HP HP-Bench-Briefs-1989-01-03 free download

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SERVICE INFORMATION FROM HEWLETT-PACKARD 1st Quarter 1989 How To Build a Stripline Filter John Kristiansen Hew lett-Packard Introduction In a n earlier issue of Bench Briefs, John Kristiansen described the me- chanical steps required to fabricate RF breadboard circuits with copper tape. In this article, John will show you how to apply those same princi- ples of fabrication, combined with a few basic microwave formulas, to construct a microstrip bandpass filter using parallel resonators made of copper tape. If you desire a more accurate filter, you can use the same principles presented in this article to design a filter etched on a PC board. Figure 1. Microstrip is separated from a ground plane by a dielectric substrate (a). Since not all field lines pass through the substrate (b), a quasi-TEM analysis is used. Since we are now dealing with mi- crowave frequencies above 0.5 GHz, this article assumes that the reader N6JH; Rick Campbell, KK7B; and wave hairpin filter. This filter has its has a fair amount of knowledge in James Davey, WASNLC. These arti- elements folded in half with every microwave and microwave cles cover interdigital filters, micro- other element reversed (see Figure 2 instrumentation. wave local oscillators u s i n g a (c)). No ground connections are re- combination of filter and MMICs, and quired. Coupling between elements Fundamental Concepts experiments with microstrip band- of the hairpin filter is closer than in pass filters in the range of 2160 to the parallel strip filters and needs to Let me start out by defining what I 5780 MHz. There is also an IEEE be adjusted through trial and error. mean by a microstrip transmission paper by J . Wong that comes close to According to Mr. Davey, test results line. A microstrip (see Figure 1) a cookbook design of microstrip filters. of the hairpin filter were very good. transmission line consists of a strip Filter loss was 1.5 dB and the ripple conductor and a ground plane sepa- The filters that I have experimented was 0.2 dB. rated by a dielectric medium. The with since 1970 are shown in Figure 2: the 4-pole ungrounded quarter- Using the copper tape fabrication dielectric material serves as a struc- procedure, you can experiment with tural substrate upon which the thin- wave bandpass filte