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Ultra Wideband Evaluation Board
- Optimized RF Design for Maximum Coverage
Starts from 2021/Aug/02 to 2021/08/21 23:56 (Last Modification)
This project aims to design an UWB evaluation board based on Qorvo’s DW1000 Ultra-Wideband Transceiver IC for real time location system (RTLS) applications.
Following topics are studied in this project:
- UWB Front-End Design
- Omnidirectional/Directional UWB Antenna Design
UWB Front-End Design
Fig.1 UWB Front-End Design
According to the datasheet, DW1000's optimized load impedance is differential 100 Ohm. Thus, the impedance needs to be matched from differential 100 Ohm to single end 50 Ohms and the impedance bandwidth also requires covering 3000Mhz to 7000Mhz.
Fortunately, multi-layer balun HHM1595A1 is capable to meet above impedance matching requirements. The theoretical performance is shown in Fig.2. Fig.2 HHM1595A1's Theoretical Performance
According to HHM1595A1's performance, the design will be almost no challenge once the SMA connector is not necessary. However, the SMA connector is required by this evaluation board, because several UWB Antenna Designs need to be evaluated by this board. The Performance comparison between “With SMA connector but no optimization” and “Without SMA connector” is shown in Fig.3. Fig.3 The Performance comparison between “With SMA connector but no optimization” (Left) and “Without SMA connector” (Right)
Due to impedance mismatching at point M, the performance is downgraded significantly because of the SMA connector. The impedance mismatching can be solved by building a matching circuit using inductor and capacitor. However, this method will be either downgrading the impedance bandwidth or enlarging the PCB footprint. For balancing between the impedance bandwidth and PCB footprint, the impedance mismatching can also be eliminated by adjusting the distance between the microstrip line and the reference plane. For the multi-layer PCB, we just need to select the layer stack carefully and cut suitable slot between the microstrip line and the GND plane under the SMA connector (Fig.4). The Insertion Loss comparison between “Without Slot” and “With Slot” is shown in Fig.5. Fig.4 Four layers design with a slot on the second layer under SMA connector Fig.5 The Insertion Loss comparison between “Without Slot” (Left) and “With Slot” (Right)
The Insertion Loss is improved about 1.5dB to 2.5dB across the impedance bandwidth by the slot. The Insertion Loss of the slot edition is as small as ignorable. Therefore, we could conclude the impedance mismatching is eliminated by slot.
Omnidirectional UWB Antenna Design
Symmetric Antenna Candidate 1
Symmetric Antenna Candidate 1 is a revised edition of Candidate 2. It also uses rectangular slot and attaching strip for size reduction . This antenna is still printed on a 30mm*32mm PCB with desirable symmetrical radiation pattern. The bandwidth is expected to cover UWB Channels 2, 3,5 and 7.
The difference between the simulation results and measurement results is not only due to the accuracy of the simulation model. In the measurements of small antennas, the RF cable usually affects the performance of antenna under test greatly . I reproduced this phenomenon by using different kind and different length SMA cables with the same VNA Tektronix TTR506A and VNA calibration kit. Notable difference of results was observed.
Symmetric Antenna Candidate 2
Rectangular slot notching onto the radiator and attaching strip to the radiator can reduce the size of UWB antenna . This antenna is printed on a 30mm*32mm PCB with desirable symmetrical radiation pattern. The bandwidth is expected to cover UWB Channels from 1 to 7 (3244.8Mhz to 6998.9MHz).
Directional UWB Antenna Design
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 Anurag Bhargava. RF Design-20: Mitigating Impedance Mismatch due to SMD Pads in RF/Microwave and High Speed Boards. Retrieved Aug 02, 2021, from https://youtu.be/ysaiwtnCrlE
 Zhi Ning Chen; Terence S. P. See; Xianming Qing. Small Printed Ultrawideband Antenna With Reduced Ground Plane Effect. Retrieved Aug 07, 2021, from https://ieeexplore.ieee.org/document/4084807