Multiband antenna structure and methods

A multiband antenna apparatus, comprising:

• a first radiator configured to resonate in a low frequency band;
• a second radiator configured to resonate in a high frequency band;
• and
• a matching circuit in communication with a feed point and at least the first radiator and the second radiator, the matching circuit configured to cause a plural resonance in the first radiator in the low band.

Multiband antenna apparatus for use in a small form factor mobile device, the apparatus comprising:

• a first radiator configured to resonate in a first frequency band;
• a second radiator configured to resonate in a second frequency band, the second frequency band being lower in frequency than the first band, the second radiator comprising at least first and second radiator elements coupled by a reactive element, the coupling at least in part causing reinforcement of said resonance of the first radiator in the first band;
• and
• circuitry in communication with at least the first radiator and the second radiator, the circuitry configured to cause a plural resonance in the second radiator in the second band, said plural resonance enhancing usable frequency band width in said second band.

A high isolation multi-band antenna, comprising:

• a low frequency band radiator;
• at least one high frequency band radiator;
• and
• a common feed that is (i) coupled to a first feed point associated with the at least one high frequency band radiator, and (ii) coupled through circuitry to a second feed point associated with the low frequency band radiator;
• wherein said circuitry is configured to band-pass filter a signal applied to said common feed so as to pass only any portions of said signal substantially within the low frequency band to said second feed point, and substantially attenuate any portions of said signal substantially above the low frequency band, said attenuation providing said high isolation.

A multiband antenna structure of a radio device which has resonances both in a low band and a high band, comprising:

• a main radiator having an operating band in the low band;
• a second radiator and a parasitic radiator having an operating band in the high band, the parasitic radiator being located between the main radiator and the second radiator;
• a ground plane comprising a signal ground for the radio device;
• and
• a matching circuit connected to a feed point of the multiband antenna structure, the matching circuit comprising a serial resonance circuit configured to implement a double resonance for the main radiator in the range of the low band and further configured to enhance the isolation between the main radiator and the second radiator;
• wherein a slot radiator is in the main radiator to provide an additional resonance in the high band;
• and
• wherein a reactive element joins the main radiator to decrease the electric size of the main radiator at the frequencies of the high band for strengthening resonances in the high band and to increase the electric size of the main radiator at the frequencies of the low band for widening the low operating band.