The 2.7/5.4 GHz Reference Repeater

Figure 6.15 illustrates the reference repeater. The receive 2.7 GHz antenna is fed by a λg/21 101 Ω ML and the transmit 5.4 GHz antenna is fed by a λg/8.4 100 Ω ML and a λg/7.8 shunt shorted stub with a Zo of 93 Ω. Similar to the doubler circuit of the sensing repeater, an additional shunt shorted stub of an electrical length of λg/5.25 and Zo of 93 Ω was added to fine tune the impedance match. To maximize the CG at RF input power of -30 dBm, the ADS simulation shows that the receive and transmit antennas should present an impedance of 70+j285 Ω at 2.7 GHz and an impedance of 40+j230 Ω at 5.4 GHz, respectively. The reference repeater reflection coefficients between the antennas and doubler circuit, as well as the radiation patterns, are similar to those of the sensing repeater (see Figure 6.16 and Figure 6.17). The variation over the receive antenna H-plane is 1 dB while it is 1.35 dB for the transmit antenna. The receive antenna peak gain is 0 dBi with a simulated radiation efficiency of 63%. The peak gain and radiation efficiency of the transmit antenna are 1.95 dBi and 81.4%, respectively.

  Figure 6.15: Illustration of the 3-D printed node reference repeater, side view (left) and top view (right).

Transmit antenna

Receive antenna

Ground Plane Via Holes

14.5 mm 12 mm

GND PAD

Z X

Y

  Figure 6.16: The simulated reflection coefficient between the receive antenna and the doubler input (left) and between the transmit antenna and the doubler output (right) of the 3-D printed node repeater at -30 dBm input power and 0V bias.

Figure 6.17: The simulated E-and H-plane radiation patterns of the 3-D printed node reference repeater receive antenna at 2.7 GHz (left) and transmit antenna at 5.4 GHz (right).

Figure 6.18: Simulated CG of the 3-D printed node reference repeater and multiplier for different input power levels at f1 of 2.7 GHz.

The simulated CG of the doubler and the entire reference repeater at f1 of 2.7 GHz and

Frequency (GHz)

is -17.5 dB. The peak CG value is -12.3 dB, occurs at RF power level of -18 dBm. Compared to the reference repeater presented in Chapter 5, the CG is degraded by 4 dB.

6.4 Conclusions

Two 3-D cube antennas have been designed and fabricated using the additive manufacturing and micro-dispensing method. Good agreement is found between the expected and measured results for both of the designs. The first cube antenna substrate was fabricated using the stereolithography process. The SLA material has good surface smoothness that allows patterning small feature size traces, however, it has high dielectric loss. Due to the lossy material used, the antenna gain was decreased by 2.5 dB relative to the PCB version of the antenna that was made using low loss microwave laminate. Approaches to improve the SLA antenna performance include using grooved structures for feed lines and reducing the amount of the substrate material in the vicinity of the antenna. The second cube antenna was fabricated with the fused deposition modeling using the ABS material. The ABS material has good impact resistance, toughness, and electrical properties that are comparable to the commercial microwave laminates, however, printing the ABS material using the FDM process results in a poor surface smoothness that can limit the minimum realized trace width. This issue is mitigated in this work by depositing a channel for the thin conductive traces to guide the silver ink flow. A comparison with other designs from the literature fabricated with different processes shows that the presented FDM design compares well with the high efficiency electrically small antennas. This comparison also reveals that using FDM and 3-D printing is promising and high performance antennas can be realized with the currently available materials. The use of the advanced 3-D manufacturing methods addressed issues of design reliability and fabrication repeatability and significantly reduces the antenna weight.

A 3-D dual-channel passive transceiver has also been designed to be fabricated with the fused deposition modeling and conformal 3-D printing. The design of the node is similar to the dual-channel transceiver presented in Chapter 5. The simulated maximum conversion efficiency of the reference and sensing repeater is 5.9% and 3.2%, respectively. Compared to the design presented in Chapter 5, the weight is reduced by 67%, the occupied volume is similar, the peak CG of the reference repeater is reduced by 4 dB and the peak CG of the sensing repeater is degraded by 3 dB, and the mass production difficulty and the manual assembly of the design is improved. Using silver ink material with conductivity similar to copper improves the efficiency of the reference repeater by 2 dB and the sensing repeater by 3 dB.

CHAPTER 7 : DUAL-CHANNEL HARMONIC INTERROGATOR ANTENNA DESIGN  

7.1 Introduction

An approach for the harmonic interrogator antenna design is to use a dual-channel antenna array, where one channel is used for transmission and the second channel is used for reception. The advantages of this approach are; 1) the high isolation between the receiving and transmitting channels, 2) the reduced number of components and complexity of the interrogator unit, and 3) the potential for smaller size compared to a single-channel broadband antenna.

In this chapter, two dual-channel harmonic interrogator antenna designs are presented.

The first design contains two four-element circular patch antenna (CPA) arrays, one for reception and one for transmission. The transmitting channel array operates at 2.4 GHz with a measured 10 dB RL BW of 2% and the receiving channel array operates at 4.8 GHz with a measured 10 dB RL BW of 4.2%. The measured gain and HPBW of the transmitting and receiving arrays are 12.1 dBi and 40^o, and 13 dBi and 35^o, respectively. The FBR ratio of both of the arrays is greater than 33 dB. The integrated planar array is very low profile and has a size of 1.28 λ × 1.28 λ × λ/50 at fo of 2.4 GHz and weight of 49.5 g. To miniaturize the CPA array, the 3-D printing technology can be used to print the patches on conformal curved substrate surface. Using this approach, the array occupied area and weight can be reduced by 14% at the expense of 2 dB gain degradation.

In order to provide the capability to interrogate various sensor nodes that operate at different frequencies, the second dual-channel interrogator antenna is designed based on an integrated two two-element quasi-Yagi dipole antenna (QYDA) arrays. The transmitting array is