**3.1 Antenna performance using conventional materials and techniques**

We base the hybrid substrate-shared aperture antenna on the shorted annular ring and concentric patch geometry explored by Dorsey and Zaghloul [15–17]. **Figure 1** (left) shows the geometry of the dual-band antenna on two nested dielectric substrates, and **Figure 1** (right) shows the layout of the nested substrates themselves. **Table 1** gives the values in millimeters for the antenna dimensions illustrated in **Figure 1**. We shrink the overall footprint of the dual-band antenna by 30% by increasing the dielectric constant of the substrate under the annular ring from *εr1* = 2.33 to *εr1* = 6.15.

Two pairs of orthogonal microstrip pin feeds control the different operational modes of the antenna by exciting either S- or X-band frequencies and either vertical or horizontal polarization. **Figure 2** gives the locations of the pin feeds with respect to the annular ring and concentric patch antennas respectively. **Figure 2** also shows a shorting wall grounding the inner perimeter of the annular ring to diminish surface waves. Suppression of surface waves on the dielectric substrates helps

#### **Figure 1.**

*Top view geometry of the dual-band antenna (left), layout of the nested substrates (center), and top view of the prototype dual-band antenna.*

> increases isolation between the excitation ports of the dual-band antenna. The antenna comprises a top metal layer, a hybrid Rogers 3006/Rogers 5870 substrate layer, and a bottom metal ground layer. All metal layers are 0.1 mm thick, and the

*Measured and simulated normalized radiation pattern at S-band horizontal port.*

*Comparison of simulated return loss to measured return loss of the horizontal port at S-band.*

*3D view of the dual-band antenna and pin feed network. The outer dielectric layer is transparent for clarity.*

**Figures 3** and **4** show the measured versus simulated return loss and normalized radiation patterns of the dual-band antenna at S-band. **Figures 5** and **6** show the

dielectric substrate layer is 5.05 mm thick.

**Figure 2.**

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

**Figure 3.**

**Figure 4.**

**193**


#### **Table 1.**

*Antenna dimensions in millimeters of Figure 1.*

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

**Figure 2.**

**3. Hybrid material dual-band and dual-polarization antenna design**

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

shelf materials and fabrication techniques, to the same antenna geometry

**3.1 Antenna performance using conventional materials and techniques**

newfound complexities of emerging multifunction antenna designs.

from *εr1* = 2.33 to *εr1* = 6.15.

**Figure 1.**

**Table 1.**

**192**

*prototype dual-band antenna.*

*Antenna dimensions in millimeters of Figure 1.*

manufactured using AM materials and 3D printing manufacturing processes. The idea being that the versatility allowed via AM of antennas can help navigate the

We base the hybrid substrate-shared aperture antenna on the shorted annular ring and concentric patch geometry explored by Dorsey and Zaghloul [15–17]. **Figure 1** (left) shows the geometry of the dual-band antenna on two nested dielectric substrates, and **Figure 1** (right) shows the layout of the nested substrates themselves. **Table 1** gives the values in millimeters for the antenna dimensions illustrated in **Figure 1**. We shrink the overall footprint of the dual-band antenna by 30% by increasing the dielectric constant of the substrate under the annular ring

Two pairs of orthogonal microstrip pin feeds control the different operational modes of the antenna by exciting either S- or X-band frequencies and either vertical or horizontal polarization. **Figure 2** gives the locations of the pin feeds with respect to the annular ring and concentric patch antennas respectively. **Figure 2** also shows a shorting wall grounding the inner perimeter of the annular ring to diminish surface waves. Suppression of surface waves on the dielectric substrates helps

*Top view geometry of the dual-band antenna (left), layout of the nested substrates (center), and top view of the*

*L1 L2 L3 L4 D εr1 εr2* 36.7 22.57 10.23 7.08 5.07 6.15 2.33

As the world continues to move to fully integrated multifunction antennas, the design of new multiband and multimode antenna geometries continues to yield structures that are more complicated to manufacture. However, current challenges in maintaining, upgrading, and networking an ever-increasing number of antenna nodes are alleviated through adapting these types of multifunction antennas and other RF devices. The low profile and lightweight designs of references [15–18] show great promise for multifunction antenna applications. This chapter compares the performance of a multifunction antenna prototyped using traditional off-the-

*3D view of the dual-band antenna and pin feed network. The outer dielectric layer is transparent for clarity.*

**Figure 3.** *Comparison of simulated return loss to measured return loss of the horizontal port at S-band.*

**Figure 4.** *Measured and simulated normalized radiation pattern at S-band horizontal port.*

increases isolation between the excitation ports of the dual-band antenna. The antenna comprises a top metal layer, a hybrid Rogers 3006/Rogers 5870 substrate layer, and a bottom metal ground layer. All metal layers are 0.1 mm thick, and the dielectric substrate layer is 5.05 mm thick.

**Figures 3** and **4** show the measured versus simulated return loss and normalized radiation patterns of the dual-band antenna at S-band. **Figures 5** and **6** show the

with the extrusion of high-dielectric filaments, discussed in Section 2.1, allow cus-

**Figure 7** shows a to-scale 3D printed prototype of the antenna shown in **Figures 1** and **2**. The antenna utilizes a microstrip stack of a printed copper layer, hybrid dielectric layer, and a copper ground layer. We printed all pieces separately and assembled by hand afterward. All conductive layers are 1.0 mm thick. The hybrid substrate layer is 5.05 mm thick. The total profile of the antenna is 6.05 mm

**Table 2** shows the dimensions of the geometries given in **Figure 2** as they pertain to **Figure 7**. We chose two AM filaments compatible with a Fuse Deposition Modeling (FDM) 3D printer. For the high dielectric, we chose Preperm ABS 650 with a reported dielectric constant of *ε<sup>r</sup>* = 6.5 to mimic the Rogers 6010 material with *ε<sup>r</sup>* = 6.15. However, after conducting waveguide measurements on a 3D printed sample, we found anisotropic values of *εrx* = *εry* = 5.7 and *εrz* = 5.3. We chose ABS to mimic the Rogers 5870 material with *ε<sup>r</sup>* = 2.33. Measured values of the ABS were nearly isotropic with a value of *ε<sup>r</sup>* = 2.38. The loss tangents of both materials were

. We printed the metal layers via the selective laser sintering (SLS) method allowing us to print actual copper as opposed to using a lower conductivity ink. Using a substrate of *εr1* = 5.3 instead of *εr1* = 6.15 under the S-band element shifts the resonances from 3.2 to 3.8 GHz. Changing the dimensions of the concentric slot and X-band patch, shown in **Figure 1** and **Table 2**, shifts the X-band

*L1 L2 L3 L4 D εr1 εr2* 37.08 25.36 11.03 7.38 7.05 5.3 2.38

*Antenna dimensions in millimeters of 3D printed antenna based on schematic in Figure 1.*

We choose a slightly modified version of the antenna design presented in Section 3.1. Due to the hybrid material design and the utilization of a fully embedded vertical shorting wall, we believe this is a good design to test capabilities of AM as it pertains to antennas. For this investigation, we design the dual-band antenna for S-band and X-band respectively. We perform all simulations using the finite

tomized dielectric constants not previously achievable [2].

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

due to printing thicker metal layers to prevent warping.

about 10<sup>3</sup>

**Figure 7.**

**Table 2.**

**195**

frequency from 11.1 to 9.35 GHz.

*Fully assembled AM dual-band antenna.*

difference time domain (FDTD) solver of CST Studio Suite 2019.

**Figure 5.** *Measured and simulated return loss at X-band horizontal port.*

**Figure 6.** *Measured and simulated normalized radiation pattern at X-band horizontal port.*

same for at X-band. The radiation shows good agreement at both S-band and Xband. **Figures 3** and **5** show a return loss measurement of 17.5 dB at the resonant frequency of 3.2 GHz and measurement of 11.0 dB at the resonant frequency of 11.1 GHz. There is a second S-band resonance seen at a frequency of 2.7 GHz in **Figure 3**, but the radiation characteristics in **Figure 4** show that this is not the dominant S-band resonance. We attribute discrepancies in the depth of the return loss curve in **Figure 5** to manufacturing tolerances in the placement of the pin feeds with respect to the edges of the concentric patch. Since electrical length decreases with wavelength at X-band, smaller tolerance errors can have larger effects than at S-band on the impedance match quality. However, both the simulated and measured resonant frequency at X-band is the same as expected.

### **3.2 Antenna performance using additive manufacturing**

AM allows engineers to rethink the RF design space. AM facilitates complex designs that required properties not achievable by traditional manufacturing methods. Strides in AM produce robust structural and mechanical parts, but industry has yet to develop a full suite of electromagnetic properties for AM feedstocks. Low dielectric constants of commercial feedstocks limit current antenna designs, but recent research into the composition of high-dielectric feedstocks for AM opens the design space for antennas [12–14]. Additionally, space-filling algorithms paired

#### *Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

with the extrusion of high-dielectric filaments, discussed in Section 2.1, allow customized dielectric constants not previously achievable [2].

We choose a slightly modified version of the antenna design presented in Section 3.1. Due to the hybrid material design and the utilization of a fully embedded vertical shorting wall, we believe this is a good design to test capabilities of AM as it pertains to antennas. For this investigation, we design the dual-band antenna for S-band and X-band respectively. We perform all simulations using the finite difference time domain (FDTD) solver of CST Studio Suite 2019.

**Figure 7** shows a to-scale 3D printed prototype of the antenna shown in **Figures 1** and **2**. The antenna utilizes a microstrip stack of a printed copper layer, hybrid dielectric layer, and a copper ground layer. We printed all pieces separately and assembled by hand afterward. All conductive layers are 1.0 mm thick. The hybrid substrate layer is 5.05 mm thick. The total profile of the antenna is 6.05 mm due to printing thicker metal layers to prevent warping.

**Table 2** shows the dimensions of the geometries given in **Figure 2** as they pertain to **Figure 7**. We chose two AM filaments compatible with a Fuse Deposition Modeling (FDM) 3D printer. For the high dielectric, we chose Preperm ABS 650 with a reported dielectric constant of *ε<sup>r</sup>* = 6.5 to mimic the Rogers 6010 material with *ε<sup>r</sup>* = 6.15. However, after conducting waveguide measurements on a 3D printed sample, we found anisotropic values of *εrx* = *εry* = 5.7 and *εrz* = 5.3. We chose ABS to mimic the Rogers 5870 material with *ε<sup>r</sup>* = 2.33. Measured values of the ABS were nearly isotropic with a value of *ε<sup>r</sup>* = 2.38. The loss tangents of both materials were about 10<sup>3</sup> . We printed the metal layers via the selective laser sintering (SLS) method allowing us to print actual copper as opposed to using a lower conductivity ink. Using a substrate of *εr1* = 5.3 instead of *εr1* = 6.15 under the S-band element shifts the resonances from 3.2 to 3.8 GHz. Changing the dimensions of the concentric slot and X-band patch, shown in **Figure 1** and **Table 2**, shifts the X-band frequency from 11.1 to 9.35 GHz.

#### **Figure 7.**

same for at X-band. The radiation shows good agreement at both S-band and Xband. **Figures 3** and **5** show a return loss measurement of 17.5 dB at the resonant frequency of 3.2 GHz and measurement of 11.0 dB at the resonant frequency of 11.1 GHz. There is a second S-band resonance seen at a frequency of 2.7 GHz in **Figure 3**, but the radiation characteristics in **Figure 4** show that this is not the dominant S-band resonance. We attribute discrepancies in the depth of the return loss curve in **Figure 5** to manufacturing tolerances in the placement of the pin feeds with respect to the edges of the concentric patch. Since electrical length decreases with wavelength at X-band, smaller tolerance errors can have larger effects than at S-band on the impedance match quality. However, both the simulated and mea-

*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

AM allows engineers to rethink the RF design space. AM facilitates complex designs that required properties not achievable by traditional manufacturing methods. Strides in AM produce robust structural and mechanical parts, but industry has yet to develop a full suite of electromagnetic properties for AM feedstocks. Low dielectric constants of commercial feedstocks limit current antenna designs, but recent research into the composition of high-dielectric feedstocks for AM opens the design space for antennas [12–14]. Additionally, space-filling algorithms paired

sured resonant frequency at X-band is the same as expected.

*Measured and simulated normalized radiation pattern at X-band horizontal port.*

**Figure 5.**

**Figure 6.**

**194**

*Measured and simulated return loss at X-band horizontal port.*

**3.2 Antenna performance using additive manufacturing**

*Fully assembled AM dual-band antenna.*


#### **Table 2.**

*Antenna dimensions in millimeters of 3D printed antenna based on schematic in Figure 1.*

We show the measured versus simulated return loss and realized gain of the dual-band antenna at S-band in **Figures 8** and **9** as well as at X-band in **Figures 10** and **11**. We took all realized gain versus frequency measurements at boresight to the antenna. We see general agreement at both bands for all measurements. One

discrepancy is in the S-band realized gain where measurements are up to 2.0 dB lower than expected from 3.25 to 3.6 GHz. The resonance at S-band is also about 100 MHz or 2.6% off. The X-band resonance and realized gain curves show better agreement than those at S-band. The return loss at X-band is even better than that predicted by simulation and this shows up in **Figure 11** where the measured realized

We attribute measured differences in the return loss to manufacturing toler-

This chapter describes both the benefits and current challenges facing AM for antennas and RF devices. The forefront of which is a lack of commercially available high-dielectric materials that are compatible with filament fed 3D printers. As a comparison, we fabricated two similar antenna designs utilizing multiple nested dielectrics and an embedded shorting wall within the dielectrics to compare performance between traditional materials and manufacturing methods versus those of AM. Due to restricted access to an AM feedstock with the proper dielectric constant, direct comparisons of the two antennas is not the preferred way of comparison. However, experimental results for both prototypes agree well with the simulation data. There also seems to be no degradation in the performance of the AM prototype over the traditional prototype in terms of the agreement with the respective antenna models. With new methods of extruding higher dielectric filaments for FDM 3D printers, AM seems to be a good fit for future work in antenna design especially as antenna and RF front ends grow increasingly complex and more fully

ances since the pin fed patch is an extremely resonant type of feed.

gain is higher than simulation at resonance.

*Realized gain to boresight at S-band horizontal polarization port.*

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

**4. Conclusions**

**Figure 11.**

integrated.

**197**

**Figure 8.** *S-parameters at S-band horizontal polarization port.*

**Figure 9.** *Realized gain to boresight at S-band horizontal polarization port.*

**Figure 10.** *S-parameters at X-band horizontal polarization port.*

*Additive Manufacturing for Antenna Applications DOI: http://dx.doi.org/10.5772/intechopen.92363*

**Figure 11.** *Realized gain to boresight at S-band horizontal polarization port.*

discrepancy is in the S-band realized gain where measurements are up to 2.0 dB lower than expected from 3.25 to 3.6 GHz. The resonance at S-band is also about 100 MHz or 2.6% off. The X-band resonance and realized gain curves show better agreement than those at S-band. The return loss at X-band is even better than that predicted by simulation and this shows up in **Figure 11** where the measured realized gain is higher than simulation at resonance.

We attribute measured differences in the return loss to manufacturing tolerances since the pin fed patch is an extremely resonant type of feed.
