an open source host software Pronterface was used for the user to control the gantry system manually or with a script.

Fig.8 Pronterface graphical UI

Cooling System

The design of the cooling system for the antenna under test consists of the following components:

• Liquid Cooling System for CPU

A Corsair H80i liquid cooling system for CPU was used to control the temperature the antenna under test during experiments. Because the liquid cooling system is widely used in high-performance PCs, it could deliver excellent performance while providing ease for maintenance. 

• Relay & Thermistor

In order to minimize the fan noise during experiments, a relay and a thermistor were used to automatically turn on and off the liquid cooling system based on the temperature of the antenna under test.

Fig.10 Circuit diagram of the cooling system

• 3D Printed PCB Board Holder & Liquid Cooler Holder

    In order to mount the liquid cooler with the antenna module, a 3D printed PCB board holder and a 3D printed liquid cooler holder were used to fix the antenna modules in the center of the antenna range and to mount the liquid cooler with the     antenna module.

Fig.9 3D Printed PCB board holder and liquid cooler holder