Drewniak, James L.

Mayes, P. E.

Tanner, D.

Waller, R.

English

Missouri University of Science and Technology (Missouri S&T): Scholars' Mine

Missouri University of Science and Technology Scholars' Mine Electrical and Computer Engineering Faculty Research & Creative Works Electrical and Computer Engineering 01 Jun 1986 A Log-Spiral, Radiating-Line Antenna James L. Drewniak Missouri University of Science and Technology, drewniak@mst.edu P. E. Mayes D. Tanner R. Waller Follow this and additional works at: https://scholarsmine.mst.edu/ele_comeng_facwork  Part of the Electrical and Computer Engineering Commons Recommended Citation J. L. Drewniak et al., "A Log-Spiral, Radiating-Line Antenna," Proceedings of the Antennas and Propagation Society International Symposium (1986, Philadelphia, PA), pp. 773-776, Institute of Electrical and Electronics Engineers (IEEE), Jun 1986. The definitive version is available at https://doi.org/10.1109/APS.1986.1149695 This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in Electrical and Computer Engineering Faculty Research & Creative Works by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact scholarsmine@mst.edu. A LOG-SPIRAL, RADIATING-LINE ANTENNA J. Drewniak, P. Mayes, D. Tanner, and R. Waller Electromagnetics Laboratory Electr ical  and Computer Engineering Department University of I l l i n o i s ,  Urbana, I l l i n o i s  INTRODUCTION The log-spiral,  radiating-line  antenna has low-profile geometry similar to   t ha t  of microstrip  patch  antennas, b u t  has  the potential for operating  over much wider  bandwidths. To achieve th i s  r e su l t ,  a mode of operation that is fundamentally different  from that of conventional  c vity-backed s p i r a l s  has been investigated. ANTENNA STRUCTURE The log-spiral,  radiating-line  antenna is a traveling wave s t ruc ture   in  which one or more logarithmic  spiral  arms are  excited  against a closely  spaced  conical ground surface.  Side and top views of a one-arm antenna  are shown in  Figure 1 .  The space between t h e  f l a t  s p i r a l  and the conical conductor contains just enough foam d ie l ec t r i c   t o  support  he  spiral. The center conductor of a small-diameter  coaxial  cable is attached  to  the s p i r a l  through a transition region and the shield of the cable is attached to the cone. ANTENNA PERFORMANCE Near-field measurements have been made by probing  through the conical  conducting  surface  underneath  t e  edges of the arm. These data correspond closely to a wave traveling faster than the free-space phase velocity along the outside edge and slower than the free-space phase velocity along t h e  inside edge. As a resu l t  there is appreciable radiation from the wave a s  it travels along the spiral  a r m .  The near-field measurements have a l so  shown that  t h e  amplitude of the wave decays rapidly with distance away from the Peed point. Since  v ry l i t t l e  energy  reaches  the outer  radius of the structure,  the truncation at  that  point has l i t t le influence upon the  b havior of the  input impedance. Measurements of input impedance over the  band of 1-12 GHz form a relat ively compact locus,   as shown i n  Figure 2. In  order  to  obtain  this  result  it is important to construct the feed-point and transit ion regions with great care. So far ,  radiation  patterns have been measured for only a few CH2325-9/86/0000-0773$01 .OO @ 1986 IEEEE 773 antennas. The degree of rotat ional  symmetry in  the  patterns of one-arm antennas is dependent upon the   r a t e  oP sp i ra l .  The radiation  tends t o  be circularly  polarized  over much of the pattern.  Figure 3 shows Pour polar  cuts measured using a spinning d ipo le  t o  i l l u s t r a t e  t h e  variation of polarization with polar angle. Side View k P p a I t  (8r 8 1.071l Groundplans Figure 1. A one-arm log-spiral fed against a closely spaced conical ground surface, 774 1 - 3 GHz 3 - 6 M z  6 - 9 G H z  9 - 12 CHZ Figure 2. Measured Sll versus Prequency for a one-arm, log-spiral, radiating l i n e  antenna. 775 Figure 3. Polar radiation patterns at Pour cuts (4-0, 45,90,135 f=5 GHZ. dewees) Of a one-arm, log-spiral. radiating-line antenna, 776 

A Log-Spiral, Radiating-Line Antenna

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A Log-Spiral, Radiating-Line Antenna

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