Transition between rectangular and relatively large circular waveguide for a UHF broadcast antenna

• US 4,630,316 A
• Filed: 04/12/1983
• Issued: 12/16/1986
• Est. Priority Date: 12/14/1982
• Status: Expired due to Fees

• Current Assignee: Smart Communications Incorporated (PLDT, Inc.)
• Original Assignee: Thomas J. Vaughan
• Inventors: Vaughan, Thomas J.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Lee, Benny T.
• Application Number:
  US06/484,220
• Time in Patent Office: 1,344 Days
• Field of Search: 333/21 A, 333/21 R, 333/239, 333/242, 333/248, 333/251, 343/890, 343/884, 343/874, 343/905, 343/756, 343/850, 455/129
• US Class Current: 455/129
• CPC Class Codes: H01P 1/16 for mode selection, e.g. mode suppression or mode promotion; for mode conversion

Abstract

A high power TV antenna for operation at the ultra high frequency (UHF) frequency F includes a radiating antenna located at the top of a tower structure (often hundreds of feet high), a transmitter at the bottom of the tower and a main circular waveguide transmission line of diameter Dl between the transmitter and the antenna carried by the tower; the feed to and/or from the transmission line including transition sections such that wave propagation in the transition sections is below cutoff for the TM01 mode while it is above cutoff for the dominant TE11 mode while wave propagation in the main circular waveguide transmission line of diameter Dl is substantially totally in the dominant TE11 mode even while it is above cutoff for the TM01 mode, whereby the transition sections tend to inhibit wave propagation in the system in the undesired TM01 mode.

Claims

1. In a high power antenna system for UHF TV frequency (F) broadcast wherein a radiating antenna is located at the top of a tower structure many hundreds of feet high and a transmitter is located at the bottom of the tower, a relatively large diameter circular waveguide transmission line of diameter D1 is provided for conducting the UHF power from the transmitter up the tower to the antenna and the UHF power is fed to said circular waveguide transmission line from said transmitter by an input rectangular waveguide transmission line, and there is transmission line means between said input rectangular and said circular waveguide transmission lines for insuring that wave propagation in said circular waveguide transmission line is substantially totally in the dominant TE11 mode at the frequency F, although F is above the cut off frequency of the TM01 mode therein, the improvement comprising,

(a) wave propagation in said input rectangular waveguide transmission line is substantially totally in the dominant TE10 mode therein at the frequency F,

(b) a section of relatively small diameter circular waveguide of diameter Ds that has an input end and an output end, said diameter Ds being such that F is below the cutoff frequency of the TM01 mode in said small diameter circular waveguide section,

(c) a tapered transition section having a rectangular waveguide cross section at the input end thereof that connects to and matches said input rectangular waveguide transmission line from said transmitter and has a circular waveguide cross section at the output end thereof that connects to and matches said circular waveguide section of diameter Ds and

(d) a tapered circular waveguide section having an input end of diameter Ds connected to the output end of said circular waveguide section of diameter Ds and an output end of diameter D1 connected to the input end of said circular waveguide transmission line of diameter D1,

(e) all of said connections being substantially matched,

(f) whereby the propagation mode of waves launched into said circular waveguide transmission line from said input rectangular waveguide through said sections is substantially totally in the dominant TE11 mode at the frequency F, although F is above the cut off frequency of the TM01 mode therein and resonance of said dominant TE11 mode therein is avoided.

2. An antenna system as in claim 1 wherein Ds is such that F is above the cutoff frequency of the TE11 mode in said small diameter circular waveguide section.

3. An antenna system as in claim 1 wherein successive cross sections of said tapered transition section along the length thereof from said input rectangular transmission line to said small diameter circular waveguide section exhibit a gradual change from a rectangle to a circle of diameter Ds.

4. An antenna system as in claim 1 wherein the cross sectional dimensions of said input rectangular waveguide transmission line are such that F is below the cutoff frequency of the TM11 mode therein.

5. An antenna system as in claim 2 wherein the cross sectional dimensions of said input rectangular waveguide transmission line are such that F is below the cutoff frequency of the TM11 mode therein.

6. In a high power antenna system for UHF TV frequency (F) broadcast wherein a radiating antenna is located at the top of a tower structure many hundreds of feet high and a transmitter is located at the bottom of the tower, a relatively large diameter circular waveguide transmission line of diameter D1 is provided for conducting the UHF power from the transmitter up the tower to the antenna and the UHF power is fed from the circular waveguide transmission line to the antenna by an output rectangular waveguide transmission line, and there is transmission line means between said circular waveguide transmission line and said output rectangular waveguide transmission line to the antenna for insuring that wave propagation in said circular waveguide transmission line is substantially totally in the dominant TE11 mode at the frequency F, although F is above the cut off frequency of the TM01 mode therein, the improvement comprising,

(a) wave propagation in said output rectangular waveguide transmission line is substantially totally in the dominant TE10 mode therein at the frequency F,

(b) a section of relatively small diameter circular waveguide of diameter Ds that has an input end and an output end, said diameter Ds being such that F is below the cutoff frequency of the TM01 mode in said small diameter circular waveguide section,

(c) a tapered transition section having a rectangular waveguide cross section at the output end thereof that connects to and matches said output rectangular waveguide transmission line to the antenna and has a circular waveguide cross section at the input end thereof that connects to and matches the output end of said circular waveguide section of diameter Ds and

(d) a tapered circular waveguide section having an input end of diameter D1 connected to the output end of said circular waveguide transmission line of diameter D1 and an output end of diameter Ds connected to the input end of said circular waveguide section of diameter Ds,

(e) all of said connections being substantially matched,

(f) whereby said wave propagation in said circular waveguide transmission line is substantially totally in the dominant TE11 mode at the frequency F, although F is above the cut off frequency of the TM01 mode therein and the propagation mode of waves launched into said output rectangular waveguide from said circular waveguide transmission line through said sections is substantially totally in the TE10 mode therein and resonance of said dominant TE11 mode therein is avoided.

7. An antenna system as in claim 6 wherein Ds is such that F is above the cutoff frequency of the TE11 mode in said small diameter circular waveguide section.

8. An antenna system as in claim 6 wherein successive cross sections of said tapered transition section along the length thereof from said output rectangular transmission line to said circular waveguide section of diameter Ds exhibit a gradual change from a rectangle to a circle of diameter Ds.

9. An antenna system as in claim 6 wherein the cross sectional dimensions of said output rectangular waveguide transmission line are such that F is below the cutoff frequency of the TM11 mode therein.