Microstrip fed printed dipole with an integral balun

• US 4,825,220 A
• Filed: 11/26/1986
• Issued: 04/25/1989
• Est. Priority Date: 11/26/1986
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Rees, Daniel F., Edward, Brian J.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): LE, HOANGANH T
• Application Number:
  US06/935,030
• Time in Patent Office: 881 Days
• Field of Search: 343/795, 343/700 MS, 343/806, 343/807, 343/821, 343/820, 343/822, 343/859, 343/829, 343/846, 333/26
• US Class Current: 343/795
• CPC Class Codes: H01Q 9/065 Microstrip dipole antennas patch antenna H01Q9/0407
• CPC Class Codes: H01Q 9/285 Planar dipole H01Q9/065 takes precedence; patch antenna H01Q9/0407

Abstract

A microstrip fed printed dipole with an integral balun is disclosed, fabricated upon a planar dielectric substrate by patterning metallizations disposed on the two surfaces of the substrate. In the arrangement, the ground plane of the unbalanced microstrip transmission line is bifurcated by a central slot to form a balanced transmission line coextensive with the slot which becomes a part of the arms of the dipole and which at the same time serves as the ground plane of a continuation of the microstrip feed. A continuation of the strip conductor of the unbalanced microstrip feed having a "J" shaped configuration continues over the bifurcated ground planes and crosses the slot in proximity to the dipole for effecting an efficient unbalanced feed to the balanced dipole. The arrangement has a double tuned characteristic with two available and independent adjustments facilitating reproducable, optimized broadband performance.

Claims

1. A microstrip fed printed dipole with an integral balun comprising:

a planar dielectric substrate having a first metallization layer disposed on the under surface and a second metallization layer disposed on the upper surface,

(1) an unbalanced microstrip transmission line with a ground plane formed from said first metallization and a strip conductor formed from said second metallization,

(2) a dipole radiating element having two spaced arms formed from said first metallization and exhibiting a first impedance at resonance, and

(3) a transition in which a continuation of the ground plane of said unbalanced transmission line is bifurcated by a central slot extending to the arms of said dipole to form a first and a second ground plane, the bifurcated ground planes forming a balanced transmission line coextensive with the slot and exhibiting a characteristic impedance approximately matching said first impedance, and

a continuation of the strip conductor of said unbalanced transmission line forming a three part strip conductor disposed over said bifurcated ground planes to continue said unbalanced transmission line, the continuation of said unbalanced transmission line exhibiting a characteristic impedance approximately matching said first impedance, said three part strip conductor having a "J" shaped configuration,

a first part continuing over said first bifurcated ground plane toward said dipole radiating element,

a second part extending across said slot over said dipole from said first bifurcated ground plane to said second bifurcated ground plane, and

a third part extending back toward said unbalanced transmission line and ending in an open circuit,

said dipole radiating element being formed as a diverging extension of said first and second bifurcated ground planes, the inner portions of the arms of said dipole underlying and strongly coupled to said second part, and the outer portions of said arms extending beyond said second part for efficient radiation, and wherein;

the electrical length (theta b) of said unbalanced transmission line, measured from said slot to said open circuited end is approximately one-quarter wavelength so as to provide a low shunt RF impedance to unbalanced mode currents at the dipole load (Zl), and

the electrical length (theta ab) of said balanced transmission line measured from the base of the slot to the half width of the dipole arm is approximately one-quarter wavelength so as to provide a high shunt RF impedance to balanced mode currents at the dipole load, thereby facilitating the conversion of RF current flowing in an unbalanced mode in said microstrip transmission line to a balanced mode in the dipole arms in transmission, the reverse occurring in reception.

2. The arrangement set forth in claim 1 wherein

the characteristic impedance of said balanced line is set equal to the dipole impedance at resonance, and the characteristic impedance of said continuation of said unbalanced line is set equal to the dipole impedance at resonance, and

the electrical length of at least one member of the set theta b and theta ab is displaced from 90 electrical degrees to effect a double tuned, broadband characteristic.

3. The arrangement set forth in claim 2 wherein

the quantity theta b is adjusted above 90 degrees for broadbanding.

4. The arrangement set forth in claim 2 wherein

the quantity theta b is adjusted above 90 degrees and theta ab is adjusted below 90 degrees for broadbanding.

5. The arrangement set forth in claim 2 wherein

the quantity theta b is adjusted by trimming the length of said third part of said second metallization, and

the quantity theta ab is adjusted by trimming the depth of said slot in said first metallization.

6. The arrangement set forth in claim 1 wherein

the characteristic impedance of said balanced line is set equal to the dipole resonant impedance, and the characteristic impedance of said continuation of said unbalanced line is set equal to the dipole resonant impedance,

the arrangement facilitating adjustment of the electrical length theta b by selection of the length of said third part of said unbalanced transmission line, and adjustment of the electrical length theta ab by selection of the depth of said slot, said adjustments being substantially independent and permitting optimal electrical performance.