Chapter 3 圆极化微带天线

1、11. Analyze and calculate the inner and outer field expression for circular microstrip patch antenna?2. Design the size and feed point location (back feeding) for both rectangular and circular microstrip patch antenna with the parameters:3. f0=5GHz; dielectric constant=4.5; h=1.8cm; 2In general, an

2、antenna will radiate an elliptical polarization, which is defined by three parameters: axial ratio, tilt angle and sense of rotation.When an axial ratio is infinite or zero, the polarization becomes linear with the tilt angle defining the orientation. Sense is not applicable in this case. The qualit

3、y of a linear polarization is usually indicated by the level of the cross polarization. For a unity axial ratio, a perfect circular polarization results and the tilt angle is not applicable. The axial ratio is generally used to specify the quality of the circularly polarized waves.3Antennas produce

4、circularly polarized waves when two orthogonal field components with equal amplitude but in phase quadrature are radiated. Various MAs are capable of satisfying these requirements. They can be classified as resonator and traveling-wave types.A resonator type antenna consists of a single patch antenn

5、a that is capable of simultaneously supporting two orthogonal modes in phase quadrature;A traveling-wave type of antenna is usually constructed from a microstrip transmission line. It generates circular polarization by radiating orthogonal field components with appropriate phasing along discontinuit

6、ies in the traveling-wave line.4 Characteristics of circular polarized wave Parameters of circular polarized wave Tilt angle Axial ratio5 Polarized lossy coefficient6Typical configurations of dual-fed circularly polarized MAs (a) Circular patch (b) Squre patch Two types of excitations for circularly

7、 polarized MAs(a) Dual-fed patch (b) singly fed patch7In this section, a method for designing a circularly polarized MA with one point feed is given. The derivation is based on a variarional method for resonant frequency of a perturbed cavity as derived by Haneishi. The derivation is first given for

8、 a rectangular patch and then for a cylindrical patch.8The following derivation is applicable for different types of perturbations. They have been classified into type A and type B depending on the feed location. In type A, the feed location is either on the x or the y axis; In type B, the feed is p

9、laced on the diagonal axis of a patch. Note that the feed is always located diagonal to perturbation segments that are appropriately selected to produce two orthogonally degenerate modes in the patch for circularly polarized radiation.3.3.1 Rectangular Type Circularly Polarized MAs9Different types o

10、f antenna for type A and type B1011Following the Ritz-Galerkin method, P and Q can be determined from:This will result in a set of homogeneous equations that have nontrivial solutions only if the determinant vanishes. Exact parameters of the determinant depend on the type of feed and perturbation pl

11、acements. It can generally be written in the form:12Type A Patch Perturbation segments13 Equivalent circuit and equivalent parameters14Type B Patch15 Circular polarization radiation condition16Design equations:Type A patchType B patch17 Design Procedure for Circularly Polarized Patch with a Single-P

12、oint Feed 1. Determine the unloaded Q0 of the patch, which depends on dimensions a, substrate thickness h, and the substrate dielectric constant r. For better accuracy Q0 should be selected to ensure the patch radiation efficiency 90%. 2. Determine the amount of perturbation (S/S) from equation.3. T

13、he location of the feed on the axis can be selected to provide a good match; alternatively a quarter-wavelength transformer can be used for matching purpose.4. Depending on whether each type of the antenna is type A or type B, the sense of circular polarization can be changed by switching the feed a

14、xis.18Variation of radiation efficiency versus substrate thickness (Single fed patch with dimension a=9.14mm, substrate thickness h=1.18mm and r =2.55)19Variation of perturbation segments (S/S) versus patch unloaded Q0.20Variation of axial ratio versus f/f0Variation of CPBW versus Q factor21Variatio

15、n of impedance versus frequency22Design parameters of CP rectangular patch and optimized axial ration frequency23The configuration of a circular patch antenna and its feed system is show beside. The feed is always located at a diagonal with respect to the perturbation segments. Similar to the case o

16、f square patches, the dominant mode TM110 will be separated into two orthogonal degenerated modes by perturbation segments. The analysis follows the same procedure as described in the pervious section for a square patch. 3.3.2 Circularly Polarized Circular MAs24Perturbation segments for CP circular

17、MAs25The equivalent circuit for circular singly fed circularly polarized patch antennas is similar to that of a singly fed rectangular patch. The following parameters are obtained:26Variation of S/S versus Q0Design Equation1101SSQ27Optimized axial ration frequency and S/S for different type of anten

18、nas28Calculate E field radiation patternMeasured radiation pattern29AR versus frequencyInput impedance versus frequency30Optimized AR frequency versus antenna radius a311. Rectangular CP MAs32Dielectric constant versus W/with different d33Relative level versus W/34Dielectric versus d2. Circular CP M

19、As35E-plane and H-plane radiation pattern with different d36Effective permittivity for dual-layer substrates versus h1/h237The fundamental element of microstrip line antennas: (a) Rampart line antenna; (b) chain antenna; (c) square=loop microstrip line antenna; (d) crank-type microstrip line antennaCP traveling-wave microstrip line arrays utilize a rad