Method and apparatus for predictably switching diversity antennas on signal ...

(12) United States Patent

Kenkel et al.

US006296565B1

(io) Patent No.: US 6,296,565 Bl (45) Date of Patent: Oct. 2,2001

(54) METHOD AND APPARATUS FOR

PREDICTABLY SWITCHING DIVERSITY
ANTENNAS ON SIGNAL DROPOUT

(75) Inventors: Mark A. Kenkel, Schaumburg; Edgar C. Reihl, Northbrook, both of IL (US)

(73) Assignee: Shure Incorporated, Evanston, IL (US)

( * ) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.

(21) Appl. No.: 09/304,972

(22) Filed: May 4, 1999

(51) Int. C I. H04B 1/06

(52) U.S. Cl 457/277.2; 455/272; 455/269;

455/277.1

(58) Field of Search 455/272, 272.2,

455/277.1, 249.1, 269, 275, 276.1, 78, 133, 134, 135, 136

(56) References Cited

U.S. PATENT DOCUMENTS

4,153,878 * 5/1979 Osborrn 455/221

4,293,955 10/1981 Gehr et al. .

4,370,522 * 1/1983 Takeda et al 381/3

4,549,311 * 10/1985 McLaughlin 455/277.1

4,625,178 * 11/1986 Mannerstrom 330/149

4,737,733 * 4/1988 LaPrade 330/277

4,737,991 * 4/1988 Sugai et al 381/13

4,943,739 * 7/1990 Slaughter 326/30

5,263,180 * 11/1993 Hirayama et al 455/139

5,307,512 * 4/1994 Mitzlaff 455/126

5,333,175 * 7/1994 Ariyavisitakul et al 455/423

5,465,411 11/1995 Koike .

5,517,686 5/1996 Kennedy et al. .

5,548,836 8/1996 Taromara .

5,603,107 2/1997 Gottfried et al. .

5,697,075 * 12/1997 Kim 455/423

5,697,081 * 12/1997 Lyall, Jr. et al 455/249.1

5,697,083 12/1997 Sano .

5,710,995 * 1/1998 Akiwa et al 455/277.2

5,742,896 4/1998 Bose et al. .

5,754,583 * 5/1998 Eberhardt et al 375/147

5,777,693 6/1998 Kishigami et al. .

6,115,591 * 9/2000 Hwang 455/277.2

OTHER PUBLICATIONS

Article dated Aug. 11, 1999 from Lectrosonics, Wireless Guide obtained from http://www.lectro.com/wg/wgdiv.htm regarding Diversity Reception.

Advertisement dated Aug. 11,1999 purportedly from "Samson" obtained from http://www.samsontech.con/wireless/ press/coniv_press.html regarding the Concert IV System. Advertisement dated Aug. 11, 1999 from Samson from the Internet at http://www.samsontech.com/wireless/press/series_one_press. html regarding the UHF Series One. Article dated Aug. 11, 1999 from the Internet at http:// www.telex.com/PSE/WebPages . . . regarding Professional Audio Technical Information How Wireless Work; Diversity Reception.

Article "Wireless Microphone Systems: Description," publication date unknown, author unknown.

* cited by examiner

Primary Examiner—Nay Maung

Assistant Examiner—Sonny Trinh

(74) Attorney, Agent, or Firm—Banner & Witcoff, Ltd.

(57) ABSTRACT

A low-cost diversity antenna switching system and method is realized by controlling bias voltages on PIN diodes. By increasing the reverse bias voltage impressed upon a PIN diode, an RF signal impressed upon the diode is increasingly attenuated. As the PIN diode is forward biased to conduct in the forward direction, RF attenuation decreases. Two or more PIN diodes are used to increasingly attenuate signals from one antenna as attenuation of signals from another antenna is gradually decreased. The progression of the bias voltages is accomplished using a microprocessor that monitors a received signal strength indicator (RSSI) signal from a radio receiver. The RSSI is used to control which of two antennas are coupled into the receiver by predicting a signal fade.

21 Claims, 2 Drawing Sheets

1

METHOD AND APPARATUS FOR
PREDICTABLY SWITCHING DIVERSITY
ANTENNAS ON SIGNAL DROPOUT

FIELD OF THE INVENTION

This invention relates to diversity antenna switching systems. In particular, this invention relates to a low cost, diversity antenna switching system for use with high fidelity audio equipment.

BACKGROUND OF THE INVENTION

Diversity receiving systems and diversity antennas are well known in the communications art. In general, diversity antenna systems are used to accommodate the RF signal fading and multi-path signal propagation anomalies that are common at VHF and UHF frequencies. Signal fading and multi-path signals can adversely effect reception of a radio frequency's signal and, by selectively choosing one of two or more spatially separated antennas that pick up a signal, fading and multi-path effects can be reduced. Multiple antennas are routinely used with cellular telephones and automobile radios.

Multiple antennas are now also used with wireless microphone systems, which include a remote, low-power portable transmitter, the signals of which are received and demodulated by a receiver. As a wireless microphone is moved about a room, multi-path signals can adversely affect the demodulated audio output from the receiver because multi-path signals will produce phase anomalies in the reception process that sound like popping noise or may even cause complete audio loss. Accordingly, diversity antenna systems are now employed in such wireless microphone systems to overcome the adverse effects of multi-path and signal fading.

At least one problem with a diversity antenna system is switching the appropriate antenna to the receiver in such a way so as to seamlessly couple the receiver to the proper antenna. Prior art systems exist for selecting one, or a combination of two or more antennas to be coupled to a radio receiver. Some of these prior art systems are disclosed in U.S. Pat. Nos. 5,777,693 to Kishigoami, et al. for a "diversity receiving apparatus for a mobile unit;" U.S. Pat. No. 5,517,686 to Kennedy, et al. for a "diversity Receiver for FM Stereo Utilizing a Pilot Tone Multiple For Phase Alignment of Received Signals;" U.S. Pat. No. 5,548,836 to Taromaru for a "Diversity Receiver;" U.S. Pat. No. 5,465, 411 to Koike for a "Diversity Receiver With Switching Noise Reduction;" U.S. Pat. No. 4,29,955 to Gehr, et al. for a "Diversity Reception System;" U.S. Pat. No. 5,742,896 to Bose, et al. for a "Diversity Reception With Selector Switching at Super Audible Rate;" U.S. Pat. No. 5,697,083 to Sano for a "Diversity Receiver;" and see U.S. Pat. No. 5,603,107 to Gottfried, et al. for a "Switching System For Diversity Antenna FM Receiver."

When high fidelity audio reproduction is required in a small size package and at the lowest possible cost, prior art diversity antenna switching system are too complex, too large or too expensive. Prior art low cost, switching systems also suffer from audio switch noise spikes that they produce in the receiver when they perform a hard instantaneous switch over from one antenna to another. A low cost, compact, method, and apparatus for selecting one or more antennas in such a way that audio fidelity reproduction is maximized would be an improvement over the prior art .

SUMMARY OF THE INVENTION

Using PIN diodes as variable RF signal attenuators, in series between each of the antennas of a diversity antenna

2

system and the radio receiver input in a wireless microphone system, the strongest signal received from a transmitter can be seamlessly selected at the receiver without producing noise spikes caused by phase differences between the anten

5 nas. The PIN diode will conduct radio frequency energy when biased in the forward direction. By gradually biasing a PIN diode to conduct in a forward direction, its attenuation of a RF signal can be gradually increased and decreased. In a diversity antenna system, a PIN diode connected in series

10 between the antenna and the receiver input, can be gradually forward biased, thereby gradually reducing the attenuation of RF signals passing through the diode from the antenna to the input. Simultaneously, another PIN diode connected in series with another antenna and coupled to the receiver

15 input, can be gradually reversed biased so as to gradually attenuate signal from the other antenna.

By gradually modulating the bias current of PIN diodes, they can be used to progressively attenuate and de-attenuate signals from two or more diversity antennas that arc coupled

20 to a common summing node that is coupled to the input of the radio receiver. Signals received by one antenna can be seamlessly combined with signals from another antenna so as to avoid sudden phase shifts that can produce unacceptable audio output noise spikes.

25 PIN diodes are small, inexpensive and easily controlled to modulate their RF attenuation level.

BRIEF DESCRIPTION OF THE DRAWINGS

30 FIG. 1 shows a schematic diagram of the preferred embodiment of a diversity receiving apparatus for coupling the signals from at least one of two antennas into the input of a receiver.

FIG. 2 shows a schematic diagram of an alternate embodi35 ment of the invention.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT

40 FIG. 1 shows a schematic diagram of the preferred embodiment of diversity receiving, apparatus for coupling radio frequency signals from at least one antenna of a pair of such antennas into a radio receiver for demodulation. The diversity receiving apparatus 100 is comprised two radio

45 antennas 102 and 104 for detecting signals radiated from a transmitter not shown. While the antennas 102 and 104 are only shown schematically in FIG. 1, for improving signal reception, the actual antennas are preferably spaced as far apart as practical.

50 The first antenna 102 is capacitively coupled 112 to the cathode of a first PIN diode 106. The anode of the first PIN diode 106 is connected to a summing node 109 that is capacitively coupled 130 to the input of a radio frequency receiver 110 which demodulates radio frequency signals

55 picked up at antenna 102 and outputs an audio frequency signal. The second antenna 104 is also capacitively coupled 123 to the cathode of a second PIN diode 108, the anode of which is also capacitively coupled 130 to the receiver input 110. As shown in the figure, the anodes of the PIN diodes

60 106 and 108 are coupled to a common node 109 which is considered a summing node for the signals passing through the PIN diodes 106 and 108.

The diodes 106 and 108 act as variable RF signal level attenuators by gradually modulating bias voltages applied to

65 these diodes. When the PIN diodes are reversed biased with a dc voltage applied to the cathodes and anodes the PIN diodes block the passage of RF signals across the PIN