FIELD OF THE INVENTION

This patent application relates to antennas and more particularly to compact single band and multiband antennas for wireless systems such as satellite aided navigation and mobile satellite communications.

BACKGROUND OF THE INVENTION

A global satellite navigation system (satnav) or global navigation satellite system (GNSS) is a system that exploits a network of autonomous geo-spatially positioned satellites to provide geolocation and time information to a suitable receiver anywhere on or near the Earth where there is an unobstructed line of sight. Whilst timing information can be obtained from line of sight to a single satellite geo-spatial location requires line of sight to three (at sea level) or four satellites as a minimum.

In applications where relatively low precision is required low complexity surface mount patch antennas are generally employed accessing a single GNSS signal. However, other applications requiring high precision of timing and/or location require accurately tuned, wider bandwidth, antennas which, ideally, support multiple frequency operation providing higher fidelity reception and thereby improved multipath rejection and better output phase linearity.

Even within these applications there is a constant drive for compact multiband antennas that can be easily integrated into portable devices or more generally into mobile platforms and equipment. These antennas should provide a controlled radiation pattern, namely a uniform coverage of the upper hemisphere of their radiation pattern and circular polarization purity to improve cross-polarization rejection and hence multipath rejection. Additionally, it is desirable for these antennas to be electromagnetically isolated from the chassis and/or any conductive ground structures external to the antenna allowing for their integration into multiple platforms with minimal redesign.

However, the overall footprint of a GNSS antenna is a combination of both the physical antenna itself and its associated electronics. Accordingly, a GNSS antenna is normally deployed together with an impedance matching circuit and either a low noise amplifier for receivers or power amplifier for transmitters. Where multiple antenna elements are employed to either receive or transmit a common signal, e.g. with four antenna elements each fed with the common signal with defined phase relationships for each antenna element, then a microwave circuit such as a quadrature splitter or combiner for example is also employed.

However, with multiple antenna elements within a single antenna the design of the matching network can be challenging as the multiple antenna elements should be matched simultaneously.

Accordingly, it would be beneficial to provide designers of a wide range of electrical devices and systems with compact multiple frequency band antennas which, in addition to providing the controlled radiation pattern and circular polarization purity are impedance matched without substantially increasing the footprint of the antenna and/or the complexity of the microwave/RF circuit interfaced to them which provides the multiple signals to the multiple antenna elements. This is achieved through provisioning one or more capacitive series reactances discretely or in combination with one or more shunt capacitive reactances.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate limitations within the prior art relating to antennas and more particularly to compact single band and multiband antennas for wireless systems such as satellite aided navigation and mobile satellite communications.

In accordance with an embodiment of the invention there is provided a filar antenna comprising:a feeding network on a circuit board comprising a ground plane and a combining network with a plurality of feed points; anda filar antenna with an equal plurality of filar nodes, whereinsaid combining network comprised of circuit elements effective to constructively sum microwave electrical signals present at each of said feed points, each of said electrical signals having a predetermined relative phase relationship, each of said feed points connected to a matching circuit consisting of a capacitive series reactance, each of said series reactances connecting one of said feed points to a corresponding one of said filar nodes, effective to present a characteristic impedance at each of said feed points;said filar antenna comprising a plurality of first filar elements and a plurality of second filar elements alternately arranged about a circumference and above the circuit board, wherein the plurality of first filar elements each have a first electrical length and the plurality of second filar elements each have a second electrical length, different from the first length, wherein the first electrical length of each of the plurality of first filar antennal elements is established in dependence upon an odd multiple of quarter wavelength of a first operating frequency and wherein the second electrical length of each of the plurality of second filar antenna elements is established in dependence upon an odd multiple a quarter wavelength of a second operating frequency, wherein each of the plurality of first filar elements includes a first end and an open, distal second end, and wherein each of the plurality of second filar elements includes a first end and an open, distal second end, said first ends of first filar elements constitutes one of said filar nodes, each of said filar nodes further coupled to a corresponding one of said first ends of said second filar elements.

In accordance with an embodiment of the invention there is provided a filar antenna comprising:a feeding network on a circuit board comprising a ground plane and a combining network with a plurality of feed points; anda filar antenna with an equal plurality of filar nodes, whereinsaid combining network comprised of circuit elements effective to constructively sum microwave electrical signals present at each of said feed points, each of said electrical signals having a predetermined relative phase relationship, each of said feed points connected to a matching circuit consisting of a capacitive series reactance, each of said series reactances connecting one of said feed points to a corresponding one of said filar nodes, effective to present a characteristic impedance at each of said feed points;said filar antenna including a plurality of sets of filar antenna elements each comprising a plurality of filar elements arranged in a first predetermined configuration within each set of filar antenna elements of the plurality of sets of filar antenna elements and in a second predetermined configuration relative to and above the circuit board, wherein each filar element of the set of filar elements of the plurality of sets of filar elements has an electrical length different from an electrical length of the other filar elements of the set of filar elements of the plurality of sets of filar elements which is established in dependence upon an odd multiple of quarter wavelength of an operating frequency of the filar element of the plurality of filar elements, has a first end and an open, distal second end, and wherein said first end of the first filar element within each the set of filar elements of the plurality of sets of filar elements constitutes one of said filar nodes, each of said filar nodes further coupled to a corresponding said first end of each other filar element of the set of filar elements of the plurality of sets of filar elements.

In accordance with an embodiment of the invention there is provided a filar antenna element comprising:a first filar antenna element comprising a first conductor of first predetermined length, a first predetermined width and first predetermined thickness disposed above a ground plane; anda first capacitor electrically coupled between a first end of the first conductor and a feed point for either receiving a first microwave signal to be radiated by the first conductor or receiving a second microwave signal from the first conductor.

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

