A simplified probe feed input impedance for a rectangular patch antenna based on the Green's function is used to design a dual frequency matched antenna. The predicted results at design frequencies of 1.9 and 2.4 GHz are in close agreement with experimental measurements

Korolkiewicz, Edward

Lu, Qing

Shaikh, Z. H.

English

Northumbria Research Link

1APPLICATION OF A SIMPLIFIEDPROBE FEED IMPEDANCEFORMULA TO THE DESIGN OF ADUAL FREQUENCY PATCHANTENNAAuthors: Q.Lu, Z. H. Shaikh, E.Korolkiewicz.School of Computing, Engineering andInformation SciencesNorthumbria University,Newcastle upon Tyne,NE1 8STEngland.ABSTRACT: A simplified probe feed inputimpedance for a rectangular patch antenna basedon the Green’s function is used to design a dualfrequency matched antenna. The predictedresults at design frequencies of 1.9GHz and2.4GHz are in close agreement withexperimental measurements.1. INTRODUCTIONAs there is an increasing demand for wirelesscommunications probe feeds are widely used in,dual frequency, broad band and multi-frequencyband antennas[1, 4]. A number of analyticalmethods have been proposed for the design ofthe patch antennas including, full wave analysis[5, 6], cavity model [7, 8] and transmission-line[7, 9]. In the design of antennas havingcomplicated geometries segmentation and de-segmentation analysis is normally used [10] anda probe feed impedance of a rectangular segmentis required.In this paper, the probe feed impedance for arectangular segment is obtained from thecoupling impedance between a probe feed andanother port. This impedance is then simplifiedand then used to locate the required feed positionto obtain matching at the two frequencies of apatch antenna.The electrical and physical parameters of thesubstrate PCB FR4 used are: dielectric constantis 4.3, the height of substrate is 1.575 mm, theloss tangent is 0.019 and the thickness of thecopper patch is 0.035mm.2. DERIVATION OF THESIMPLIFIED PROBE FEEDIMPEDANCEFigure 1 shows the locations of the probe fedport p and an arbitrary port q of a rectangularpatch antenna.Figure 1 Locations of ports p and qThe coupling impedance (Zpq) between the twoports in terms of the Green’s function is given by2where dyp and dyq are incremental distances overthe port widths Wp, Wq [11]. To ensure that thecurrent density does not vary appreciably acrossthe ports Wp, Wq Wp , Wq << λ [12]. The Green’sfunction for a rectangular segment is given by[12]where,ω=2πf, h is the thickness of the dielectricsubstrate, k2 =ω2με0εreff (1 - j/Q), Q is the totalquality factor (Q is equal to 43.5), A=ak/πandB=bk/π. Letting the ‘q’ approach ‘p’ and theintegrating each part of the partition Green’sfunction the probe feed impedance Zpp is givenby [14]Where,and, ,And Wp = 1.3 mm, which is the diameter of theprobe feed.In examining equation 3 it is found that thecombined contribution of the terms –Wp² /k2, andthe infinite series S3 is negligible so that equationfor the final simplified probe impedance ZPPbecomes3. DESIGN OF A DUALFREQUENCY MATCHED PATCHANTENNAFor a rectangular patch antenna shown in figure2, the physical lengths L (1.9GHz), W (2.4 GHz)and the feed position ‘C’ for matching need to bedetermined.Figure 2 Dimensions and Feed Position of thePatch Antenna3The effective dimensions of the patch and thepermittivity for the TM10 and TM01 modes aregiven by the equations below [13]In Table 1 the initial length L1 is obtainedassuming εr = εreff = 4.3 and then W1 isdetermined using equation 5(b). The final valuesL5 and W5 are determined by an iterative process(see table 1) where a very rapid conversion isobtained. The final physical dimensions of theantenna are L (1.9GHz) =38mm and W (2.4GHz)=29mm.Table 1The approximate feed position ‘C’ is shown onin Figure 2 [14], where matched feed positions‘A10’ and ‘B01’ are for the TM10 and TM01 modesrespectively.For the TM10 mode the position ‘A10’ is obtainedusingFor the TM01 mode the position ‘B01’ is obtainedusingThe equivalent circuit of the antenna shown infigure 3 was fine tuned using AWR software toobtain the optimum feed position (A10= 25.42mm and B01= 20.92 mm) for matching at bothfrequencies.Figure 3 Transmission Line Equivalent Circuitof the Antenna4. Results and ConclusionsA photograph of the fabricated antenna is shownin figure 4.Figure 4 Photograph of the Fabricated PatchAntenna4The frequency responses of the return lossobtained from practical measurements and fromthe derived probe feed equation are shown infigure 5.Return Loss-40-35-30-25-20-15-10-501.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8Frequency (GHz)ReturnLoss(dB)Practical ResultPredicted ResultFigure 5 Practical and Simulated Results forthe Return LossThe polar patterns of the antenna at 1.9GHz and2.4GHz are shown in figure 6 where there is avery good isolation between the two modes hasbeen obtained.(a)(b)Figure 6 Polar Pattern at (a) 1.9 GHz and(b) at 2.4 GHzConclusionA simplified equation for the probe fedrectangular patch has been derived and used inthe design of a dual frequency rectangular patchantenna. The predicted results for the feedimpedance were compared with those obtainedfrom the transmission line model and frompractical measurements. A very good agreementhas been obtained for all results.The derived equation can also be used insegmentation/d-segmentation analysis ofcomplicated antenna geometries where the probefeed segment has rectangular geometry.References[1] R.C. Hua, C. F. Chou, S. J. Wu and T. G. Ma,“Compact multiband planar monopole antennasfor smart phone applications”, IET Microwave.Antennas and Propagation. Vol. 2, No. 5, pp.473–481, 20085[2] D. Guha, Y.M.M. Antar, J.Y. Siddiqui andM. Biswas, “Resonant resistance of probe andmicrostrip-line-fed circular microstrip patches”,IEE Proc. Microw. Antennas Propag, Vol. 152,No. 6, December 2005.[3] R. Garg, P. Bhartia, I. Bahl, and A.Ittipiboon, “Microstrip Antenna DesignHandbook”. London: Artech House, 2001.[4] E. G. Lim, “Circular polarized microstripantenna design using segmental methods,” Ph.D.Thesis, University of Northumbria at Newcastle,U.K., 2002.[5] J. R. Mosig and F. E. Gardiol, “Generalintegral equation formulation for microstripantenna and scatterers,” IEE Proc., part H, vol.132, no. 7, pp. 424-432, Dec. 1985.[6] R. Garg, P. Bhartia, I. Bahl, and A.Ittipiboon, “Microstrip Antenna DesignHandbook”. London: Artech House, 2001.[7] Y. T. Lo, D. Solomon, and W. F. Richards,“Theory and experiment on microstripantennas,” IEEE Trans. Antennas Propagat. ,vol. AP-27, no. 2, pp. 137-145, Mar. 1979[8] M.A. Matin, B.S. Sharif and C.C. Tsimenidis,“Dual layer stacked rectangular microstrip patchantenna for ultra wideband applications”, IETMicrow, Antennas Propag, 1, (6), pp. 1192–1196, 2007[9] K. Moussakhani and A. Ghorbani, “A noveltransmission line model for analyzing bowtiepatch antennas,” in Progress in ElectromagneticsResearch Symp., Cambridge, USA, Mar. pp.168-171, 2006[10]T. Okoshi, Y. Uehara and T. Takeuchi, ‘Thesegmentation method-an approach to the analysisof microwave planer circuits,’ IEEE Trans.Microw. Theory Tech., 24. pp. 662-668, 1976.[11] T. Okoshi, Planar Circuits for Microwaveand Lightwaves. New York: Springer-Verlag,1985.[12] R. Garg, P. Bhartia, I. Bahl, and A.Ittipiboon, Microstrip Antenna DesignHandbook. Norwood, MA: Artech House, 2001.[13] C. A. Balanis, Antenna Theory: Analysisand Design. New York: Wiley, 1997.[14] J. S Chen and K. L. Wong, “A single-layerdual-frequency rectangular microstrip patchantenna using a single probe feed,” Microwaveand Optical Technology Letters, Vol.11, pp.83-84, 1996

A novel transmission line model for analyzing bowtie patch antennas,”

A single-layer dual-frequency rectangular microstrip patch antenna using a single probe feed,”

Antenna Theory: Analysis and Design.

Circular polarized microstrip antenna design using segmental methods,” Ph.D. Thesis,

Compact multiband planar monopole antennas for smart phone applications”,

Dual layer stacked rectangular microstrip patch antenna for ultra wideband applications”,

General integral equation formulation for microstrip antenna and scatterers,”

Microstrip Antenna Design Handbook.

Microstrip Antenna Design Handbook”. London: Artech House,

Planar Circuits for Microwave and Lightwaves.

Resonant resistance of probe and microstrip-line-fed circular microstrip patches”,

The segmentation method-an approach to the analysis of microwave planer circuits,’

Theory and experiment on microstrip antennas,”

Application of a simplified probe feed impedance formula to the design of a dual frequency patch antenna

Application of a simplified probe feed impedance formula to the design of a dual frequency patch antenna

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