Abstract: A catheter shaft carries a coaxial cable, the terminal end of which contains a dipole antenna with opposing first and second helical elements. The first and second helical elements originate from a common connection to an outer conductor of the coaxial cable. The first and second helical elements are formed by winding flat wire around an outer insulator of the coaxial cable near a terminal end of the coaxial cable. A tubular-shaped capacitor is connected between an inner conductor of the coaxial cable and a point on the second helical element where the resistive component of the antenna's impedance matches the characteristic impedance of the coaxial cable. This match minimizes reflective losses of the antenna, thereby maximizing power transfer to the antenna. The antenna has an effective electrical length which is equal to one half the wavelength of the radiation emitted, independent of the physical length of the antenna.

Abstract: A method of selectively treating interstitial tissue following microwave thermal therapy includes an intraurethral Foley-type catheter shaft. The catheter shaft contains a microwave antenna which is capable of generating a cylindrically symmetrical thermal pattern in tissue, within which temperatures are capable of exceeding 45.degree. C. The antenna is surrounded by means within the shaft for asymmetrically absorbing electromagnetic energy emitted by the antenna so as to concentrate thermal energy on a first side of the shaft. This asymmetrical absorption alters the thermal pattern generated by the microwave antenna, making it possible to focus microwave thermal therapy toward undesirous tissue and away from healthy tissue. The absorption means is also capable of absorbing heat from adjacent tissue by thermal conduction. Operation of the absorption means upon the conclusion of microwave thermal therapy aids in reducing edema of the treated tissues caused by the elevated temperatures of those tissues.

Abstract: An intraurethral, Foley-type catheter shaft contains a microwave antenna capable of generating a cylindrically symmetrical thermal pattern, within which temperatures are capable of exceeding 45.degree. C. The antenna, which is positioned within the shaft, is surrounded by means within the shaft for absorbing thermal energy conducted by the tissue and asymmetrically absorbing electromagnetic energy emitted by the antenna--a greater amount of electromagnetic energy being absorbed on one side of the shaft. This asymmetrical absorption alters the thermal pattern generated by the microwave antenna, making it cylindrically asymmetrical, which effectively focuses microwave thermal therapy toward undesirous benign tumorous tissue growth of a prostate anterior and lateral to the urethra, and away from healthy tissue posterior to the urethra.

Abstract: A catheter shaft carries a coaxial cable, the terminal end of which contains a dipole antenna with opposing first and second helical elements. The first and second helical elements originate from a common connection to an outer conductor of the coaxial cable. The first and second helical elements are formed by winding flat wire around an outer insulator of the coaxial cable near a terminal end of the coaxial cable. A series capacitance is connected between an inner conductor of the coaxial cable and a point on the second helical element where the resistive component of the antenna's impedance matches the characteristic impedance of the coaxial cable. This match minimizes reflective losses of the antenna, thereby maximizing power transfer to the antenna. The antenna has an effective electrical length which is equal to one half the wavelength of the radiation emitted, independent of the physical length of the antenna.