39 3.1 Variation of gain in the lower and upper operating bands of dual-band ETDRA. The motivation for this thesis is discussed according to the latest in the analysis and design of dielectric resonator antennas.
Dielectric Resonator Antennas
Certain properties of DRA make it an outstanding candidate among small antennas. By choosing the right material and the value of ǫr, the size of the antenna can be significantly reduced.
Fundamentals of Dielectric Resonator Antennas
The DRA is mounted on a conductive ground plate and the coaxial feed probe protrudes into the cylindrical dielectric block through the bottom of the ground plate. The DRA drilling is required for maximum coupling between the coaxial probe and the excited mode fields within the cylindrical dielectric block.
Survey of relevant literature
Survey of DRA shapes
Other forms of triangular shaped DRA have also been recently reported in the literature [68–70]. DRAs of other different cross-sections available in the literature include conical DRA [71, 72], pyramidal DRA [73, 74], elliptical DRA [75–79], tetrahedral DRA [19, 80], hexagonal DRA [81– 83]; most of them have not yet been thoroughly researched. The geometry of some available and popular DRAs in the literature is shown in Figure 1.2.
Survey based on utility and performance
- Survey on broadband DRAs
- Survey on multi-band operating DRAs
- Survey on high gain DRAs
- Survey on circularly polarized DRAs
Other techniques such as cavity back [160], integration of DRA with slots [161], defect ground plane [162] and introduction of fractal geometry [163] of DRA are also reported in the literature to achieve dual-band operation. DRA with metallic coating for tri-band operation is also reported in the literature as described in detail in [166].
Motivation of the Present Work
Some of the wideband circularly polarized DRA reported in the literature using other approaches are discussed in [224–229] . The dielectric loading basically affects the impedance matching of the antenna around the desired operating frequency.
Thesis Contribution
However, understanding this dielectric loading phenomenon in a broader perspective can solve some of the challenges in designing multiband antennas. Some of the challenges and considerations in designing dual-band/multi-band DRAs are also discussed. iv).
Thesis Organization
The chapter initially discusses the design of dielectric charged monopole antenna for dual band operation that can be operated in the WLAN frequency bands of 2.4-2.5 GHz and 5.75-5.85 GHz. A discussion on dielectric loading with different dielectric shapes is then presented and case studies, where deviations in the modeling of the proposed antenna are observed, are also presented in the subsequent section.
Summary
Issues effecting resonant frequency of the excited modes inside ETDRA
Such deviations in the resonant frequency of the TMm,n,p mode were first reported by Yoshihiko in [53]. The modified ETDRA resonance frequency can then be expressed as detailed in [62] given by;. 2.11).
Quality factor of TM 10δ mode in ETDRA
Theoretical Background
For a perfectly matched dielectric resonator antenna with a lossy dielectric material, excited with a source of characteristic impedance Z0, the Q factor can be expressed in terms of fractional impedance bandwidth (BW) as given in The bandwidth (BW) of this antenna operated in such a mode can be estimated from the quality factor Q.
Q-factor curves for TM 10δ mode in ETDRA
Therefore, the quality factor serves as a useful information about the bandwidth of the antenna operating with a particular mode at a specific resonant frequency. The resonant frequency obtained through simulation is compared and verified with the theoretical resonant frequency before calculating Q.
Q-factor comparison with the reported ETDRA in the literature
Bandwidth Performance of TM 10δ mode in ETDRA
However, the percentage change in impedance bandwidth depends on the size and dielectric value of the DRA. At a certain value of T (T6= 1), the impedance bandwidth is higher than the impedance bandwidth obtained in the case of T=1.
Summary
The proposed dual-band ETDRA configurations are excited using a conventional coaxial feed. We also propose two configurations of dual-band ETDRA; (i) use of single ETDRA and (ii) use of two ETDRAs.
Dual-band ETDRA: A preliminary investigation
Design of dual-band ETDRA for WLAN application: Design-I
Furthermore, the performance comparison of the proposed configurations of the dual-band ETDRA with other dual-band DRAs reported in the literature is also discussed in this section.
Results and discussions: Design-I
This ETDRA configuration can be used as a dual-band antenna for WLAN applications. Although this dual-band ETDRA configuration was intended to achieve a similar radiation pattern at both operating frequencies, it is noticeable that they are not alike.
Investigation on dual-band ETDRAs for WLAN applications
Dual-band ETDRA: Configuration-I
- Results and discussion: Configuration-I
By careful examination of the field distribution in the standing wave as shown in Fig. The peak gain variations in the lower and upper operating bands of Configuration-I are shown in Fig.
Dual-band ETDRA: Configuration-II
- Results and discussion: configuration-II
The radiation pattern of the configuration-II at the frequencies of 2.45 GHz and 5.8 GHz is shown in Fig.
Comparison of the proposed antennas with existing dual-band DRAs in the
Therefore, both configurations have similar differences (in terms of gain performance) from other dual-band DRAs reported in the literature. Therefore, the proposed configurations of ETDRAs can work as a dual-band antenna and be used for WLAN applications.
Challenges in the design of dual-band/ multi-band DRAs
A similar effect is observed at 5.8 GHz of configuration II of the proposed dual-band ETDRAs. The specification of the dielectric material used in the design of DRAs also makes a significant contribution to antenna performance.
Summary
In the previous chapter we discussed how ETDRAs can be designed to work as a dual band antenna. However, some of these challenges are not present in the design of wideband DRAs, since the wideband DRAs are much easier to realize.
Introduction to the modes of Rhombic DRA
This mode can be easily excited within the proposed Rhombic DRA by the angle feeding technique, i.e., the mode field distributions are similar to the TExδ11 mode excited within the rectangular DRA.
Higher order TE modes
The field distribution of the (TE2)x mode is similar to that of the TExδ21 mode in the rectangular DRA. The E-field distribution of the (TE3)y mode has three half-cycles along the diagonal d1, allowing another excitation point where the power supply is placed at ∼d1/3 of the angle of the DRA along the x-axis.
Resonant frequency calculation of the new Rhombic DRA
All empirical resonance frequency values of the excited modes are within a margin of error of 6% of the simulated value. This is due to the small error introduced in the empirical formulas, as well as the small shift in the measured resonant frequency due to manufacturing tolerances.
Feeding techniques
A prototype of the proposed Rhombic DRA is fabricated and the same is shown in Figure 4.10(a). The DRA is excited near one of the corners of the DRA containing the diagonal d1 (as shown in Figure 4.10(b)).
Radiation characteristics of higher order TE modes of Rhombic DRA
- Characteristics of (TE 2 ) y mode operation
- Characteristics of (TE 2 ) x mode operation
- Characteristics of (TE 3 ) y mode operation
- Characteristics of (TE 3 ) x mode operation
Low profile Rhombic DRA: Resonant frequency and Radiation characteristics
The theoretically calculated resonance frequency of (TE3)x mode excited within the fabricated prototype of the proposed Rhombic DRA is obtained 6.5198 GHz. In this configuration, the resonance frequency of the dominant and the higher order TE modes are very close.
Design and Excitation of wideband Rhombic DRA
Results and discussions
The wide impedance bandwidth achieved with this configuration of the proposed Rhombic DRA is shown in |S11| plot of Figure 4.22. The measured impedance bandwidth of the fabricated prototype of the proposed DRA is nearly 1 GHz.
Performance comparison with existing DRAs in the literature
Summary
The performance characteristics of the proposed broadband Rhombic DRA are also compared with the performance of other basic DRA geometries presented in the literature. The performance of these proposed antennas is also compared with some of the practical DRAs reported in the literature.
Design of dielectric loaded monopole dual-band antenna
The dimensions of the block are fine-tuned to achieve an upper operating impedance bandwidth in the range of 5.75-5.85 GHz, without compromising impedance matching in the lower operating band of 2.4-2.5 GHz. The impedance matching and the resonance seen in the 5.75-5.85 GHz band is due to the presence of the dielectric, which allows higher harmonics to appear due to the dielectric loading effect.
Modeling of dielectric loaded monopole dual-band antenna
For example, when the simulations are run for resonance around 6.2 GHz and impedance matching in the 6.15-6.25 GHz band, the curve follows equation (5.1) with a k-value of 26.7. The variation of dielectric volume with ûr for both bands is shown in Figure 5.4.
Dielectric loading with different geometries
Effect of choosing different volume and dielectric constant for different shapes . 98
Representative plots for the following cases are presented: (a) radiation diagrams for rectangular volume dielectric (ǫr=4.1) charged monopole as shown in Figure 5.8, (b) radiation plots for triangular prism shaped volume dielectric (ǫr=6.15) charged monopole as in Figure 5.9 shown, (c) radiation plots for semi-cylindrical volume dielectric (ǫr=9.2) charged monopole as shown in Figure 5.10 and (d) radiation plots for axially cut conical volume dielectric (ǫr=10.2) charged monopole as shown in Figure 5.11. However, at 5.8 GHz a small variation in the gain is observed for different shapes of the dielectric load.
Cases where deviations are observed
Height of the geometries not comparable to the height of metal strip monopole 102
The simulated realized gain of the monopole strip loaded with dielectrics at 2.45 GHz and 5.8 GHz, for some of the dielectric shapes are shown in Table 5.2 We observe that at 2.45 GHz, the realized gain does not change much. Here, the radius of the dielectric shape, which is the only possible dimension that can be changed, is kept comparable to the height of the metal strip, and simulations are performed to observe the effect of loading on impedance matching as well as resonance around operating frequencies.
5.8 GHz curve fitting line 6 GHz curve fitting line 6.2 GHz curve fitting line HFSS Simulation 5.8 GHz HFSS Simulation 6 GHz HFSS Simulation 6.2 GHz. The volume of the dielectric block corresponding to the value of the dielectric constant is almost doubled, which requires loading the monopole with bulky dielectric blocks to ensure proper impedance matching and resonance around 5.8 GHz.
Practical observations of dielectric loaded dual-band antennas
A prototype of such a geometry with rectangular dielectric loading across the monopole strip has also been fabricated and is shown in Figure 5.15(a). The return loss for a monopole antenna only and with dielectric load is shown in Figure 5.15(b).
Conclusion
A prototype of the same is made for the case of a rectangular dielectric loaded monopole that can be used as a dual-band antenna for WLAN applications. We investigated the Q-factor and impedance bandwidth performance of the dominant TM10δ mode excited inside an ETDRA.
Suggestions for possible Future Work
Zhang, "Compact Asymmetrical T-Shaped Dilectric Resonator Antenne for Broadband Applications," IEEE Transactions on Antennas and Propagation, vol. Niroo-Jazi, "Z-Shaped Dilectric Resonator Antenna for Ultrawideband Applications,"IEEE Transactions on Antennas and Propagation, vol.
Geometry of the proposed Rhombic DRA
Feeding techniques: (a) Type-I feeding (b) center feeding and (c) Type-II feeding
Feed configuration for exciting wideband Rhombic DRA
