Abstract— Thispaper proposes a novel design and performance analysis of a corporate-feedmicrostrip patch aerial array and a rectangular microstrip patch aerial. Thedesign has been performed by considering flame retardant glass epoxy substrate(FR4) having a thickness ‘h’ of 1.6mm, loss tangent () of 0.02 and a value of 4.4 as dielectric constant ().
The simulations are done using HFSS by Ansoft for the corporate-feedaerial array (the array axis along the non-radiating slot of the aerial) aswell as for the single patch aerial resonating at 2.4GHz. This proposed work isfocused on providing a great support to the increasing medical applicationsusing microstrip patch aerials. The boosted gain obtained from this design is agreat deal for all the ISM band applications. Index Terms—Corporate feed, Dielectric Constant, Loss Tangent, Microstrip, Patch, Non-RadiatingSlots, Substrate. I. INTRODUCTIONThe constantincrease in the devices operating in the ISM bands has generated a need forthis paper.
The usage of microstrip patch aerials for medical applications hasbeen immensely growing in the recent years. This is predominantly due to thesize compatibility, ease in fabrication process and the robustness of themicrostrip patch aerials. These aerials can be made to resonate at radiofrequencies with a great ease. The ISM band applications includes diathermy,microwave ovens, microwave ablation, etc. Once the design is done it can befabricated easily on a printed circuit board (PCB). Generally in an aerialmodel the patch is the radiator (either transmitter or receiver) which isplaced on the top of the substrate. The flame retardant glass epoxy substrate(FR4) is used as dielectric medium between patch and ground. The ground elementwhich is also a conducting plane is placed on the base of the substrate.
Aninset feed is designed to match an impedance of 50Ohms for the main feed and100Ohms for the array elements. Arectangular shaped patch is taken with the dimensions of LxW, where the lengthof the patch is ‘L’ and the width of the patch is ‘W’. This rectangular patchcan be arranged in an array manner fed by the either through corporate-feedconfiguration or through series-feed configuration.
The importance is given toparametrical analysis of return loss, gain and field pattern of the aerialresonating at 2.4GHz. Though a detailed analysis of all the aerial parametersis appreciable, the focus has been prioritized mainly on gain parameter sincethe design is established for arrays. A comprehensive study is done among thetwo proposed models namely the single patch aerial and the corporate-feed aerialarray (the array axis placed along the non-radiating slot of the aerial). It isvital that length ‘Lm’ of the main feed, the distance ‘d’ between the twopatches and the length ‘Lf’ of the individual feeds should be optimized.
Consequently it is also essential to take an account of various other effects whichincludes internal reflections and coupling.II. Design of Corporate-Feed aerial arraysThe proposed aerial is designed for two array elements in acorporate-fed manner. The dimensions of the aerial are calculated for aresonant frequency of 2.4GHz. Let the distance between the patches be ‘d’ andthe length of the feed be ‘Lm’ and ‘Lf’ as shown in the Fig. 2.
The width ‘Mf’and ‘Wf’ are designed to match the impedance of 50Ohms and 100Ohmsrespectively. The Fig. 1 shows the rectangular microstrip patch aerial and theFig.
2 shows the design of the corporate-feed aerial array. A. Geometry of asingle patch aerial Let, the width of the patch be W, the length of the patch be L, theeffective dielectric constant be and the incremental length be for the account of fringing effect. The designformula of patch aerial are given as follows, (1) (2) (3) (4) Using the above said formula, thevarious aerial parameters are calculated and tabulated as shown in the Table 1. TABLE 1SPECIFICATIONS OF THE SINGLE PATCH AERIAL Symbol Quantity Values (in m) W Width of the patch 0.03802 L Length of the patch 0.02946 h Substrate thickness 0.
0016 g Gap between feed line and patch 0.0003 Lf Feed length 0.02093 y Inset Depth 0.01032 Wf Feed width 0.
00257 a,b Effective Length and Width 0.005 Fig.1.
Rectangular microstrip patch aerial To match the input impedance, thefeed width (Wf) and inset depth are calculated as 2.57mm and 10.32mmrespectively. For better result, the gap ‘g’ between the inset feed line and thepatch is optimized to 0.
3mm. B. Geometry of an Aerialarray using corporate-feedThe Fig. 2shows the proposed aerial array using the corporate-feed configuration.
Optimization is done for the parameters ‘d’, ‘Lf’ and ‘Lm’. For thecorporate-feed, the main feed ‘Mf’ is calculated to be 2.57mm and the width’Wf’ of the individual feeds are calculated to be 0.44mm.Fig. 2.
Corporate-feed microstrip patch aerial array ormicrostrip patch aerial array in non-radiating slot.III. SimulationAnd AnalysisA.
Simulated result analysis The various parameters like field pattern, impedance matching,return loss and gain are analyzed using HFSS (High Frequency StructureSimulator). The variation in length ‘Lm’of the main feed shows that as the length increases, the gain decreases whichis shown in the Fig.3. The variation in length ‘Lf’ of the individual showsthat as the feed length increases, the gain increases steadily as shown in theFig. 4. Similarly the Fig. 5 shows the variation of the distance ‘d’ betweenthe patches.
The variation in ‘d’ shows that as the distance between thepatches increase the gain of the aerial increases constantly. Since the size ofaerial is a very critical constraint, the optimum distance is chosen as 50mm.The optimized values are highlighted as shown in the Table 2, 3 and 4. TABLE 2 TABLE3 TABLE4VARIATION OF’Lm’ VARIATIONOF ‘Lf’ VARIATIONOF ‘d’ ‘Lm’ (in mm) Gain (in dB) Return Loss (in dB) (At 2.4GHz) 1 5.04 -10 5 5.30 -10.
5 10 5.76 -9.5 15 4.85 -9 20 4.
43 -8.5 41.86 2.8 -11.5 ‘Lf’ (in mm) Gain (in dB) Return Loss (in dB) (At 2.4GHz) 5 4.16 -14 10 4.98 -11 20.
93 5.3 -10.5 30 5.
57 -11.5 35 5.70 -12 41.86 5.73 -13 ‘d’ (in mm) Gain (in dB) Return Loss (in dB) (At 2.4GHz) 10 4.39 -10.5 15 4.
78 -9.5 20.93 5.06 -9 25 5.09 -9.
5 35 5.25 -10.8 50 5.55 -12.2 Fig. 3 Fig.4 Fig.5VARIATION OF’Lm’ VARIATIONOF ‘Lf’ VARIATIONOF ‘d’ The gainobtained for both the aerials are 3.
41dB and 5.55dB as shown in the Fig. 6 andFig.7. The single patch aerial resonates at a frequency of 2.4GHz with a returnloss of -23dB as shown in the Fig.
8 with a lower gain than that of the corporate-feedaerial. The Fig. 9 shows that the corporate-feed aerial array resonating at2.35GHz with a return loss of nearly -12.5dB. The Fig.
10 and Fig. 11illustrate the field pattern of the single patch and aerial array networkrespectively. The Fig. 12 and Fig. 13 depicts the impedance matchingcharacteristics of the two aerials respectively using the Smith chart. Inaddition, it may be proven that by adjusting the distance between the elementsin the array, the impedance can be matched more accurately. Fig.
6. Gain of the single patch aerial Fig. 7. Gain of the corporate-feed microstrip patch aerial array Fig. 8.
Return loss of the single patch aerial Fig. 9. Return loss of the corporate-feed microstrip patch aerial array Fig. 10. Field pattern of the single patch aerial Fig. 11.
Field pattern of the corporate-feed microstrip patch aerial array Fig. 12. Smith chart of the single patch aerial Fig. 13. Smith chart of the corporate-feed microstrip patch aerial array The radiation pattern of single patchaerial has minimum level of minor lobe compared to that of the corporate feedaerial array, while the latter aerial still having a higher gain. Reasonable levelof impedance matching is achieved in single patch aerial. Due to structuralvariation, the impedance of array aerial changes from the calculated value andhence, better impedance matching could not be achieved. The gain (in dB) andthe return loss (in dB) of two aerials are tabulated in Table 5.
The gain of the single patch aerial is 3.41dBand the gain of the corporate-feed aerial array is about 5.6dB.TABLE5COMPARISON BETWEEN THE SINGLEPATCH AERIAL AND CORPORATE-FEED ARRAY Parameter Single Patch Aerial Aerial Array (Corporate-Feed) Gain 3.
41dB 5.55dB Return Loss -23dB at a frequency of 2.4GHz -12.5dB at a frequency of 2.5GHz B. Measurement and inferencesA well calibrated vector networkanalyzer is chosen for testing the fabricated aerials: single patch andcorporate-feed array.
The calibration is performed using calibration kit whichincludes open, matched loads and short. The measurement is done for both thesingle patch aerial and the corporate-fed aerial. A good correspondence is obtained between thesimulated results and the measured results for the return loss.
The slightdeviation in the measured result from the simulated result is endorsed due tothe fabrication. The Fig. 14 and Fig. 15 shows the hardware testing of thesingle patch aerial and the corporate-feed aerial array using the vectoranalyzer. The performance curves are recorded as illustrated in the Fig 16 andFig.
17 for the single patch aerial and the corporate-feed aerial arrayrespectively. Fig. 14 Testing of the Single Patch Aerial using VNA Fig. 15. Testing of the microstrip Patch Aerial array in corporate-feed configuration using VNA Fig. 16.
Response of the Single Patch Aerial using VNA Fig. 17. Response of the microstrip patch Aerial array in corporate-feed configuration using VNA IV.
ConclusionAn experimental analysis andsimulation analysis has been done for the proposed aerials which has been constructedwith the dimensions 55.33mmx48.02mmx1.60mm for the single patchaerial and 60.39mmx136.04mmx1.
60mm for the array aerial in the non-radiatingslot. It has been observed that the corporate-feed aerial has boosted gainmaking it very suitable for the ISM band applications as well as for otherwireless applications. Thus, in comparison with the 3.
41dB gain obtained fromthe single patch aerial, the designed aerial array has shown an improvement ingain which is nearly 5.6dB. Hence this improvement in gain is achieved incompensation with the return loss. AcknowledgementAuthors are thankful to the University GrantCommission (UGC), New Delhi for sanctioning fund and supporting this work underUGC minor research project. References 1 Constantine. A.Balanis, “Microstrip Antannas,” in Antenna Theory, 3rd ed.
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