FIELD OF THE INVENTION

This invention relates to a digital radio receiver with a low-cost multi-band antenna design; it finds a particular application in consumer digital radios. A multi-band antenna is one that is tuned to more than one frequency band, e.g. band II (FM), band III (DAB) and/or L- band (DAB).

DESCRIPTION OF THE PRIORART

Existing multi-band antennas are generally complex to manufacture and therefore expensive. The construction of a typical dual-band antenna for Digital Audio Broadcasting (e.g. DAB — Eureka 147) car radios includes a non-conducting rod on which an L-band (0.39 - 1.55 GHz) _ wave antenna is formed and a separate monopole for Band III. The non-conducting rod acts as a coil former for an inductive trap at L-band. The sections are made separately and soldered together with a cable to connect the antenna to the receiver. The assembly is then encapsulated to make it weatherproof and aesthetically pleasing. It is obvious that this antenna does not lend itself easily to automated assembly. As a consequence, many low cost DAB receivers include only a Band III antenna.

Low-cost, single band antennas also exist, e.g. retractable, or telescopic whip antennas for FM reception.

Printed circuit board antennas are also known, as are multi-band printed circuit board antennas, such as that shown in US patent 4356492. However, to date, no-one has provided

a low cost multi-band antenna fot a consumer digital radio receiver. In particular, no-one has implemented a L band antenna on a printed circuit board.

SUMMARY OF THE PRESENT INVENTION

The invention is a digital radio teceiver including a multi-band antenna, the multi-band antenna comprising: (i) a printed circuit board antenna tuned to one frequency band, and

(ii) a whip antenna tuned to another frequency band.

The printed circuit board antenna may be a L Band monopole and the whip antenna may be a Band III antenna. Hence, where the radio is a DAB radio (or other digital radio, such as DRM, or HD Radio), then the conventional and costly conducting L Band rod normally used is replaced with a PCB antenna and the Band III antenna is a low cost and simple whip antenna. In this way, a DAB radio can be manufactured with both L Band and Band III antennas, yet at much lower cost than conventional dual band DAB radios. The term digital radio receiver should be expansively construed to cover any receiver that can receive and process broadcast digital signals. It therefore includes receivers that can receive and process^ digital audio broadcasts, such as DAB (Eureka 147), DRM (Digital Radio Mondiale), Ibiquity etc. and also digital television broadcasts, such as DVB-H. Generally, the receiver is a receive only device; it is not a terminal capable of transmitting. For such receivers, low cost and manufacturing ease are very valuable; the L Band conducting rod has previously been considered to be the simplest solution and has therefore been used for many years. The present invention enables a yet simpler and cheaper L Band antenna to be made.

Printed circuit boards (PCBs) are normally used to create the bulk of the wiring in electronic circuits. PCBs are made in very large volume at low-cost for use in consumer electtronic equipment. An antenna can be considered to be a circuit and could be made from PCB material. So, instead of using mechanical assembly, we form the antenna from conventional printed circuit material. The PCB creates an antenna at one particular band. When the PCB is. connected in between a radio and an existing whip antenna it allows multi-band reception. This has the following advantages:

1. The PCB assembly is low-cost compared to conventional antenna construction.

2. The PCB antenna can be supplied as an upgrade.

3. It does not require any modifications to the radio.

4. The whip antenna does not need to be retracted to get ultimate performance at the PCB antenna's design wavelength.

In one implementation, the printed circuit board antenna comprises a linear, electrically conducting trace on one side of a printed circuit board, the trace being of a length selected to enable it to operate as the receiving element of the printed circuit board antenna. The linear trace can terminate at one end in a printed inductor that presents a high impedance at the frequency band that the printed circuit board antenna receives at and a low impedance at the frequency band received by the whip antenna.

The printed circuit board can include a connector for connecting the printed circuit board antenna to RF circuitry in the radio and a further connector for connecting the whip antenna to the PCB antenna. The PCB antenna is hence positioned in between the whip antenna and the RF circuitry connector, so that this connector is the single feed for both antennas. Having a single feed is cheaper than having two separate feeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with reference to the accompanying drawings, in which:

Figute 1 is a schematic view of a L Band printed circuit board antenna for use with a Band III whip antenna (not shown) in a radio as defined in the present invention;

Figure 2 is a view of such a radio;

Figure 3 is a view of a L Band printed circuit board antenna that is not connected to a Band III whip antenna.

DETAILED DESCRIPTION

Referring to Figute 1, a PCB 1 is used to form an L-Band monopole. Typically the PCB is made from standard 1 ounce copper clad 1.6mm thick FR4 material. This material was chosen for lowest cost but other PCB dielectrics and thicknesses may be used, as well as single-sided material. The PCB 1 has a linear copper trace 2 formed on one side; this is 1/4 wavelength long and hence approx 5cm for L-Band. Trace 2 acts as the receiving (or radiating) element in the L band antenna. Other types of antenna (1/2, _ wave and/ or dipoles) and wavelengths may be constructed by varying the design/dimensions.

A printed inductor 3 at the end of the PCB forms a trap and provides the inductance for the PCB monopole 2. The inductance 3 is chosen to create a high-impedance (several hundred ohms) at L-Band and is relatively low-impedance (less than a hundred ohms) at frequencies received by the whip section. This means that the PCB /whip combination will be tuned to L-band and the design frequency of the whip antenna (typically Band III and FM), Le. it is a multi-band antenna. The inductance of the trap will be a function of the number of turns in the trap, the width of the copper trace and the gap between the arms of the trace. In an implementation for L-Band, the trap is 4 turns, spacing and thickness is 0.4 mm. Inductance is then approximately 56 nH.

Approximately half of the surface of the PCB 1 is covered with a copper section 5 to raise the level of the monopole section 2 above the shielding in the radio as shown in Figure 2. Trace 2 is an extension of copper section 5. Section 5 may not be necessary in certain radio designs; e.g. if the antenna input is directly on the top of the product.

A connector 7 at one end of the PCB 1 is used to mate with the RF circuitry in the radio and a further connector 6 at the other end is used to mate with a conventional retractable whip (not shown). Connector 7 is hence the single feed for both the L Band monopole and the Band III/FM whip antenna, although it would be possible to include separate feeds.

In another embodiment the connector 6 could be left off and the whip section fixed using solder or some other arrangement e.g. by screw attachment. In a product, we would expect that the PCB 1 would be encapsulated or covered by a plastic sleeve. This would protect the surface of the PCB 1 and improve the cosmetic appearance.

On the underside of the PCB 1, a copper trace 4 creates a ground plane to screen the RF input and form a transmission line to feed signals back to connector 7 and from there to the RF circuitry of the radio receiver.

This assembly works at L-band, FM and Band III. Without the whip attached, the PCB works as an L-band antenna and has some response at Band III and FM. Indeed, the connector for the whip antenna may be excluded. In this case the trap will not be required, as shown in Figure 3.