GPS Patch Antenna Considerations. Advanced Material On TECHnology

Transcription

1 GPS Patch Antenna Considerations Advanced Material On TECHnology

2 Contents Antenna Element Impedance and Resonant Frequency Axial Ratio Voltage Standing Wave Ratio (VSWR) Bandwidth Result of Measurement AMOTECH

3 Antenna Element The antenna s size and shape compact size using ceramic material RHCP(Right Hand Circular Polarization) patch Offset fed rectangular patch Slotted square patch Truncated corner square patch AMOTECH 3

4 Antenna Element AMOTECH - GPS Patch Antenna Õ Õ3.0 compact size : 5mm 5mm 4mm excellent temperature stability (silver plated) truncated corner square patch AMOTECH 4

5 Impedance and Resonant Frequency An antenna s impedance depends on many factors : how it is constructed, how it is fed, and to some degree, the surrounding environment Amicrostrip patch antenna placed in a plastic enclosure (radome), for example, can have its resonant frequency shifted downward by several MHz, depending on the thickness of the radome its dielectric constant and the distance between the antenna face and inner radome. AMOTECH 5

6 Impedance and Resonant Frequency Radome effect on resonant frequency Final Assembly 0 AMOTECH GPS Patch Antenna PCB Radome -5-0 Infinite Ground Sheild Can SMA Type Connector Double Sided Adhesive Tape Assembly without radome Return Loss [db] -5-0 Infinite Ground Frequency shift caused by radome different environment Final Assembly Assembly without Radome Patch on 70 by 70 GND Patch on 70 by 70 ground by70 Ground Frequency [MHz] The final assembly obtains optimized operation over 575.4MHz ± 3MHz AMOTECH 6

7 Axial Ratio General description To be maximally sensitive to GPS signals, the ideal GPS antenna should be perfectly RHCP The more elliptically polarized it is, the lower its RHCP sensitivity The degree of ellipticity is given by the antenna s axial ratio Good GPS antennas have an axial ratio in the zenith direction of 3dB or better. A measurement of the VSWR alone does not guarantee the antenna s axial ratio performance. AMOTECH 7

8 Axial Ratio Measure the Axial Ratio Measuring system in AMOTECH The GPS Patch antenna transmits at the desired frequency. Rotates the linear polarization probe AR = A - B, in db 3 m rotate test probe 7.6 m <Anechoic Chamber> A B è Polarization ellipse Spectrum Analyzer Signal Generator AMOTECH 8 PC

9 Voltage Standing Wave Ratio An important consideration is the antenna-receiver connection. This is achieved with a transmission line, usually a coaxial cable. To maximize signal transfer from the antenna to the receiver, we must minimize power loss. Power may be lost if the coupling between the antenna and the cable is imperfect and also within the cable itself. To prevent power loss at the interface between the cable and the antenna, the impedance of the cable and the antenna must be the same. The formula for relating mismatch loss to VSWR is: VSWR- Mismatch_Loss(dB)=0log - VSWR+ AMOTECH 9

10 Bandwidth Operating bandwidth is defined as frequency range satisfied following: VSWR (<.0) or Return loss (< 0 db) Axial ratio (< 3.0 db) GPS patch antenna designed by AMOTECH satisfies all criteria over the operating frequency range of MHz ± 3 MHz. AMOTECH 0

11 Result of Measurement GPS Antenna installed on Infinite Ground Geometry of final assembly Axial Ratio AMOTECH GPS Patch Antenna PCB Radome 0 8 Infinite Ground Sheild Can SMA Type Connector Double Sided Adhesive Tape Axialratio [db] Frequency [MHz] AMOTECH

12 Result of Measurement GPS Antenna installed on Infinite Ground Return Loss Smith chart 7 May 000 3:8:0 7 May 000 3:8:39 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : m.57 pf GHz.5754 GHz BW : GHz.5754 GHz : m GHz cent : GHz 3: Q: GHz 0 _ loss : db 0 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH

13 Result of Measurement GPS Antenna installed on 70mm 70mm Ground Return Loss Smith chart 7 May 000 3:0:8 7 May 000 3:0:33 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : m pf GHz GHz BW : GHz GHz : GHz cent : GHz 3: Q: GHz _ loss : db 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 3

14 Result of Measurement GPS Antenna installed on 50mm 50mm Ground Return Loss Smith chart 7 May 000 3:4:44 7 May 000 3:5:0 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : pf GHz.576 GHz BW : GHz.576 GHz : GHz cent : GHz 3: Q: GHz 6 _ loss : db 6 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 4

15 Result of Measurement GPS Antenna without Ground Return Loss Smith chart 7 May 000 3:7:44 7 May 000 3:7:57 CH S LOG 5 db/ REF 0 db :-3. 7 db GHz CH S U FS : nh GHz GHz BW : GHz : GHz cent Q: GHz : GHz 3: GHz _ loss : db 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 5

16 Result of Measurement GPS Antenna without Radome on Infinite Ground Geometry of assembly without radome Axial Ratio 0 Infinite Ground Axialratio [db] Frequency [MHz] AMOTECH 6

17 Result of Measurement GPS Antenna without Radome on Infinite Ground Return Loss Smith chart 7 May 000 4:8: 7 May 000 4:8:50 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : ph GHz.585 GHz BW : GHz.585 GHz : GHz cent : GHz 3: Q: GHz 0 _ loss : db 0 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 7

18 Result of Measurement GPS Antenna without double sided adhesive tape Return Loss Smith Chart 7 May 000 4::33 7 May 000 4::55 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : ph GHz.5776 GHz BW : GHz.5776 GHz : GHz cent : GHz 3: Q: GHz _ loss : db 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 8

19 Result of Measurement GPS Patch Antenna on 70 by 70 AMOTECH Test Jig Geometry of patch antenna Axial Ratio 0 70by70 Ground 8 Axialratio [db] Frequency [MHz] AMOTECH 9

20 Result of Measurement GPS Patch Antenna on 70 by 70 AMOTECH Test Jig Return Loss Smith Chart 7 May 000 3:3:03 7 May 000 3:3:8 CH S LOG 5 db/ REF 0 db : db GHz CH S U FS : pf GHz.6086 GHz BW : GHz.6086 GHz : GHz cent : GHz 3: Q: GHz 6 _ loss : db 6 4: GHz CENTER GHz SPAN GHz CENTER GHz SPAN GHz AMOTECH 0