A substrate for small patch antennas providing tunable miniaturization factors

TLDR: In this paper, a patch antenna tested the performance of the magnetic metamaterial as a substrate and validated that a single substrate can achieve a range of miniaturization values with acceptable loss-factor levels.

Abstract: Magnetic properties were imparted to a naturally nonmagnetic material by metallic inclusions. A patch antenna tested the performance of the magnetic metamaterial as a substrate and validated that a single substrate can achieve a range of miniaturization values. The effective medium metamaterial substrate employed electromagnetically small embedded circuits (ECs) to achieve permeability and permittivity greater than that of the host dielectric. Geometric control of the ECs allowed mu and epsi to be tailored to the application. The magnetic metamaterial exhibited enhanced mu and epsi with acceptable loss-factor levels. Models for predicting mu and epsi are presented, the benefits of employing metamaterial substrates are discussed, and the results in this antenna experiment are presented. The metamaterial exhibits performance characteristics not achievable from natural materials. Of particular significance is that with the permeability varying strongly and predictably with frequency, the miniaturization factor may be selected by tuning the operating frequency. Simulations indicate that such performance can be extended to several gigahertz with current technology. Relative permeability values in the mur=1-5 range are achievable for moderately low-loss applications. Representative antenna miniaturization factors on the order of 4-7 over a moderate (approximately 10%) transmission bandwidth and efficiencies in a moderate range (20%-35%) are demonstrated with the possibility of higher efficiencies indicated

Figures

TABLE II MINIATURIZATION AND EFFICIENCY

Fig. 1. Measured magnetic permeability and loss tangent of Z-phase Cobalt HexaFerrite (solid and dashed lines, respectively).

Fig. 11. Finite-element method (FEM) boundary conditions to test resonance frequency.

Fig. 12. Relative permittivity and permeability of metamaterial. At 250 MHz,

Fig. 10. Higher order spiral-loop equivalent-circuit model.

Fig. 3 is printed onto an planar surface. These infinite

Frequently asked questions

Q1. What are the contributions mentioned in the paper "A substrate for small patch antennas providing tunable miniaturization factors" ?

Models for predicting and are presented, the benefits of employing metamaterial substrates are discussed, and the results in this antenna experiment are presented. 

Q2. How many air holes were drilled into the center of each spiral resonator cell?

To reduce substrate mass, 33/64-in-diameter air holes were drilled along the -axis into the center of each spiral resonator cell. 

Q3. What is the effect of magnetic moments on a ferrimagnetic material?

In the presence of a magnetic field, the magnetic moments of a ferrimagnetic material tend to become aligned with the applied field and to reinforce it by virtue of their own magnetic fields. 

Q4. What is the purpose of this method of assembly?

This method of assembly allows for the critical control of geometrically determinedcircuit parameters and thereby selection of resonant frequency and coupling factors. 

Q5. What is the design for optimal magnetic permeability?

A good design for optimal magnetic permeability would “enclose” as much of the unit-cell area as possible to achieve the highest coupling of incident magnetic energy while maximizing packing density. 

Q6. What is the benefit of minimizing the energy loss due to the reflection at this interface?

The benefit to minimizing the energy loss due to the reflection at this interface is obvious and further anticipated benefits are improvements in matching and bandwidth as a result of increasing the proportion of magnetic energy storage. 

Q7. What is the mechanism of low-loss operation of a magnetic material?

If a mechanism similar to natural magnetics can be developed for microwave operation by synthetic means, low-loss operation may be pushed into the microwave region and low-loss microwave magneto-dielectrics may become a reality. 

Q8. What frequency is the upper frequency end of the magnetic region for high-quality ferrites?

for magnetic materials, the upper frequency end of the magnetic region for high-quality ferrites, limited by the gyromagnetic resonances, occurs in the VHF–UHF range, which is too low a frequency for microwave applications. 

Q9. What is the effective permittivity of the parallel-plate capacitor?

The host dielectric itself (Rogers-RO4003) possesses a permittivity of only at 2.5 GHz, whereas the parallel-plate capacitor fabricated from the EC metamaterial substrate exhibited an effective permittivity of . 

Q10. What is the promising magnetism in ceramics?

and most promisingly is ferrimagnetism—a magnetism exhibited by some ceramics as a result of their complex crystal structure. 

Q11. What is the effect of gyromagnetic resonance on the materials?

As gyromagnetic resonance is approached, the materials loss factor increases dramatically, as exhibited in Fig. 1, and above resonance, the material becomes essentially nonmagnetic. 

Q12. What is the reason for the deviation from theory?

This deviation from theory (11) may be due to fringing fields coupling into the under hanging and adjacent loops, or variances in the distances between the spiral edge and the ground-plane or patch metallization. 

Q13. What is the popular area of research for EC metamaterials?

Recent experimental work builds upon the theoretical development for left-handed materials provided by Veselago and is perhaps the most popular area of research for EC metamaterials [10]–[15]. 

Q14. How much did the air holes reduce the effective permittivity of the medium?

It was found that the inclusion of these air holes reduced the effective permittivity of the medium along the - and -axis by only 5%. 

Q15. What is the effect of the nonmagnetic orientation of operation on the antenna?

That the nonmagnetic orientation of operation yields significant losses indicates that the losses observed in the permeability-enhanced orientation are not entirely caused by the magnetic loss tangent itself. 

Q16. What is the miniaturization factor of a patch antenna?

A patch antenna in free space will resonate with a length of approximately and, for their purposes, the miniaturization factor is defined as the fraction of this size for which the patch resonates. 

Q17. What is the frequency independent form for permittivity?

The frequency independent form for permittivity given in (11) indicates that a low-frequency measurement of a parallel-plate metamaterial capacitor would give a reasonable estimate of the high-frequency permittivity in the patch-antenna design if the host dielectric itself is nondispersive.